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Saldanha Bay Strategic Environmental Assessment

Natural Capital Theme: Coastal Physical Features and Processes

Prepared by: Geoff Smith, WSP

Dr Melanie Luck-Vogel, CSIR

Jessica Eichhoff, University of Stellenbosch

John April, CSIR

Luanita Snyman van der Walt, CSIR

SUMMARY

The marine environment of the Greater Saldanha Bay region (GSB) is influenced by a range of coastal physical

processes, including winds, waves, currents, associated sand transport and resulting morphological changes

to sandy sea-beds and beaches.

These physical processes can be altered by anthropogenic influences, particularly:

Port development: Previous modelling has demonstrated that both dredging and reclamation (with

associated revetments) can cause moderate beach erosion which manifests on a time scale of decades.

This is generally mitigatable, at least in part, by altering the configuration and slopes of dredged

channels and reclamation edging, where practical. Beach protection measures and/or sand supply is a

less likely but possible mitigation;

Urban development impacts on sand transport corridors/sources: This can block sand transport

corridors and/or sequestrate sand in dunes or beaches which may serve as erosion and/or flood

protection. This can be avoided by careful planning with knowledge of the sand transport environment

and can be mitigated to some extent but at considerable cost (by artificially moving sand);

Urban development storm water discharges: Localised beach scour through storm water discharge is

generally recovered naturally, but can induce/attract the formation of rip current cells which, in turn,

result in localised erosion. This can be mitigated by appropriate storm water discharge design,

featuring retention ponds to reduce discharge rates and/or scour protection and/or pipelines

discharging beyond the shoreline.

Unmanaged recreational access through coastal vegetation. This can be mitigated through the prompt

construction of boardwalks and/or barriers for prevention of pedestrian access at sites that suddenly

become popular.

Monitoring is key to the early identification of potential impacts from anthropogenic influences, allowing for

them to be timeously mitigated. The following is recommended:

Regular (2 to 4 times a year) topography survey (conventional or Lidar) of wave-exposed sandy coasts,

and of coasts bordered by urban development, where erosion issues are possible and/or are known to

have occurred recently. These should aim to add to existing data (e.g. targeting beach profile locations

previously measured);

Periodic (annual or post-event) assessment of beaches, dunes, and sand transport corridors (and/or

evolving corridors) by means of high resolution stereo satellite imagery and/or LiDAR, with ground

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truthing observations if necessary. The purpose of the assessment is to identify changes in sand

volumes in these corridors over time.

With the availability of these data, it can be assessed whether the beach and dune system contains a

sufficient volume of sand to accommodate an extreme (1:100 year advisable) storm and whether the beach

profile can accommodate extreme water-levels and associated wave run-up events (1:100 year advisable). If

either of these criteria do not comply, mitigation and/or coastal protection measures should be considered.

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1. Key environmental attributes and ecosystem services

The marine environment of the Greater Saldanha Bay region (GSB) is strongly affected by physical processes.

Dominant south-westerly swells impact persistently on the region’s shores, while prevailing southerly winds

provide a second component of wave action. Through the interaction with headlands, islands and shoals,

the processes of refraction and diffraction effect a transformation in height and direction as waves approach

the shore. The resulting breaking waves and associated wave-driven currents and consequent sand transport

shape the beaches of the GSB. While south-westerly waves dominate at the more ocean-exposed beaches

in the west of the GSB, the orientation and configuration of bays in the north and also within Saldanha Bay

results in sheltered conditions. In the wave sheltered lagoon of Langebaan, tide- and wind-generated flows

and associated sediment transport are the dominant processes.

Apart from these relatively localised hydrodynamic processes, the more regional action of southerly wind-

induced upwelling is conducive to a productive fishing industry. With the added benefits of tidal exchange,

the nutrient rich and productive aquaculture climate in Saldanha Bay results.

Superimposed on these processes is climate change. International climate change scenarios agree on a rising

sea level for the next 80 years in the range between 0.3 and 1.0m (IPCC-4, 2013). Local measurements

(Mather et al., 2009) suggest a slower rate of sea-level rise (1.8mm/per year). Regardless of the exact rate of

sea-level rise, the ultimate consequence is clear: a generally higher mean sea level will lead to the permanent

flooding of very low lying coastal areas and will elevate storm related flood levels, even if the intensity and

frequency remains the same (or even decreases, as forecasted by Engelbrecht (2019) for the West Coast of

South Africa).

