royal beach coastal assessment final report revision 0

ROYAL BEACH COASTAL ASSESSMENT

FINAL REPORT REVISION 0

Prepared for:

Seacliff Properties(RB) Ltd. Vancouver, BC

Prepared by:

Northwest Hydraulic Consultants Ltd. Nanaimo, BC

16 April 2019

NHC Ref No. 3003631

nhc Report Prepared by:

Wil Hifsen,. P.Geo.

Geosdentist I Assoicate

Report Reviewed by:

Grant Lamont:, P .. Eng. Coastal Engineer I Principal

DIS.CLAIMER

laura Ramsden, M.Sc.,. EH Coastal Engrneer

This report has been prepared by N~orthwest Hydraufic Consu1ltants Ltd .. for the benefiit of SEACUFF

PROPERTIES (RB) LTD. for spedfic application to the Coastline Erosi:on Study,. Risk Ana[ysiis, and

Protection Plan for Seadiff Properties ltd.'s Royal Bay Beach Prop,erty. The information and data

contained herein represent Northwest Hydraulic Coinsultants ltd. best professional judgment in light of

the knowfedge.· and information available to Northwest Hydraulic Consultanits Ltd .. at the time of

preparation, and was prepared in accordance with genernHy accepted engineering and geosdences pradices.

Except as requked by law, thiis report and the information and data contained heremn are to be treated

as confrdenUal and may be used and relied upon only by SEACUFF PROPERTIES (RB) LTD., its officers and

employees. Northwest Hydraulic Consultants ltd. denies any liabiUty whatsoever to other parties who

may obtain ac:c:ess to this report for any injury, loss or damage suffered by such parties arisJng from their

use of, or reliance upon, this report or any of its contents.

Royal Beach Coastal Assessment I Final Report

TABLE OF CONTENTS

1 INTRODUCTION ..................................................................................................................................... 1 1.1 Site Description ................................................................................................................................ 1 1.2 Former Mining Operations .............................................................................................................. 1 1.3 Beach Response to Mine Closure .................................................................................................... 2 1.4 Royal Beach Coastal Bluff ................................................................................................................ 4

2 TIDES, STORM SURGE, AND WAVES ...................................................................................................... 5

3 FUTURE POTENTIAL IMPACTS WITH SEA LEVEL RISE ............................................................................ 6

4 COASTAL PROCESSES ............................................................................................................................. 7 4.1 Sediment Transport Mechanisms .................................................................................................... 7 4.2 Coastal Bluff Processes .................................................................................................................... 9

5 WAVE INDUCED BLUFF EROSION – A CONCEPTUAL MODEL .............................................................. 10

6 FLOOD HAZARD AREA LAND USE MANAGEMENT GUIDELINES .......................................................... 11 6.1 Estimated Future Natural Boundary of the Sea ............................................................................ 11

6.1.1 Tectonic Adjustment ................................................................................................................ 12 6.1.2 Future Natural Boundary Computation ................................................................................... 12

6.2 Tsunami Hazard ............................................................................................................................. 13 6.3 Provincial Guidelines for Recommended Setbacks at Royal Beach Coastal Bluff ......................... 13 6.4 Development Set-Back Computation ............................................................................................ 14

7 FUTURE SHORELINE RECESSION SCENARIOS ...................................................................................... 15 7.1 Methodology ................................................................................................................................. 15

7.1.1 Low Lying Beach Retreat Methodology (Zone 4) ..................................................................... 15 7.1.2 Steep Bluffs Retreat Methodology ........................................................................................... 16

7.2 Estimated potential magnitude of bluff recession with SLR ......................................................... 17

8 RISK ASSESSMENT ............................................................................................................................... 20 8.1 Methodology ................................................................................................................................. 21 8.2 Mitigation Concepts ...................................................................................................................... 22 8.3 Results ........................................................................................................................................... 24

9 CONCLUSION ....................................................................................................................................... 26

10 REFERENCES ........................................................................................................................................ 27

APPENDIX A

Drawing Sheet 1 – Coastal Zones and Typical Sections: Plan View Drawing Sheet 2 – Estimated Tsunami Hazard Lines: Plan View Drawing Sheet 3 – Estimated Future Shoreline Retreat and Tsunami Hazard Lines with 2 m Sea Level Rise, and Computed Development Setbacks: Plan View Drawing Sheet 4 – Impacts of Sea Level Rise: Section Views STA 0+855, 0+987, 1+213, 1+355 Drawing Sheet 5 – Impacts of Sea Level Rise: Section Views STA 1+559, 1+771, 1+824, 1+976, 2+122, 2+412

ii Royal Beach Coastal Assessment Final Report

LIST OF TABLES

Table 2.1 Tide elevations at Esquimalt Harbour. .................................................................................... 5 Table 6.1 Computed BC Government SLR coastal development set-back requirements. ................... 14 Table 7.1 Estimated potential magnitude of coastal bluff recession with SLR, shown as a horizontal

distance (m) from the present-day bluff position. ................................................................ 18 Table 8.1 Consequence of coastal processes for the Royal Beach development assets ...................... 20 Table 8.2 Advantages and disadvantages of mitigation options .......................................................... 22 Table 8.3 Risk assessment of mitigation options .................................................................................. 25

LIST OF FIGURES

Figure 1.1. Historical Beach Profiles near the Royal Bay Coastal Bluff (2005 and 2018). ............................. 3 Figure 3.1. Projected global SLR from the BC Ministry of Environment (2011). .......................................... 6 Figure 4.1 Boundary of the Littoral Drift model and varying sediment sizes (granulometry) applied

along the Royal Bay Beach Unit. The approximate Southwestern and Northeastern boundaries of SeaCliff’s property is shown for reference. ..................................................... 8

Figure 6.1. Definitions from the BC Ministry of Environment (2011). ........................................................ 11

LIST OF PHOTOGRAPHS

Photo 1. South westerly view of Royal Beach and Coastal Bluff during low tide. Image on the left is from 20 July 1997 (From CORI and TEL 1997) and image on the right is from 19 June 2018. ........ 3

Photo 2. January 2017 view of Royal Beach Coastal Bluff. ........................................................................... 9

Royal Beach Coastal Assessment 1 Final Report

1 INTRODUCTION

The foreshore area around Coburg Peninsula is an important focal point for the City of Colwood, and the property owned by SeaCliff Properties (RB) Ltd. (SeaCliff) is a key part of this beach unit. As the owners of a waterfront property with plans for substantial development, SeaCliff retained Northwest Hydraulic Consultants Ltd (NHC) to complete a coastal assessment to understand the various processes affecting the shoreline and to plan the future appropriate development setbacks along the coast.

NHC is pleased to present the results of an assessment of coastal processes at Royal Beach for Seacliff. This report summarizes the coastal processes that can cause the shoreline to retreat, describes the methods used to evaluate shoreline retreat scenarios, summarizes the provincial guidelines that apply to development setbacks in coastal flood zones, and presents potential future shoreline position with 2 m of future sea level rise (SLR) as a conservative and appropriate approach for development planning. Estimated preliminary tsunami hazard lines are also presented to inform the development planning process as per the BC Flood Area Land Use Management Guidelines.

Several future shoreline positions were computed for a 2 m SLR scenario, and the median estimated position was selected as the baseline for Seacliff’s geotechnical consultants to examine slope stability along the bluffs and identify appropriate development setbacks. It should be noted the estimated future shoreline position presented herein assumes no mitigation measures are applied, which could reduce the shoreline recession rate. Applying a future potential 2 m SLR position reflects Seacliff’s determination to apply best practices that recognizes the uncertainty with projections of future SLR and coastal erosion rates projections, and applies a precautionary approach to land development in coastal areas that includes provisions for adaptive management following the spirit of the BC coastal guidelines.

This is a preliminary assessment that will be used to inform other studies being carried out by geotechnical consultants and biologists to support Seacliff’s development planning process. Further investigation is required to determine site specific set-back.

1.1 Site Description

Royal Beach is located on the South Coast of Vancouver Island in the Strait of Juan de Fuca. It is primarily comprised of sand and gravel glaciofluvial deltaic sediments locally known as the Colwood Delta and is part of a dynamic coastline system that extends from Albert Head to Fisgard Lighthouse. For the purpose of this assessment, this entire stretch of coastline is termed the Royal Bay Beach Unit, whereas the term Royal Beach refers to that portion of the beach that adjoins the property owned by Seacliff.

1.2 Former Mining Operations

Mining of the Colwood Delta sediment started sometime near the start of the 20th century and lasted until it was closed in 2007. A previous report (Seabulk Systems Inc. 2008) indicates the sand component of the excavated material was disposed on the beach during early years of operation because there was

2 Royal Beach Coastal Assessment Final Report

no commercial market for it. Prior to the 1970’s, sediment was supplied to the beach in substantial amounts (O.Conner et al 2014), most recently from a dike located within the pit that breached sometime not too long before 2007 and deposited sand on the foreshore (TEL 2007).

