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Haskoning UK Ltd

Cornwall SMP2: Fal, Camel and Fowey Estuaries Date: October 2009 Project Ref: R/3834/1 Report No: R.1558

Cornwall SMP2: Fal, Camel and Fowey Estuaries

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Summary ABP Marine Environmental Research Ltd (ABPmer) was commissioned by Haskoning UK Ltd to undertake the estuaries assessment component of the Cornwall and Isles of Scilly SMP2 for the Fal, Camel and Fowey Estuaries. This assessment was undertaken in accordance with Defra guidelines (Defra, 2006a) for a number of tasks as follows: Baseline understanding of estuarine processes up to the tidal limit within each estuary (Defra

guidance Task 2.1). The assessment of each estuary in terms of appropriate limits for the coastal processes

component of the SMP2 (Defra guidance Appendix F assessment). The determination of baseline scenarios within each estuary to determine the future behaviour

of the shoreline under a “No Active Intervention” and a “With Present Management” scenario for 0-20 years (to 2025), 20-50 years (to 2055) and 50-100 years (to 2105).

The mapping of flood outlines under a present day 1 in 200 yr extreme water level with additional sea level rise (Defra, 2006b) for 2025, 2055 and 2105.


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Acknowledgements Thanks to Duncan Pirrie (University of Exeter and Helford Geoscience) for supplying a number of references.


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Cornwall SMP2: Fal, Camel and Fowey Estuaries Contents

Page Summary .................................................................................................................................................. i

Acknowledgements.................................................................................................................................. ii

1. Introduction.................................................................................................................................1 1.1 Report Structure .........................................................................................................................1 1.2 Geographical Extent ...................................................................................................................1 1.3 Baseline Understanding (Task 2.1) ............................................................................................2 1.4 Appendix F Assessment.............................................................................................................3 1.5 Baseline Scenarios (Task 2.2)....................................................................................................3

1.5.1 Methodology.................................................................................................................4

2. Fal Estuary .................................................................................................................................4 2.1 Overview ....................................................................................................................................4 2.2 Existing Policy ............................................................................................................................5

2.2.1 Shoreline Management Plan........................................................................................5 2.2.2 Catchment Flood Management Plan............................................................................6 2.2.3 River Basin Management Plan.....................................................................................6

2.3 Geology ......................................................................................................................................7 2.3.1 Solid Geology...............................................................................................................7 2.3.2 Superficial Geology ......................................................................................................7

2.4 Hydrodynamics...........................................................................................................................7 2.4.1 Tides ............................................................................................................................7 2.4.2 Wave Climate...............................................................................................................8 2.4.3 Fluvial Flows ................................................................................................................9 2.4.4 Extreme Water Levels ..................................................................................................9

2.5 Holocene to Recent Evolution ....................................................................................................9 2.6 Present Geomorphology...........................................................................................................10

2.6.1 St Anthony Head to St Mawes ...................................................................................10 2.6.2 St Mawes ...................................................................................................................10 2.6.3 Castle Drive to St Just................................................................................................11 2.6.4 St Just ........................................................................................................................11 2.6.5 St Just to Turnaware Point .........................................................................................11 2.6.6 North of Turnaware Point ...........................................................................................11 2.6.7 Feock to Restronguet Point........................................................................................11 2.6.8 Restronguet Creek .....................................................................................................12 2.6.9 Restronguet Point to Mylor Creek ..............................................................................12 2.6.10 Mylor Creek................................................................................................................12 2.6.11 Mylor ..........................................................................................................................12 2.6.12 Mylor to Flushing........................................................................................................13 2.6.13 Flushing......................................................................................................................13 2.6.14 Penryn River ..............................................................................................................13 2.6.15 Falmouth Harbour ......................................................................................................13


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2.7 Anthropogenic Intervention.......................................................................................................14 2.7.1 Mine Spoil ..................................................................................................................14 2.7.2 Dredging.....................................................................................................................14 2.7.3 Future Development...................................................................................................16

2.8 Sediment Transport Pathways and Budget ..............................................................................16 2.8.1 Sediment Sources......................................................................................................16 2.8.2 Sediment Sinks ..........................................................................................................17 2.8.3 Sediment Transport Pathways ...................................................................................17

2.9 Impact of Sea Level Rise..........................................................................................................18 2.10 Appendix F Assessment...........................................................................................................19

2.10.1 Estuaries Assessment................................................................................................20 2.10.2 Discussion..................................................................................................................22

2.11 Baseline Scenario assessment ................................................................................................22 2.11.1 No Active Intervention ................................................................................................22 2.11.2 With Present Management.........................................................................................26 2.11.3 Flood risk....................................................................................................................31

3. Camel Estuary ..........................................................................................................................31 3.1 Overview ..................................................................................................................................31 3.2 Existing Policy ..........................................................................................................................32

3.2.1 Shoreline Management Plan......................................................................................32 3.2.2 Catchment Flood Management Plan..........................................................................32 3.2.3 River Basin Management Plan...................................................................................32

3.3 Geology ....................................................................................................................................32 3.3.1 Solid Geology.............................................................................................................32 3.3.2 Superficial Geology ....................................................................................................33

3.4 Hydrodynamics.........................................................................................................................33 3.4.1 Tides ..........................................................................................................................33 3.4.2 Wave Climate.............................................................................................................34 3.4.3 Fluvial Flows ..............................................................................................................34 3.4.4 Extreme Water Levels ................................................................................................35

3.5 Holocene to Recent Evolution ..................................................................................................35 3.6 Present Geomorphology...........................................................................................................35

3.6.1 Stepper Point to Padstow...........................................................................................36 3.6.2 Padstow .....................................................................................................................36 3.6.3 Dinas/Portilly Cove to Tregenna/Dinham ...................................................................36 3.6.4 Tregenna/Dinam to Wadebridge ................................................................................37 3.6.5 Rock and Porthilly Cove.............................................................................................37 3.6.6 Rock to Daymer Bay ..................................................................................................38 3.6.7 Daymer Bay ...............................................................................................................38 3.6.8 Daymer Bay to Polzeath ............................................................................................38

3.7 Anthropogenic Intervention.......................................................................................................38 3.7.1 Embankments and Bridges ........................................................................................38 3.7.2 Dredging.....................................................................................................................39 3.7.3 Mine Spoil ..................................................................................................................39

3.8 Sediment Transport Pathways and Budget ..............................................................................39 3.8.1 Sediment Sources......................................................................................................39 3.8.2 Sediment Sinks ..........................................................................................................40 3.8.3 Sediment Transport Pathways ...................................................................................41

3.9 Impact of Sea Level Rise..........................................................................................................42


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3.10 Appendix F Assessment...........................................................................................................43 3.10.1 Estuaries Assessment................................................................................................44 3.10.2 Discussion..................................................................................................................46


4. Fowey Estuary..........................................................................................................................53 4.1 Overview ..................................................................................................................................53 4.2 Existing Policy ..........................................................................................................................54

4.2.1 SMP ...........................................................................................................................54 4.2.2 Catchment Flood Management Plan..........................................................................54 4.2.3 River Basin Management Plan...................................................................................54

4.3 Geology ....................................................................................................................................54 4.3.1 Solid Geology.............................................................................................................54 4.3.2 Superficial Geology ....................................................................................................54

4.4 Hydrodynamics.........................................................................................................................55 4.4.1 Tides ..........................................................................................................................55 4.4.2 Wave Climate.............................................................................................................55 4.4.3 Fluvial Flows ..............................................................................................................56 4.4.4 Extreme Water Levels ................................................................................................56

4.5 Holocene to Recent Evolution ..................................................................................................56 4.6 Present Geomorphology...........................................................................................................57 4.7 Anthropogenic Intervention.......................................................................................................57

4.7.1 Dredging.....................................................................................................................57 4.7.2 Mine Spoil ..................................................................................................................57 4.7.3 Embankments ............................................................................................................57

4.8 Sediment Transport Pathways and Budget ..............................................................................58 4.8.1 Sediment Sources......................................................................................................58 4.8.2 Sediment Transport Pathways ...................................................................................59 4.8.3 Sediment Sinks ..........................................................................................................59

4.9 Impact of Sea Level Rise..........................................................................................................59 4.10 Appendix F Assessment...........................................................................................................60

4.10.1 Estuaries Assessment................................................................................................61 4.10.2 Summary....................................................................................................................63


5. References ...............................................................................................................................66

Appendix A. Estuary Guidance Tables (Appendix F of the SMP Guidance)


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Tables 1. Levels of confidence in predicting the shoreline position ............................................................4

2. SMP1 coastal policies ................................................................................................................6

3. Tidal parameters at Falmouth.....................................................................................................8

4. Summary of fluvial flows from gauging station data....................................................................9

5. Extreme water levels within the Fal Estuary ...............................................................................9

6. Shoreline predictions for the Fal Estuary under a no active intervention scenario....................23

7. Shoreline predictions for the Fal Estuary with present management ........................................27

8. Water levels used for flood mapping ........................................................................................31

9. SMP1 coastal policies ..............................................................................................................32

10. Tidal parameters at Padstow ....................................................................................................33

11. Tidal flow parameters recorded in the Camel Estuary ..............................................................34

12. Extreme water levels in the Camel Estuary ..............................................................................35

13. Shoreline predictions for the Camel Estuary under a no active intervention scenario ..............47

14. Shoreline predictions for the Camel Estuary with present management...................................50


16. SMP1 coastal policies ..............................................................................................................54

17. Tidal parameters at Fowey .......................................................................................................55

18. Summary of gauging station data .............................................................................................56

19. Extreme water levels within the Fowey Estuary........................................................................56

20. Shoreline predictions for the Fowey Estuary under a no active intervention scenario ..............64

21. Shoreline predictions for the Fowey Estuary with present management ..................................65



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Figures 1. Location of Estuary Study Areas

2. Fal Estuary, Locations and Process Unit Boundaries

3a-c. Fal Estuary: Predicted Evolution of Mean High Water Springs with No Active Intervention

4a-c. Fal Estuary: Predicted Evolution of Mean High Water Springs with Present Management

5a-c. Fal Estuary: Flooding Extents for Successive Epochs (1 in 200yr event and sea level rise)

6. Camel Estuary, Locations and Process Unit Boundaries

7a-c. Camel Estuary: Predicted Evolution of Mean High Water Springs with No Active Intervention

8a-c. Camel Estuary: Predicted Evolution of Mean High Water Springs with Present Management

9a-c. Camel Estuary: Flooding Extents for Successive Epochs (1 in 200yr event and sea level rise)

10. Fowey Estuary

11. Fowey Estuary: Predicted Evolution of Mean High Water Springs with No active Intervention

12. Fowey Estuary: Predicted Evolution of Mean High Water Springs with Present Management

13. Fowey Estuary: Flooding Extents for Successive Epochs (1 in 200yr event and sea level rise)


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1. Introduction ABP Marine Environment Research Ltd (ABPmer) was commissioned by Haskoning UK Ltd. in February 2009 to undertake a number of tasks in support of the production of the second generation Shoreline Management Plan (SMP) for the length of coast from Rame Head on the South Cornwall coast around Lands End to Hartland Point on the North Cornwall coast and includes the Isles of Scilly. This project is being led by Royal Haskoning, on behalf of the Cornwall and Isles of Scilly Coastal Authorities Group (CISCAG), with Caradon District Council as lead authority. The coastline covered by the Cornwall and Isles of Scilly SMP comes within the boundaries of seven maritime district councils. They and the Environment Agency have certain permissive powers for managing the risk of coastal flooding and erosion. This report documents the geomorphology of three estuaries in Cornwall and has been undertaken in support of the production of the Cornwall and Isles of Scilly Shoreline Management Plan (SMP). The estuaries under investigation are the Fal and Truro Rivers, the Camel Estuary and the Fowey Estuary (Figure 1). This report has been produced according to Department for Environment, Food and Rural Affairs (Defra) Guidelines for the production of the second generation of Shoreline Management Plans (Defra 2006a). This report constitutes: The development of baseline understanding (Task 2.1). The determination of appropriate study limits for the SMP (Appendix F assessment). The development of baseline scenarios (Task 2.2).

1.1 Report Structure Section 1 provides background information to the study and the methodology used for each assessment. Sections 2, 3 and 4 provide the local scale review of estuarine processes for the Fal, Camel and Fowey Estuaries respectively, which highlights the underlying geology, past evolution over both long and more recent timescales, the major sediment sources, pathways and sinks, and the forces driving these processes, including tides and waves, and the present geomorphological forms within the estuaries. This understanding is then used to inform the Appendix F assessment and the resulting baseline scenarios.

1.2 Geographical Extent There are seven significant estuaries or tidal rivers within the boundaries of the Cornwall and Isles of Scilly SMP Review: Looe River; River Fowey; Fal Estuary (including Carrick Roads and Truro and Tresillian Rivers); Helford Estuary; Hayle River; The Gannel; and the Camel Estuary.


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In addition to these main tidal watercourses there are numerous smaller rivers and streams that discharge into the sea through steep valleys and across many of the beaches. These mostly have very limited upstream tidal limits and are small-scale in terms of water and sediment exchange with the open coast (although historically some smaller rivers delivered significant sediment amounts to the open coast due to inland mining activities). ABP Marine Environmental Research Ltd (ABPmer) were commissioned to undertake the estuaries assessment for only three of the significant estuaries: River Fowey, the Fal Estuary and the Camel Estuary. The remaining four estuaries (Looe, Helford, Hayle and Gannel) were included within the SMP Review from the outset and therefore excluded from the estuaries assessment phase. This decision was based on the following assumptions: These estuaries have well-established links with the open coast in terms of flood risk to

communities and erosion in their lower reaches. Information regarding sediment exchange between these estuaries and the open coast

is known from SMP1. These estuaries are well defined and boundary limits on each are easily identified with

reference to other documents including SMP1, the relevant Catchment Flood Management Plan and the Cornwall and Isles of Scilly SMP2 Scoping Report.

These estuaries are relatively small (with the exception of the Helford) and have low residential populations at risk (with the exception of the Looe River). Therefore they would be unlikely to warrant individual estuary management plans.

The remaining minor rivers and streams are also excluded from the estuaries assessment and are therefore dealt with directly within the SMP Review, based upon their insignificant water and sediment exchange with the open coast. The overall strategic SMP policy area covers the estuary as far as the upstream normal tidal limit and the study area for this baseline study considers this area.

1.3 Baseline Understanding (Task 2.1) The aim of Task 2.1 is to provide a baseline understanding of coastal behaviour and dynamics. In particular “to provide a review of coastal behaviour and dynamics, which will be used to inform the Appendix F assessment and develop the baseline scenarios, identify risks and test the response and implications of different management policy scenarios over different timescales. As well as considering natural features along the coast, there is also a consideration of existing defences (Defra, 2006a). Defra outlines two specific activities for this task: Assess coastal processes and evolution; and Assess coastal defences. At the time of completion of this report coastal defence data remained outstanding and the assessment of coastal defences therefore could not be undertaken. As such, this report assesses only the coastal processes and evolution.


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1.4 Appendix F Assessment

The main objective of the Appendix F assessment is to assess the need (or otherwise) for the inclusion of three specific estuaries in the study area within the SMP process. An assessment has been undertaken and conclusions provided for the following estuaries: (1) The Fal and Truro Rivers; (2) The Camel Estuary; and (3) The Fowey. Each estuary has been assessed to address three key questions relating to the inclusion of an estuary in the SMP process, as follows: Should the Estuary be included in the SMP process? If so, how should the estuary be included? How far upstream should the estuary be included? The conclusions and answers to each of these questions for each estuary informs the overall SMP development process. To address these questions Defra’s 2006 SMP Guidance Volume 1: Aims and Requirements and Volume 2: Procedures (March 2006) has been used (see Appendix A).

1.5 Baseline Scenarios (Task 2.2) The aim of Task 2.2 is to provide an appreciation of how the shoreline is behaving and the influence that shoreline management has on this behaviour. Tables have been created with the aim of developing an understanding of the coastal evolution within three epochs. The epochs are 0-20 years (to 2025), 20-50 years (to 2055) and 50-100 years (to 2105). Two scenarios have been assessed as part of this investigation: ‘No Active Intervention’, which assumes that the defences are no longer maintained

and will fail over time; and ‘With Present Management’, which assumes that all defences are maintained to

provide a similar level of protection to that provided at present. The predicted shoreline changes have also been mapped for both scenarios at each estuary to provide an indication of the likely evolution of the mean high water springs (MHWS) position of the shoreline. In addition to the changes to the shoreline due to coastal evolution, ABPmer have also been requested to provide flood risk mapping for each of the 3 epochs (2025, 2055 and 2105). Extreme water levels for a 1 in 200yr event has been sourced from Posford Haskoning (2003a) and combined with the relevant sea level rise guidance from Defra (2006b) to create a resultant sea level for each epoch. This sea level has been applied to the most recent available LiDAR (LIght Detection And Ranging) dataset to give an indication of how flood risk may change with sea level rise.


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1.5.1 Methodology

The methodology applied is based on historical rates of retreat, local geology, topography and the existing defences and their present condition. It is worth noting that there are limited historical rates of retreat for the majority of the areas and so much of the analysis has been undertaken without these data, where data are available the historical rates of erosion have been extrapolated to the future scenarios. Much of the coastline is hard geology which is resistant to erosion and so the overall rates of erosion within the estuary will be low. The assessment has not included any accelerated erosion following failure of the sea defences as this would not occur due to the hard rock geology. In many areas the rate of retreat has been calculated as only a couple of metres over the entire period and so the MHWS position looks unchanged on the supporting mapping. Shoreline which is backed by low lying land has been analysed further using LiDAR data from the Environment Agency 2007 survey. The areas are then classified according to the United Kingdom Hydrographic Office (UKHO 2008) MHWS water level and the future sea level rise predictions following the latest Defra guidance (2006b). Due to the protected nature of the estuaries, increased storminess has not been included. For the no active intervention scenario, it has been assumed that all flood defences will fail in 20 years with complete failure of the defences thereafter. For areas where the coastline is fronted by commercial docks (i.e. Falmouth) the structures have been assumed to be maintained for both scenarios. An assessment of the level of confidence in the predicted shoreline position has also undertaken for each unit. The levels of confidence are based on the data availability and the sensitivity of the coastline to change. The levels of confidence are shown in Table 1 below. Table 1. Levels of confidence in predicting the shoreline position

Quality of Data and Method High Example: Good geological data showing stable coastline backed by hard rock cliffs. Medium Example: Some historical data on a coastline change showing clear evolutionary trends. Low Example: Area susceptible to erosion but with little data to derive rates.

2. Fal Estuary

2.1 Overview The Fal Estuary is located on the south coast of Cornwall with its mouth positioned within Falmouth Bay. The estuary is classed as a ria and the mouth, which is fixed by the headlands of Pendennis Point and St Anthony Head, is relatively deep with depths of up to 34mCD (Chart Datum) in the main channel. The estuary is branching with a number of tributaries and creeks. The main body of the estuary is referred to as the Carrick Roads. At the northern edge of the


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Carrick Roads three creeks, namely the Ruan Creek, and the Tresillian and Truro Rivers flow into the Carrick roads. Along the western bank of the Carrick Roads three more creeks are present, Restronguet Creek, Mylor Creek and Penryn River. On the eastern side of the Carrick Roads, St Just Creek and the Percuil River converge with the estuary. The mouth of the estuary is open to swell propagating from the open sea and wave modelling suggests that these waves have limited propagation to the north of the headlands of Trefusis Point and Castle Point (St Mawes) (Halcrow, 1999a). Sediment within the Carrick Roads is likely to come from marine sources however, the source of this sediment is not described in the literature, but as there is little evidence of significant levels of accretion, the amount of sediment entering the estuary is likely to be low. The creeks up-estuary of the Carrick Roads has historically accreted rapidly as a result of catchment derived sources such as mine waste. The coastline outside of the estuary is cliffed and interspersed with a number of sandy beaches. The nature of the coast, along with the prominent headlands forming the estuary mouth, would suggest that little longshore drift occurs along the open coast outside of the estuary. Grab samples show that the bed sediment throughout the study area is variable, ranging from mud to large shell and stones (HR Wallingford, 1985). Relatively limited data is available concerning the transport of sediment within the estuary. The estuary is relatively undeveloped overall although some development is present at Falmouth, Feock, Penryn, Restronguet, Devoran, St Mawes, Mylor, Flushing and St Just in the form of coastal defence, quays, harbour walls and docks. The main concentration of development is at Falmouth where a cruise terminal and dock facilities are situated. There are currently plans to extend the cruise terminal through the deepening of the main approach channel and the lengthening of the quay. Small amounts of historical reclamation are present in Restronguet Creek, Truro River and Mylor Creek (outside of the SMP2 area). The largest amount of reclamation is within Falmouth Docks. However, in the context of the estuary these reclaimed areas do not represent a significant proportion.