Long-term changes to sediment transport regimes (both anthropogenic and naturally induced) can result in

erosion of shorelines and/or sandbars and corresponding accretion elsewhere. Superimposed on such

change is episodic cross-shore erosion by storm waves and coincident storm surges (and corresponding

flooding in some cases). Flooding and erosion on a natural, uninhabited shoreline has limited consequences

(particularly when mitigated by natural beach volume and vegetated dune protection). However, these

natural coastal dynamics and hazards become a problem where the coast is occupied by human

infrastructure and supports livelihoods.

The GSB is very much reliant on its coastal natural resources and also on the ocean as a means of transport.

The local tourism sector is greatly dependent on the beaches, marinas and natural (fishing) resources.

Accordingly, most of the economically important infrastructure is located close to the shore. Current and

future planning should therefore aim to:

1. Preserve natural coastal ecosystems resources such as fish and crustaceans as a baseline for

recreational, subsistence and commercial harvesting and as a baseline for the tourism industry;

2. Avoid development of coastal infrastructure in areas susceptible to coastal erosion and flooding;

3. Identify and protect existing coastal infrastructure susceptible to coastal hazards;

4. Plan future development in a way that it does not impair or alter natural coastal dynamics (e.g.

sediment transport) which might increase the vulnerability to erosion or flooding and does not

negatively impact other coastal income sectors.

The GSB coastal region features the Port of Saldanha, the largest commercial port along South Africa’s west

coast, under the jurisdiction of Transnet National Ports Authority (TNPA). The port occupies a considerable

area and its boundaries are extensive. Figure 1 and Figure 2 indicate the existing and future (for the year

2045) port master plans (TNPA, 2017) which features expansion to the south, into Big Bay. The port influence

includes the channel (dredged to -23 m relative to Chart Datum) which extends offshore to a point opposite

Marcus Island.

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Figure 1: Port of Saldanha – current layout (Source: TNPA, 2017:2-101)

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Figure 2: Port of Saldanha – medium term layout (Source: TNPA, 2017:2-103).

The coast of the GSB municipality also features several small harbours, including:

Small fishing harbours in Saldanha Bay (within the commercial port footprint) and at St Helena Bay

town. Minor fishing jetties are found in the sheltered Stompneus Bay as well;

Recreational facilities, including a yacht club within the Saldanha Bay port, Yacht club at Langebaan,

and the small recreational craft harbour at Club Mykonos;

SA National Defence force jetties at Langebaan and at Donkergat (within the Postberg Reserve).

Coastal physical features and processes can provide an array of ecosystem services to society. These are

summarised in Table 1.

Table 1: Ecosystem Services provided by Coastal Physical Features and Processes

Category Ecosystem Service

Provisioning Protection of property from storm surge and waves

Naturally wave-sheltered environments for vessel launching, mooring, on/offloading, maintenance

Regulating Wastewater assimilation (through mixing/dilution by coastal processes)

Moderation of extreme sea conditions (by naturally sheltered areas)

Nutrient cycling (related to upwelling and tidal water exchange)

Supporting Refugia for resident and transient animal populations

Big Bay

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Genetic resources (source of unique/scarce biological material and products)

Nursery area for marine biota

Cultural Amenity and aesthetic value (e.g. real estate value)

Ecotourism and recreation

Cultural, inspirational, religious services (education, art, research)

2. Drivers and Pressures

The key drivers, and associated activities, posing risks to possible alteration of physical coastal processes

(which in turn can result in both coastal erosion and coastal flooding) along the GSB region were identified

during a stakeholder workshop held in Saldanha Bay and refined during a specialist workshop held in

Stellenbosch. The key drivers (or sectors) of risk include Ports and small harbours, urban development, and

tourism. These lead to the pressures of hydrodynamic alteration, land transformation, and removal of coastal

vegetation (Figure 3). These pressures in turn usually have a negative impact on the ecosystem services

provided by the coastal physical environment (see Table 1 above).

Figure 3: Conceptual illustration of key sectors/drivers, associated activities and developments, and the pressures to which these contribute in terms of altering physical coastal features and processes.

The activities and developments are discussed below.

2.1 Dredging and breakwaters

Minimal sediment accumulation occurs within the Saldanha port, which consequently requires minimal

maintenance dredging (TNPA, 2014). Thus no meaningful loss of sand or changes to sea bed bathymetry

occur from routine dredging.