1.3 Beach Response to Mine Closure

Since closure of the mine the beach profile has lowered, and this lowering is attributed to a natural response to the reduction in sediment supplied to the coastal system (TEL 2007). Photo 1 shows a 1997 and 2018 southwesterly view of the beach and coastal bluff that fronts the southwestern portion of Royal Beach. Both photos were taken near low tide, and the absence of the sand bar in the 2018 image indicates that the seaward portion of the beach profile has lowered overtime.

Figure 1.1 presents three beach profiles surveyed immediately south of the Royal Beach access point. Net longshore sediment transport patterns are from the northeast to southwest along this part of the coastline. Each plot shows series of profiles surveyed between 2005 and 2018, and the 2007 and 2018 beach profiles are highlighted to show the changes since the closure of the mine. Beach lowering is most evident in the northeastern most beach profile (Profile 1), with lesser but discernable lowering of the beach mid-way along the shoreline adjacent to the bluff (Profile 2), and relatively minor to no lowering in the southernmost profile (Profile 3). The image shown in Photo 1 is located approximately near the location of Profile 2.


Photo 1. South westerly view of Royal Beach and Coastal Bluff during low tide. Image on the left is from 20 July 1997 (From CORI and TEL 1997) and image on the right is from 19 June 2018.

Figure 1.1. Historical Beach Profiles near the Royal Bay Coastal Bluff (2005 and 2018).

Notes: 1) Solid Black profile line –

2018 2) Dash Black profile line –

2007 3) 5 times vertical

exaggeration 4) HHWLT – Higher High

Water Large Tide 5) MSL – Mean Sea Level 6) LLWLT – Lower Low

Water Large Tide

HHWLT

MSL

LLWLT

HHWLT

MSL

LLWLT

HHWLT

MSL

LLWLT

PROFILE 1

PROFILE 2

PROFILE 3

PROFILE 1

PROFILE 2

PROFILE 3

N


1.4 Royal Beach Coastal Bluff

The BC coastal development guidelines include special provisions for lots containing coastal bluffs that are steeper than 3H:1V and susceptible to erosion from the sea. A portion of the Royal Beach coastline is steep coastal bluff, with localized lower lying land near the former gravel pit and loading facilities. The Royal Beach coastal bluff was formed by meltwater that drained from retreating glaciers during the last ice age, and reportedly consists primarily of sand and gravelly sand overtop relatively impermeable deposits (TEL 2007). The differing permeability of the two layers causes groundwater to become perched and seep out of the contact layer between the two materials. The bluff is presently vegetated with shrubs and mature trees.

Several failures appear to be seepage triggered slope instabilities and gully formations where water has concentrated on the slope surface. Erosion of the bluff toe appears relatively minor under present day conditions indicating the bluff toe is presently rarely exposed to wave action.

At the time of delta formation, relative sea levels were much higher because of isostatic pressure from the weight of the glaciers. Under the post-glacial environment, continued isostatic rebound caused a drop in relative sea level and exposed the deltaic sediments to wave action. Continued isostatic rebound and fluctuating sea levels caused the bluff to eventually emerge to a height of approximately 60 m to 65 m above sea level. Subsequent mining operations have since lowered the bluffs to a height of approximately 40 m to 45 m above sea level (CORI and TEL 2007).

Sediment containment berms were constructed on top of the bluff and used to contain sediment ponds during operation of the mine (Jay McIntyre, P.Eng., TEL, personal communication, 31 October 2018). It is understood that the berms provide some level of seismic stability to these deposits and future destabilization of the containment berms from bluff retreat could affect the stability of the land and therefore must be considered in the development planning process. NHC and Thurber Engineering Ltd. (TEL) have been hired separately by Seacliff to support their development process and we understand the results of this report will be incorporated into geotechnical studies being carried out by TEL. Future estimates of bluff retreat (presented in Section 7) assume no mitigation measures are applied.


2 TIDES, STORM SURGE, AND WAVES

Tides, storm surge, and waves are the main driving forces affecting coastal process, such as erosion, longshore transport and deposition of sediment. An assessment of coastal processes is necessary to understand how these processes could impact Royal Beach under present and future potential conditions. Section 3 describes future potential changes with SLR and Section 4 describes the coastal processes along the Royal Bay Beach Unit.

Tides at Royal Beach are mainly semi-diurnal, experiencing two highs and lows per day of unequal strength. Table 2.1 summarizes the range in tide levels at Esquimalt Harbour, based on Chart 3419 from the Canadian Hydrographic Service. The levels are expressed in both local chart datum (relative to Lowest Low Water) and in Canadian Geodetic Vertical Datum1 (where 0 m approximately corresponds to mean water level).

Table 2.1 Tide elevations at Esquimalt Harbour.

Tide Condition Chart Datum (m)

Geodetic Datum (m)

Higher High Water Large Tide 3.4 1.5 Higher High Water Mean Tide 2.5 0.6

Mean Water Level 1.9 0

Lower Low Water Mean Tide 0.7 -1.2

Lower Low Water Large Tide 0.1 -1.8

Storm surges and wave runup elevate the ‘still water level’ above predicted tidal elevations. Surges can occur over large areas of the Strait in response to intense low pressure zones that form during storms. As waves approach the shoreline and the depth becomes shallower, the momentum of the wave energy pushes sea water up the beach slope. This dynamic process in known as wave runup and it has a major role in transport of sediment between the beach and nearshore areas (Davidson-Arnott 2010). Wave runup can cause seawater to impact areas that are farther up on the shoreline, above the level that would be governed by tides alone.

Tides, storm surge, and wave run-up values have been applied to estimate the future natural boundary of the sea (Section 6) and to estimate the future shoreline position with 2 m SLR (Section 7).

1 Unless otherwise specified, elevations in this report reference Canadian Geodetic Vertical Datum 1928 (HT2.0).


3 FUTURE POTENTIAL IMPACTS WITH SEA LEVEL RISE

Changes in global sea levels can potentially reduce the liveability of coastal regions in the future. Future changes in sea levels are difficult to predict and the timing of changes are highly uncertain.

Global sea levels remained relatively static over the 20th century (Clague 1989). However, it is now recognized that sea levels are rising and will continue to rise in the future. At present, the BC Ministry of Environment (BC MoE 2011) recommends applying a 1 m global SLR between 2000 and 2100 and a 2 m rise between 2000 and 2200. Figure 3.1 shows the projections adopted by BC MoE and a wider band that shows the uncertainty in global SLR projections varies between 0.5 m to 1.3 m by 2100 and 1.4 m to 3.4 m by 2200. Research on sea level rise has been ongoing since the provincial guidelines were issued, the most recent comprehensive study relevant to this project was published by the National Oceanographic and Atmospheric Administration in 2017 (NOAA, 2017) and includes higher SLR projections than presented in the BC guidelines.

There seems to be a consensus that SLR in excess of 2 m will occur eventually; therefore, future shoreline recession at Royal Beach was examined for a 2 m SLR scenario. This is intended to provide a precautionary approach for determining land development set-back requirements for SeaCliff (RB).

Figure 3.1. Projected global SLR from the BC Ministry of Environment (2011).


4 COASTAL PROCESSES

Waves and tides shape and modify the physical features that form the Royal Bay Beach Unit through erosion, transport, and deposition of sediment. Understanding the key driving forces are important to guide land use planning decisions, evaluate alternative mitigation measures, and limit undesirable impacts. Responsiveness of the Royal Bay Beach Unit to coastal processes occurs on many scales and timeframes, sometimes persisting for decades. Therefore, it is necessary to be aware of past trends and potential future changes such as SLR.

4.1 Sediment Transport Mechanisms

The Royal Bay Beach Unit is exposed to wind generated waves that can cause substantial changes to the beach morphology. Erosion, transport and deposition of sediment along the Royal Bay Beach Unit occurs through wave generated currents and turbulence. Sediment transport along the shoreline is driven by wind generated currents, tidal flows, and direction of incident waves. Longer scale changes that have occurred to the shoreline position, profile, and sediment composition include:

Altered sediment supply rates and patterns since the closure of the sand and gravel mine;

Shoreline hardening (anthropogenic construction of shoreline protections such as riprap); and,

Sea level rise (which has so far been limited due to crustal uplift).

Storm-generated coastline retreat is usually temporary, and the beach profile rebuilds if the storm occurs at a low to medium water elevation. However, the beach is not be able to naturally rebuild if the storm coincides with an exceptionally high-water elevation; this generally occurs from the joint occurrence of a high tide event with a significant storm surge. Furthermore, the probability of a storm event occurring at a high water elevation will increase over time due to SLR because mean sea level will be shifted upwards and therefore water elevations that rarely occur under present day conditions will occur more frequently in the future. For instance, a storm occurring at 1.5 m (which is the present day higher high water large tide level) will occur more frequently in the future.