2.2 Existing Policy

2.2.1 Shoreline Management Plan The first round SMP (Halcrow, 1999a) considered the Fal Estuary as far as the Carrick Roads including St Mawes and Falmouth. The coastal sections and policies are outlined in Table 2.


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Table 2. SMP1 coastal policies

Coastal Unit Preferred Policy

St Anthony Head to Castle Drive Do nothing strategy to maintain zonal succession of important intertidal and subtidal habitats.

St Mawes

Hold the line of existing defences along developed frontage to maintain character and economic assets, with monitoring of undefended areas to assess long term erosion trend and determine acceptability of either long term hold or retreat policy.

St Mawes to St Just Do nothing strategy to maintain protected maerl and eel grass beds.

St Just Hold the existing defence line to protect assets with possible establishment of new defences along undefended frontages where required, subject to impact on subtidal habitats of cSAC (candidate Special Area of Conservation).

St Just to Turnaware Point Do nothing strategy to maintain important marine habitats.

Feock to Restronguet Point Hold the existing defence line to protect assets at risk and do nothing along undefended frontages which are not at risk.

Restronguet Weir to Mylor Creek Do nothing to protect important biological habitats.

Mylor Hold the existing defence line to maintain quays and protect frontage for commercial and recreational use.

Myler Creek toFlushing Do nothing strategy to minimise any impacts on important intertidal and subtidal habitats.

Flushing

Hold the existing defence line to maintain the character and economic assets of the frontage, with monitoring of undefended areas to assess long term erosion trend and determine acceptability of either a long term hold or retreat policy.

Falmouth Harbour

Hold the existing defence line to ensure continued commercial operation of the port and industrial assets of the town. Do nothing in the short term along undefended length, with cliff stability monitoring to assess acceptability of either a long term hold or retreat the line policy.

(Halcrow, 1999a)

2.2.2 Catchment Flood Management Plan A Catchment Flood Management Plan (CFMP) gives an overview of flood risk and how this may change over the next 100 years. The CFMP sets out a plan for managing this risk into the future based on these findings. The West Cornwall CFMP (EA, 2008a) considers the Fal Estuary in its entirety and therefore overlaps with the SMP2 area. For this reason it is important to be aware of policy decisions made as part of the CFMP so they do not conflict with policy decisions for the SMP2. The CFMP policy for the Fal estuary is to take further action to sustain the current level of flood risk into the future.

2.2.3 River Basin Management Plan The draft river basin management plan (EA, 2009) focuses on achieving the protection, improvement and sustainable use of the water environment - surface freshwaters (including lakes, streams and rivers), groundwater, some wetlands that depend on groundwater, estuaries and coastal waters out to one nautical mile beyond baseline and as such covers the Fal Estuary SMP2 area. The draft river basin management plan has been prepared under the


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Water Framework Directive, which requires all countries throughout the European Union to manage the water environment to consistently high standards. The findings for the Fal are as follows: Current overall status: Moderate; Proposed status objectives: Good ecological and chemical status by 2027; Current chemical status: Not good (low).

2.3 Geology

2.3.1 Solid Geology The solid geology predominantly consists of slates and sandstones of the Porthscatho formation of middle Devonian age (Pirrie et al, 2003a). Outcrops of the Porthscatho formation form the cliffs at Trefusis Point and along the eastern side of the estuary. Between Mylor Creek and Trefusis Point the Mylor Slate formation is present. The Portscatho Formation shows a general NNE-SSW structural trend resulting in the resistant strata forming headlands that are orientated in a SSW direction (Halcrow, 1999a). Analysis of the headlands just outside of the estuary indicates that Pendennis Point and St Anthony’s Head can be expected to retreat by 1-2 and 0-1m respectively over the next 100 years along the seaward side (Halcrow, 1999a). As the geological composition of the cliffs outside the estuary is similar to that within the estuary it can be inferred that the cliffs in the estuary are relatively resistant to erosion and hence the solid geology exerts a significant control on the estuary shape.

2.3.2 Superficial Geology Throughout the Fal Estuary the Devonian metasediments are overlain with Quaternary (last 1.6 million years) sediments. These sediments are typically Pleistocene (1.6 million to 10,000 years ago) which overlie raised shore platforms cut into the Devonian metasediments. Typically these deposits comprise raised beach deposits comprising of pebbles and cobbles deposited during interglacial conditions. In turn these deposits are overlain by poorly sorted head deposits which were formed under periglacial conditions during the last glacial interval (Pirrie et al, 2003a). During the periglacial period sea level was much lower resulting in the Fal estuary extending further seaward than at present and these valleys would have been partially infilled by head deposits (Pirrie et al, 2003a).

2.4 Hydrodynamics

2.4.1 Tides

2.4.1.1 Tidal levels The Fal is a macro tidal estuary, tidal parameters at Falmouth are summarised in Table 3.


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Table 3. Tidal parameters at Falmouth

Parameter Levels at Falmouth (mCD) Levels at Falmouth (mODN) Highest Astronomical Tide (HAT) 5.8 2.89 Mean High Water Springs (MHWS) 5.4 2.49 Mean High Water Neaps (MHWN) 4.3 1.39 Mean Sea Level (MSL) 3.2 0.29 Mean Low Water Neaps (MLWN) 2.1 -0.81 Mean Low Water Springs (MLWS) 0.8 -2.11 Lowest Astronomical Tide (LAT) 0.0 -2.91 Tidal Range (m) Mean spring tidal range 4.6 Mean neap tidal range 2.2

(UKHO, 2008) All of the tributaries are tidal, with the maximum inland tidal limit at Tresillian which is 18.1km from the mouth of the Fal Estuary (IECS, 1996). Other tidal limits are situated at Truro (Truro River), Ruan Lanihorne (Ruan Creek), Devoran and Perran Wharf (Restronguet Creek), Mylor Bridge (Mylor Creek), Penryn (Penryn River) and Trethern Mill and Gerrans (Percuil River).

2.4.1.2 Tidal flow Datasets collected throughout the study area (HR Wallingford, 1985, Andrews Hydrographics, 1990 and Totaltide) and modelled data (HR Wallingford, 2008) suggest that in terms of peak velocities the flood tide is stronger than the ebb tide throughout the majority of the Fal Estuary. In terms of fine sediment transport this does not necessarily imply a net input of fine sediment, other factors such as the duration of the tidal cycle and the length of the slack water period (and hence the amount of time available for fines to settle out of suspension) are also important. Tidal gauge data suggests that in general the ebb tide phase lasts longer than the flood (IECS, 1996 and HR Wallingford, 1985); further tidal analysis would be required to demonstrate the net transport of sediments.

2.4.2 Wave Climate The wide southerly entrance to the Fal Estuary allows the swell from offshore to propagate into the Carrick Roads. Modelling by Halcrow (1999a) indicates that the bathymetry limits the penetration of this swell and the largest wave heights are found at Trefusis Point (1.5m) and Castle Point (2m). Beyond these headlands offshore wave penetration is limited with the most of the estuary being dominated by locally generated waves of 0.5 to 1.0m (Halcrow, 1999a). These results broadly agree with modelling of remotely and locally generated waves for the proposed Cruise Terminal Environmental Statement (ES) which indicated that waves from offshore during a 1 in 1 year event do not penetrate significantly into the estuary further than the coast between Trefusis Point and Mylor Creek (HR Wallingford, 2008) and that significant wave heights generally did not exceed 3m within the Carrick Roads. The largest wave heights were observed in the entrance of the estuary and during some scenarios reached a height


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of 4m. Locally generated waves by winds from 10˚N form the largest waves in the vicinity of Falmouth Docks and in agreement with Halcrow (1999a) which indicated significant wave heights do not exceed 1m at any point in the estuary (HR Wallingford, 2008).

2.4.3 Fluvial Flows Fluvial flows within the estuary are low relative to its size, there is no single dominant supply of freshwater to the Fal Estuary with the Fal, Truro, Tresillian, Percuil, Penryn, Kennal and Carnon Rivers all contributing. Mean river flows from the Centre for Ecology & Hydrology (CEH) gauging station database is summarised in Table 4. Table 4. Summary of fluvial flows from gauging station data

River Station Measurement Period Mean Flow (m³/s) Fal Tregony 1978 – 2006 2.04

Kennal Ponsanooth 1968 – 2006 0.51 Kenwyn Truro 1968 - 2008 0.38

2.4.4 Extreme Water Levels

Still extreme water levels for the year 2002 were derived for the south west by Posford Haskoning (2003a). As part of this work water levels were calculated for Falmouth, Penryn, Devoran, Truro River and Tresillian, the study found that the extreme water levels are the same at all the locations considered, these levels are summarised in Table 5. Table 5. Extreme water levels within the Fal Estuary

Return Period Water Level (mODN) 1:1000 3.96 1:500 3.85 1:200 3.72 1:100 3.63 1:50 3.50 1:25 3.43 1:10 3.30 1:5 3.22 1:1 3.03

(Posford Haskoning, 2003a)

2.5 Holocene to Recent Evolution The Fal Estuary is a ria or a river valley flooded during sea level rise following the last glaciation. Relatively little sediment has been deposited in the Fal during the Holocene, which has resulted in the distinct morphology of the estuary, namely its narrow winding creeks, steep banks and deep channels (IECS, 1996). The lack of Holocene sediment infill is the reason for the relatively small amount of intertidal when compared to estuaries on the east coast such as the Thames.


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2.6 Present Geomorphology

The Fal Estuary is a relatively deep estuary and is orientated along a north to south axis and as such has a small degree of protection from the prevailing south westerly wind direction. The presence of the Lizard Peninsula to the west of the estuary mouth also provides some protection from swells propagating into the estuary from the open ocean. The main body of the estuary (the Carrick Roads) has limited intertidal area although saltmarsh and mudflat is present further up the tributaries. The Carrick Roads have been very stable over the last 200 years (IECS, 1996) which demonstrates the limited amount of sediment deposition occurring in the outer estuary. It has been noted by IECS (1996) that this lack of sediment infill means the Fal has not developed a morpho-dynamic equilibrium when compared to other estuaries in the UK. For example, when compared to estuaries on the east coast of the UK the area of the estuary mouth is an order of magnitude higher than expected given the estuaries tidal prism. This means that velocities are low at the mouth which should lead to deposition reducing the cross sectional area which in turn will eventually bring the mouth into equilibrium (IECS, 1996). A further dis-equilibrium has also been noted for the estuary length/tidal wave length, this indicates that the estuary is relatively deep throughout the Carrick Roads and that there is potential for large amounts of accretion throughout the SMP2 study area although the sediment supply required is unlikely to exist (IECS, 1996). The following sections provide a description of the geomorphology of each of the process units within the estuary (Figure 2). These process units are largely based on the units used in the SMP1 (Halcrow, 1999a) and are chosen based on areas of similar geomorphology and coastal behaviour.

2.6.1 St Anthony Head to St Mawes St Anthony Head is a rocky headland marking the eastern side of the mouth of the Carrick Roads. The coastline to the north of St Anthony Head comprises a relatively low cliffline fronted in places by a number of small sandy coves. Within the Percuil River mudflats are present with a large intertidal area at Place Creek.

2.6.2 St Mawes The area is developed throughout with a series of seawalls fronted by sand and shingle beaches and rock platforms. At Summers Beach the beaches are backed by a low cliffline. Analysis of maps from 1907 and 1998 show that the defences have fixed Mean High Water (MHW) along much of the frontage whereas some retreat has been noted along Summers Beach where the cliff has eroded by up to 4m (Halcrow 1999a). Mean Low Water (MLW) is also stable along this frontage. It has been suggested that the beaches were originally formed by head deposits and that there is no contemporary supply of material (Halcrow, 1999a).


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2.6.3 Castle Drive to St Just The coast along this section is natural with no development. The coastline is characterised by a low cliff fronted by rock platforms and a mixed sand and shingle beach.

2.6.4 St Just St Just is a small tidal inlet, the coastline is low cliffline with a sand, shingle and mud intertidal. A relic shingle spit, St Just Bar, forms a barrier between the main part of the inlet and St Just Pool, a shallow waterbody on the south bank of the inlet. The spit has historically been maintained through reprofiling and beach nourishment on its seaward face, although this is no longer carried out (Halcrow, 1999a). There is some development along the coast with a seawall and a slipway, the spit provides storage for boats. None of the existing defences appear to be having a detrimental impact on sediment supply or transport (Halcrow, 1999a).

2.6.5 St Just to Turnaware Point This stretch of coast is natural with no development, the intertidal is rock platform with some narrow sand and shingle beach.

2.6.6 North of Turnaware Point This part of the estuary is characterised by a number of branching tributaries extending up-estuary to the tidal limits at Truro (Truro River), Tresillian (Tresillian River) and Ruan Lanihorne (Ruan Creek). Within these tributaries the intertidal area is larger than that within the Carrick Roads. Historically all of these tributaries have experienced accretion with the highest levels in Ruan Creek where large volumes of sediment were deposited as a result of the deposition of sediment from the china clay industry. The recorded accretion upstream of Malpas Point on the Truro River indicates that accretion has also occurred in areas where no mine waste was deposited showing that sediment must also be supplied by natural sources. Some saltmarsh is present in Ruan Creek, this saltmarsh grades into woodland and may be able to migrate landwards as a result of future sea level rise. The saltmarsh increased in area rapidly throughout the 19th and early 20th century’s as a result of sediment from mining activities being deposited as shown by the white chalky nature of much of the sediment. Evidence from maps and aerial photographs indicates that the saltmarsh advanced seawards by 800m between 1878 and 1973 in Ruan Creek (IECS, 1996). It is likely that this saltmarsh development has slowed since the 1950s when the supply of sediments from mining activities significantly reduced. Some undercutting of the saltmarsh edge was reported in 1996 which could indicate erosion of the saltmarsh but no quantification of the entire saltmarsh area since 1973 is known.

2.6.7 Feock to Restronguet Point As in much of the upper estuary the coast is characterised by a low cliffline fronted by an intertidal rock platform. Loe Beach is present at the eastern end of this frontage and comprises


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a sandy intertidal area. The village of Feock stretches along most of this frontage and a number of properties with private defences and slipways are situated along the coast.

2.6.8 Restronguet Creek Restronguet Creek is characterised by an extensive intertidal area with much of the creek drying out at low water. This large intertidal area formed primarily as a result of the deposition of mine spoil and although this accretion has slowed since 1907, low levels of accretion have continued up until the present day (IECS, 1996). Some saltmarsh is present within the upper part of the creek and an analysis of OS maps from 1908 and 1973 indicates that the saltmarsh has increased by 20.8ha in 65 years (IECS, 1996). There is no evidence to determine the behaviour of the saltmarsh since 1973. Restronguet Creek has been subject to some modification through open cast mining in the intertidal area commencing in 1702 and reclamation for port construction at Devoran during the 1820s (IECS, 1996). One of the banks formed during the mining operations in 1785 now forms the A39 road and marks the present day tidal limit which was formally further upstream at Bissoe (IECS, 1996). Although the creek was heavily industrialised in the past little remains of the docks and open cast mines in the present day.

2.6.9 Restronguet Point to Mylor Creek This part of the coast is also characterised by a low cliff fronted by a narrow rock platform.

2.6.10 Mylor Creek Mylor Creek has a large intertidal area with almost the entire creek drying out at low water. There is no historical analysis available to determine historical behaviour. The lack of contaminated sediment within Mylor Creek (Pirrie et al, 2003a and 2003b) suggests that there has been no deposition of mine spoil and therefore that the creek has probably not experienced the same rapid sedimentation such as within Restronguet and Ruan Creeks. There is no significant saltmarsh development within Mylor Creek.

2.6.11 Mylor This frontage covers Mylor Churchtown, a small harbour and marina at the mouth of Mylor Creek. The intertidal beach is made up of sand and shingle and has been described as a relic beach with no significant sediment movement (Halcrow, 1999a). There is a quay, a slipway, pontoons and a number of masonry walls. Due to the absence of significant sediment movement it is unlikely that the defences will have any impact on coastal processes (Halcrow, 1999a). Analysis of historic Ordnance Survey (OS) data from 1907 and 1998 shows limited change to MHW and MLW. Part of the old naval docks was reclaimed in 2000/2001 where 6,500m³ of treated sediment was used to create a car park, quay and slipway (Carrick District Council, 2005).


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2.6.12 Mylor to Flushing

This coast comprises low cliff fronted by a rocky intertidal, the coast is natural throughout this frontage with no development.

2.6.13 Flushing Trefusis Beach is situated to the east of this frontage which is comprised of sand and shingle. Between Trefusis Quay and New Quay the intertidal comprises a rock platform overlain in places with relic beaches comprising intertidal sand and shingle. The intertidal is backed by a low cliff, some of the properties have private defences and slipways.

2.6.14 Penryn River Penryn River is fairly well developed along its southern bank with a number of docks and marinas present and the northern bank is largely undeveloped. A relatively large intertidal area is present on both sides of the main channel and no saltmarsh is present. Historically the Penryn River has accreted at a slower pace than the Ruan and Restronguet Creeks due the absence of mining in this part of the Fal Estuary. Comparison of navigation charts between 1693 and 1994 showed 0.8m of accretion over a 300 year period.

2.6.15 Falmouth Harbour The section of coast fronting Falmouth consists of an intertidal comprised of shingle and rock platform. This coast is heavily developed with a series of seawalls, quays and docks. Comparison of historical maps from 1907 and 1998 show that changes can be attributed to the construction of new coastal structures. Both Greenbank Quay and Custom House Quay restrict the longshore movement of sediment creating pocket beaches with a limited contemporary supply of sediment (Halcrow, 1999a). Historical reclamation of the rock platform and the intertidal area has been undertaken to construct the docks (IECS, 1996). Prior to reclamation for the docks, a tongue of rock was present forming a tidal creek (IECS, 1996). The area of coast between Sandy Cove and the Eastern Breakwater is a former landfill site, waste from the docks was disposed at this site until 1994 and included shot blast residue from ship maintenance, bagged asbestos, paints, oils, glass and fabric (Nicholas Pearson, 1998). Following 1994, sewage treatment works were constructed on the easterly facing part of the landfill and the rest of the landfill was used as a car park and helipad by A&P (Nicholas Pearson, 1998). During the construction of the sewage treatment works a revetment was built across the easterly facing part of the frontage. Prior to the construction of this defence the coastline was quoted as eroding at a rate of 1m/yr (Nicholas Pearson, 1998), this estimation was not based on measured data and was assumed to provide an absolute worst case scenario for the sewage works ES. Erosion along this frontage is predominantly a result of wave action and is mainly restricted to the east facing shoreline (ABP Research, 1999) which is now protected.


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Although erosion was greatest along the eastern facing frontage (prior to the construction of the sea defences) erosion is still apparent along the northerly facing frontage from aerial photos and photos taken on site (ABP, 1999, Royal Haskoning, 2009 and Google Earth Imagery). As a result of this erosion, boulders, coarse sediments and landfill debris (including stone, bricks, concrete, soil and wire ropes) have been spread over the upper beach. It has been proposed that the landfill area be redeveloped as a car park for the new Falmouth Dock cruise terminal and as part of this a sea defence will be built across the remainder of the frontage to prevent further erosion (Royal Haskoning, 2009). Historical map evidence (Royal Haskoning, 2009) shows that prior to the landfill the coastline had a similar geomorphology to the adjacent coast with rock platforms and cliffs, this shows that the coast will not erode further landward than this point. Between the docks and Pendennis Head the intertidal comprises of rock platform interspersed with a number of sandy coves, the rock platform flanking the coves indicates that the beaches receive little or no sediment from longshore processes. Some defences are present and are related to the fortifications for the castle comprising of masonry walls, old gun emplacements and a fort on the point itself.

2.7 Anthropogenic Intervention Some coastal structures are present within the SMP2 area at Falmouth, Feock, Devoran, Restronguet, Truro, St Mawes, Mylor, Flushing and St Just in the form of coastal defence, quays, harbour walls and docks. The main concentration of development is at Falmouth where a cruise terminal and dock facilities are situated. Further coastal defence information from the Environment Agency’s National Flood Coastal Defence Database (NFCDD) will be provided separately to this document.

2.7.1 Mine Spoil The discharge of spoil from mining operations led to the silting of Ruan and Restronguet Creeks (IECS, 1996). Analysis of subtidal and intertidal sediment samples throughout the Fal Estuary indicates that the area between Restronguet and Mylor Creek has elevated metal levels (Pirrie et al, 2003a and 2003b). This contamination has been interpreted as particulate mine waste which has been reworked and deposited by tidal currents (Pirrie et al, 2003a and 2003b) and may indicate that a limited amount of sediment from mine spoil from Restronguet Creek has been deposited in the Carrick Roads as well as the upper tributaries and creeks.