However, capital dredging (to accommodate expansion such as iron ore, LNG, LPG developments) can have

an impact. The sediment removal from Saldanha Bay would however amount to a fraction of a percentage

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of the total sediment budget within the bay. It is expected that quantities of sand removed would have no

impact on beach dynamics (erosion/accretion) in terms of sand supply. However, dredging, particularly in

the more wave-exposed Big Bay would induce changes in wave height and direction, consequent changes in

longshore transport of sand, and consequent erosion/accretion. Previous studies (unpublished) which assess

dredged channels, turning basins and berth pockets in Big Bay indicated induced beach shoreline changes in

the order of 5-10 m which manifest over a period of a few decades.

No extension of the harbour breakwaters is planned at the Port of Saldanha by 2045. However, reclamation

into Big Bay is proposed (TNPA, 2016). Apart from the obvious removal of beach habitat and amenity, the

protective revetments bordering the reclamation will induce local changes in wave conditions at the interface

between the revetment and the beach. Depending on the local configuration of this revetment, localised

erosion or (more likely) accretion may occur. While localised accretion would seem to be a benefit, this

would occur at the expense of (i.e. with sand from) the neighbouring beach further south, translating to

erosion of this beach.

2.2 Urban development and land transformation

Urban development and land transformation in the coastal zone can impact on coastal functioning, if not

done in careful consideration of natural flows and processes. Globally a “coastal squeeze” trend can be

observed, i.e. coastal settlements are moving closer and closer to the coast, mainly due to its aesthetic appeal

and recreational value. This development can:

Reduce the function of the natural coastal dunes or vegetation as a buffer against erosion.

Obviously, the more the natural ecosystem belt is diminished, the higher is the exposure of the

development to coastal erosion and flooding;

Reduce the function of the natural coastal dunes or vegetation as trap for wind-blown sand. If not

trapped, this windblown sand can cause problems as it accumulates on roads, in car parks, and in

residential areas;

Cause construction over the beach and/or dune area and associated sequestration of

sand/sediment from the coastal system;

Cause blockage of aeolian sand transport corridors.

2.3 Stormwater discharges

Stormwater discharges resulting from heavy rainfall cause localised scouring of the beach. The locally

scoured beach generally recovers as a result of wave action (and aeolian sand transport) “smoothing” the

scour channel and returning sand ejected offshore to the beach. However, a localised scour channel

extending into the nearshore zone can attract wave run-up flows, aggravating localised beach erosion. This

in turn may impact on beach dynamics, causing subtle changes in currents (bathing safety a concern) and

sediment transport (resulting in localised erosion/accretion). Further, storm water discharge is a massive

source of coastal pollution.

2.4 Touristic and recreational activities

Touristic and recreational activities put a variety of pressures on natural resources. The pressures on the

marine biotic resources through fishing and harvesting are described in the marine ecology section of this

report. Of major concern in the context of coastal physical dynamics is mainly the uncontrolled access to the

coast by pedestrians and possibly vehicles. Uncontrolled access leads to pathways being trampled through

the natural vegetation. These areas bare of vegetation are prone to wind and wave erosion, thus weakening

the protective function of the natural vegetation. Pollution and littering are another pressure on the coastal

environment. These are described elsewhere.

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Figure 4 below shows main tourism attractions, facilities and activities in the Greater Saldanha Bay

Municipality. This map highlights the importance of the area for tourism in the region, with a high

concentration of tourism attractions especially within the Bay and highlight the need to consider coastal

access.

2.5 Aquaculture in the bay

The existing and proposed aquaculture in the bay is extensive (Figure 5 below illustrates Mariculture

concession areas in Saldanha Bay). Mariculture rafts and associated facilities are designed to float on the

water-surface and to allow free circulation of water containing the food source. Such structures therefore

have negligible impacts on the energetic, long-period waves impinging on the Saldanha shoreline (explaining

why such floating structures are not employed as breakwaters on South African coasts, only to reduce small

wave chop within sheltered harbours/marinas – CEM, 2006). In addition, the floating structures featuring

slender moorings have a negligible impact on currents. Thus no meaningful alteration of physical coastal

processes will ensue.

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Figure 4 Main tourism attractions, facilities and activities in the Greater Saldanha Bay Municipality (Source: DEA&DP, 2017:89)

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Figure 5: Mariculture concession areas in Saldanha Bay 2017 (464ha). The total area leased to the aquaculture sector currently comprises 316.5ha. Currently farmed areas will be incorporated into the Aquaculture Development Zone comprising 884 ha set aside for mariculture (Anchor Environmental, 2018).

Table 2 summarises the finer-scale relationships between the system variables outlined in Figure 3.