Figure 4.1 shows the extents of the Littoral Drift2 model boundary used to assess sediment transport mechanisms. Model simulations assume the beach is comprised of a single grain size type that remains constant over time. This is a model limitation; therefore, a range of grain sizes were modelled to assess the sensitivity of the simulations and the results were interpreted in context of other analytical methods applied to estimate potential impacts to the shoreline associated with single storm events and with longer term littoral drift processes.

2 LitPack is a ‘MIKE powered by DHI’ software product that applies a deterministic approach to simulate coastal processes, and includes a suite of modules such as LitDrift.


Figure 4.1 Boundary of the Littoral Drift model and varying sediment sizes (granulometry) applied along the Royal Bay Beach Unit. The approximate Southwestern and Northeastern boundaries of SeaCliff’s property is shown for reference.

The model results indicate:

Cross-shore transport (or onshore-offshore movement) generated by storms is the dominant component of sediment transport for the Royal Bay Beach Unit compared to the littoral drift transport mechanism (or movement parallel to the shoreline).

A single storm could potentially generate a coastline retreat of 2 to 4 meters, while the littoral drift transport would likely require a period of approximately 20 years to cause the same scale of erosion. This is based on a model run using a typical storm event3 coinciding with a very high tide. The model results assume no protective measures have been implemented, which could alter the magnitude and rate of retreat and affect sediment transport processes.

A net loss of sediment is expected over time along substantial portion of Royal Beach, assuming sediment supply rates do not change. However, future erosion of the bluff is expected to deliver substantial volumes of sediment to the upper beach zone that will offset some of these losses.

In summary, the LitPack model suggests wave erosion has a more dominant immediate impact on the beach in front of Seacliff’s property than littoral drift processes. Mitigation measures applied to the shoreline could reduce the impacts of wave erosion; however, they would need to be carefully planned and designed to avoid or mitigate longer term impacts associated with altered littoral drift process. Erosion of the coastal bluff’s are likely to become more frequent over time with SLR, and this will supply sediment to the beach unit.

3 The modelled storm event took place on 10 March 2016, with a maximum wind speed of 57 km/h from ESE.

Fisgard Lighthouse Albert

Head

SW Property Boundary

NE Property Boundary

Focus area of simulated potential impacts


4.2 Coastal Bluff Processes

Coastal bluffs are relatively high relief features that are generally steeper than 40°, cannot be overtopped by wave run up, and are formed in unconsolidated or poorly consolidated sediments (Davidson-Arnott 2010). Assuming no mitigative measures are applied, erosional forces will break down the bluff material overtime causing it to recede. It is important to recognize bluff erosion and bluff recession as two distinct but closely interrelated processes. Bluff erosion refers to the rate of loss of material from the bluff due to slope failures or coastal erosion of material from the bluff toe, whereas bluff recession can be defined as the horizontal movement of the bluff toe over time.

Under present conditions, waves typically shoal and break on the shore platform4 and run up the beach slope only reaching the bluff toe during storm events that coincide with high tides. In its present state, the shore platform is exposed to and eroded by breaking waves, whereas the bluff toe is exposed to erosion from turbulent forces of sea water that can run up the beach and hit the bluff toe, associated abrasion from any beach sediment carried in the swash bore, and physical damage from log strike. Photo 2 shows a typical view of the present condition of the southern bluff. Logs and sediment deposits along the upper beach indicate waves are occasionally capable of reaching the bluff toe. Loose, unvegetated material on the slope is visible in the photo and is believed to be sediment deposited from a localized subaerial slope failure.

Photo 2. January 2017 view of Royal Beach Coastal Bluff.

4 The shore platform is the flat area located at the base of a coastal bluff that was created by erosion.


5 WAVE INDUCED BLUFF EROSION – A CONCEPTUAL MODEL

A geomorphic concept model of wave induced bluff erosion at Royal Beach can be described in general terms as a function between the resistance of the bluff to erosion and the force of waves reaching the bluff toe. This model assumes the episodic and spatially dispersed subaerial erosion5 of the bluffs that occurs under present conditions would continue, and is independent of wave induced erosion and slides triggered by the loss of bluff toe material. The concept model does not factor in mitigation measures that could alter natural processes and potentially reduce erosion rates. Conceptual mitigation options are discussed in Section 8.

At present, most waves do not reach the bluff except during storms that coincide with relatively high tides; however, future SLR will increase the exposure of the bluff toe to wave impacts. For instance, a storm occurring at the present day higher high water large tide level will occur more frequently in the future than it does today. Model results described in Section 4.1 indicate annually occurring storms are capable of causing shoreline erosion and recession from the combined effects of wave attack and cross-shore sediment transport of the eroded sediment to deeper water. Under present conditions this type of erosion is often temporary (e.g. seasonal) except when these storms coincide with exceptionally high tides. In the future there will be a greater probability of coinciding high water levels and significant storm events, which may change the profile of the upper beach near the bluff toe.

The rate and pattern of bluff erosion is complex and difficult to predict. The rate of bluff erosion will depend on the characteristics of the bluff sediment, such as the material hardness, thickness of bedding layers, presence of joints or fractures, relative strength of each sediment layer in the bluff, and the condition of the upper beach in front of the bluff.

The bluff and beach characteristics vary spatially, therefore the bluff’s exposure to wave attack and resistance to erosion will similarly vary along the bluff and will determine the bluff recession rate. At present, the surface of the upper beach profile in front of the bluff toe is generally comprised of a mixture of sand and cobbles. With SLR, the upper beach will become inundated more often and therefore more exposed to wave action that could potentially erode and transport this coarse surface layer of material and expose finer sediment that could be more susceptible to erosion. Similarly, erosion of the existing bluff slope surface will remove vegetation cover and could expose softer sediment in the bluffs, which could reduce the slope’s resistance to erosion and increase the recession rate.

Bluff retreat patterns may also vary over time, which makes it challenging to predict the rate and timing of coastal erosion. The conceptual model conservatively assumes that sediment that is eroded from the bluff and deposited at the bluff toe would be eventually be eroded and therefore would not offer any substantial protection over the long term.

5 Subaerial erosion refers to erosion processes that occur outside of the influence of coastal processes.


6 FLOOD HAZARD AREA LAND USE MANAGEMENT GUIDELINES

In January 2018, the BC Ministry of Forests, Lands, Natural Resource Operations, and Rural Development issued an update to the Flood Area Land Use Management Guidelines. The guideline incorporates SLR, based on a 0.5 m SLR by 2050, 1.0 m SLR by 2100, and 2.0 m SLR by 2200 (with adjustments for regional uplift or subsidence). The guideline recommends a minimum requirement of SLR to Year 2100 for buildings, zoning, and subdivisions, based on a flood hazard with a 1:200 annual exceedance probability (AEP)6. The guidelines include special conditions for determining setback requirements for coastal bluffs and tsunami hazards based on the future location of the natural boundary of the sea.

6.1 Estimated Future Natural Boundary of the Sea

The future location of the natural boundary of the sea is defined by the BC Ministry of Environment (BC MoE 2011) in Figure 6.1 and includes SLR, high tide, storm surge, and wave effects.

Figure 6.1. Definitions from the BC Ministry of Environment (2011).

6 1:200 AEP has a 0.5% chance of occurring in any given year, a 22% probability of occurring once in a 50 year period and 39% probability of occurring once in a 100 year period.


6.1.1 Tectonic Adjustment

Estimated rates of tectonic adjustment vary across the region and are relatively uncertain. For instance, BC Ministry of Environment (2011) identified 0.6 mm/year tectonic adjustment for Albert Head, 1.4 mm/year for Esquimalt, and 1.2 mm/year for Victoria. A more recent study commissioned by the Capital Regional District (AECOM 2015) identified 1.1 mm/year of vertical land movement for a ‘zone’ that encompasses Albert Head, Esquimalt, and Victoria. As such, the estimated future natural boundary will depend to some degree on which rate of tectonic adjustment is adopted.

A Year 2100 tectonic adjustment of 0.11 m (upwards) has been adopted for this report. Tectonic adjustment refers to long-term adjustment of tectonic plates over a time frame of centuries to millennia, and does not account for shorter-term geological processes such as uplift or subsidence from an earthquake along the Cascadia Subduction Zone.

6.1.2 Future Natural Boundary Computation

There are two approaches for determining the future natural boundary. Both methods apply a 1.0 m Global SLR (GSLR) for 2011 with regional adjustment for tectonic adjustment, and estimated wave effects. A separate freeboard amount is not included in the estimated future natural boundary. Two methods for computing future natural boundary are:

Probabilistic: based on a probabilistic analysis of high tide and storm surge; and,

Combined: based on combined Higher High Water Large Tide (HHWLT) elevation7 and estimated storm surge for a 1:500 year Annual Exceedance Probability event, assuming the total storm surge equals the storm surge in deeper water (BC MoE 2011).