2.7.2 Dredging A limited amount of dredging is undertaken within the Fal Estuary as summarised in the following sub-sections. The dredged amounts are limited in quantity and as such are unlikely to have any discernable impact on estuarine processes at their current scale.


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2.7.2.1 Falmouth Falmouth Harbour Commissioners have a requirement to remove 1,000m³ of dredged material from the visitors yacht haven every 10 years which is disposed of at sea, this follows capital works that were undertaken in 1999 when 6,538m³ were dredged (Carrick District Council, 2005). Falmouth Docks and Engineering Company dredge approximately 1,800m³ every 3 years and Port Pendennis (situated near to Falmouth Docks) dredge between 4,000 and 6,000m³ every 6 years (Carrick District Council, 2005). All of this spoil is recorded as being disposed of at sea Within Falmouth Yacht Marina 4,425 tonnes (3404m³) was dredged in 1994 and 3,900 tonnes was dredged in 1995. All of this spoil was disposed of at sea. Challenger Marina also dredges approximately 5,000 tonnes (3846m³) every ten years which is disposed of at sea The approach channel to Falmouth Docks occasionally requires dredging and was dredged to a depth of 5.8m LAT in 1940 and 5.4m in 1992 (IECS, 1996). Historically, the expansion of Falmouth Docks has required dredging. Firstly in 1938 to the west of the western breakwater where depths were increased to 7.6m below LAT from an area ranging between intertidal and 2.7m below LAT (IECS, 1996). Secondly in 1942 areas around the western breakwater were dredged to a depth of 5.8m below LAT that were formally intertidal and 2.7m below LAT (IECS, 1996). Finally the southern end of the western breakwater was dredged in the early 1950s (IECS, 1996).

2.7.2.2 Truro The Truro River was dredged on a regular basis between the 1930s and 1991, approximately 5,770m³ was dredged annually between 1952 and 1991 (Carrick District Council, 2005). This spoil was used to reclaim the intertidal mudflats (formally used as a municipal dump) which now form Boscawen Park. Occasionally at intervals of about 7 years an additional 4,000-5,000 tonnes (3077m³ – 3846m³) was dredged and disposed of at sea in addition to the spoil used for reclamation. Since 1991 the dredging commitment has reduced considerably primarily because of financial reasons with 7,825 tonnes (6019m³) in 1999, 5,850 tonnes (4500m³) in 2000, 5,031 tonnes (3870m³) in 2003 and 5,720 tonnes (4400m³) in 2005 dredged and disposed of at sea.

2.7.2.3 Mylor Yacht Harbour The redevelopment of Mylor Yacht Harbour in 2000/2001 required a capital dredge of 36,000m³, it has been estimated that there will be a maintenance requirement of 1,000m³ every six to seven years (Carrick District Council, 2005).

2.7.2.4 St Mawes Between 77-115m³ of sediment is removed adjacent to the jetty where it builds up as a result of propeller wash (Carrick District Council, 2005). In addition the inner harbour is also dredged


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approximately every seven years with about 769m³ being removed from the area (Carrick District Council, 2005).

2.7.3 Future Development Changes to Falmouth’s cruise terminal are planned for the future, this will include deepening and straightening of the navigation channel between the Carrick Roads and the terminal and a longer cruise quay which will combine the Queens and Northern Wharves. The Environmental Impact Assessment (EIA) for this development (Royal Haskoning, 2009) predicted that the wave climate could increase in height under certain conditions and that tidal speeds overall will decrease slightly. These impacts are predicted to not extend outside of the estuary. Some coastal defence work is also planned with a proposed seawall to be built fronting the presently eroding former landfill site to the east of the eastern breakwater.

2.8 Sediment Transport Pathways and Budget

2.8.1 Sediment Sources

2.8.1.1 Marine source Historical analysis of charts has indicated that there has been little deposition in the study area over the last 200 years (IECS, 1996). The tributaries have experienced rapid deposition from catchment sources namely mine spoil and a natural fluvial supply (discussed below). As the Carrick Roads has not experienced this rapid sedimentation it is thought that the sediment deposited within the main body of the estuary is predominantly from a marine source and not from a catchment source (IECS, 1996). The limited scale of this deposition indicates that this source of marine sediment is low.

2.8.1.2 Mine spoil Large amounts of mine spoil contributed to the silting of the intertidal creeks to the north of the study area. Spoil has been deposited in the Tresillian River and Restronguet Creeks from tin mining activity and Ruan Creek from the china clay industry (IECS, 1996). Analysis of sediment samples within the Fal Estuary suggest that only a very limited amount of this sediment has subsequently been deposited within the Carrick Roads between Restronguet and Mylor Creeks (Pirrie et al, 2003a and 2003b). The cessation of the release of mine tailings into Restronguet Creek by 1950, and the reduction in volume up to this date (Pirrie et al, 2003a and 2003b), suggests that this supply is no longer available to the system and has not been available for at least the last 60 years. Mine spoil is discussed further in Section 2.7.1.

2.8.1.3 Fluvial source The river flows are low and as such it is unlikely that the rivers supply any significant supply of sediment to the Carrick Roads under normal flow conditions. However, it is likely that rivers supply some sediment to the estuary as evidenced by the accretion recorded within both


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Penryn and Truro Rivers in the absence of any mining activity. It is possible that the rivers supply significant quantities of sediment during low frequency, high magnitude flow events.

2.8.1.4 Cliff erosion A small amount of cliff erosion (4m between 1907 and 1998) has been identified along the cliffline backing Summers Beach at St Mawes (Halcrow, 1999a). There is no other information on any cliff erosion elsewhere in the estuary.

2.8.2 Sediment Sinks

2.8.2.1 Subtidal and intertidal The main sinks for sediment are the tidal creeks and tributaries which have in the past experienced rapid accretion as a result of deposited mine spoil (Sections 2.7.1 and 2.8.1.2) within Restronguet and Ruan Creeks and natural fluvial supply in Penryn and Truro Rivers. There is some evidence that the mine spoil has been reworked by tidal currents and subsequently deposited in the Carrick Roads between Restronguet and Mylor Creeks (Pirrie et al, 2003a and 2003b) although available information suggests that this deposition is largely restricted to this area only. Historical analysis of bathymetric charts by IECS (1996) showed that deposition in the creeks and tributaries of the Fal was far more rapid than that in the Carrick Roads. This led IECS (1996) to conclude that deposition of fluvial (mine spoil) sediments was largely restricted to the upper tributaries and rivers and the limited amount of accretion observed in the Carrick Roads was due to instead a limited supply of marine sediments. The findings of sediment analysis within the Fal (Pirrie et al, 2003a and 2003b) which show largely low levels of contamination throughout the Carrick Roads would appear to broadly support this hypothesis.

2.8.2.2 Saltmarsh Saltmarsh has developed in the upper reaches of both Ruan and Restronguet Creeks as a result of mine spoil deposition, comparison of OS maps from 1908 and 1973 indicate that there has been 17ha of saltmarsh development in Ruan Creek and 20.8ha within Restronguet Creek. There is limited evidence to determine the present behaviour of the saltmarsh within the Fal Estuary.

2.8.3 Sediment Transport Pathways

2.8.3.1 Suspended sediment Suspended sediment pathways are poorly understood within the Fal and suspended sediment loads are very low throughout the estuary. Samples were taken in 1985 within the SMP2 study area along a series of transects in the Falmouth to St Mawes area of the estuary (HR Wallingford, 1985). These showed very low average readings with concentration of between 5 and 10 ppm (parts per million). The cross


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section to the north of both the Percuil and Penryn Rivers showed slightly higher readings with the results being generally between 5 and 20ppm. During the ebb, the eastern side of the estuary showed slightly higher readings of between 15 to 40ppm, however this does not correlate with tidal flows which peak on the flood and it was concluded that there is little connection between suspended sediment concentrations and tidal currents (HR Wallingford, 1985). Out of the 774 samples 5 near bed samples had a concentration of above 100ppm. Further sampling in the tributaries suggests that concentrations tend to increase with distance from the sea (MBA, 2003) indicating that fluvial sediment sources are more important than marine sources although as discussed in Section 2.8.1.2 the majority of this sediment is deposited upstream of the Carrick Roads. It has also been suggested that the presence of buried river channels in Falmouth Bay (seaward of the study area) may indicate a pathway for fine sediments whereby sediments from the tributaries pass through the Carrick Roads and are deposited in Falmouth Bay (Halcrow, 1999). However, based on the lack of deposition in the Carrick Roads this is thought to be unlikely. It is considered that much of the sediment deposited within the Carrick Roads area comes from limited marine sources, with deposition of sediment from fluvial sources largely restricted to the upper areas of the estuary.

2.8.3.2 Bedload Modelling of sand transport in the Fal Estuary showed the potential for a net transport of sand into the Fal Estuary (HR Wallingford, 2008); this assumes a supply of sand. Given the low levels of historic accretion in the area it is unlikely that there is a significant supply of sand entering the Carrick Roads. Littoral transport along many of the sandy beaches is low due to the sheltered nature of the estuary.

2.9 Impact of Sea Level Rise The intertidal area ratio within the Carrick Roads is low indicating that there is potential for more sediment to be deposited within the estuary, this however depends on a sufficient supply of sediment in the future. The limited deposition within the Carrick Roads suggests that the current supply is limited, meaning that it is unlikely that the estuary will accrete in line with accelerated sea level rise in the future. IECS (1996) considered the potential response of the estuary to sea level rise. They suggest that the inner creeks and rivers are likely to experience erosion as a result of sea level rise, however there is some space for saltmarsh to migrate as sea levels rise due to the general undeveloped nature of the upper estuary (IECS, 1996).


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Within the Carrick Roads the estuary is likely to experience accretion in response to sea level rise, although the supply of sediment is likely to be limited as evidenced by the current low levels of accretion and the absence of a significant sediment supply.

2.10 Appendix F Assessment Based on the available data, the estuary can be split into two distinct sedimentary zones: Zone 1: The tidal creeks and rivers which are experiencing rapid sedimentation,

predominantly from fluvial and ultimately anthropogenic (mining and quarrying) sources. This part of the estuary has historically been a strong sink for fine sediment. As mining activity has reduced in recent times the source of this sediment has lessened thereby reducing the rate of accretion.

Zone 2: The Carrick Roads, which has been relatively stable in terms of morphology

over at least the last 200 years. The low levels of accretion suggests that the main estuary has not been receiving significant amounts of sediment from fluvial sources but instead is sourcing sediment from a small unknown source of marine sediment (IECS, 1996). The lack of available sediment from outside of the estuarine system means that the Carrick Roads is probably a very weak sink.

It is possible, but not proven that some fluvial derived sediment is transferred between Zone 1 and Zone 2, however, given the different historical accretion rates within the two zones it is unlikely that this transfer is significant.

2.10.1


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Estuaries Assessment

Estuary Fal Estuary Location Cornwall, south coast Classification 3b (Ria) Estuary Main characteristics Macrotidal, large estuary. Data availability

Futurecoast Estuaries Assessment (Halcrow, 2002). SMP from Rame Head to Lizard Point (Halcrow, 1999). Coastal processes and Conservation: Fal Estuary (IECS, 1996). Falmouth Cruise Project ES (Royal Haskoning, 2009).

Stage 1 Step 1: significance of water exchange (EGT2)

Total area: The Fal is considered to be large in terms of total estuary area relative to the range of estuaries in England and Wales. Intertidal area: The estuary has a very small intertidal zone relative to its total area; saltmarsh is only found in the upper reaches of the estuary. Channel length: The length of the estuary is considered to be moderate to large. Mouth cross-sectional area: The estuary has a very large cross-sectional mouth area. Mouth width: The estuary has a large mouth width which is constrained by rocky headlands on both sides. Tidal range: The tidal range in the estuary is large. Mean freshwater flow: Freshwater flows are very low compared to the size of the estuary with a mean freshwater flow of 2.92 m³/s. Stratification calculations indicate that the estuary is very well mixed. % Area: The estuary has a small % area indicating that significant amounts of water will remain in the estuary at low water. Tidal velocities: At the mouth of the estuary, maximum recorded tidal velocities during a spring tide are 0.42m/s on the flood and 0.35m/s on the ebb and during a neap tide 0.19m/s on the flood and 0.19m/s on the ebb (Andrews Hydrographics, 1990). Tidal prism: The tidal prism is 9.10 x 107 m³ at mean low water and 1.81x108 m³ at mean high water.

Verdict Verdict on significance: The estuary is large in size and also relatively deep, the magnitude of tidal currents in the mouth are low to average although the volume of the estuary means that a large amount of water is exchanged with the open coast. Overall in accordance with EGT2, in terms of water exchange, the estuary is assessed as significant with respect to the interaction with the open coast.

Stage 1 Step 2: significance of sediment exchange (EGT3)

Tidal asymmetry: The estuary is ebb dominant at the mouth according to Dronkers gamma (Halcrow, 2002). Measurement of peak velocities show that the estuary is flood dominant during a spring tide except in the location of the Falmouth approach channel which is ebb dominant (IECS, 1996). Morphological features: The estuary mouth faces southeast and as such is relatively sheltered from the prevailing swell and wind directions although swell can propagate into the estuary under certain conditions. The estuary is branched with many tributaries; the main part of the estuary (Carrick Roads) is relatively deep. Mudflats and saltmarshes are only present in the upper tributaries and creeks. Source sink relationship: The estuary is currently a sink, mainly for fine sediments. Historical analysis indicates the main body of the estuary (the Carrick Roads) has been relatively stable with only some marine sourced sediment depositing in the estuary. The tributaries and creeks have however historically experienced a rapid rate of infilling and much of this sediment is derived from fluvial rather than marine sources and can be attributed in part to the areas past mining activities which released large amounts of sediment into the creeks. This input of sediment has reduced in recent years; there is also evidence for a fluvial supply of sediment prior to mining activities (IECS, 1996). Plume generation: The maximum flow ratio suggests that a plume of fine sediment may be formed on ebb tides.


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Verdict Verdict on significance: The estuary imports a small amount of sediment from marine sources, this source is limited. There is limited evidence of a supply of sediment to the open coast from the estuary. Overall, in accordance with EGT3, in terms of sediment exchange, the estuary is assessed as insignificant in terms of the interaction with the open coast.

Stage 1 Step 3: relevance of process issues (EGT5)

Verdict on relevance of coastal process issues: Step 1 – water exchange: significant Step 2 – sediment exchange: insignificant Step 3, therefore, from EGT5, process issues are considered to be Grade B

Stage 1 Step 4: significance of management issues (EGT4)

Historic reclamation: The main area of reclamation is the dock area at Falmouth which involved the loss of part of the intertidal rock platform and subtidal area from Port Pendennis to the north of Pendennis Castle. In the late 1700s intertidal reclamation was undertaken in Restronguet Creek around Devoran where mud from open cast mining in the creek was used to build up embankments. These embankments later became the causeway for the A39 road (which is now the tidal limit within Restronguet Creek) and the land on which Devoran Port was situated. Further reclamation also occurred during the construction of the port at Devoran. An artificial island was also created in the mid 1800s within Restronguet Creek into which a mine shaft was sunk; this is still visible at low water. The area which is now Boscawen Park at the head of the Truro River was reclaimed in the mid 1900s. The recreational ground in Mylor Bridge at the head of Mylor Creek is also reclaimed. Presence/absence of jetties at the estuary mouth: There are no structures at the mouth of the estuary. Maintenance dredging: Some limited dredging occurs within Falmouth docks and along Truro River. Occasional dredging is also undertaken in the various small harbours and yacht havens. Coastal Defences: Some coastal defences, quays and jetties are present along the major settlements in particular Falmouth, Flushing, St Mawes, St Just, Mylor, Penryn and Truro, these do not affect interactions between the open coast and the estuary. Tidal barrages: A tidal barrage was constructed at the head of the Truro River in 1992; this would have had the effect of increasing tidal velocities at this location although as there is no monitoring or modelling evidence it is difficult to comment on the magnitude of any effects on the overall estuary. Future management of the estuary: Changes to Falmouth’s cruise terminal are planned for the future, this will include deepening and straightening of the navigation channel between the Carrick Roads and the terminal and a longer cruise quay which will combine the Queens and Northern Wharves. The EIA for this development (Royal Haskoning, 2009) predicted that the wave climate could increase in height under certain conditions and that tidal speeds overall will decrease slightly. These impacts are predicted to not extend outside of the estuary.

Verdict Verdict on significance: Insignificant, although there are a number of structures and management practices within the Fal Estuary these are unlikely to affect the open coast.

Stage 1 Step 5: recommendation on whether the estuary should be included in the SMP process (EGT5)

Verdict: Step 3 – Process issues assessed as Grade B Step 4 – Management issues assessed as insignificant. Therefore from Step 5 of EGT5, the Fal scores 3 in terms of overall significance and does not need to be included in the SMP process.


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2.10.2 Discussion The above estuary assessment in terms of the interaction of the estuary with the coast can be summarised as follows: 1. The Fal is a very large macro tidal estuary and as such, exchanges large volumes of

water with the open coast. 2. The Fal estuary is supplied with some sediment from the open coast although there is

little available information to describe the size and nature of this supply. 3. There are a number of management practices and some development within the

estuary although these have not been large enough to impact significantly on the open coast.

The interactions identified are subject to some uncertainty due to the relatively poorly understood processes and interactions with the coast. The Fal Estuary is a large deep ria with plenty of potential for the deposition of sediments. However, due to the nature of the open coast and the prominent headlands on either side of the mouth there is unlikely to be a significant amount of sediment entering the estuary. In addition to this there is no evidence of any sediment export to the open coast from within the estuary. There is a basis for including the Carrick Roads as far as the mouths of the tidal creeks and tributaries; as the Carrick Roads exchanges a relatively large volume of water with the adjacent coastline and also has many attributes of the adjacent open coast such as limited sandflats, mudflats or saltmarsh. However, wave modelling has suggested that offshore wave penetration into the estuary is not significant beyond Trefusis and Castle Points and beyond this locally generated waves become more important. This factor along with the limited sediment transfers with the open coast discussed above suggests that in terms of interactions with the open coast that the Fal Estuary need not be included in the open coast SMP. It is important however to consider additional factors that are not taken into account during the Appendix F assessment such as the incorporation of the estuary into any other management plans and other risks such as coastal flooding risk. Taking these factors into account, it has been decided to incorporate the Carrick Roads and the seaward parts of the Percuil and Penryn Rivers in terms of the coastal processes assessment. Further to this, Restronguet and Mylor Creeks have been incorporated in terms of flood risk mapping.

2.11 Baseline Scenario assessment

2.11.1 No Active Intervention The following tables report the predicted evolution of the shoreline for the next 20, 50 and 100 years under a no active intervention scenario. This assumes that there is no further maintenance of the defences and they are left to deteriorate. The likely evolution of the MHWS position of the shoreline are shown for the Fal Estuary for the ‘No Active Intervention’ scenario in Figures 3a to c.


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Table 6. Shoreline predictions for the Fal Estuary under a no active intervention scenario

Predicted Change For Location/Confidence Years 0 – 20 (2025) Years 20 – 50 (2055) Years 50 – 100 (2105)

Unit 1: St Anthony Head to St Mawes

Along the majority of the frontage there are no defences. The only defences are de facto in front of the Place Manor.

Complete failure of the seawall at the start of this period.

No defences.

Confidence: High for majority of unit due to solid geology. Low at Place Manor where there is no data to indicate potential erosion rates following failure of seawall.

Westerly facing frontage exposed to both swell and wind waves. Pocket beaches and cliff will remain stable with some limited erosion. The seawall will hold the position of the coastline in front of Place Manor.

Continued stability with limited erosion of the pocket beaches and west facing cliffs. As the seawall fails there will be erosion in front of Place Manor. However, as the tidal and wave energy in this area is low, the retreat will be gradual.

Continued stability with limited erosion of the pocket beaches and west facing cliffs. (potential erosion in the order of 1-2m over 100 years). Continued erosion along the frontage to Place Manor.

Unit 2: St Mawes

Majority of the frontage is defended by seawall and harbour breakwater. The area between St Mawes beach and St Mawes Castle is unprotected.

Complete failure of the defences.

No defences.

Confidence: Medium for defended frontage as there is some historical records of change. High for the undefended frontage due to solid geology and cliffs.

The defences will continue to hold the location of MHWS. The undefended frontage will be stable with limited erosion.

Erosion resulting from the failure of defences is limited to the cliffs backing Summers Beach. Historically this area has eroded by 20m over 100 years, a similar rate to this is expected. Continued stability with limited erosion along the undefended frontage.

Continued erosion of the cliffs backing Summers Beach. The remaining frontage with intertidal rock platform will remain stable with limited erosion (1-2m per 100 years).