The combined method is more conservative, and uses readily available information. Probabilistic methods will yield less conservative results, and are more computationally intensive. The combined method has been applied for this assessment; however, further studies may incorporate the probabilistic approach which will shift the location of the estimated future natural boundary seaward of the estimate computed using the combined method. The combined method is appropriate for an initial examination of setback requirements in context of the bluff recession scenarios assessed in Section 7. The estimated future natural boundary is defined as the intersection between the present-day topography and the Flood Construction Reference Plane. The Flood Construction Reference Plane is computed as follows:

Flood Construction Reference Plane = 1 m (GSLR) – 0.11 m (Tectonic Adjustment) + 1.5 m (HHWLT) + 1.3 m (Storm Surge) + 0.6 m (Estimated wave effects) = 4.34 m, relative to Canadian Geodetic Vertical Datum 28 Geoid Ht. 2.0.

7 HHWLT values are defined in Canadian Hydrographic Services (CHS) tide tables.


6.2 Tsunami Hazard

Royal Beach is located within tsunami hazard zone D as defined by the BC Flood Area Land Use Management Guidelines. Tsunami hazard lines have been estimate based on modelling results completed for a tsunami inundation and run-up study in for Capital Regional District (AECOM 2013) from a tsunami wave generated by an earthquake with a magnitude of 9.0 on the Richter scale and a Higher High Water Mean Tide condition. The AECOM model results do not appear to include influences from the slope of the backshore zone, and reports the same predicted maximum water levels for the steep bluff slopes and the beach. It is likely that the maximum water level generated from the tsunami would vary along the Royal Beach shoreline due to the significant variation of the slope of the backshore. Presumably, the tsunami generated run up at the bluff would be of greater elevation than the wave impacting the lower gradient shoreline. The AECOM model grid (19 m) is not fine enough to accurately represent the slopes in the backshore for this area of the shoreline. For the purposes of this report, the variability in the slope of the backshore was accounted for by applying the 50% safety factor recommended by AECOM to account for variations in water level and quality of topographic data, and the potential for higher earthquake magnitudes. However, for more detailed studies it is recommended to develop a refined estimate of the tsunami generated water level to account for the variability of the backshore.

The maximum computed tsunami generated water level for Royal Beach is 2.7 m, including subsidence and the estimated present-day tsunami hazard line is 4.1 m. The tsunami hazard line for 1 m and 2 m SLR is 5.1 m GD and 6.1 m, respectively.

Although tsunami waves would not impact land on top of the coastal bluff, lower lying portions of the Royal Beach waterfront could potentially be impacted. Furthermore, run-up from tsunami waves could potentially cause severe erosion and retreat of the coastal bluff during and immediately following the tsunami, which could accelerate the estimated long term bluff recession rate. Bluff recession rates presented in Section 7 consider SLR and effects from wind generated waves over a period of decades; the potential episodic erosional impacts from tsunami waves are not considered.

6.3 Provincial Guidelines for Recommended Setbacks at Royal Beach Coastal Bluff

For Royal Beach, the following provincial Flood Area Land Use Management Guidelines apply:

For coastal bluffs, it is determined as the greater of either:

˗ 30 m from the estimated Year 2100 natural boundary of the sea; or,

˗ A horizontal distance of at least 3 times the height of the bluff, measured from 15 m landwards from the location of the Year 2100 natural boundary.

For other areas, the setback accounts for tsunami hazards and is defined as 30 m from the estimated Year 2100 natural boundary of the sea.


The guidelines state that, “the setback may be modified provided the modification is supported by a report, giving consideration to the coastal erosion that may occur over the life of the project, prepared by a suitably qualified Professional Engineer experienced in coastal engineering”. We understand the required setback at this site also must consider geotechnical and seismic stability of the bluff and the ground on top of the bluff, which is under way.

6.4 Development Set-Back Computation

Development set-backs computed for this report consider effects associated with SLR as per the BC Flood Area Land Use Management Guidelines. The computed set-backs presented herein should be considered preliminary and should be refined in conjunction with a land surveyor to interpret land features defined in the guidelines. Computed set-backs are intended to present the Provincial set-back requirements in the absence of a more detailed study of coastal processes at the site, which has been carried out for the Royal Beach development to estimate the future position of the shoreline or bluff toe. At the time of preparation of this report, geotechnical analysis was underway to evaluate the slope conditions and other geotechnical factors in the determination of an appropriate site-specific development set-back. Following completion of an assessment of slope stability that considers the future position of the bluff and shoreline toe and other relevant geotechnical factors, the computed development set-backs presented herein may be adjusted. Geotechnical factors have not been addressed in this report.

Preliminary development set-back requirements for ten discrete beach profiles along Royal Beach are presented in Table 6.1, along with computed bluff height values used to compute the set-back distance. The bluff is non-existent near Station 1+771, 1+824, and 1+976, therefore bluff height values are not shown and the set-back requirements for these locations are based on tsunami zone requirements.

Table 6.1 Computed BC Government SLR coastal development set-back requirements.

Station (m)1 Bluff Height (m) Set-back Distance (m)2 0+855 41 138 0+987 29 103 1+213 36 123 1+355 38 129 1+559 25 90 1+771 - 30 1+824 - 30 1+976 - 30 2+122 18 69 2+412 31 108

Notes: 1. Station refers to the distance along the Royal Bay Beach Unit, with 0 m reference at the Southwestern end. 2. Set-back distance is measured landward of the estimated future natural boundary. 3. Set-backs for locations that are not within the coastal bluff zone are computed differently and bluff height is

shown with a ‘-‘.


7 FUTURE SHORELINE RECESSION SCENARIOS

A precautionary approach to land development in coastal areas is important because of the potentially high consequences that can occur from flooding or erosion of residential properties, and because of the high degree of uncertainty with future SLR and coastal erosion rates. The provincial government has integrated the precautionary principle into its coastal flooding guidelines (MoE 2011), which states that, “land use and building approvals based on FCL for 2100 should also include provisions for adaptive management of land uses to Sea Level Rise to the Year 2200 and beyond”. A 2 m SLR scenario has been applied to estimate the future position of the shoreline, referencing the toe of the coastal bluff or bank.

7.1 Methodology

Several computational and conceptual methods have been used to assess future shoreline recession rates to address uncertainties with any single approach, spatial variability in the sediment composition of the bluff and potential for sub-aerial slope failures that are independent of coastal processes; and to show the range in future projections for SLR rates of 1 m and 2 m. Future shoreline recession scenarios assume no mitigation measures are applied to alter the natural coastal processes.

The mechanism for shoreline erosion depends on the rate of SLR, geomorphology of the coast and backshore characteristics. Shoreline retreat for Royal Beach was assessed by “zone” (Appendix A – Sheet 1); based on shore zone units, elevation of the backshore, and steepness of the beach (CORI and TEL 1997). The three major shore zone units within Royal Beach are:

Zone 3 – Sand from bluffs is a beach sediment sources; beach backshore is generally stable with minor erosion at the north end of the unit;

Zone 4 – Sand in upper foreshore with variable riprap armour and concrete debris; and

Zone 5 – Rapid low cliff shoreline erosion.

The shoreline is backed by steep bluffs, except for Zone 4. Two approaches were applied to estimate retreat of the shoreline: the first assumes a low lying beach profile and the second accounts for steep bluffs in the backshore. The methodology used to estimate the beach (Zone 4) and steep bluff retreat (Zone 3 and 5) due to SLR is discussed in the following sections.

7.1.1 Low Lying Beach Retreat Methodology (Zone 4)

Bruun Rule (Bruun 1962, Ranasinghe et al. 2007) is a 2 dimensional theoretical relationship between shoreline position and SLR that is based on the conservation of mass and the concept of an “equilibrium” beach profile. The equilibrium profile concept assumes that the mean sea level, wave climate and sediment characteristics of the beach profile are in balance. According to the Bruun rule, an increase in mean water level due to SLR will cause the shoreline profile to shift landward and upward, and sediment in the upper part of the profile will erode and deposit onto the lower part of the profile until the former equilibrium shoreline profile is re-established. There is little field data to verify that actual recession


rates match those projected with the Bruun Rule, and this approach is considered more relevant for regional applications. Limitations include the following:

Applies to soft-sediment coasts;

Assumes the beach material is homogeneous sand material;

Assumes there is no external source or sink or sediment;

Assumes a static response to very slow rates of SLR over long time periods;

Assumes the present-day shoreline is in equilibrium and will be in-equilibrium with SLR; and,

Assumes all eroded sediment is redistributed to the lower part of the profile, and that the nearshore bed increases to the same degree as SLR.

An “equilibrium” beach profile concept was also applied numerically to the surveyed cross sections of the beach in Zone 4 to evaluate beach retreat. The beach profile was adjusted until a “mass balance” was achieved. (US Army Corps of Engineers, 2002).

7.1.2 Steep Bluffs Retreat Methodology

Retreat of the steep bluffs due to SLR were estimated using five approaches: (i) Bruun Modified and (ii) mass balance approach (Young et al., 2013), (iii) Soft Cliff and Platform Erosion (SCAPE) (Walkden and Dickson, 2008), (iv) Sunamura (Sunamura, 1988), and (v) maximum wave run up. SCAPE and Sunamura are both based on historical extrapolation methods. The steep bluff retreat methodology for each method are described in further detail in this section.

Bruun Modified and Mass Balance Method

The Bruun Modified and mass balance approaches (Young et al., 2013) are both based on the equilibrium profile theory, assuming the overall shape of the profile (bluff and beach cross section) will remain generally constant. The theory of these approaches is similar to the application of the Bruun rule described in the previous section. However, the height of the bluff, loss of sediment to longshore sediment transport, and percentage of coarse material in the bluff face is included in the analysis.

Historical Extrapolation Methods

Soft Cliff And Platform Erosion (SCAPE) (Walkden and Dickson, 2008) is a modelling tool for assessing erosional responses of bluffs. It was developed at the University of Bristol and is a freely available open source software. Originally, this model was developed for soft cliffs in eastern England composed of mixed sand and gravel, clays, and glacial till. SCAPE assumes a low volume of beach material (< 30m3/m). The model divides the bluff into a series of cross sections and includes several parameters including, tidal range, wave height, and rock strength. Cross section information from a 2018 topographic survey and available LiDAR data was applied and the model was run over a period of 82 years (between 2018 and 2100) using an estimated bluff recession rate of 5 cm/year and 15 cm/year, which is the range of natural recession rates estimated by TEL (1988) based on natural recession rates in other bluffs in the region and engineering judgement on the condition of the bluff.


The Sunamura (1988) model of cliff erosion was developed for shorelines with no dissipative beach and assumes the cliff is exposed to wave action continuously . Cliff retreat is therefore dependent on material strength and wave power which is assumed to be represented by the observed rate of cliff retreat in the present day. This method is highly conservative when applied to the Royal Bay shoreline because there is a dissipative beach protecting the cliffs, which would likely be maintained with SLR as the cliff material is deposited onto the beach over time.

Maximum Run-up Computation

A third approach is based on a computational of the theoretical maximum potential wave run-up assuming the present-day beach conditions and wave climate, and assuming SLR impacts. Wave run-up is the landward extent that waves could reach as it washes up the beach. This approach assumes shoreline recession would only be limited by the capacity of the waves to wash up the beach. The maximum wave run-up (vertical) was calculated for a relatively gentle slope using the methodology in EurOtop II (EurOtop, 2016). The exceedance of the vertical wave run-up above the toe of the cliff for the given sea level was converted to a horizontal retreat based on the existing slope of the upper beach. It is assumed that the wave action at the toe of the cliff would cause erosion of the bluff up to the limit of the wave run-up.

7.2 Estimated potential magnitude of bluff recession with SLR

The methods described in Section 7.1 have been applied to estimate the potential magnitude of bluff recession with SLR, and the results are summarized in Table 7.1. table assumes each method is equally applicable and valid and the results have been equally weighted. These estimates are preliminary and may be refined, pending the collection and review of additional geotechnical or hydrotechnical information. Application of protective mitigation measures could alter the estimated potential magnitude of bluff recession; and the practicality and feasibility of this type of mitigation could be explored in future studies.

The range in values highlights the degree of uncertainty in sediment characteristics, present-day recession rate, spatial variability of recession rates, future projections of SLR, and computations and analysis used to estimate future recession rates. Future estimated potential magnitude of shoreline recession ranges between 10 m and 41 m for the 1 m SLR scenario and between 14 m and 64 m for the 2 m SLR scenario. These values represent the upper and lower bound estimates of shoreline recession under the selected future SLR scenarios.

Methods producing outliers, values either much greater or lower than other methods, were not used to calculate the median retreat estimate. For example, the Sunamura (1988) method assumes there is no dissipative beach protecting the cliffs and therefore would tend to overestimate retreat and was removed as an outlier value for most sections. Additionally, the mass balance methodology produced very low estimates of retreat for the steep bluffs and was also not used in the calculated median value shown in Table 7.1.


Table 7.1 Estimated potential magnitude of coastal bluff recession with SLR, shown as a horizontal distance (m) from the present-day bluff position.

Station (m) Zone 1 m SLR 2 m SLR

Lower Upper Median Lower Upper Median

0+855 3A 15 32 23 24 45 35 0+987 3B 14 36 25 23 46 34 1+213 3C 12 32 22 18 45 32 1+355 3D 15 32 24 24 45 35 1+559 3E 15 34 24 24 45 35 1+771 4A 10 12 11 20 24 22 1+824 4B 12 14 13 23 28 26 1+976 4C 12 13 13 25 26 25 2+122 5A 15 41 28 64 24 44 2+412 5B 19 39 29 32 51 42

Notes: 1. Station refers to the distance along the Royal Bay Beach Unit, with 0 m reference at the Southwestern end

of the beach unit. 2. Median value is the computed median of the upper and lower bound estimates for each SLR scenario.

The median value is the computed median of the upper and lower bound estimates of bluff recession with 2 m SLR ranges between 22 m to 44 m, which overlaps with the upper bound estimate with 1 m SLR (between 12 m to 41 m). Estimated retreat rates assume no intervention is carried out to protect the slopes from erosion. Mitigation measures could alter the rate of bluff retreat; however, they would need to be carefully planned and designed to avoid transferring risk to other parts of the shoreline and to be approved by local, regional, provincial, and federal jurisdictions.

The estimated rate of bluff retreat depends on several factors including the height of the bluff, the slope of the upper beach, and the length of the active beach profile. Therefore, the estimated retreat rates vary spatially due to these factors.

Based on the assumptions applied to the analysis, the median value of the upper and lower bound estimates of shoreline recession with 2 m SLR is a reasonable scenario for input into the geotechnical analysis to determine the corresponding position of the top of bluff or beach slope and evaluate other factors that will determine the appropriate development set-back location.

Several drawing sheets are presented to illustrate the results of the coastal analysis. Seacliff’s property boundary and the estimated future natural boundary are shown on each boundary for reference.

Appendix A – Sheet 2 presents the estimated present-day, and future tsunami hazard lines with 1 m and 2 m SLR and the estimated position of the Year 2100 future natural boundary.


Appendix A – Sheet 3 presents the location of the toe of bluff or beach slope (median value) and the tsunami hazard line for 2 m SLR. The computed set-back described in Section 6.1.2 and reference points for the future estimated shoreline position are shown for reference.

Appendix A – Sheets 4 and 5 present the present-day bluff and beach profiles at ten locations. The computed set-back described in Section 6.1.2 and reference points for the future estimated shoreline position are shown for reference.


8 RISK ASSESSMENT

Risk is defined as the probability of a hazard occurring multiplied by the corresponding consequences. For Royal Beach, the hazard is coastal erosion of Seacliff’s property and loss of beach materials that have ecological and public use value. The consequences of coastal erosion for the assets identified within the development are described for various time periods and coastal processes in Table 8.1.

Table 8.1 Consequence of coastal processes for the Royal Beach development assets

Asset Exposed

Years Decades to Century

Extreme storm events Beach retreat caused by SLR

Riprap Wall & Settling Pond

Scour of sediment at toe of wall and potential for failure that could breach settling pond embankment and release of ponded water into the environment

Failure of armour wall and breach of settling pond embankment and release of ponded water into the environment

Temporary Royal Bay Park

Access between the temporary park and foreshore may be disrupted.

Depends on future use of this land

Seaside Trail

Damage to walking path and occasional repairs required

Loss of walking path (located on Crown Lease land)

Coastal Bluffs

Base of coastal bluffs potentially exposed to wave action at HHWLT; Bluffs potentially exposed to wave action during coinciding HHWLT and storm surge leading to erosion of the bluffs.

Likely long term retreat of the coastal bluff and landward retreat of the bluff face; Possible increase in sediment supply from bluff erosion


8.1 Methodology

Risk assessment for this study was conducted using qualitative criteria that classified various elements and potential mitigation options for the assets located within the Royal Beach development. The risk assessment of coastal erosion for the Royal Beach development includes consideration of the following four categories:

1) Failure rating – Evaluation of the risk to structures or natural features that considers the likelihood of potential failure caused by either a large storm event in the short term, or a combination of a large storm event, coastal erosion, and SLR in the long term.

2) Coastal process rating – A qualitative assessment of the potential impact of mitigative measures on natural coastal processes. For example, riprap shoreline armour has a high impact on coastal processes because it interrupts sediment transport processes that allow the natural shoreline to respond to seasonal variability in waves and currents. However, a buried revetment would have little or no impact on coastal processes until such time that it becomes exposed. A detached breakwater will likely have substantial impacts to coastal processes; however, it may be designed in a way to reduce potential for shoreline erosion while limiting the degree that longshore processes are altered.