Unit 3: Castle Drive to St Just

No defences are present along the frontage. It is characterised by hard rock cliffs with a narrow rock and sand intertidal zone.

No defences. No defences.

Confidence: High due to solid geology.

The cliffs are likely to remain relatively stable with the potential for slight erosion owing to wave activity.

Cliffs remaining predominantly stable with some limited erosion.

Cliff remaining stable with potential erosion, the southwest facing frontage will be most at risk (erosion rates in the order of 1-2m per 100 years is possible).

Unit 4: St Just

The seawall in front of the church at St Just will remain in place. The relict bar is likely to remain in place over this period.

Failure of the seawall in front of the church and partial degradation of the relict bar.

The relict bar is likely to fail in this period, but it is unknown where the sediment will be transported or if the bar will just be shifted and close up St Just Pool.


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Confidence: High for the undefended areas due to the solid geology. Medium for the St Just frontage as the area is relatively stable but there is limited data.

The area of intertidal is likely to reduce owing to the limited sediment input and the increase in sea level.

Potential for limited erosion of the creek to the north of St Just owing to the increase in tidal prism. Low rate of erosion in front of the church as the area is very sheltered. Potential for the relict bar to be overtopped and start narrowing or moving during storms.

The creek to the north of St Just is likely to continue eroding, with potential for scour and an increase in the width of the creek. The response of the St Just frontage depends on how the relict bar behaves. It may either be lowered and retain its present position, be rolled inland to cut off the entrance to St Just Pool or it may maintain its present form. No matter which occurs it likely that there will be either no or only very limited erosion within St Just Pool.

Unit 5: St Just to Turnaware Point

No defences are present along the frontage. It is characterised by hard rock cliffs with a narrow rock or no intertidal zone.


Confidence: High due to the solid geology.

The cliffs are likely to remain relatively stable with the potential for slight erosion owing to locally generated wind waves.

Cliffs remain stable with limited erosion.

Cliffs continuing to remain stable with limited erosion (it is unlikely that the erosion will be in excess of 1-2m over 100 years).

Unit 6: Feock to Restronguet Point

Small sections of private defences along this frontage, predominantly slipways with some seawalls.

Failure of all defences. No defences.

Confidence: High due to the solid geology of the majority of the frontage. Medium at Loe Beach owing to the lower elevation of the beach and the defences.

The area is likely to remain stable with the intertidal rock cut platform being unlikely to erode significantly with the defences in place combined with the limited wave exposure.

The frontage will remain stable with limited erosion of the rock platform with sea level rise although owing to the high elevation of the coast this is unlikely to be more than a few metres.

Frontage remaining stable with limitied erosion. There is also likely to be inundation of the car park and boat yard behind Loe Beach as sea level rises. As the spit like formation leading to Restronguet Point is actually a geological structure held in place by bedrock it will not be prone to any movement or reorientation as a non-geological spit might.

Unit 7: Restronguet Point to Mylor Creek

There are small areas of privately maintained seawalls and slipways, with no defences along the remaining frontage.

Failure of all structures. No defences.


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Confidence: High – medium owing to the solid geology backing the frontage but there is a lack of data describing the defences.

The area is likely to remain stable.

Frontage will remain stable with limited erosion and inundation where the defences have failed especially around the entrance to Restronguet Creek. Limited erosion of the rock platform fronting the east facing shoreline.

Continue to remain relatively stable with limited erosion and inundation, the rates are likely to be low (1-2m per 100 years).

Unit 8: Mylor Harbour

This frontage is defended by harbour and quay walls.

Failure of defences which are not related to the harbour. Harbour defences are assumed to be maintained.

Harbour defences are assumed to continue to be maintained.

Confidence: Medium for the area owing to the uncertainties in the defence failures.

With all defences in operation there will be no change to the coastline.

The frontage to the east of Mylor Habour where the seawall has failed will remain stable with limited erosion, as this area is sheltered from most wave conditions the erosion will be small.

The area to the east of Mylor Harbour will continue to remain stable with some limited erosion. Potential inundation of the low lying areas behind the harbour owing to the sea level rise.

Unit 9: Mylor to Flushing

No defences are present along the frontage. It is characterised by hard rock cliffs with an intertidal rock platform.


Confidence: High due to the solid geology backing the frontage.

The area will remain relatively stable but maybe subject to some limited erosion owing to its exposure to swell and wind waves.

Continued stability of the coastline with some erosion.

Continued stability of the coastline with limited erosion, but these rates will be low (1–2m per 100 years) owing to the presence of the intertidal rock platform and elevated land behind.

Unit 10: Flushing

There are some short expanses of privately owned defences present. These include quay walls, slipways and seawalls.

Failure of defences. No defences.

Confidence: High as the area is backed by solid geology and historical data show little change.

Historically there has been no change in the shoreline and so with the defences in place this trend of no change is likely to continue.

As the defences fail the frontage will remain stable with a potential for limited erosion, although the coastline is predominantly fixed by the intertidal rock platform and it is not exposed to any swell waves so any erosion will be minimal.

The shoreline will continue to be predominantly stable with some limited erosion. There could be a narrowing of the intertidal zone as the sea level rises but the hard geology behind prevents much erosion, this would be more pronounced at the beaches.


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Unit 11: Falmouth Harbour

The majority of the frontage is defended up to the start of Pendennis Castle; from the Castle to Pendennis Point there are no defences. The defences along the majority of the Falmouth frontage are made up of a variety of seawalls, quay walls, harbour walls as well as large areas of reclaimed land around the docks. The former landfill site situated between the eastern breakwater and Sandy Cove is undefended and eroding along the northerly facing coast and defended with a rock revetment along the easterly facing coast.

Failure of the defences which are not related to the Docks and Harbours which are assumed to be maintained.

No defences except for those related to the Docks and Harbours which are assumed to be maintained.

Confidence: High due to the solid geology behind the undefended coastline and the continued maintenance of the remaining structures. Low at the landfill site between the eastern breakwater and Sandy Cove due to uncertainty over likely recession rates (recession has been plotted for both a erosion rate of 0.5 and 1m/yr to allow for uncertainty)

No change along the defended frontage and some erosion (0.5-1m/yr) along the undefended frontage.

No change along the Dock and Harbour defended frontages. Limited erosion along the areas of defence failures. Relatively quick erosion of the former landfill site on which the sewage works are built as the defences fail (0.5-1m/yr). Continued low rates of erosion along frontage from Pendennis Castle to Pendennis Point.

No change to the Dock and Harbour frontages. Some low rates of erosion in the areas where the defences failed. Relatively rapid erosion of the formerly defended landfill site in the vicinity of the sewage works (0.5-1m/yr) and in places may erode as far as the historic cliff face. Very limited erosion along the frontage from Pendennis Castle to Pendennis Point due to the solid geology along this frontage.

2.11.2 With Present Management Table 7 reports the predicted evolution of the shoreline for the next 20, 50 and 100 years assuming that the current defences are maintained, the ‘with present management’ scenario. The table is supported by Figures 4a to c.


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Table 7. Shoreline predictions for the Fal Estuary with present management


Unit 1: St Anthony Head to St Mawes

Along the majority of the frontage there are no defences. The only defences are de fecto in front of the Place Manor.

Continued maintenance of defences fronting Place Manor.

Continued maintenance of defences fronting Place Manor.

Confidence: High for majority of unit due to solid geology. Low at Place Manor where there is no data to indicate potential erosion rates following failure of seawall.

Westerly facing frontage exposed to both swell and wind waves. Pocket beaches and cliff will remain stable with some limited erosion. The seawall will hold the position of the coastline in front of Place Manor.

Continuation of generally stable frontage with limited erosion of the pocket beaches and west facing cliffs.

Continuation of generally stable frontage with limited erosion of the pocket beaches and west facing cliffs, although any erosion will be of a low rate, in the order of 1-2m per 100 years.

Unit 2: St Mawes

There are defences along the majority of the frontage. It is defended by seawalls and the Harbour breakwater. The area between St Mawes Beach and St Mawes Castle is unprotected.

Continued maintenance of all defences.


Confidence: Medium for defended frontage as there is some historical records of change. High for the undefended frontage due to solid geology and cliffs.

The defences will continue to hold the location of MHWS, with the undefended frontage remaining stable with limited erosion.

Sea level rise may result in coastal squeeze at Summers and St Mawes Beaches as the seawalls fix the landward extent of the beaches. Owing to the relatively sheltered location of the beaches this should not result in significant erosion of the beaches. There will be little impact elsewhere.

Continued coastal squeeze at the beaches, narrowing the intertidal and potentially lowering the MHWS and MLWS levels. Again, as a result of the sheltered nature of the area, only small amounts of sediment is likely to be lost from the beaches. Potential narrowing of the rock platform elsewhere owing to sea level rise, this will add additional pressure to the defences.

Unit 3: Castle Drive to St Just

No defences present and therefore same as No Active Intervention Scenario

N/A Unit 4: St Just

The seawall in front of the church at St Just will remain in place. Relict bar is likely to remain in place over this period.

Continued maintenance of the seawall in front of the church will ensure it maintains its position. The natural relict bar will become partially degraded.

The seawall in front of the church will require continued maintenance. The natural relict bar is likely to fail in this period, but it is unknown where the sediment will be transported or if the bar will just be shifted and close up St Just Pool.


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Confidence: High for the undefended areas due to the solid geology. Medium for the St Just frontage as the area is relatively stable but there is limited data.

The area of intertidal is likely to reduce owing to the limited sediment input and the increase in sea level.

Slight erosion of the creek to the north of St Just owing to the increase in tidal prism. Narrowing of the intertidal in front of the church as there is insufficient supply of sediment to allow it to accrete with sea level rise. Potential for the relict bar to be overtopped and start narrowing or moving during storms.

The creek to the north of St Just is likely to continue eroding, with potential for scour and an increase in the width of the creek. The relict bar may either be lowered and retain its present position, be rolled inland to cut off the entrance to St Just Pool or it may maintain its present form. If the bar cuts off St just Pool then the intertidal in this area will stop narrowing, if it doesn’t then the intertidal will continue narrowing.

Unit 5: St Just to Turnaware Point


N/A

Unit 6: Feock to Restronguet Point

Small sections of private defences along this frontage, predominantly slipways with some seawalls.

Continued maintenance of private defences.

Continued maintenance of private defences.

Confidence: High due to the solid geology of the majority of the frontage. Medium at Loe Beach owing to the lower elevation of the beach and the defences.

The area is likely to remain stable with the intertidal rock cut platform being unlikely to erode significantly with the defences in place combined with the limited wave exposure.

The area is likely to remain stable with limited erosion, although owing to the high elevation of the coast and the small sections of private defences any erosion will be of a low rate. Some coastal squeeze may occur at Loe Beach as sea level rises owing to the partial seawall fixing its landward location, there could also be some inundation behind the beach as the seawall does not cover the whole frontage. However, owing to the limited wave energy in the area this is not likely to result in a significant lowering of HW and LW.

Continued stability of the frontage with limited erosion. Continued narrowing of Loe beach is likely as a result of the sea level rise. There is also likely to be inundation of the car park and boat yard behind Loe Beach as sea level rises as the seawall does not extent the full length of the beach and is not to a sufficient elevation to protect after 100 years of sea level rise. As the spit like formation is actually a geological structure held in place by bedrock it will not be prone to any movement or reorientation as a sand spit would.


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Unit 7: Restronguet Point to Mylor Creek

Along the majority of the frontage there are no defences, but there are small areas of privately maintained seawalls and slipways.



Confidence: High – medium owing to the solid geology backing the frontage but there is a lack of data describing the defences.

The area is likely to remain stable.

Narrowing of the intertidal zone along the defended areas owing to sea level rise. Continued stability with limited erosion of the rock platform which fronts the east facing shoreline.

Continued narrowing of intertidal zone along defended areas, although there should not be significant beach sediment lost owing to the limited wave energy in the area. Potential for some inundation of the areas behind the defences depending on their elevation relative to the sea level. Continued stability with some limited erosion along the undefended frontage, any erosion rates are likely to be low.

Unit 8: Mylor Harbour

This frontage is defended by harbour and quay walls.



Confidence: High owing to the continued maintenance if all defences.

With all defences in operation there will be no change to the coastline.

There could be some narrowing of the intertidal zones along the frontage as a result of sea level rise, but there will only be limited erosion of the beach sediment as the area is sheltered from the majority of wave conditions.

Potential for inundation of the area adjacent to the defences dependent on the elevation of the defences relative to sea level rise. Continued narrowing of the intertidal zone, this should not completely remove all beach sediment.

Unit 9: Mylor to Flushing


N/A

Unit 10: Flushing

There are some short expanses of privately owned defences present. These include quay walls, slipways and seawalls.



Confidence: High as the area is backed by solid geology and historical data show little change.

Historically there has been no change in the shoreline and so with the defences in place the trend of no change is likely to continue.

The undefended section of the frontage will remain stable with the potential for limited low rates of erosion, although the coastline is predominantly fixed by the intertidal rock

Continued stability with some limited erosion along the undefended sections. There maybe some narrowing of the intertidal zone as the sea level rises, but there will


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platform and it is not exposed to any swell waves so any erosion rates will be low. The quay wall at Trefusis Beach will fix its position, and help prevent it from narrowing significantly with sea level rise.

only be small quantities of sediment lost from the beaches.

Unit 11: Falmouth Harbour

The majority of the frontage is defended up to the start of Pendennis Castle, from here to Pendennis Point there are no defences. The defences along the majority of the Falmouth frontage are made up of a variety of seawalls, quay walls, harbour walls as well as large areas of reclaimed land around the docks. The landfill site to the east of the eastern breakwater is undefended along its northerly facing coastline and defended with a rock revetment along the easterly facing coastline where a sewage works is situated.



Confidence: High due to the solid geology behind the undefended coastline and the continued maintenance of the remaining structures. Low at the landfill site between the eastern breakwater and Sandy Cove due to uncertainty over likely recession rates (recession has been plotted for both a erosion rate of 0.5 and 1m/yr to allow for uncertainty)

No change along the defended frontage and the majority of the undefended frontage will also remain stable. Some erosion of the undefended part of the landfill site between the eastern breakwater and the sewage works is expected (0.5-1m/yr).

No change along the defended frontage. The undefended part of the landfill site will erode relatively rapidly (0.5-1m/yr) compared to the adjacent coast. Continued stability with limited erosion along frontage from Pendennis Castle to Pendennis Point.

No change along the defended frontages. Potential for inundation over the top of the defences owing to the sea level rise. Relatively rapid erosion of the undefended landfill site (0.5-1m/yr) and in places may reach the hard cliffline behind the landfill. Continued stability with limited erosion (rates of up to 1-2m per 100 years) along the frontage from Pendennis Castle to Pendennis Point.

N/A = Not applicable


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2.11.3 Flood risk

The 1 in 200yr extreme sea level (Posford Haskoning, 2003a) has been combined with the relevant sea level rise guidance (Defra, 2006b) and the resultant sea level (Table 8) has been applied to the most recent LiDAR dataset to give an indication of how flood risk may change due to sea level rise. Table 8. Water levels used for flood mapping

Level 2002 2025 2055 2105 Defra Sea level rise (m) 0 0.08 0.32 0.96 Resultant 1 in 200 year water levels (mODN) 3.85 3.93 4.17 4.81

The results of this analysis are shown in Figure 5.

3. Camel Estuary

3.1 Overview The Camel Estuary is located on the northern coast of Cornwall and is classified as a ria. The estuary is large and relatively shallow with large areas of intertidal sandflats. The mouth is orientated towards the north and as such is exposed to offshore waves which can propagate into the outer part of the estuary, although the estuary is sheltered to a certain extent by the presence of Doom Bar at the entrance of the estuary and Town Bar which is adjacent to Padstow Harbour. The estuary is macro-tidal and tidal currents are relatively strong. There is some development along the estuary mostly at Rock and Padstow with harbours and defences present. A small amount of reclamation has also taken place in the upper estuary where some of the tidal creeks have been either partially or totally blocked off from the main estuary for either the creation of grazing marsh or during the construction of railway embankments (now the Camel Trail). Dredging for sand extraction has been undertaken in the past with the majority removed from Doom Bar. Presently dredging is still undertaken for navigational purposes in the Rock Channel. Large amounts of both fine and sand sized sediment were introduced to the estuary via the River Camel from mine waste, this supply ceased in 1930. The contemporary source of sand sized sediment into the estuary is not described within the literature. As the coast outside of the estuary is typified by cliffs interspersed with sandy pocket beaches, it is likely that the majority of sand is sourced from offshore sources rather than from the adjacent coast. There is probably a sufficient potential supply of sand sized sediment to allow the estuary sediment budget to remain positive into the future.


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3.2 Existing Policy

3.2.1 Shoreline Management Plan The first round SMP (Halcrow, 1999b) considered the Camel Estuary as far as the Amble Tidal Barrier. The coastal sections and policies are outlined in Table 9. Table 9. SMP1 coastal policies

Coastal Unit Preferred Policy Trevone Bay to Padstow

Do nothing with continued maintenance of beach access point.

Padstow Hold the existing defence line along entire length to maintain character and operation of harbour whilst also protecting the Camel Trail and backing properties.

Dinas to Porthilly Cove

Do nothing strategy in conjunction with strategic saltmarsh management implementation guidance.

Rock and Porthilly Cove

Hold the existing defence line along defended frontage with future hold the line elsewhere to protect assets currently undefended. Possible future advancement of the line depending on development proposals.

Rock to Daymer Bay

Do nothing to conserve important dune habitats and species.

Daymer Bay Hold the existing defence throughout the back of the bay. Dune management will be required in order to attempt to stabilise the dunes as attempts to date have failed.

Daymer Bay to Polzeath

Do nothing as no assets in need of defence.

(Halcrow, 1999b)

3.2.2 Catchment Flood Management Plan The East Cornwall CFMP (EA, 2008b) considers the Camel Estuary in its entirety and therefore overlaps with the SMP2 area. For this reason it is important to be aware of policy decisions made as part of the CFMP so they do not conflict with policy decisions for the SMP2. The policy for the Camel estuary is to take further action to reduce flood risk.

3.2.3 River Basin Management Plan The findings for the Camel are as follows: Current overall status: Moderate; Proposed status objectives: Good ecological status by 2027, good chemical status by

2015; and Current chemical status: Good.

3.3 Geology

3.3.1 Solid Geology The estuary bedrock is mainly Devonian grey slate, becoming purple with green bands further north and cut by large igneous intrusions of dolerite and blue elvan at Stepper Point,


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St Saviour’s Point, Brea Hill, Cassock Hill and the foreshore at Rock (McMullen and Associates and Herrington Geoscience, 1989). Slate forms low cliffs around much of the estuary and also the shore platform at Trebetherick Point. Where this bedrock is present at the high water mark, it forms a constraint that prevents some movement of the estuary.

3.3.2 Superficial Geology Pleistocene deposits comprising of granite boulders are present at both Tregunna and Trebetherick, these were probably deposited by glaciers during the last glaciation indicating that the Irish Sea ice sheet reached the shoreline in this area (Halcrow, 1999b). Raised beaches dating from the Plestociene also indicate that the valley was formally at a higher level during a period of raised sea levels in the Ipswichian interglacial period. Large areas of wind-blown sand typify the area around Rock and the sandbanks and intertidal area of the outer estuary. Beneath the beaches and banks a compact gravel substrate is present with a sandy silty matrix (Halcrow, 1999b). The gravel base overlain with sand and silt were deposited during post-glacial sea level rise and ranges in thickness between 20m on the west side and 3-5m on the east side of the Camel (Royal Haskoning, 2005).

3.4 Hydrodynamics

3.4.1 Tides

3.4.1.1 Tidal levels The Camel Estuary is macro tidal at Padstow, the tidal parameters at Padstow are summarised in Table 10. Table 10. Tidal parameters at Padstow

Parameter Levels at Padstow (m CD) Levels at Padstow (mODN) Mean High Water Springs (MHWS) 7.3 3.5 Mean High Water Neaps (MHWN) 5.6 1.8 Mean Low Water Neaps (MLWN) 2.6 -1.2 Mean Low Water Springs (MLWS) 0.8 -3.0

Tidal Range (m) Mean spring tidal range 6.5m Mean neap tidal range 3.0m

(UKHO, 2008)

3.4.1.2 Tidal flows The most comprehensive study of tidal flows was undertaken by McMullon and Associates and Herrington Geoscience (1989) which collected flow data throughout the estuary during two half-spring tidal cycles. These measurements were presented as a plot of vectors so absolute values were not always available, where values were presented in the report they have been reproduced in Table 11. Readings were taken at both 1m above the bed and 2m from the surface, these showed no significant differences in velocity between the bed and the surface.