3) Coastal ecology rating – Mitigation measures can have both direct and indirect impacts on shoreline ecosystems such as:

˗ Loss of sandy sediment from the beach that will not be replaced and is habitat for forage fish species;

˗ Loss of natural dune habitat and vegetation on the coastal bluffs; and,

˗ Erosion protection structures may have both negative impacts (loss of habitat) and positive impacts (preventing erosion, providing new habitat such as rock spaces in detached breakwaters.

˗ Impact of the potential failure of an existing structure, such as the rip rap wall containing the settling pond, on the coastal ecology.

4) Public use and amenity rating – This rating is based on the potential impact on the public use of the space and the limitations of future development.


8.2 Mitigation Concepts

There are several potential mitigation options that SeaCliff can consider, and for this site it is likely that Seacliff will apply different measures along the shoreline either individually or jointly in some areas. More detailed evaluation of appropriate and feasible mitigation measures is anticipated during future phases of work. There are four broad categories of mitigation options including:

1) Protection,

2) Accommodation,

3) Avoid or retreat, and

4) Do-nothing.

The mitigation options considered for the Royal Beach development include protection (both hard and soft), avoid or retreat, and do nothing. The accommodation option was not included for this site due to the relative lack of infrastructure currently on the development that would be impacted by coastal processes. The advantages and disadvantages of the mitigation options identified in this section are discussed in Table 8.2.

Table 8.2 Advantages and disadvantages of mitigation options

Mitigation Option Advantages Disadvantages

Prot

ectio

n

Beach Nourishment

Relatively inexpensive capital investment in comparison to “hard” protection options such as a revetment or detached breakwaters.

Minimal environmental impact given the thickness of the beach nourishment is less than 1 to 1.5 m, allowing existing shellfish to move to the surface of the deposited material.

Sediment from the beach nourishment will supply the entire beach unit as the deposited material is regraded by waves and currents.

The nourished beach will continue to erode, likely faster than the current rate because the underlying coastal processes causing the natural erosion of the beach have not changed.

Requires re-nourishment at regular intervals to maintain its effectiveness.

Long-term cost of beach nourishment may potentially exceed that of a revetment, depending on the area being protected.

The continued erosion of the beach may cause a negative perception that the money was wasted on the nourishment.


Mitigation Option Advantages Disadvantages

Prot

ectio

n

Revetment

Protects structures vulnerable to wave action at high tide such as the settling pond.

Revetment will have a longer life expectancy than beach nourishment, which would have to be replenished over time in order to remain effective.

Destroy vegetation along the footprint of the revetment.

Does not mitigate the erosion of the foreshore.

Impacts sediment transport processes The beach in front of the rock armour

will eventually be eroded in the long-term due to SLR which will make the beach more difficult to navigate and less attractive

If constructed on the foreshore it would likely require an environmental impact assessment to determine whether lost habitat would have to be compensated for.

Detached Breakwater

Modify the existing littoral processes to encourage nourishment of the beach between the detached breakwater and the shoreline.

Adaptable for moderate amounts of SLR by raising the height of the breakwaters above sea level.

The most expensive “protect” option. Long-term environmental impact to

the organisms within the footprint of the breakwater.

Impacts sediment transport processes.

Would require an environmental impact assessment to determine whether lost habitat would have to be compensated for.

Avoi

d or

Ret

reat

Avoid Limit costs for additional

mitigation requirements in the future.

Loss of land that is presently potentially developable.

Retreat

Return the coastal zone to a more natural state.

Eliminate the potential for failure of the existing assets.

Loss of developed land.

Do-N

othi

ng

Do- Nothing

No current action required.

Expensive in the long-term because it will damage existing shoreline infrastructure and impact the steep cliffs. Protective measures will likely be more expensive to implement in the future and shoreline losses could impact areas that are presently potentially developable.

Fewer available options if/when adaptation becomes necessary.


Protection

Several protection mitigation strategies could potentially be applied at the Royal Beach development including beach nourishment, revetments, or detached breakwaters. Beach nourishment is an example of a “soft” protection approach, or a protection measure that incorporates features that are intended to mimic natural processes and preserve shoreline dynamics. Structures that create a fixed boundary between the beach and upland area such as revetments or detached breakwaters are examples of a “hard” protection approach.

An existing protection measure at the site is a rock wall that runs along the front of the settling pond. This structure is overly steep and does not appear to have a properly designed filter layer below that outer armour rock. It is susceptible to wave damage and scour that could undermine the structure, causing it to eventually fail. One option for protection is to construct a more stable revetment by adjusting its angle of repose and upgrading the section to meet coastal protection standards for design. This would likely require that the seaward edge of the settling pond is pulled farther back to accommodate the revetment and walking path. However, it appears feasible to shift the northeastern edge of the pond farther to the northeast to accommodate for the pond volume that would be taken up by the structure.

Avoid or Retreat

Avoidance is a particularly feasible option for the Royal Beach development for the medium to long term due to the relative lack of development currently on the site. However, there are currently several assets located within the coastal zone that may have to be removed; retreat and avoidance measures could include:

Eventual de-commissioning of the rip rap wall and settling pond;

Eventual de-commission the lower terrace of the Royal Bay land area presently being used as a temporary park;

Re-align walking path further up the beach; and,

Limit development within the erosion zone (which includes set-back areas along the top of the steep coastal bluff); or allow only natural “park” areas within these zones.

Do Nothing

Lastly, do nothing is a “business-as-usual” approach, where no current action is taken to mitigate the impacts of coastal flooding and erosion. This approach generally ends up costing the most in the long term, because eventually the cost to repair damages from flooding or erosion ends up exceeding the initial costs of a more proactive mitigation approach.

8.3 Results

The results of the qualitative impact assessment for various adaptation options are provided in Table 8.3. Under the “do nothing” adaptation option, the resilience of existing infrastructure and the coastal bluffs in the Royal Beach development is poor and there is a risk of damage occurring from cumulative


effects. Coastal processes and ecology could be substantially impacted if the coastal bluffs were to fail because it could result in losses of mature vegetation that is growing at the toe of slope and could cause large deposits of sediment to erode from the cliffs and accumulate on the foreshore. All options considered have at least a moderate level of risk for at least one category. For example, the “retreat” and “avoid” options leave the coastal bluffs open to erosion and setback of the cliff face over time is likely.

Table 8.3 Risk assessment of mitigation options

Adaptation Option Item Description

Failure Rating

Coastal Process Rating

Coastal Ecology Rating

Public Use and Amenity

Rating

Do N

othi

ng Rip Rap Wall &

Settling Pond High High High Moderate Temporary Royal Bay Park Moderate Low Low Moderate Walking Path High Low Low High Coastal Bluffs High High High Moderate

Retr

eat

Re-align Walking Path Low Low Low Moderate

De-commission Settling Pond Low Moderate Low Low

De-commission lower terrace Low Moderate Low Moderate

Avoi

d Limit Development using setbacks Low High High Moderate

Prot

ect Beach Nourishment Moderate Low Low Low

Revetment Moderate High High High

Detached Breakwaters Moderate Moderate Moderate Moderate


9 CONCLUSION

Several future shoreline positions were computed for a 2 m SLR scenario, and the median estimated position was selected as the baseline for Seacliff’s geotechnical consultants to examine slope stability along the coastal bluffs and identify appropriate development setbacks. Estimated future shoreline position assumes no mitigation measures are applied, which could reduce the shoreline recession rate. Applying a future potential 2 m SLR position reflects Seacliff’s determination to apply best practices that recognizes the uncertainty with projections of future SLR and coastal erosion rates projections, and applies a precautionary approach to land development in coastal areas that includes provisions for adaptive management following the spirit of the BC coastal guidelines.

Coastal erosion processes are complex and difficult to predict with certainty. The rate of erosion is expected to vary both spatially and temporally over time. In addition to coastal processes, the bluff will be affected by sub aerial processes (e.g. weathering and other slope processes). Along the bluffs shoreline recession from coastal processes is estimated to range between 10 m and 41 m for the 1 m SLR scenario and between 14 m and 64 m for the 2 m SLR scenario. These values represent the upper and lower bound estimates of shoreline recession under the selected future SLR scenarios. Other natural processes could further erode the slope and cause it to further recede.

Based on the methods applied for this study, coastal bluff recession with 1 m and 2m SLR will impact the sediment containment berms located along the top of bluff. This is a preliminary assessment that will be used to inform other studies being carried out by geotechnical consultants to assess for the future bluff position due to processes other than coastal erosion, and to evaluate development setback requirements from a geotechnical perspective.