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These measurements indicated that in terms of peak currents the outer estuary over Doom Bar was slightly flood dominate and the adjacent main channel approximately equal on the ebb and the flood. South of Doom Bar the Cassock Narrows showed a very slight flood dominance in the channel and ebb dominance over the intertidal area adjacent to St Georges Cove. Measurements on the northern edge of Town Bar showed flood dominance and an ebb dominance in the main channel. The main channel in the vicinity of Rock also shows an ebb dominance. The vectors over Halwyn Bank indicate a flood dominance, although this trend is not clear with vectors orientated perpendicularly to the estuary axis. No measurements were taken further up-estuary of Halwyn Bank. Table 11. Tidal flow parameters recorded in the Camel Estuary

Location Peak Flood (m/s) Peak Ebb (m/s) Doom Bar 0.49 0.3 Main channel east of Doom Bar 0.77 0.77 Cassock Channel 0.72 0.70 Rock Moorings 1.4 1.5

(McMullon and Associates and Herrington Geoscience 1989) In summary in terms of peak current speeds the estuary appears to be slightly flood dominant at the mouth, becoming slightly ebb dominant up estuary in the main channel towards Rock with some evidence of flood dominance over Halwyn and Town Bank. It should be noted that this assessment is based on a limited dataset which only considers one tidal cycle and does not take into account parameters such as the duration of peak velocity or the duration of the tidal cycle above a threshold able to transport sand sized sediment. Because of this the dataset cannot be used to fully detail tidal asymmetry patterns and subsequent movements of sediment, to do this more data would need to be collected over a longer timescale.

3.4.2 Wave Climate Wave modelling by Halcrow (1999b) indicates that the orientation of the Camel provides effective shelter against swell propagating in from offshore with the largest wave heights (Hs=1.9m) at Daymer Bay. Elsewhere within the estuary, the wave height is dominated by locally generated waves which can reach a height of Hs=1.0m. The ability for waves to propagate up the estuary and to also generate within the estuary is likely to be affected by the state of the tide. The large intertidal sandbanks and sandflats at low water provide the estuary with a large degree of shelter, in particular, the presence of Doom Bar at the estuary mouth.

3.4.3 Fluvial Flows The Camel Estuary is fed by the Rivers Camel, Amble and Allen, the input from these rivers is minor with Environment Agency data showing a mean flow of 6m³/s between 1964 and 1997 (Royal Haskoning, 2005). An analysis of freshwater gauging stations data concluded that extreme fluvial events did not correlate with any observed or recorded morphological changes in the Camel Estuary (McMullon and Associates and Herrington Geoscience, 1989).


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3.4.4 Extreme Water Levels Still extreme water levels for the year 2002 were derived for the south west by Posford Haskoning (2003a). As part of this work water levels were calculated for Padstow and Wadebridge, the study found that the extreme water levels are the same at both the locations considered, these levels are summarised in Table 12. Table 12. Extreme water levels in the Camel Estuary



3.5 Holocene to Recent Evolution The Camel Estuary is a ria which is a drowned river valley formed during post-glacial sea level rise. During this period the estuary would have been partially filled with Holocene sediments with thicknesses of 20m present on the west side of the Camel and 3-5 m on the east side (Selwood et al, 1998).

3.6 Present Geomorphology The mouth of the Camel Estuary is orientated in a northerly direction meaning that swell can propagate into the estuary from offshore although it is sheltered from the predominant south westerly winds. The estuary is large and relatively shallow and has a large surface area, with large expanses of sandflat exposed at low tide. Beaches and dune systems are also present near the mouth on both the east and west banks of the estuary. Large sandbanks are present at the estuary mouth (Doom Bar) adjacent to Rock and Padstow (Town Bar) and in the region where the estuary changes orientation (Halwyn Bank). The estuary is dynamic and the position of the main channel has changed in the past, although the presence of the main sandbanks described above have remained largely fixed since the first Admiralty Chart published in 1839 (McMullon and Associates and Herrington Geoscience, 1989). The following sections provide a description of the geomorphology of each of the process units within the estuary (Figure 6). These process units are based on those developed for the previous SMP (Halcrow, 1999b) and are chosen based on areas of similar geomorphology and coastal behaviour.


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3.6.1 Stepper Point to Padstow This part of the coast is on the west side of the outer estuary and the majority of the section fronts Doom Bar, a large sandbank which is uncovered at low water. Presently Doom Bar is connected to the western shoreline of the estuary forming a large intertidal sandflat. Historical charts from 1839 and 1903 show that the main channel was formally located on the west side of the estuary and by 1931 the channel had switched to the east side of the estuary in the same position as today. It has been suggested that this switch occurred in 1929 (McMullon and Associates and Herrington Geoscience, 1989). Harbour Cove is situated to the south of Doom Bar and forms a northerly facing beach backed by sand dunes. Further south, between Harbour Cove and Padstow, the estuary narrows from approximately 1.5 to 0.5km. This part of the estuary is also fronted by an intertidal sandflat, which is essentially an extension of Doom Bar. St Georges Cove, a small pocket beach is present along this stretch of the estuary.

3.6.2 Padstow This section of the estuary is dominated by the fishing harbour of Padstow and as such the coastline is fronted by a range of harbour structures, breakwaters and walls (Halcrow, 1999b). Fronting Padstow is the Town Bar, a large intertidal sandflat with the main channel presently flowing around the east side (on the Rock side of the estuary). Historic Admiralty charts published in 1839, 1903 and 1931 show that the main subtidal channel was formally on the Padstow side of the estuary and by 1954 the main channel had switched to its present position (McMullen and Associates and Herrington Geoscience, 1989). Anecdotal evidence suggests that this switch occurred in about 1942, studies have not been able to correlate this change with fluvial flows (McMullen and Associates and Herrington Geosciences, 1989) and instead it could be possible that the switch is a delayed response to the change in channel position at the mouth (Royal Haskoning, 2005). All changes at MHW along this frontage have been as a result of construction or changes to the coastal structures.

3.6.3 Dinas/Portilly Cove to Tregenna/Dinham This section of estuary covers both banks as far upstream as the SMP2 limit at Tregunna to the south and Dinham to the north. Along this length of the estuary, its orientation changes from a north to south to an east to west axis. The estuary is characterised by a number of sand flats and sand banks. Halwyn Bank, the main sandbank is located immediately east of Town Bar, although this feature is persistent and appears on historic charts and maps in a similar position, its shape and orientation has varied greatly over the years as a result of changes to the deep water channels flanking it to the south and north (McMullon and Associates and Herrington Geosciences, 1989 and Royal Haskoning, 2005). Between Dinas and Tregunna (the southern side), a number of creeks and coves have been partially cut off from the main estuary by embankments which were originally built for the railway but are now used as a cycle path (The Camel Trail). These are (from west to east)


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Dennis Cove, Little Petherick Creek, Old Town Cove, Pinkson Creek and an unnamed inlet west of Tregunna. As there are sluices incorporated into the embankments, these inlets and coves (apart from Dennis Cove which is largely freshwater and cut off from the estuary) are still tidally influenced. At Little Petherick Creek the embankment only stretches halfway across the mouth with the remainder being crossed by an iron bridge. At both Little Petherick Creek and Pinkson Creek the sheltering effect of these embankments has encouraged mudflat and saltmarsh development in the lee of these features. Between Portilly Cove and Dinham (the north side), there is no evidence of reclamation with the two inlets of Cant Cove and Trevelver Cove (west to east) still fully open to the estuary.

3.6.4 Tregenna/Dinam to Wadebridge Within this process unit the estuary character changes with the intertidal sediments comprising predominantly of mud and the presence of saltmarsh. The construction of a training wall in 1870 and the embankments across the mouths of Dinham and Amble Creeks in the 1950s resulted in reductions in tidal flows along the northern bank of the estuary and a corresponding increase in sediment deposition resulting in expansion of the saltmarsh. Aerial photographs show that saltmarsh has increased in extent between 1947 and 2002 (Royal Haskoning, 2005). Upstream of the training wall some areas of the south bank were reclaimed by 1839 for use as a railway line which is now the Camel Trail. A strip of saltmarsh fronts this reclamation, aerial photographs from 1947 and 2002 show little change to the extent of this saltmarsh (Royal Haskoning, 2005).

3.6.5 Rock and Porthilly Cove This area of the estuary assumes a north to south orientation, with the town of Rock to the east positioned opposite Padstow (to the west). Porthilly Cove is a shallow sandy cove situated south of Rock; and is backed by a low cliff. Analysis of historic OS maps indicates that MHW has advanced by 20m since 1907. Rock has a rocky and sandy foreshore with a number of defences present comprising of masonry walls, timber piles and rock armour (fronting the boat storage area along Rock Beach) and a rock groyne to the west of the passenger ferry (Halcrow, 1999b). The rock groyne has the impact of reducing longshore transport along this frontage although there is no evidence of any detrimental impact to the coast. The rock armour along Rock Beach prevents interactions between the beach and the dunes behind the armour although as the beach is fed from the north the impacts of this are minimal on beach levels. The sand dunes here form part of the Rock Dunes SSSI (Site of Special Scientific Interest), which are currently accreting (Halcrow, 1999b). The main deep water channel currently flows past Rock and, as discussed earlier, formally flowed along the Padstow side, switching at some point between 1931 and 1954. This channel migration led to extensive erosion of MLW along the Rock frontage. OS map evidence also indicates that MHW has retreated by some 120m at the beach to the west of Rock.


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3.6.6 Rock to Daymer Bay The shoreline along this stretch is dominated by a sandy intertidal backed by extensive sand dunes which are currently accreting (Halcrow, 1999b). These sand dunes are part of the Rock Dune SSSI. There are no defences along this frontage.

3.6.7 Daymer Bay Daymer Bay is a sandy beach flanked on either side by cliffs and backed by dunes. OS map analysis indicates that the MLW has retreated due to changes to the main estuary channel and that MHW has advanced by about 50 to 60m and that the dunes have retreated slightly (Halcrow, 1999b). Aerial photographs show retreat of the dunes between 1988 and 1998 and little change between 1998 and 2002 (Royal Haskoning, 2005).

3.6.8 Daymer Bay to Polzeath The coast between Daymer Bay and Polzeath is characterised by low lying cliff and a rock platform with a small sandy beach present at Trebetherick, north of Trebetherick Point which is also backed by a low rock cliff. The erosion of the cliffline along this frontage is estimated to be eroding at a rate of 1 to 2 m over the next 100 years (Halcrow, 1999b).

3.7 Anthropogenic Intervention There are tidal defences at Rock and Padstow. The tidal defence schemes in Padstow are designed to protect properties from frequent flooding and for more extreme events, up to and including the 0.5% tidal flood event (CFMP). There is no evidence that the shoreline defences are having any significant impacts on coastal and estuarine processes. Further coastal defence information from the Environment Agency’s NFCDD will be provided separately to this document.

3.7.1 Embankments and Bridges Within the study area a number of embankments have been built along the coast between Dinas and Wadebridge during the construction of the railway (now the Camel Trail cycle track) which partially closed off a number of creeks and coves, this has been described in Section 3.6.3 and 3.6.4. Tidal embankments were also constructed across the mouths of Dinham and Amble Creeks in the 1950s, this completely closed of the tidal flow from these creeks, and the implications of this is discussed further in Section 3.6.4. The construction of the tidal embankments resulted in the reclamation of 510,986m² and 49,364m² at Amble and Dinham Creeks respectively (Posford Duvivier & Mott McDonald, 2003). A further 152,414m² was also reclaimed downstream of Wadebridge on the southern bank of the estuary during the construction of the Camel Trail. A training wall was also installed in 1870 along the northern bank adjacent to Amble Creek, the implications of this is discussed in Section 3.6.4.


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3.7.2 Dredging

Through the analysis of historic records it has been estimated that around 10 million tons (6Mm³) of sediment has been removed from the estuary between 1836 and 1989 (McMullen and Associates and Herrington Geoscience, 1989). The majority of this was removed from Doom Bar for agricultural purposes during the 19th century although this also includes dredging of the navigation channel at Rock (McMullen and Associates and Herrington Geoscience, 1989). As this calculation is based on an incomplete dataset it is a best estimate of the actual volume removed. Since 1989, dredging of the Rock navigation channel has continued with around 60,000m³/yr being removed between 1990 and 2003. In 2004 this amount increased to 100,000m³ because a larger hopper was used (Royal Haskoning, 2005). Dredging records between 2005 and 2009 were not available.

3.7.3 Mine Spoil Cores taken outside the Amble Tidal barrier indicate that mining released some fine sediment into the estuary around the start of the 20th Century (Pirrie et al, 2000). The present distribution of sediment within the study area suggests that much of this material was deposited upstream of Tregenna. Based on historic records, it has also been suggested that some 5 million tonnes of sand sized sediment may have been discharged into the estuary (McMullen and Associates and Herrington Geoscience, 1989). Although it is noted that much of this may have accreted in the Wadebridge area to the north of the SMP2 boundary (McMullen and Associates and Herrington Geoscience, 1989). It is also important to consider that this calculation is based on a number of large assumptions and as such is very approximate.



3.8.1.1 Marine source The main source of sand sized sediment within the Camel Estuary is thought to be marine with sediment sampling within the estuary identifying high levels of marine-derived calcium carbonate (McMullen and Associates and Herrington Geoscience, 1989).

3.8.1.2 Mine spoil Mine spoil was deposited in the estuary during the early 19th century although much of this was upstream of Tregenna; the deposition of mine spoil is discussed above in Section 3.7.3.


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3.8.1.3 Fluvial sources

The flow of the rivers entering the Camel is low and it is thought that they contribute little sediment to the estuary. Much of the fine sediment entering the estuary is deposited on the mudflats and saltmarshes upstream of Tregenna.


3.8.2.1 Subtidal channels and intertidal sand flats Although the subtidal channels and intertidal flats are dynamic within the estuary, it is thought that the area of these features has remained constant due to a sufficient supply of marine sourced sand (McMullen and Associates and Herrington Geoscience, 1989 and Royal Haskoning, 2005). It is important to note that this conclusion is not based on quantified volumetric calculations (such as a comparison of sequential LiDAR (Light Detection and Ranging) or bathymetric survey datasets), but instead is based on the following information: The geochemical source of the sand in the estuary (McMullen and Associates and

Herrington Geoscience, 1989). The historical dredge requirement. The presence of asymmetric bedforms on intertidal sandflats which indicate a net

transport of sediment into the estuary and a stable intertidal zone.

3.8.2.2 Sand dunes Available evidence suggests that sand dunes within the Camel Estuary are a net sink for sediment. The dunes between Rock and Brea Hill have progressively advanced seaward by 140m between 1931 and 1988 (McMullen and Associates and Herrington Geoscience, 1989). This is likely to be due to slight changes in the channel fronting the coast resulting in a widening area of intertidal sandflat and hence an increased supply of sand (Royal Haskoning, 2005). Aerial photographs show that the dunes advanced seawards by a further 30m between 1988 and 1998 with little change between 1998 and 2002. In 1839 sand dunes were absent in Harbour Cove, formation of dunes began following the migration of the main channel to the east side of the estuary in 1929. This resulted in the attachment of Doom Bar to the west side of the estuary forming a large intertidal supply of sediment (Royal Haskoning, 2005). Limited dune development could be observed in an aerial photograph from 1947 (although this does not cover the entire Harbour Cove area) and no accretion has been recorded in aerial photographs between 1998 and 2002 (Royal Haskoning, 2005). Dunes at Harbour Cove have accreted slower than those between Rock and Brea Hill as the dunes on the west side of the estuary benefit from the prevailing southwesterly wind direction (Royal Haskoning, 2005). Conversely, the dunes at Daymer Bay are eroding with aerial photographs showing 20m of erosion between 1988 and 1998 and stability between 1998 and 2002 (Royal Haskoning, 2005). Halcrow (1999b) also note an un-quantified “slight retreat” of the dunes in Daymer Bay


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since 1907 from OS maps and suggest that this could be linked to the advance of MHW which could have been fed by sediment from the dunes. As the dunes at Daymer represent a relatively small proportion of the dunes in the Camel Estuary it is considered that sand dunes are an overall sink for sand sized sediment.

3.8.2.3 Saltmarsh and intertidal mudflats Comparison of aerial photographs between 1947 and 2002 has shown that the area of saltmarsh in the region of Amble and Dinham Creeks has increased (Royal Haskoning, 2005). This is likely to be due to the construction of the Dinham and Amble tidal barriers in the 1950s and the construction of a training wall in 1870 which greatly reduced the tidal flow in this area and subsequently encouraged the deposition of sediments and the increase in saltmarsh area. Saltmarsh on the southern bank of the estuary near Wadebridge has remained stable between aerial photographs taken in 1947 and 2002 (Royal Haskoning, 2005). Large amounts of sediment were deposited on the intertidal mudflats as a result of the deposition of mine spoil at the start of the 20th Century (Section 3.7.3). Throughout the Camel Estuary saltmarsh increased by 10ha between 1988 and 1995 (Royal Haskoning, 2005)

3.8.2.4 Dredging Dredging within the Camel has been undertaken in the past for both agricultural and navigation purposes, the trends of dredge volumes are discussed in Section 3.7.2.


3.8.3.1 Suspended sediment The levels of suspended sediment are very low within the main estuary. ABP Research and Consultancy (1995) reported levels of suspended solid between 1992 and 1995, sourced from National Rivers Authority (NRA) data, of 16mg/l in the outer estuary, 20mg/l at both Portilly Cove and Padstow, 24 mg/l in the mid-estuary and 26mg/l at Wadebridge. A single relatively high level of 102mg/l was recorded within Little Petherick Creek which could be due to the embankment and a railway bridge built across the creek mouth which would be expected to reduce flushing of sediments from the creek. The fine suspended sediment within the Camel is sourced from both natural processes, which is mainly thought to be fluvial, and discharges from sewage treatment works at Wadebridge, Little Petherick Creek and Porthilly Cove (ABP Research and Consultancy, 1995).

3.8.3.2 Bedload As the vast majority of sediments within the study area are coarse sediments derived from marine sources the predominant sediment transport pathway will be by bedload processes. The estuary is highly dynamic and therefore has a complex sediment transport pattern that has not yet been mapped in detail.


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Bedforms visible on the intertidal areas of Town Bar, Halwyn Bank and Doom Bar have been viewed in oblique aerial photographs by Royal Haskoning (2005). These bedforms show a flood tide asymmetry which is not reversed on the ebb tide, indicating a net transport into the estuary of coarse bedload material across the intertidal. The outer estuary in the vicinity of the Doom Bar is likely to be wave dominated (McMullen and Associates and Herrington Geoscience, 1989) and therefore wave processes as well as tidal processes will contribute to the up estuary transport of bedload sediments in this location. Patterns of peak flow within the Camel Estuary indicate flood dominance at the mouth of the estuary becoming ebb dominant at Rock. However, as already noted in Section 3.4.1.2 this is based on a limited dataset recorded over one tidal cycle and only takes into account peak flows and not flow duration. Because of this the dataset cannot be used to derive sediment transport pathways.

3.8.3.3 Aeolian processes As mentioned in Section 3.8.2.2 there are a number of accreting dune systems in the outer region of the estuary. The growth of these dunes can be attributed to the development of intertidal flats in front of the dunes which provides a sediment source at low water. It is noted that dune systems on the eastern side of the estuary have developed faster than those on the west, this is probably due to prevailing wind direction rather than a lack of sediment.

3.9 Impact of Sea Level Rise Based on the presumed large potential supply of sand sediment to the estuary and the past stability of the estuary, Royal Haskoning (2005) suggest that it is likely that the Camel will be able to maintain pace with sea level downstream of Tregenna. The intertidal ratio is fairly high for a ria (Defra, 2002) and the estuary is generally quite high sided and constrained hence there is little scope for expansion of intertidal area. The relatively small areas of intertidal saltmarsh and mudflat within the study area have shown evidence of some small-scale increases in area between 1947 and 2002 (Royal Haskoning, 2004). However, it is likely that much of the sediment has been sourced from mine spoil and a limited fluvial supply. The cessation of mining activity means that a significant supply of fine grained sediment is no longer available to the estuary. The lack of any significant contemporary supply of fine grained sediment would also suggest that the intertidal area will not continue to increase in the future with sea-level rise. There is limited scope for the intertidal to migrate landwards due to the nature of the estuary and therefore saltmarsh and mudflat area can be expected to decrease in the future. Within the study area, some of the saltmarsh and mudflat have colonised areas behind railway embankments, the response of these areas to sea level rise will depend on the future management of these structures. It is possible that if the embankments are maintained into the future it will encourage the further deposition of limited fine sediments behind the embankments and as a consequence the area of saltmarsh and mudflat in these locations could be maintained.


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3.10 Appendix F Assessment

Based on the available data, the estuary can be broadly split into two distinct sedimentary zones: Zone 1: This zone stretches between the estuary mouth and Dinham. This section is a

sink for marine sands and has areas of wide sand flats, sand banks, some sand dunes and beaches. This part of the estuary is very dynamic with intertidal areas such as Doom Bar, Halwyn Bank and Town Bar changing size and shape.

Zone 2: Upstream of Dinham the estuary is predominantly muddy in character. The

source of these fine sediments has not been investigated in detail although it is likely to be mainly from fluvial sources (Royal Haskoning, 2005). Saltmarsh and mudflats are present in this part of the estuary. Although sediment from fluvial sources are thought to be small they have been sufficient in the past to allow the intertidal saltmarsh and mudflat to gain a very small amount of area between 1988 and 1998 (Royal Haskoning, 2005). Sediment within this zone has been sourced in the past from anthropogenic (mining at the open pits of Mulberry and Wheal Prosper, near the Camel-Allen confluence) as well as from natural sources (Pirrie et al, 2000 and McMullen and Associates and Herrington Geoscience, 1989).

3.10.1


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Estuaries Assessment

Estuary Camel Estuary Location Cornwall, north coast Classification Origin: Drowned river valley;

Type: Ria Main characteristics Macro Tidal (Padstow), small to medium sized estuary. Data availability

Futurecoast Estuaries Assessment (Halcrow, 2002), Lower Camel Estuary: Geomorphology Scoping Study (Royal Haskoning, 2003). Camel Estuary Geomorphological Audit (Royal Haskoning, 2005).


Total area: The Camel is considered to be small to medium size in terms of the total estuary area relative to the range of estuaries in England and Wales. Intertidal area: The estuary has a relatively large intertidal area compared to its total area with saltmarsh present in the upper parts of the estuary. Channel length: The length of the estuary is considered to be moderate. Mouth cross sectional area: The estuary has a moderate to large cross sectional mouth area. Mouth width: The mouth has a moderate to large width which is constrained by rocky headlands. Tidal range: The tidal range in the estuary is moderate to large Mean freshwater flow: The freshwater input is considered to be minor (Royal Haskoning, 2005) in comparison to the size of the estuary with a mean river flow of 5.96 m³/s. Stratification calculations confirm that the estuary is well mixed. % Area: The estuary has a fairly high % area, i.e. The intertidal area ratio is fairly high, as the estuary does not fully empty at low water. Tidal velocities: At Rock, peak ebb and flood velocities on a spring tide are 1.5 and 1 m/s. Near the mouth at Trebetherick Point flood and ebb velocities are approximately equal with values of around 0.8 m/s. Tidal prism: The tidal prism is 8.2 x 106 m³ and 3.6 x 107 m³ at mean low water and mean high water respectively.

Verdict Verdict on significance: The estuary is medium in size and the mouth width is about average relative to the channel length resulting in average tidal velocities at the mouth. Tidal range is high and the intertidal ratio is fairly high indicating relatively large fluxes of water are transferred between the estuary and the open coast. Overall, in accordance with EGT2, in terms of water exchange, the estuary is assessed as significant with respect to the interaction with the coast.


Tidal asymmetry: The estuary is ebb dominant at the mouth according to Dronker’s gamma. Tidal velocity measurements indicate that this ebb dominance increases in magnitude further up-estuary. Morphological features: The estuary is largely natural although some reclamation of mudflats occurring in the upper estuary and dredging in the outer estuary does occur. The outer estuary (between Trebetherick and Padstow) is orientated in a northerly direction and therefore is open to swells from the Atlantic and consists of large intertidal sandflats backed by beaches and dunes with the sediment type dominated by sands of marine origin. The estuary changes orientation upstream of Padstow to an east to west direction, upstream of Dinham the estuary becomes dominated by muddy sediments with expanses of mudflats and saltmarshes present. Source sink relationship: Measurements of tidal currents (McMullan & Associates and Herrington Geoscience, 1989) and estuary dimensions (Halcrow, 2002) would suggest that the estuary is ebb dominant. In terms of sand, historical analysis suggests that the estuary is infilling and that sediments are derived from a marine source, in addition bedform analysis suggests that sand is transported into the estuary (McMullen& Associates and Herrington Geosciences, 1989). In terms of muds, sediment supply from the rivers is small, although, saltmarshes and mudflats have grown in area indicating that the supply of sediment is at present sufficient (Royal Haskoning, 2004). This would indicate that overall the Camel has a positive sediment budget and is currently a sediment sink. Plume generation: The relatively high flow ratio (Halcrow, 2002) and the predominantly coarse sand sized sediments mean that there is limited potential for plume generation during the ebb tide.


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Verdict Verdict on significance: Interactions between the open coast and estuary are likely to be limited to the outer part of the estuary with the outer estuary acting as a sink for marine sediment. Overall in terms of EGT3, in terms of sediment exchange, the estuary is considered to be significant in terms of the interaction with the coast.


Verdict on relevance of process issues: Step 1 – water exchange: significant Step 2 – sediment change significant Step 3, therefore, from EGT5, process issues are assessed as Grade A.


Historical reclamation: Some reclamation has occurred in the upper part of the estuary mostly to create grazing land from mudflats and saltmarsh with a total of 867,764m² of land cut off from the estuary including some small creeks that have been cut off from the main estuary with tidal embankments (Royal Haskoning, 2004). This is restricted to the upper parts of the estuary and is not considered to be significant relative to the size of the estuary (the amount reclaimed amounts to some 10% of the total estuary intertidal area prior to reclamation). Presence/absence of jetties at the mouth: There are no jetties or any other structures built at the mouth of the estuary. Maintenance dredging: Some dredging occurs at Padstow. Coastal Defences: Coastal defences, quays and jetties are present at both Rock and Padstow; these do not affect interactions between the open coast and the estuary. A training wall near Wadebridge probably helped mudflat and saltmarsh develop near Trewornan and caused the main channel downstream of the wall to move from the north to the south bank (Royal Haskoning, 2005). Future management of the estuary: A number of locations in the upper Camel (above Wadebridge) have been identified as potential sites for realignment with the potential for grazing marsh being flooded to form mudflat and saltmarsh. It has been suggested that the areas of Railway Junction and Trereven Wood are most appropriate as they will have least impact on tidal propagation and the flood defences at Wadebridge (Posford Haskoning, 2003b). Changes to the coastal management: No changes are known.

Verdict Verdict on significance: There are no coastal management issues that are likely to significantly affect interactions between the coast and the estuary therefore a rating of insignificant is applied.


Verdict: Step 3 – Process issues assessed as Grade A. Step 4 – Management issues assessed as insignificant. Therefore form Step 5 of EGT5, the Camel scores 2 in terms of overall significance and should be included within the SMP process.

Stage 2 Recommendation on how the estuary should be included in the SMP process (EGT6)

It is considered practicable for the estuary to be considered within the relevant open coast SMP.

Verdict Verdict: Include within open coast SMP. Stage 3 Recommendation on how far upstream the estuary should be included (EGT7)

The main interaction with the coast occurs in the outer estuary where the Camel is open to wave processes and the sediment type is dominated by sands of marine origin. Upstream of Dinham the estuary changes character with mainly muds of fluvial origin present. This part of the estuary is unlikely to be influenced by or have an influence on the coast outside of the Camel.

Verdict Verdict: The inclusion of the Camel within the open coast SMP should be limited to the mouth of the estuary through to Dinham.


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3.10.2 Discussion The above estuary assessment in terms of the interaction of the estuary with the coast can be summarised as follows: 1. Processes within the Camel are relatively well understood in comparison to the Fal and

the Fowey. 2. The Camel is macrotidal and exchanges relatively large volumes of water with the

open coast. 3. Large amounts of sediment are supplied from offshore into the estuary although the

ultimate source of this material is unknown. 4. Although reclamation, dredging and development are present within the estuary these

practices are not thought to be significant and it is unlikely that will affect the open coast.

The Camel is a relatively large and dynamic estuary with extensive sandflats towards its mouth and some mudflats and saltmarsh present in the upper estuary. Based on the available information, it is suggested that the SMP boundary could be placed at one of two possible locations. Firstly, the boundary could be placed immediately to the east of Halwyn Bank. This is because there is some evidence from historical change analysis that there is no link between channel changes upstream of this point and Halwyn Bank indicating that the influence of down-stream processes ends at this point and Halwyn Bank is instead controlled by flood tidal flows (Royal Haskoning, 2005). The estuary also changes orientation at this point so that it is no longer aligned towards the coast and therefore would be expected to be more sheltered than the estuary further downstream. Secondly, it is suggested that the SMP limit could be set at a line between Dinham and Tregunna as this represents the limit of marine sediment extent. To the east of this point sediment is derived mainly from fluvial sources and mining waste rather than the open coast. It is recommended that due to large amount of sediment imported into the estuary from the open coast that the boundary should be set at this location. In addition to the assessment of interactions between the open coast and the estuary provided by the Appendix F assessment it is important to set the boundary of the SMP whilst considering other factors such as the coverage of other management plans and coastal flooding risk. When considering these factors it was decided to consider the estuary in terms of the coastal process assessment to the limit suggested by the Appendix F assessment. The estuary was also considered as far as Wadebridge for flood risk mapping.


3.11.1 No Active Intervention Table 13 reports the predicted evolution of the shoreline for the next 20, 50 and 100 years under the no active intervention scenario for the Camel Estuary. This assumes that there is no


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further maintenance of the defences and they are left to deteriorate. The table is supported by Figures 7a-c. Table 13. Shoreline predictions for the Camel Estuary under a no active

intervention scenario


Unit 1: Stepper Point to Padstow

No defences. No defences. No defences.

Confidence: High for majority of unit due to solid geology. Low at Hawkers Cove due to dependence on channel position controlling exposure and uncertainties regarding this position.

This stretch of coastline is backed by hard rock which will prevent erosion. The sand dunes at Hawkers Cove have been accreting, this trend is predicted to continue unless the main channel shifts to the west side of the estuary in which case the dunes would erode. However it is impossible to predict when or if the channel might migrate. There would also be a narrowing of the intertidal if the channel migrated.

Majority of the frontage will remain stable as the high water level is fixed at most locations by hard rock cliff. In addition as the estuary is sediment rich it should be able to accrete with sea level rise. The main changes to this section of shoreline are likely to be to the dunes of Hawkers Cove which have accreted by 230m over 90 years. The accretional trend is predicted to continue unless the main deep channel migrates back over to this side of the estuary, in which case the dunes are likely to erode. If the channel does migrate back to the west side of the estuary there will also be a reduction in the intertidal width and the LW level will retreat landwards.

Majority of the frontage will remain stable, with the only area of potential shoreline change being at the dunes of Hawkers Cove. This change is still likely to be accretion unless the channel migrates in which case there would be erosion but only back as far as the hardrock cliff behind.

Unit 2: Padstow

The Padstow frontage is defended by a combination of seawalls, quay walls, harbour walls and a lock gate leading into Padstow Harbour. A channel connecting the harbour to the main channel is currently maintained.

Failure of the seawalls to the south of the harbour and quay. The harbour and quay structures are assumed to be maintained.

Continued maintenance of the harbour and quay structures with no other defences remaining.

Confidence: High for the areas fronted by harbour and quay structures as these are deemed to remain in position. Medium for remaining defended areas as

No change along the frontage as it is all defended.

There is still no change to the shoreline fronted by the harbour and quay walls. The area where the seawall has failed will become prone to erosion but owing to the underlying geology and the presence

No change to the harbour and quay walls, although if the channel migrates back to being adjacent to Padstow then there will be more pressure on the structures and so they may become prone to erosion.


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there are limited data but the area is predominantly backed by hard rock.

of the adjacent large expanse of intertidal the erosion rates will be low. However, if a deeper channel migrates to this area the rates of erosion will be increased as the area will become more exposed.

The area to the south of the harbour will continue to erode at low rates, but again this could be increased if a deeper channel migrates and reduces the intertidal width.

Unit 3: Dinas to Porthilly Cove

The area directly to the south of Dinas is partially protected by revetments. Between this and Porthilly Cove there are no specifically designed coastal defence structures, but there are revetments built across creek entrances in order to support the old railway line. These constrict the entrances to these creeks, only providing a narrow entrance to the creeks.

Failure of all defences and the old railway revetments, although the remains of the railway revetments are likely to continue to remain as structures and therefore continue to restrict the creek entrances.

No defences.

Confidence: Medium the area is predominantly backed by hard geology and characterised by high elevation land but there are limited data available.

The undefended frontage will remain stable with limited erosion, as the area is categorised by hard rock cliffs any erosion will be at a very low rate.

The frontage will remain stable with limited erosion, the highest rates of erosion (still only a few metres per 100 years) will be along the north east facing frontage between Dinas and the entrance to Petherick Creek. The failure of the old railway revetments may result in more rapid inundation of the creeks, although it may make very little difference.

The frontage will remain stable with limited erosion. Possible added pressure on any low lying land adjacent to the creeks as they will be more at risk from sea level rise with the failed revetments present, as when these were maintained they would have been more efficient in restricting the potential water levels within the creeks.

Unit 4: Rock and Porthilly Cove

There are some defences along the south facing shoreline of Rock, but none within Porthilly Cove. There are piles of rock armouring on Rock Beach to the south west of Rock, with a rock groyne at the east end of the beach. To the east of the groyne there is further rock armouring and to the east again there is an area of seawall around the sailing club and immediately to the east.

Failure of all defences. No defences.


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Confidence: Medium as it is difficult to assess how the frontage will respond when it is undefended and the response of the area is dependent on channel position controlling exposure and there are uncertainties regarding the channels position.

The beach to the west of Rock will be likely to retreat back to the rock armouring as this has been its historical trend, but will then be held at this position. The Rock frontage is likely to remain stable. Porthilly Cove has historically been accreting and a low rate of accretion or no change is predicted to continue over this period.

Erosion of the beach to the west of Rock will increase as the defences fail. This erosion will partially depend on whether the main channel migrates as this could increase erosion or initiate accretion. The failure of the groyne at the east end of the beach will exacerbate the erosion of the beach to the west of it, but reduce any potential erosion to the east. The remaining frontage to the east will still be prone to low rates of erosion. However, this will be much lower than the beach to the west as it is more sheltered and will have a supply of sediment from the erosion of the beach to the west. Porthilly Cove is likely to remain stable with the possibility of some accretion owing to the increase in sediment supply from the erosion to the west.

Continuation of the processes noted in the years 20 to 50. Historically the beach to the west has retreated up to 130m over 90 years, which was probably a result of channel migration and so a total retreat in this order of magnitude might be possible. Some erosion of the south facing Rock frontage would also be possible, but as this area is backed by hard rock the rates are likely to be in the order of a few metres per hundred years. Porthilly Cove is likely to either remain stable or continue accreting.

Unit 5: Rock to Daymer Bay


Confidence: Low as the evolution of the frontage is dictated to a large extent by the location of the subtidal channel controlling exposure. A high degree of uncertainty exists regarding the future position of the channel.

The sand dunes between Rock Beach and Brea Hill has historically been accreting, in the short term it is predicted to continue accreting but the location of the adjacent channel is unlikely to be a limiting factor. There is also a risk that if the channel migrates to the east side of the estuary then the sand dunes will be subject to erosion. Brea Hill is made up of hard rock cliffs and will remain stable. Daymer Bay has historically experienced erosion of the dunes whilst the beach has been accreting. This trend is predicted to continue with the overall

Daymer Bay and Brea Hill will continue to remain stable unless there is a change in the channel location when accretion would occur. The sand dunes immediately to the south of Brea Hill are likely to stop accreting and may start to slowly retreat as a result of sea level rise. The area of dunes immediately to the north of Rock Beach is likely to be subject to erosion as the defences on the adjacent section of Rock Beach fail and the entire dune frontage will be prone to erosion. The erosion rates are likely to be higher closer to the southern end

The predicted changes described in the 20 to 50 year scenario are likely to continue. The dunes immediately to the north of Rock Beach could be prone to erosion of up to 130m over 90 years as this has been recorded in this area historically. The dunes immediately to the south of Brea Hill are likely to either remain stable or be subject to some erosion. Brea Hill will remain stable and Daymer Bay maybe subject to periods of erosion and accretion but overall it is likely to remain stable. It is important to note that these predictions are


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location of the beach remaining relatively stable with isolated periods of erosion and accretion. There is a possibility that if the channel migrates to the west side of the estuary and the intertidal zone becomes much wider then there would be further accretion of the bay.

of the beach. assuming that the adjacent channel maintains its present position, if it migrates then the dunes to the south of Brea Hill could be subject to considerable erosion, Brea Hill would still remain stable and Daymer Bay could be subject to erosion.

Unit 6: Daymer to Polzeath


Confidence: High as the area is backed by hard rock cliffs and historically there has been little change.

This frontage is likely to remain relatively stable, with potential for low rates of erosion.

Likely to continue to remain stable with low rates of erosion.

Continue to remain stable with possible slight increases in rates of erosion owing to sea level rise. The erosion will be in the order of several metres per hundred years.

3.11.2 With Present Management

Table 14 reports the predicted evolution of the shoreline for the next 20, 50 and 100 years assuming that the current defences are maintained, the ‘with present management’ scenario. The table is supported by Figures 8a to c. Table 14. Shoreline predictions for the Camel Estuary with present management


Unit 1: Stepper Point to Padstow


N/A Unit 2: Padstow

The Padstow frontage is defended by a combination of seawalls, quay walls, harbour walls and a lock gate leading into Padstow Harbour. A channel connecting the harbour to the main channel is currently maintained.

Continued maintenance of the defences including the harbour and quay. Dredging of the navigation channel into Padstow is also assumed to continue.

Continued maintenance of the defences including the harbour and quay. Dredging of the navigation channel into Padstow is also assumed to continue.

Confidence: High for the areas fronted by harbour and quay structures as these are deemed to remain in position. Medium for remaining defended areas as

No change along the frontage as it is all defended.

There is still no change to any of the defended shoreline. However, if the main channel migrates back to the Padstow side of the estuary then the area will be more exposed with a much narrower

There is still no change to any of the defended shoreline as the estuary is thought to have sufficient sediment supply to adjust to any rises in sea level. Although the area could be prone to erosion if the


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there are limited data but the area is predominantly backed by hard rock.

intertidal zone. This would put pressure on the defences and potential reductions in the HW and LW levels of the intertidal and large reductions in the intertidal width.

channel migrates from the east side of the estuary to the west side as it has done in the last 100 years. Hence, the future stability of this area will be controlled by any migrations of the main channel.

Unit 3: Dinas to Porthilly Cove

The area directly to the south of Dinas is partially protected by revetments. Between this and Porthilly Cove there are no specifically designed coastal defence structures, but there are revetments built across the creek entrances in order to support the old railway line. These constrict the entrances to these creeks, only allowing a narrow entrance to the creeks.

Continued maintenance of all defences and the old railway revetments.

Continued maintenance of all defences and the old railway revetments.

Confidence: Medium the area is predominantly backed by hard geology and characterised by high elevation land but there are limited data available.

Potential for erosion along the undefended frontage, although as the area is categorised by hard rock cliffs this will only be at a very low rate.

Continued low rates (up to 1-2 metres per 100 years) of erosion along entire area.

Continued low rates of erosion throughout the entire length.

Unit 4: Rock and Porthilly Cove

There are some defences along the south facing shoreline of Rock, but none within Porthilly Cove. There are piles of rock on Rock Beach to the south west of Rock, with a rock groyne at the east end of the beach. To the east of the groyne there is further rock armouring and to the east again there is an area of seawall around the sailing club and immediately to the east.



Confidence: Medium as it is difficult to assess how the frontage will respond when it is undefended and the response of the area is

The beach to the west of Rock will be likely to retreat back to the rock armouring, but will then be held at this position. The Rock frontage is likely to remain stable. Porthilly

The beach to the west of Rock will start to reduce in width and elevation as coastal squeeze occurs. In addition this section is vulnerable from erosion of the sand dunes to the

The beach to the west of Rock will continue to lose sediment, becoming narrower and lower owing to coastal squeeze. In addition, historically the beach to the west has


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dependent on channel position controlling exposure and there are uncertainties regarding the channels position.

Cove has historically been accreting and a low rate of accretion or no change is predicted to continue over this period.

north which could potentially erode behind the defences. However, this erosion will partially depend on whether the main channel migrates as this could increase erosion or initiate accretion. The south facing frontage of Rock will remain stable with the defences in place, while Porthilly Cove will remain stable and could accrete.

retreated up to 130m over 90 years, and so there is an increasing risk that the erosion of the dunes to the north maybe subject to erosion and outflank the defences rendering them ineffective. There is a possibility of some erosion of the south facing Rock frontage, particularly between the groyne and Sailing Club as this area is starved of sediment owing to the updrift groyne. This erosion is more likely to be in the form of a reduction of beach HW and LW levels as opposed to a landward retreat. Porthilly Cove is likely to either remain stable or continue accreting.