This report also presents the Year 2011 future natural boundary (1 m SLR), a preliminary determination of the tsunami hazard line for under present-day and 1 m and 2 m SLR scenarios, and computed development set-backs at ten locations along the Royal Bay Coastal Bluff as per the provincial guidelines. The tsunami hazard lines are based on information reported by AECOM (2013) and are preliminary and subject to refinement using site specific information and analysis. The computed set-backs presented herein would need to be refined in conjunction with a land surveyor to interpret the height of the bluff as defined in the guidelines.

Mitigation measures to reduce shoreline recession rates have not been assessed in this study. Further assessment would be required to evaluate the practicality and feasibility of mitigation measures to reduce the shoreline erosion potential. Development set-back locations along the Royal Beach waterfront will be determined pending the outcome of geotechnical studies presently under way and upon further refinement of coastal recession rates and set-back computations.


10 REFERENCES

AECOM. 2013. Modelling of Potential Tsunami Inundation Limits and Run-Up. Prepared for CRD. June 2013.

AECOM 2015. Capital Regional District: Coastal Sea Level Rise Risk Assessment. Prepared for CRD. January 2015

Bruun, P. (1962). Sea-level rise as a cause of shore erosion. Journal of the Waterways and Harbors division, 88(1), 117–132.

Clague J.J. 1989. Sea Levels on Canada’s Pacific Coast: Past and Future Trends. Episodes, Vol 12 (1), PP29-33.

Coastal and Ocean Resources Inc. and Thurber Engineering Ltd. (1997). Royal Bay Development Beach Erosion and Coastal Processes (Study 1C): Draft. Prepared for Construction Aggregates Ltd. c/o Moodie Consultants Ltd. 18 November 1997.

Davidson-Arnott R. 2010. An introduction to Coastal Processes and Geomorphology. Cambridge University Press. New York.

Eurotop (2016). Manual on wave overtopping of sea defences and related structures. An overtopping manual largely based on European research, but for worldwide application. Van der Meer, J.W., Allsop, N.W.H., Bruce, T., De Rouck, J., Kortenhaus, A., Pullen, T., Schüttrumpf, H., Troch, P. and Zanuttigh, B. [online] Available from: www.overtopping-manual.com.

Le Bars D., Drijfhout S., and H. de Vries. 2017. A High-End Sea Level Rise Probabilistic Projection Including Rapid Antarctic Ice Sheet Mass Loss. Environmental Research Letters, 12, 2017, 10 pg.

Ministry of Environment 2011. Climate Change Adaptation Guidelines for Sea Dikes and Coastal Flood Hazard Land Use Guidelines for Management of Coastal Flood Hazard Land Use. Prepared by Ausenco Sandwell. 27 January 2011.

NOAA. 2017. Global and Regional Sea Level Rise Scenarios for the United States, NOAA Technical Report NOS CO-OPS 083, Prepared by Sweet W., Kopp R., Weaver C., Obeysekera J., Horton R., Thieler E., and C. Zervas. Silver Springs Maryland. January 2017.

O’Conner B, Muller N. and Perkins J. (2014). An Investigation into Erosion and Armouring Effects on the Coburg Peninsula at the Esquimalt Lagoon, Colwood, BC. Prepared for Dr. Ian Walker for University of Victoria Geography 476. 2 April 2014.

Ranasinghe R., Watson P., Lord D., Hanslow D., and P. Cowell. 2007. Sea Level, coastal recession and the Bruun Rule. Proceedings of Coasts and Ports, Melbourne, Australia Conference paper.


Seabulk Systems Inc. (2008). Coburg Peninsula Foreshore Erosion Updated Study Report. Prepared for City of Colwood. 27 February 2008.

Sunamura, T. (1988). Projection of future coastal cliff recession under sea level rise induced by the greenhouse effect: Nii-jima Island, Japan.

Thurber Engineering Ltd. 1998. Royal Bay Development Study 1C: Beach Erosion and Coastal Processes – Final Report. Prepared for CitySpaces Consulting Ltd. 24 November 1998.

Thurber Engineering Ltd. 2007. Royal Bay Development Beach Monitoring – 2007. Prepared for Royal Bay Developments. c/o Moodie Consultants Ltd. 6 June 2007.

US Army Corps of Engineers (2002). Coastal Engineering Manual (CEM): Engineer Manual 1110-2-1100. US Army Corps of Engineers, Washington, D.C. (6 Volumes) pp.

Walkden, M., and Dickson, M. (2008). Equilibrium erosion of soft rock shores with a shallow or absent beach under increased sea level rise. Marine Geology, 251(1), 75–84. doi:10.1016/j.margeo.2008.02.003.

Young, A., Flick, R., O’Reilly, W., Chadwick, B., Crampton, W. C., and Helly, J. J. (2013). Estimating cliff retreat in southern California considering sea level rise using a sand balance approach.

Appendix A: ESTIMATED COASTAL BLUFF RECESSION, COMPUTED DEVELOPMENT SETBACKS FOR COASTAL REGIONS, AND PRELMINARY TSUNAMI HAZARD LINE WITH 2 M SEA LEVEL RISE: PLAN AND PROFILE VIEWS

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DRAWING INFORMATION

DESIGNED BYDRAWN BYCHECKED BY

405 - 495 Dunsmuir St.Nanaimo, BCCanada V9R 6B9Office: 250.754.6425Fax: 250.754.9264www.nhcweb.com

PROJECT NUMBER

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GENERAL NOTES:

1. ALL ELEVATIONS AND DIMENSIONS ARE IN METRES UNLESS OTHERWISE SHOWN.2. TOPOGRAPHY COMPILED FROM NHC RTK SURVEY (20180615), CHS BATHYMETRY AND LiDAR (DEC 2017) PROVIDED BY THURBER ENGINEERING LTD.3. HORIZONTAL DATUM: NAD 83

PROJECTION: UTM ZONE 10 NORTHVERTICAL DATUM: CGVD 28 (Canadian Geodetic Vertical Datum 1928)GEOID: HT 2.0

4. CONTOUR INTERVAL: 5m.5. PROPERTY LINE APPROXIMATE, SCANNED FROM COMPOSITE PLAN OF THE ROYAL BAY PROPERTIES, PREPARED BY McILVANEY RILEY LAND SURVEYING INC.6. BEACH STATIONING IS MEASURED FROM ALBERT HEAD, FOLLOWING THE APPROXIMATE NATURAL BOUNDARY ALIGNMENT.7. BASE IMAGE FROM CRD (2015).

ZONE DESCRIPTIONS (SOURCE: CORI AND TEL, 1997)ZONE 3: SAND FROM BLUFFS IS A BEACH SEDIMENT

SOURCE; BEACH BACKSHORE IS GENERALLYSTABLE WITH MINOR EROSION AT THE NORTHEND OF THE UNIT

ZONE 4: SAND IN UPPER FORESHORE WITH VARIABLERIPRAP ARMOUR AND CONCRETE DEBRIS

ZONE 5: RAPID LOW CLIFF SHORELINE EROSION

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BEACH PROFILE TRANSECT LOCATIONS

REVISIONS 0 16 APR 2019 ISSUED FOR INFORMATION

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305-1788 West 5th Ave.Vancouver BC V6J 1P2

LEGEND

ESTIMATED PRELIMINARY TSUNAMI HAZARD LINE (BASED ON RESULTS PRESENTED IN AECOM 2013)PRESENT DAY1m SEA LEVEL RISE2m SEA LEVEL RISE

ESTIMATED FUTURE NATURAL BOUNDARY (2100)

N

100

SCALE 1:5000

2000

GENERAL NOTES:



4. CONTOUR INTERVAL: 5m.5. PROPERTY LINE APPROXIMATE, SCANNED FROM COMPOSITE PLAN OF THE ROYAL BAY PROPERTIES, PREPARED BY McILVANEY RILEY LAND SURVEYING INC.6. BEACH STATIONING IS MEASURED FROM ALBERT HEAD, FOLLOWING THE APPROXIMATE NATURAL BOUNDARY ALIGNMENT.7. BASE IMAGE FROM CRD (2015).

AutoCAD SHX Text


METCHOSIN ROAD

LATORIA RO

AD


0+60

0

0+70

0

0+80

0

0+90

0

1+00

0

1+10

0

1+20

0

1+30

0

1+40

0

1+50

0

1+60

0

1+70

0

1+80

0

1+90

0

2+00

0

2+10

0

2+20

0

2+30

0

2+40

0

2+50

0

2+60

0

ROYAL BAYBEACH PARK

1112

1314 15

16

17 18

19

20

75

6

2

3

1

4

8

9

10


0

-5

-10

30

40

2010


FUTURE POSITION OF COASTAL BLUFF/ BANK TOEWITH 2m SEA LEVEL RISE (MEDIAN BOUND ESTIMATE)

WAYPOINT TABLEXS STATION POINT #

123456789

10

NORTHING5360970.15361089.95361294.35361420.45361600.45361762.55361809.55361943.45362087.55362353.8

EASTING464016.0464076.1464176.0464247.0464338.6464480.5464505.1464567.0464612.3464727.9

ELEVATION5.05.05.05.05.03.03.04.05.06.0

0+855

2+412

1+559

1+2131+355

1+771

0+987

1+8241+976

2+122

COMPUTED DEVELOPMENT SETBACKSFOR BC COASTAL REGIONS

WAYPOINT TABLEXS STATION POINT #

11121314151617181920

NORTHING5361013.75361122.05361338.75361471.05361628.85361769.95361836.25361950.55362104.45362387.8

EASTING463918.7464010.4464093.6464164.7464288.0464468.8464463.0464551.7464583.3464671.2

0+855

2+412

1+559

1+2131+355

1+771

0+987

1+8241+976

2+122

DRAWING INFORMATION



PROJECT NUMBER

DRAWING NUMBER

REVISION

SHEET NUMBER

DATE


28 FEB 2019 ROYAL BEACHCOASTLINE EROSION STUDY

ESTIMATED FUTURE SHORELINE RETREAT ANDTSUNAMI HAZARD LINES WITH 2m SEA LEVEL

RISE, AND COMPUTED SETBACKSPLAN VIEW

3003631

3003631-004

31



N

100

SCALE 1:5000

2000

2

LEGEND

ESTIMATED PRELIMINARY TSUNAMI HAZARD LINE WITH 2m SEA LEVEL RISE (BASED ON RESULTS PRESENTED IN AECOM 2013)


EXISTING TOP OF COASTAL BLUFFEXISTING TOE OF COASTAL BLUFF / BANK

FUTURE POSITION OF COASTAL BLUFF /BANK TOE WITH 2m SEA LEVEL RISE (MEDIAN BOUND ESTIMATE)

WAYPOINT (SEE TABLES)

GENERAL NOTES:



4. CONTOUR INTERVAL: 5m.5. PROPERTY LINE APPROXIMATE, SCANNED FROM COMPOSITE PLAN OF THE ROYAL BAY PROPERTIES, PREPARED BY McILVANEY RILEY LAND SURVEYING INC.6. BEACH STATIONING IS MEASURED FROM ALBERT HEAD, FOLLOWING THE APPROXIMATE NATURAL BOUNDARY ALIGNMENT.7. BASE IMAGE FROM CRD (2015).8. DEVELOPMENT SETBACK LOCATIONS SHOWN MAY NEED TO BE ADJUSTED TO ACCOUNT FOR ADDITIONAL GEOTECHNICAL CONSIDERATIONS


AutoCAD SHX Text


ELEV

ATIO

N (m

)

OFFSET (m)

STA. 0+987

-505

10152025303540455055

0 5 10 15 20 25 300-5-10

-15

-20

-25

-30

-35

-40

-45

-50

-55

-60

-65

-70

-75

-80

-85

-90

-95

-100

-105

-110

-115

-120

-125

-130

ELEV

ATIO

N (m

)

OFFSET (m)

STA. 1+355

-505

101520253035404550

0 5 10 15 20 25 300-5-10

-15

-20

-25

-30

-35

-40

-45

-50

-55

-60

-65

-70

-75

-80

-85

-90

-95

-100

-105

-110

-115

-120

-125

-130

-135

-140

-145

-150

-155

ELEV

ATIO

N (m

)

OFFSET (m)

STA. 1+213

-505

101520253035404550

0 5 100-5-10

-15

-20

-25

-30

-35

-40

-45

-50

-55

-60

-65

-70

-75

-80

-85

-90

-95

-100

-105

-110

-115

-120

-125

-130

-135

-140

-145

-150

-155

-160

ELEV

ATIO

N (m

)

OFFSET (m)

STA. 0+855

-505

101520253035404550556065

0 5 10 15 20 25 300-5-10

-15

-20

-25

-30

-35

-40

-45

-50

-55

-60

-65

-70

-75

-80

-85

-90

-95

-100

-105

-110

-115

-120

-125

-130

-135

-140

-145

-150

-155

-160

-165

1

3

11

HHWLT (TYP)MSL (TYP)LLWLT (TYP)

2

12

13 14

4

CURRENT BEACH PROFILE, TYP (LiDAR + 15JUNE 2018 NHC SURVEY + CHS BATHYMETRY)


ESTIMATED FUTURE NATURALBOUNDARY (2100)


ESTIMATED FUTURE NATURALBOUNDARY (2100)

LEGENDPROPERTY LINE LOCATION (APPROXIMATE)EXISTING POSITION OF COASTAL BLUFFWAY POINT (SEE TABLES, SHEET 3)4

DRAWING INFORMATION



PROJECT NUMBER

DRAWING NUMBER

REVISION

SHEET NUMBER

DATE


28 FEB 2019ROYAL BEACH

COASTLINE EROSION STUDYIMPACTS OF SEA LEVEL RISE

SECTION VIEWSSTA 0+855, 0+987, 1+213, 1+355

3003631

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41



CROSS SECTIONSSCALE 1:1000

NOTES:

1. ESTIMATED FUTURE NATURAL BOUNDARY REFERS TO THE HORIZONTALPOSITION OF THE BOUNDARY ONLY (YEAR 2100).

2. PROPERTY LINE SCANNED FROM COMPOSITE PLAN OF THE ROYAL BAYPROPERTIES, PREPARED BY McILVANEY RILEY LAND SURVEYING INC.


AutoCAD SHX Text


ELEV

ATIO

N (m

)

OFFSET (m)

STA. 1+771

-15-10-505

1015202530

0 5 10 15 20 25 30 35 40 45 500-5-10

-15

-20

-25

-30

-35

-40

-45

-50

-55

-60

-65

-70

-75

-80

-85

-90

-95

-100

ELEV

ATIO

N (m

)

OFFSET (m)

STA. 1+976

-10-505

101520

0 5 10 15 20 25 30 35 40 45 500-5-10

-15

-20

-25

-30

-35

-40

-45

-50

-55

-60

-65

-70

-75

-80

-85

-90

ELEV

ATIO

N (m

)

OFFSET (m)

STA. 2+412

-505

101520253035404550

0 5 10 15 200-5-10

-15

-20

-25

-30

-35

-40

-45

-50

-55

-60

-65

-70

-75

-80

-85

-90

-95

-100

-105

-110

-115

-120

-125

-130

-135

-140

-145

-150

-155

ELEV

ATIO

N (m

)

OFFSET (m)

STA. 2+122

-10-505

1015202530354045

0 5 10 15 200-5-10

-15

-20

-25

-30

-35

-40

-45

-50

-55

-60

-65

-70

-75

-80

-85

-90

-95

-100

-105

-110

-115

-120

-125

-130

-135

-140

-145

-150

-155

-160

-165

-170

ELEV

ATIO

N (m

)

OFFSET (m)

STA. 1+824

-10-505

101520

0 5 10 15 20 25 30 35 40 45 500-5-10

-15

-20

-25

-30

-35

-40

-45

-50

-55

-60

-65

-70

-75

-80

-85

-90

ELEV

ATIO

N (m

)

OFFSET (m)

STA. 1+559

-505

10152025303540

0 5 10 15 20 25 30 35 40 45 500-5-10

-15

-20

-25

-30

-35

-40

-45

-50

-55

-60

-65

-70

-75

-80

-85

-90

-95

-100

-105

-110

-115

-120

-125

-130

HHWLT (TYP)MSL (TYP)LLWLT (TYP)

15

5

166

7

17

19

9

818

10

20



ESTIMATED FUTURE NATURAL BOUNDARY (2100)ESTIMATED FUTURE NATURAL BOUNDARY (2100)ESTIMATED FUTURE NATURAL BOUNDARY

ESTIMATED FUTURENATURAL BOUNDARY (2100) ESTIMATED FUTURE NATURAL BOUNDARY (2100)

LEGENDPROPERTY LINE LOCATION (APPROXIMATE)EXISTING POSITION OF COASTAL BLUFFWAY POINT (SEE TABLES, SHEET 3)4

DRAWING INFORMATION



PROJECT NUMBER

DRAWING NUMBER

REVISION

SHEET NUMBER

DATE


28 FEB 2019 ROYAL BEACHCOASTLINE EROSION STUDY

IMPACTS OF SEA LEVEL RISESECTION VIEWS

STA 1+559, 1+771, 1+824, 1+976, 2+122, 2+412

3003631

3003631-004

51



CROSS SECTIONSSCALE 1:1000

NOTES:

1. ESTIMATED FUTURE NATURAL BOUNDARY REFERS TO THE HORIZONTALPOSITION OF THE BOUNDARY ONLY (YEAR 2100).

2. PROPERTY LINE SCANNED FROM COMPOSITE PLAN OF THE ROYAL BAYPROPERTIES, PREPARED BY McILVANEY RILEY LAND SURVEYING INC.


AutoCAD SHX Text


royal beach coastal assessment final report revision 0

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