Unit 5: Rock to Daymer Bay


N/A Unit 6: Daymer to Polzeath


N/A N/A = Not applicable

3.11.3 Flood risk The 1 in 200yr extreme sea level (Posford Haskoning, 2003a) has been combined with the relevant sea level rise guidance (Defra, 2006b) and the resultant sea level (Table 15) has been applied to the most recent LiDAR dataset to give an indication of how flood risk may change due to sea level rise. Table 15. Water levels used for flood mapping

Level 2002 2025 2055 2105 Defra Sea level rise (m) 0 0.08 0.32 0.96 Resultant 1 in 200 year water levels (mODN) 5.13 5.21 5.45 6.09



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4. Fowey Estuary

4.1 Overview The Fowey (Figure 10) is located on the south coast of Cornwall and is classed as a ria. It is a long and narrow estuary with a number of small tributaries, the main ones being Pont Pill, Penpoll Creek and the River Lerryn. The mouth of the estuary is exposed to the south and open to swell propagating into the estuary from offshore, although the narrow relatively deep mouth of the estuary limits the size of these waves (Halcrow, 1999a). Readymoney Cove, small beach which is fed with sediments dredged from the estuary, is situated on the western side of the estuary mouth. There is a relatively small amount of intertidal mudflats and saltmarsh (compared to the overall size of the estuary) located in the upper areas of the estuary. The outer and middle parts of the estuary are characterised by a deep water channel averaging in depth approximately 8 m and reaching a maximum depth of over 12 m off Lower Carn Point. North of Wiseman's Point water depths decrease markedly leaving a relatively shallow channel which extends up the length of the river. The estuary is macrotidal although the tidal asymmetry is not fully described in the literature. The estuary mouth is characterised by an undredged sill which acts to trap some sediment within the estuary from either upstream or offshore sources (Friend et al, 2006). Regular dredging of the harbour area between Readymoney Cove and the China Clay Dock, including the lower reaches of Pont Pill, indicates that the estuary is currently a sink for both fine and sand sized sediment. Analysis of bed sediments within the Fowey show that sediment is sourced from both marine and catchment sources (Friend et al, 2006) although the relative importance of each sediment source is difficult to quantify with present information. In addition it is difficult to identify specific areas of the estuary where deposition of sediment from the different sources predominates as very little is known about the redistribution of sediment within the estuary (Partrac, 2005). The open coast adjacent to the estuary is made up of rock cliffs and a number of pocket beaches and coves. Any longshore transport that is present is reported to be in a net west to east direction (Halcrow, 1999a) although the nature of the coast will probably hinder any longshore drift of sediment and hence magnitudes of transport are likely to be low. Sediment arising from mine waste has represented an important supply in the past; a significant volume of the present day intertidal mud and sand flats at the northern extent of the estuary is derived from this source (Pirrie et al, 2002). There is a relative lack of information describing the Fowey Estuary compared to the Fal and the Camel.


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4.2 Existing Policy

4.2.1 SMP The first round SMP considered the Fowey Estuary as far as the Boddinick Ferry crossing, excluding Pont Pill. The coastal sections and policies are outlined in Table 16. Table 16. SMP1 coastal policies

Coastal Unit Preferred Policy

Fowey Short term do nothing strategy on undefended developed frontage and undeveloped lengths with a long term hold the line strategy elsewhere.

(Halcrow, 1999a)

4.2.2 Catchment Flood Management Plan The East Cornwall CFMP (EA, 2008b) considers the Fowey Estuary in its entirety and therefore overlaps with the SMP2 area. For this reason it is important to be aware of policy decisions made as part of the CFMP so they do not conflict with policy decisions for the SMP2. The recommendations for the policy unit including the Fowey Estuary are to take further action to sustain the current level of flood risk into the future.

4.2.3 River Basin Management Plan The findings for the Fowey are as follows: Current overall status: Not yet assessed; and Proposed status objectives: Good chemical status by 2015.

4.3 Geology

4.3.1 Solid Geology The solid geology of the Fowey Estuary study area comprises mainly Devonian sedimentary rocks, typically comprising slates and sandstones with rare limestones and conglomerates (Pirrie et al, 2002). The solid geology forming the cliffs within the estuary is similar in composition to that outside. Analysis of the resistance of the cliffline outside of the study area has suggested that the cliff is likely to erode by between 0 and 1m over the next 100yrs, this can be used to infer the relatively resistant nature of the solid geology within the estuary. Because of this the geology exerts a significant control on the shape of the Fowey Estuary.

4.3.2 Superficial Geology The Devonian sedimentary rocks are overlain with Quaternary head deposits and associated valley gravels (Pirrie et al, 2002).


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4.4 Hydrodynamics

4.4.1 Tides

4.4.1.1 Tidal levels The Fowey is a macro tidal estuary, tidal parameters at Fowey are summarised in Table 17. Table 17. Tidal parameters at Fowey

Parameter Levels at Fowey (mCD) Levels at Fowey (mOD) Mean High Water Springs (MHWS) 5.4 2.35 Mean High Water Neaps (MHWN) 4.3 1.25 Mean Low Water Neaps (MLWN) 2.0 -1.05 Mean Low Water Springs (MLWS) 0.6 -2.45 Tidal Range (m) Mean spring tidal range 4.8 Mean neap tidal range 2.3

(UKHO, 2008)

4.4.1.2 Tidal flow Detailed measurements of tidal currents could not be sourced and as a result the net tidal asymmetry cannot be inferred. Some current speeds were measured by South West Water during a study for Fowey Sewage Treatment Scheme and are reported by Halcrow (1999a). These measurements show that peak ebb flows in the mouth of the estuary are in the order of 0.25 and 0.15 m/s for spring and neap tides respectively, with the strongest flows occurring towards the surface at mid ebb. Further up estuary, as the channel narrows towards Caffa Mill the velocities increase to 0.55 and 0.2 m/s respectively and again the strongest flow occurs towards the surface at mid ebb. On the flood peak flows are greatest 2 to 3 hours after low water, the lower estuary, peak flood flows are around 0.4 and 0.25 m/s for spring and neap tides respectively and occur around mid-depth. Because of the narrow nature of the estuary, flows are generally rectilinear and parallel with the axis of the estuary.

4.4.2 Wave Climate Wave propagation from the open sea into the Fowey Estuary was modelled as part of the SMP, this showed that the estuary entrance provides protection from wave penetration with the largest offshore waves measuring 0.5 to 1.0m (Hs) in the entrance (Halcrow, 1999a). Conditions within the estuary are dominated by locally generated waves these can reach a height of 0.7m (Hs) (Halcrow, 1999a).


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4.4.3 Fluvial Flows Fluvial flows within the estuary are low relative to its size, Pont Pill, Lerryn and the Fowey all supply fresh water to the estuary. Mean river flows from the CEH gauging station database is summarised in Table 18. Table 18. Summary of gauging station data

River Station Measurement Period Mean Flow (m³/s) Fowey Restormel 1961 – 2006 4.78

4.4.4 Extreme Water Levels

Still extreme water levels for the year 2002 were derived for the south west by Posford Haskoning (2003a). As part of this work water levels were calculated for Polruan, Fowey and Lostwithiel, the study found that the extreme water levels are the same at both the locations considered, these levels are summarised in Table 19. Table 19. Extreme water levels within the Fowey Estuary



4.5 Holocene to Recent Evolution The Fowey is a former river valley which has been flooded as a result of sea level rise during the last glaciation. The lack of any analysis detailing the formation of the estuary makes it difficult to comment on trends of recent evolution. The dendritic shape of the estuary and the lack of intertidal in the lower reaches could mean that parallels maybe drawn between the Fowey and the Fal whereby little sediment has entered the estuary during the Holocene when compared to the east coast estuaries and to reach equilibrium, more sediment will need to be deposited. It is possible that the extensive deposition of sediments in the upper estuary from mine spoil may have reduced the overall tidal prism of the estuary over the last 200 years, however there is however no quantification of this.


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4.6 Present Geomorphology The Fowey Estuary south of the China Clay Dock is relatively narrow and deep with a very small intertidal area. Upstream of the China Clay Dock there is some saltmarsh and extensive mudflat present. The estuary is orientated in a north-south alignment (Figure 10) and the tidal limit is at Restormel Bridge just to the north of Lostwithiel. The mouth of the estuary is relatively narrow and constrained by rocky headlands, Readymoney Cove, a small pocket beach is present on the western side of the estuary mouth. The cove itself is bordered by high cliffs which indicate that little sediment is exchanged with the adjacent coast; the beach is currently maintained using dredge spoil from Fowey Harbour and consists of shingle, pebbles and sand. Comparison of OS surveys from 1907 and 1998 indicate little change to MLW in Readymoney Cove (Halcrow, 1999a). There are cliff defences present at Readymoney Cove (Halcrow, 1999a). The towns of Polruan (east bank) and Fowey (west bank) are situated on opposite sides of the estuary. Both the frontages are characterised by cliffs and some beach which are made up of medium sand and pebbles. The foreshore at Polruan is maintained using dredge spoil from the harbour. A variety of seawalls and quays are present at both Fowey and Polruan. The town of Fowey has been historically susceptible to flooding from a combination of high tides and strong south-easterly gales (EA, 2008) and flooding can occur as a result of extreme tides only.

4.7 Anthropogenic Intervention There a number of flood defences, cliff defences, quays and walls present at both Fowey and Polruan. There is no evidence that these are currently having a negative impact on coastal processes (Halcrow, 1999a). Further coastal defence information from the Environment Agency’s NFCDD will be provided separately to this document (Annexe III).

4.7.1 Dredging Maintenance dredging of the main estuary amounts to 7-8x104 tonnes/yr which is subsequently deposited at Lantic Bay to the east of the mouth of the Fowey (Friend et al, 2006). Some of this dredged sediment is used to maintain the frontages at Readymoney Cove and Polruan.

4.7.2 Mine Spoil Large amounts of mine spoil have been deposited in the Fowey estuary, sediment sampling on the intertidal mudflats at a number of locations indicates that this mine waste was mainly released during the late 18th or early 19th century (Pirrie et al, 2002). The spoil largely consists of silts and clays (Partrac, 2005) and this release of spoil led to the rapid sedimentation of the upper Fowey Estuary.

4.7.3 Embankments Between the China Clay Docks and Lostwithiel, railway embankments have been built across the mouths of Bodmin and Woodgate Pill as well as the intertidal area fronting Golant.


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Admiralty Charts and aerial photographs show that these embankments have not completely blocked off the water flow and therefore the areas behind the embankments are still tidal. It is likely that the construction of these embankments would have led to increased levels of sedimentation both inside and outside of the barrier as the tidal flow is now restricted to the region of the outflow.



4.8.1.1 Marine source Sediment analysis has identified a landward supply of marine sediment (Friend et al, 2006). Possible sources of marine sediment include offshore sources and the erosion of cliffs and shore platforms outside of the estuary along the adjacent coast, although the most susceptible cliffs are located downdrift of the Fowey Estuary entrance, with the cliffs to the west of Fowey being relatively hard and resistant to erosion (Halcrow, 1999a). In addition it has also been suggested that dredged sediment from Fowey and Par Harbours, which is deposited in Lantic Bay to the east of the Fowey Estuary, could be transported back into the estuary (Friend et al, 2006). Distribution of the deposited marine sourced sediments is not clearly presented in the available literature and therefore the significance of this supply is not known. It seems that sediments from a marine source are generally confined to the lower estuary (Partrac, 2005).

4.8.1.2 Mine spoil As described in Section 4.7.2, silts and clays deposited from tin mining has represented an important supply of sediment in the past, as tin mining has now ceased it follows that this sediment supply is no longer available to the estuary. The presence of elevated levels of tin in Pont Creek and Mixtow Creek (Pirrie et al, 2002) suggest that this sediment has also been deposited in the lower estuary. Due to the lack of subtidal sediment information it is difficult to assess the overall significance of mine spoil as a sediment source in the SMP2 area. It is also possible that spoil sourced from disused China Clay pits in the upper estuary and spillage from the loading and shipping of china clay, this source cannot be quantified with the available data

4.8.1.3 Fluvial source Due to relatively low fluvial flows it is unlikely that the rivers supply a significant amount of sediment to the Fowey Estuary. An analysis of Environment Agency flow and spot Suspended Sediment concentrations (SSC) data showed low levels of SSC in all tributaries of typically <10 mg/l with occasional (lasting around 2 days) episodes of elevated (1-2 orders of magnitude) SSC (Partrac, 2005). This increase in SSC corresponded to an increase in flow discharge (Partrac, 2005) and illustrates that the rivers could periodically provide larger amounts of


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sediment during higher flows. Average values showed that Pont Pill, the River Lerryn and the River Fowey tributaries all contribute roughly equal amounts of sediment (Partrac, 2005).

4.8.1.4 Intertidal There has been reports of saltmarsh and mudflat erosion in the upper estuary (Partrac, 2005 and Halcrow, 2002), this sediment once eroded could be supplied to the lower estuary. However, due to a lack of information (such as a detailed historical analysis of extents) it is difficult to comment on the significance of this sediment supply.


4.8.2.1 Suspended sediment Suspended sediment values in the main estuary are not available and pathways have not been mapped in any great detail. An analysis of sediment characteristics (Friend et al, 2006) inferred both a marine and catchment source of sediments It seems likely that suspended sediment is supplied from upstream as a result of fluvial supply or reworked mine spoil (Pirrie et al, 2002, Partrac, 2005 and Friend et al, 2006). It is also possible that fine material from offshore is transported into the estuary (Friend et al, 2006).

4.8.2.2 Bedload There is no discussion of bedload transport within the Fowey Estuary.


4.8.3.1 Subtidal The dredging of Fowey Harbour suggests that the subtidal part of the estuary is accreting, as discussed above the relative significance of marine and catchment derived sediments is not clear.

4.9 Impact of Sea Level Rise Due to the lack of a detailed analysis describing the formation and past behaviour of the Fowey Estuary it is difficult to comment on the future response of the estuary to sea level rise with any certainty. The intertidal area ratio of the estuary is low (Halcrow, 2002), this indicates that the Fowey has the capacity for further potential sedimentation, this however depends on a sufficient available source. The current dredging requirement of the lower estuary indicates that there is a present day supply of sediment to the Fowey Estuary and this is likely to be sourced from a combination of the following sources:


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Sediment from offshore. Sediment from eroding mudflats and saltmarshes in the upper estuary which is

ultimately sourced from mine waste and a limited fluvial supply. A limited supply of sediment from fluvial inputs The cessation of mining within the Fowey catchment means that the estuary has experienced a marked reduction in sediment supply over the past century. The study area is characterised by a relatively steep topography which is largely constrained by the hard geology and it is likely that with future sea level rise the mudflats and saltmarshes within the estuary will erode due to a limited contemporary sediment supply. This will result in the overall intertidal area of the estuary reducing in size which may increase the tidal prism and subsequently lead to a slight increase tidal flow speeds. Overall it is likely that the estuary will continue to act as a sink for sediment and the subtidal will continue to infill and the intertidal will reduce in area.

4.10 Appendix F Assessment Broadly speaking, the estuary can be split into two zones based on the typical sediment distribution (after Partrac, 2005): Zone 1: The northern part of the estuary is characterised by extensive mudflats and

sandflats analysis has indicated that these have formed mainly as a consequence of sediment deposition arising from mining activity (Pirrie et al, 2002) and from other catchment and estuary sources such as fluvial sediment load and the erosion of channels and saltmarshes further up-estuary (Partrac, 2005). The cessation of tin mining activities in the region would imply that the primary source of sediment to the upper estuary has reduced.

Zone 2: The central and southern parts of the estuary are characterised by a lack of

intertidal area and a relatively deep channel which is maintained with annual dredging. The sediments in this area contain relatively less catchment derived sediments and more quartz sands that are probably from marine sources, although there is some uncertainty regarding the importance of this offshore source.


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4.10.1 Estuaries Assessment

Estuary Fowey Estuary Location Cornwall, south coast Classification Origin: Drowned River Valley

Type: Ria Main characteristics Macro Tidal, small estuary Data availability

Futurecoast Estuaries Assessment (Halcrow, 2002). Sediment transport pathways in a dredged ria system, southwest England. (Friend et al, 2006). Fowey Estuary Management Plan (Smith and Porter, 2003). Fowey Sedimentation Survey (Partrac, 2005).


Total area: The Fowey is considered to be small in terms of the total estuary area relative to the range of estuaries in England and Wales. Intertidal area: The estuary has a small intertidal area relative to its total area; most of the intertidal is up-estuary of Penpol Creek. Channel length: The length of the estuary is considered to be small to moderate. Mouth cross-sectional area: The estuary has a moderate cross-sectional area. Mouth width: The estuary has a moderate mouth width (but small in relation to the channel length) which is constrained by rocky headlands. Tidal range: The tidal range in the estuary is moderate. Mean freshwater flow: The freshwater flows in the estuary are considered to be relatively small with a mean river flow of 4.78 m³/s. Stratification calculations confirm that the estuary is well to partially mixed depending on tidal and river flow conditions. % Area: The estuary has a very small % area, i.e. The intertidal area ratio is very low, as the estuary does not empty at low water. Tidal Velocities: Tidal velocities cannot be quantified. Tidal prism: 1.10 x 107 m³ at mean high water and 2.97 x 106 m³ at mean low water.

Verdict Verdict on significance: The estuary has a small surface area and is narrow and relatively deep. Tidal velocities are unknown but are likely to be high at the mouth due to the relatively large tidal prism in comparison to the narrow mouth. Overall, in accordance with EGT2, in terms of water exchange, the estuary is assessed as marginal.


Tidal asymmetry: The estuary is ebb dominant at the mouth according to Dronker’s gamma (Halcrow, 2002). Morphological features: Intertidal mudflat is present only in the upper reaches of the estuary (mainly up-estuary of Penpol Creek) and saltmarsh is limited in extent. The mouth of the estuary is open to wave processes. Source/sink relationship: The regular dredging activity within Fowey Harbour indicates that the Fowey is a sink for both fine and sand sized sediment. Available analysis of sediment characteristics suggest that sediment is sourced from both the rivers and outside the estuary (Friend et al, 2006), the lack of a sediment budget means it is not possible to quantify the relative importance of each source (Partrac, 2005). Potential but unproven sources of marine sediment include eroding cliffs and shore platforms along the open coast as well as deposited dredge sediment from the harbour. In the upper estuary sediment is sourced from rivers and the reworking of mudflats, saltmarshes and channels, some of this sediment is originally derived from mine spoil (Friend et al, 2006). An undredged area across the ria mouth forms a sill, this acts as a sediment trap for sediments entering the Fowey from upstream and offshore (Friend et al, 2006). The beaches at Polruan and Readymoney Cove are enhanced and maintained using dredge spoil from the harbour. Plume generation: The flow ratio suggests that a plume maybe possible during an ebb tide and maximum fluvial flow.


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Verdict Verdict on significance: There are interactions between the open coast and estuary, in terms of an unquantified supply of marine sediment. The fluvial sediment deposited within the estuary is unlikely to be supplied to the open coast due to the morphology of the estuary. Overall in accordance with EGT3, in terms of sediment exchange, the estuary is assessed as marginal in terms of interaction with the coast.


Step 1 – water exchange: marginal Step 2 – sediment exchange: marginal Step 3, therefore, from EGT5, process issues are assessed as Grade B.


Historic reclamation: The estuary is predominantly natural with no evidence of historic reclamation. Presence/absence of jetties at the mouth of the estuary: No jetties or structures at the mouth of the estuary, some cliff stabilisation at Readymoney cove protecting property and infrastructure but these are unlikely to significantly affect coastal processes. Maintenance Dredging: Regular dredging of Fowey Harbour is undertaken, this sediment is deposited outside the estuary at Lantic Bay, it has been suggested that this could represent a possible source of sediment to the estuary (Friend et al, 2006). Future management of the estuary: The estuarine management plan does not detail any relevant management strategies. There a large amount of flood and coastal defence along with commercially important wharfs and quays present throughout Fowey and Polruan, the current policy is to hold the line as suggested in the SMP1. It is also noted that the beaches at Readymoney Cove and Polruan are currently maintained through the use of dredge spoil from the estuary. There are a number of important habitats present including seagrass beds in the upper estuary Changes to the coastal management: None known.

Verdict Verdict on significance: There are no management practices that are likely to significantly interact with processes on the open coast; because of this a rating of insignificant has been applied.


Verdict: Step 3 – Process issues assessed as Grade B Step 4 – Management issues assessed as insignificant. Therefore from Step 5 of EGT5, the Fowey scores 3 in terms of overall significance and does not need to be included within the SMP process.


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4.10.2 Summary

The above estuary assessment in terms of the interaction of the estuary with the coast can be summarised as follows: 1. The Fowey is a small estuary and as such exchanges relatively small amounts of water

with the open coast. 2. The Fowey is a sink for sediments, according to current understanding the influence of

marine sourced sediments is limited to the lower (seaward) part of the estuary although the importance of this marine source is not fully understood. The ultimate source of this sediment is likely to be from offshore as well as cliff and shore platform erosion along the adjacent open coast.

3. The morphology of the estuary suggests that sediment supply to the open coast from within the estuary could be limited by an undredged sill across the mouth of the estuary which traps some sediment within the estuary.

4. Sediment is dredged from the lower estuary and deposited in Lantic Bay on the open coast to the east of the estuary mouth, it has been suggested that this represents a source of sediment for the estuary.

Due to the overall relatively poor understanding of estuarine processes and interactions with the coast, the interactions identified are subject to some uncertainty. However, based on the available data it is recommended that the Fowey does not need to be included within the SMP. It could be argued that the lower Fowey Estuary (as far as the China Clay Dock) should be included within the open coast SMP as there is some evidence of marine derived sediments in this part of the estuary. However, the magnitude of this supply is not clear and it is unlikely to be derived from the adjacent open coast which is predominantly hard erosion resistant cliffs and small pockets bays and coves. Further to this it is suggested that Readymoney Cove should be included within the open coast SMP as it has the characteristics of an open coast cove, although it should be noted that Readymoney Cove is currently maintained with material dredged from the estuary. The Appendix F assessment concludes that based on coastal process interactions between the estuary and the open coast the SMP boundary should be from the north of Readymoney Cove (Mundy’s Rocks) to St Saviour’s Point. It is important however to consider additional factors that are not taken into account during the Appendix F assessment such as the incorporation of the estuary into any other management plans and other risks such as coastal flooding risk. Taking these factors into account, it has been decided to incorporate the Fowey Estuary as far as the china clay dock in terms of the coastal processes assessment. Further to this, the entire Fowey Estuary as far as Lostwithiel has been incorporated in terms of flood risk mapping.


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4.11.1 No Active Intervention Table 20 reports the predicted evolution of the shoreline for the next 20, 50 and 100 years under the no active intervention scenario for the Fowey Estuary. This assumes that there is no further maintenance of the defences and they are left to deteriorate. The table is supported by Figure 11. Table 20. Shoreline predictions for the Fowey Estuary under a no active

intervention scenario


Unit 1: Fowey

There are seawalls present at the back, north side and on the frontage to the north of Readymoney Beach. The defences for Fowey start approximately 500 metres to the north east of Readymoney Beach and continue to the ferry at the northern extent of Fowey. These defences consist of seawalls and quays. The defences fronting Polruan stretch for approximately 800 metres across its north and north west facing frontage. These defences are made up of seawalls, quays and slipways. In addition, Readymoney and Polruan Beaches are both renourished with sediment dredged from the central channel.

Failure of all defences and cessation of all beach nourishment and dredging.

No defences.

Confidence: Medium as the area is backed by hard rock geology but there is a lack of available data and the towns of Polruan and Fowey are of relatively low elevation and have historically been subject to tidal inundation.

There will be little change to the estuary over this period. This is because parts of the estuary remain defended and the undefended areas are backed by hard rock, with predominantly steep sides. In addition the estuary has a very low fetch for locally generated wind waves and only the entrance will be exposed to any swell waves.

Readymoney and Polruan Beaches will be subject to erosion in the form of a lowering of HW and LW and some landward retreat, the retreat will be limited by the hard rock located behind the beaches. The supply of sediment is not large enough for the estuary to silt up with sea level rise and so the shoreline within the estuary could be subject to low rates of

Continued lowering of the HW and LW levels at Readymoney and Polruan Beaches, with low rates of erosion of the rock behind. The low rates of shoreline erosion within the estuary will continue, with some parts of the estuary still remaining stable. There will be increased inundation at the low lying areas of Fowey and Polruan as sea level rises. Continued redistribution of


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erosion but will generally remain stable owing to the hard rock behind. However, with no seawalls fronting Fowey and Polruan the low lying areas of these towns adjacent to the coast could become inundated on high tides. The creek to the east of Polruan maybe subject to erosion upstream of where the dredging previously stopped and siltation within the previously dredged area.

sediment within the creek to the east of Polruan.

4.11.2 With Present Management

Table 21 reports the predicted evolution of the shoreline for the next 20, 50 and 100 years assuming that the current defences are maintained, the ‘with present management’ scenario. The table is supported by Figure 12. Table 21. Shoreline predictions for the Fowey Estuary with present management


Unit 1: Fowey

There are seawalls present at the back, north side and just to the north of Readymoney Beach. The defences for Fowey start approximately 500 metres to the north east of Readymoney Beach and continue to the ferry at the northern extent of Fowey. These defences consist of seawalls and quays. The defences fronting Polruan stretch for approximately 800 metres across its north and north west facing frontage. These defences are made up of seawalls, quays and slipways. In addition, Readymoney and Polruan Beaches are both renourished with sediment dredged from the central channel.

Continued maintenance of defences and continuation of all beach renourishment and dredging.

Continued maintenance of defences and continuation of all beach renourishment and dredging.


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Confidence: Medium as the area is backed by hard rock geology but there is a lack of available data and the towns of Polruan and Fowey are of relatively low elevation and have historically been subject to tidal inundation.

There will be little change to the estuary over this period. This is because parts of the estuary remain defended and the undefended areas are backed by hard rock, with predominantly steep sides. In addition the estuary has a very low fetch for locally generated wind waves and only the entrance will be exposed to any swell waves.

Readymoney and Polruan Beaches will remain stable owing to the continued renourishment, although the rate of renourishment may need to be increased as sea level rises to prevent narrowing of the intertidal. The shoreline within the estuary could be subject to low rates of erosion but will generally remain stable owing to the hard rock behind. However, with sea level rise the seawalls fronting Fowey and Polruan maybe under added pressure and depending on the elevation of the defences relative to the sea level rise some low lying areas behind the defences may become prone to progressively more frequent inundation.

Continued renourishment of Readymoney and Polruan Beaches will ensure they remain stable, although the quantity required will need to be increased in accordance with sea level rise otherwise the intertidal width will be reduced owing to coastal squeeze. The low rates of shoreline erosion within the estuary will continue, although some parts of the estuary will remain stable. There will be increased potential for inundation of the low lying areas of Fowey and Polruan behind the sea defences as sea level rises.

4.11.3 Flood risk

The 1 in 200yr extreme sea level (Posford Haskoning, 2003a) has been combined with the relevant sea level rise guidance (Defra, 2006b) and the resultant sea level (Table 32) has been applied to the most recent LiDAR dataset to give an indication of how flood risk may change due to sea level rise. Table 22. Water levels used for flood mapping

Level 2002 2025 2055 2105 Defra Sea level rise (m) 0 0.08 0.32 0.96 Resultant 1 in 200 year water levels (mOD) 3.80 3.88 4.12 4.76


5. References ABP Research & Consultancy. 1995. Environmental Review of the Camel Estuary. Padstow Harbour Commissioners, ABP Research & Consultancy Ltd, Research Report No. R.518, October 1995.


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ABP Research. 1999. Falmouth Sewage Treatment Scheme Phase II, Assessment of Impacts on Local Hydrodynamics and Marine Conservation Interest. ABP Research & Consultancy Ltd (ABP Research) for Pell Frischmann Water Ltd. Report No. R.0819. Andrews Hydrographics Ltd. 1990. Fal and Helford Marine Environmental Survey. Report to South West Water Services Ltd. Carrick District Council. 2005. Dredging Protocol. Baseline Document Fal and Helford Estuaries. Available from: http://www.portoftruro.co.uk/pdf/dredging_protocol.pdf Defra. 2006a. Shoreline management plan guidance. Volume 1: Aims and requirements. Department for Environment Food and Rural Affairs, March 2006. Defra. 2006b. Flood and Coastal Defence Appraisal Guidance. FCDPAG3 Economic Appraisal: Supplementary Note to Operating Authorities – Climate Change Impacts October 2006. EA. 2008a. West Cornwall Catchment Flood Management Plan. Environment Agency, September 2008. EA. 2008b. East Cornwall Catchment Flood Management Plan. Environment Agency, September 2008. EA. 2009. A consultation on the Draft River Basin Management Plan South West River Basin District. December, 2008, Corrected February 2009. Friend, , P.L., Velegrakis, A.F., Weatherson, P.D. and Collins, M.B. 2006. Sediment transport pathways in a dredged ria system, southwest England. Estuarine, Coastal and Shelf Science, Vol. 67, Issue 3, April 2006. Halcrow. 1999a. Rame Head to Lizard Point Shoreline Management Plan. Volumes 1 to 3: Produced by Halcrow Maritime in association with Herrington Geoscience, Exeter University Earth Resource Centre and Cornwall Coastal and Environmental Agency for the Cornwall and Isles of Scilly Coastal Group. Halcrow. 1999b. Lands End to Hartland Point Shoreline Management Plan. Volumes 1 to 3: Produced by Halcrow Maritime in association with Herrington Geoscience, Exeter University Earth Resource Centre and Cornwall Coastal and Environmental Agency for the Cornwall and Isles of Scilly Coastal Group. Halcrow, 2002. Futurecoast available on CD-Rom. HR Wallingford. 1985. Proposed Container Terminal at Falmouth, Field Data Collection. Report No. EX 1333. July 1985. HR Wallingford, 2008. Falmouth Cruise Terminal Hydrographic and Sedimentary Studies. Report EX 5809, Release 1.0, July 2008.


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IECS. 1996. The Fal Estuary: Coastal Processes and Conservation. Institute of Estuarine and Coastal Studies, University of Hull. Report prepared on behalf of English Nature. Marine Biological Association. 2003. Characterisation of European Marine Sites – The Fal and Helford (candidate) Special Area of Conservation. Occasional publication No. 8. McMullan and Associates and Herrington Geoscience. 1989. Technical Study of the Camel Estuary and Padstow Harbour Approach. Report to Padstow Harbour Commissioners. Project No. HM. 1809. Nicholas Pearson Associates, 1998. Falmouth Sewage Treatment Scheme Phase II: Environmental Statement. South West Water SWW/NPA/174. Partrac. 2005. Fowey Sedimentation Survey: Sources of Sediment to the Fowey Estuary: A Review. Report to Cornwall Council. Pirrie, D., Power, M.R., Payne, A., Camm, G.S. and Wheeler, P.D. 2000. Impact of mining on sedimentation; the Camel and Gannel estuaries, Cornwall. Proceedings of the Ussher Society, 10, 21-28. Pirrie, D., Power, M.R., Wheeler, P.D., Cundy, A., Bridges, C., and Davey, G. 2002. Geochemical signature of historical mining: Fowey Estuary, Cornwall, UK Journal of Geochemical Exploration, July 2002, vol. 76, no. 1, pp. 31-43. Pirrie D., Power, M.R., Rollinson, G., Hughes, S.H., Camm, G.S. and. Watkins, D.C. 2003a. Mapping and visualisation of historical mining contamination in the Fal Estuary, Cornwall. Available on CD-rom, [email protected], Camborne School of Mines, University of Exeter, Redruth, Cornwall TR15 3SE Pirrie, D., Power, M.R., Rollinson, G.S., Camm, S., Hughes, S.H., Butcher, A.R. and Hughes, P. 2003b. The spatial distribution and source of arsenic, copper, tin and zinc within the surface sediments of the Fal Estuary, Cornwall, UK. Sedimentology 50, pp579-594. Posford Duvivier and Mott Macdonald. 2003: Report on Regional Extreme Tide Levels. South west tidal levels update Feb 2003. Posford Haskoning. 2003a. Environment Agency South West Region Report on Regional Extreme Tide Levels. Final Report, February 2003. Posford Haskoning. 2003b. Camel Allen Geomorphology Study. Report to Environment Agency, South-West Region. Report No. STCG/2002/66. Royal Haskoning. 2003. Lower Camel Estuary: Geomorphology Scoping Study. Report to Environment Agency. Final Report, Project No. STCG/2001/67.


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Royal Haskoning. 2005. Camel Estuary Geomorphologic Audit. Report to Environment Agency, Cornwall South West. Final Report, No. 9P4961. Royal Haskoning. 2009. Falmouth Cruise Project Environmental Statement, Final Report. Falmouth Harbour Commissioners and Falmouth Docks & Engineering Company. Selwood, E.B., Thomas, J.M., Williams, B.J., Clayton, R.E., Durning, B., Smith, O. and Warr, L.N. 1998. Geology of the country around Trevose Head and Camelford. Memoir of the British Geological Survey, Sheets 335 and 336 (England and Wales). Smith, J. and Porter, S. 2003. Fowey Estuary Management Plan, prepared by the Fowey Estuary Partnership. UKHO. 2008. Admiralty Tide Tables Volume 1 2009 United Kingdom and Ireland including European Channel Ports. Published by the United Kingdom Hydrographic Office.

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Appendix A Estuary Guidance Tables (Appendix F of the SMP Guidance)


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Appendix A. Estuary Guidance Tables (Appendix F of the SMP Guidance) Estuary Guidance Table 1 General Decision-Support Framework The purpose of this table is to provide the overall context within which decisions will be made concerning the inclusion, or otherwise, of estuaries within the SMP process. Estuary Guidance Table 1 (EGT1) is supported by further Tables EGT2-EGT7.

Key Question Key Issues for Consideration

Indicators Reference Tables

Type, scale and significance* of physical** interactions

Physical size parameters of the estuary Physical process parameters of the estuary, and degree of sediment supply from river(s) and sediment exchange

with the open coast Presence/absence of morphological features within estuary and/or at estuary mouth Physical constraints within estuary and/or along adjacent coast (e.g. defences and/or geological controls) Potential for large-scale changes in alignment of defences within estuary and/or along open coast

Should the estuary be included in the SMP process?

Nature and complexity of management issues

Presence/absence of control structures at the estuary mouth and/or within the estuary and/or along the open coast Common sources of risk between the estuary and open coast (e.g. tidal flooding, wave erosion) Continuity, location and/or scale of receptors at risk close to the estuary/coast interface (e.g. life, development,

nature conservation, natural heritage, existing land and water uses) Limits of other ‘strategic’ flood and coastal management initiatives (e.g. CFMPs and/or CHaMPs)

EGT2-5

SMP How should the estuary be included? eSMP

Physical size (logistics) Complexity of management issues

EGT6

Consideration of estuarine processes

Balance in fluvial, tidal and coastal processes throughout estuary and extent of interactions (physical and logistical) Presence of natural or man-made constraints and assessment of cross-sectional morphological form How far upstream should

the estuary be included? Selection of shoreline management policy

Presence/absence of morphological features and their interconnectivity between different environments Location, extent and type of management issues

EGT7

* ‘Significant’ interaction need not necessarily only be confined to ‘large’, but could relate to other factors key to the development of either the coast or estuary (i.e. complexity of interactions). Assessment of ‘significance’, therefore, needs to take account of the scale of the interaction relative to other factors (e.g. resistance of geology, availability of sediment).

** Physical interactions principally relate to water and sediment exchanges between the estuary and open coast. Chemical and biological interactions and water quality issues may be incorporated, if appropriate, in consideration of ‘management issues’.


R/3834/1 A.2 R.1558

Estuary Guidance Table 2 Significance of Water Exchange This table assists the user in determining the significance of water exchange between the estuary and the open coast in order to inform the decision about whether or not an estuary should be included in the SMP process.

Assess significance of water exchange

Significant Marginal

1. Make an informed assessment about the overall scale of water exchange between the estuary and the open coast by considering the following estuary parameters from the Futurecoast estuaries database and judging whether they fall into the range ‘insignificant to low’, ‘moderate’ or ‘high to extensive’:

Total area Inter-tidal area Channel length Mouth area Mouth width Tidal range Mean freshwater flow

2. Supplement the above information with local or specific knowledge about the following estuary

parameters:

Tidal prism Tidal velocities

3. Use the above understanding to make an informed assessment of the significance of the water

exchange between the estuary and the open coast. This may be assisted by consideration of the following factors, although there may some anomalies, usually large estuaries or inlets, where the ratios do not apply:

Ratio of total area to channel length (large = wide embayment more likely to be subject to wave processes, small = longer, narrower estuary more likely to be dominated by tidal processes)

Ratio of tidal range to mean freshwater flow (large = tidal processes dominate, small = river process dominate)

Ratio of mouth area to mouth width (large = large average mouth depth and hence large water exchange, small = small average mouth depth)

Geology of mouth and adjacent coast (hard = relatively erosion resistant even with high flows associated with high water exchange, soft = erodible even with marginal water exchange)

Degree of development of adjacent coast (low = less significant, high = more significant).

Insignificant


R/3834/1 A.3 R.1558

Estuary Guidance Table 3 Significance of Sediment Exchange This table assists the user in determining the significance of sediment exchange between the estuary and the open coast in order to inform the decision about whether or not an estuary should be included in the SMP process.

Assess significance of sediment exchange


1. Make an informed assessment about the overall scale of sediment exchange between the estuary and the open coast by considering the following estuary parameters from the Futurecoast estuaries database or ‘estuaries assessment’ report (not presented here) and judging whether they fall into the range ‘insignificant to low’, ‘moderate’ or ‘high to extensive’:

Tidal asymmetry Presence or absence of morphological features such as banks and deltas Source or sink relationship with open coast (for both cohesive and non-cohesive

sediments) – (see ‘estuaries assessment’ report) Potential for plume generation during river spate (see ‘estuaries assessment’ report)

2. Supplement the above information with local or specific knowledge about the following issues:

Catchment area and existing/planned catchment land uses (influences sediment supply from estuary to coast)

3. Use the above understanding to make an informed assessment of the significance of the

sediment exchange between the estuary and the open coast, taking into consideration the following factors:

Availability of sediment (both cohesive and non-cohesive) to feed transport potential Critical thresholds for erosion, transport and deposition of estuarine and coastal sediments.

Insignificant


R/3834/1 R.1558

Estuary Guidance Table 4 Significance of Management Issues This table assists the user in determining the scale of management issues between the estuary and the open coast in order to inform the decision about whether or not an estuary should be included in the SMP process.

A.4

Assess significance of management issues


1. Take an informed assessment about the scale of management issues by considering the following factors from the Futurecoast estuaries database:

Historic reclamation Presence/absence of jetties at the mouth

2. Supplement the above understanding with local or specific knowledge about the following

issues:

Scope for large-scale anthropogenic intervention (e.g. barrage construction, development proposals)

Presence or absence of continuous ‘at risk’ zones between the estuary and coast (e.g. flood risk zones, designated habitat areas, historic environment)

Indicative residual life of existing estuarine and coastal defences and scope for widespread changes in shoreline management policy to ‘managed realignment’, ‘hold the line’ (with new defences on eroding cliffs) or ‘advance the line’ (thereby significantly changing existing estuarine tidal prism, or supply of sediment from the coast)

Consistency of approach with adjacent SMPs and relevant CHaMPs Relevance of other management issues which can influence the physical interactions

between the estuary and coast (e.g. beach replenishment, weirs and sluices, navigation and aggregate dredging, bridges and causeways, training works)

3. Combine the above information to make an informed assessment of the significance of the

management issues.

Insignificant


R/3834/1 A.5 R.1558

Estuary Guidance Table 5 Assessment of Estuarine Inclusion in SMP Process The purpose of EGT5 is to assist the user in combining findings from EGT2-4 to determine whether or not an estuary should be included in the SMP process. The sensitivity of the decision from this table to changes in the outputs from EGT2, 3 and 4.


R/3834/1 A.6 R.1558

Estuary Guidance Table 6 Assessment of Method for Inclusion of Estuaries in SMP Process This table assists the user in determining how an estuary should be included in the SMP process. It is clearly a qualitative appraisal and should only be undertaken by those familiar with the estuary and its issues.

* eSMP must overlap with open coast SMP and those producing each plan must maintain information exchange

throughout the plan preparation process

Examples of where it is not practicable to include estuary within open coast SMP are:

Where the estuary is sufficiently large to necessitate consideration of its process and management policies outside of the open coast SMP.

Where the estuarine management issues are too complex or diverse to consider within the open coast SMP.


R/3834/1 A.7 R.1558

Estuary Guidance Table 7 Assessment of Extent of Estuarine Inclusion in SMP Process This table assists the user in determining how an estuary should be included in the SMP process.

* It may be necessary to consider an estuary to the tidal limit where there is potential for large-scale change in tidal

prism or the estuary is morphologically dynamic (i.e. high natural variability).

cornwall smp2: fal, camel and fowey estuaries - … c abp estuaries report.pdf · assessment phase....

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