Table 2: Overview of potential ecological and socio-economic impacts on coastal physical features and processes associated with various relevant drivers and pressures

IMPACT DRIVER PRESSURE HOW DO THE DRIVERS, PRESSURES AND IMPACTS INTERACT

ALT

ERA

TIO

N O

F C

OA

STA

L P

HYS

ICA

L FE

ATU

RES

AN

D

PR

OCE

SSES

Ports and small harbours

Hydrodynamic alteration

Port expansions and dredged channels/basins alter currents and waves, in turn altering sediment transport and in turn altering patterns of sediment deposition and erosion. A possible (albeit less likely) feedback loop can occur whereby altered processes can adversely impact port operations and maintenance through the creation of adverse navigation conditions (waves, reflected waves, currents), and shoals.

Urban development


Stormwater discharges from heavy rainfall cause localised scouring of the beach. While this generally recovers, the localised scour channel can attract wave run-up flows, aggravating localised beach erosion. This in turn may impact on beach dynamics, causing subtle changes in currents (bathing safety a concern) and sediment transport (localised erosion/accretion).

Land transformation

Development of infrastructure associated with urban development, such as landfill sites and wastewater treatment works (possibly also transport corridors/quarries) result in the transformation of land. This can take the form of (a) construction over the beach and/or dune area and associated sequestration of sand/sediment from the coastal system or (b) blockage of aeolian sand transport corridors. The same issues would ensue from development of commercial, business, and residential expansions and/or settlements.

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Tourism activities

Removal of coastal vegetation

Recreation in the form of fishing, surfing, wind-surfing, and kite-surfing can attract participants to unexpected locations having suitable conditions. Without formalised and/or controlled access, trampling can lead to destruction of dune vegetation (Figure 6). There is a consequent risk of sand transport by wind and possible loss of coastal foredune protection. A possible feedback loop can occur whereby destruction of vegetation detracts from the appeal of a natural site, or possibly mobilised sand makes for unpleasant beachgoing, thus impacting on the site’s recreational value.

Figure 6 below illustrates the impact of unregulated access and associated vegetation destruction from Kite

Surfers accessing Shark Bay, Langebaan. The open, sandy pathways are a risk for aeolian erosion of the dunes.

Further, the permanent disturbance through pedestrians might impact on biota living and nesting in the

dunes.

Figure 6: Network of coastal paths (and associated vegetation destruction) from KiteSurfers accessing Shark Bay, Langebaan

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3. Sensitivity analysis

In the context of coastal physical processes, both natural and built environments on the coast are generally

sensitive to two main risks:

1. Coastal Erosion. Recent erosion at Langebaan, which lead to the need to urgently construct a

protective rock revetment followed by groynes built from GeoContainers highlighted the sensitivity

of the coast to rapid erosion. This risk will increase with sea-level rise. The open coast of the

municipality is exposed to the wave action of the open ocean, albeit less so on the St Helena Bay

coast.

2. Coastal flooding. Although there are no explicit examples of flooding, there are relatively low-lying

areas within GSB which are susceptible to flooding, particularly with future sea-level rise.

Figure 7 illustrates areas which have been identified as being of risk of coastal flooding and erosion in the

National Coastal Assessment project which is currently undertaken by the CSIR on behalf of DEFF, Branch

Oceans & Coasts. The boundary between the low and medium flood risk class, largely at the 10m elevation

contour, largely corresponds with the Western Cape Provinces 1:100 years flood line.

Figure 7: Coastal Flood and Erosion risk in the Saldanha Bay Local Municipality. Source: DEA National Coastal Assessment project, as of July 2019.

The Erosion map largely reflects the geomorphology of the coast, with the lower risk areas being the more

rocky parts of the coast.

Table 3 presents a list of the key indicators that are used to rate the sensitivity indicators for these two main

aspects of coastal sensitivity, relating to vegetation and/or urban infrastructure.

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In Figure 8 below, this ranking is applied to the features listed in Table 3 which are located in the coast

between the high water mark and the Province’s 1:100 years flood line.

Table 3: Selected coastal erosion and flooding sensitivity indicators ratings for coastal physical features and processes

SENSITIVITY INDICATOR BRIEF DESCRIPTION SENSITIVITY

RATING

Co

asta

l Er

osi

on

Ris

k

Low value urban development: Recreational facilities, car parks, board walks, temporary beach facilities

Minor inconvenience, alternative facilities in close proximity, short rebuild times

Low

Medium value urban development: Tidal pools, piers, recreational facilities, sewerage pump stations.

Local impacts, loss of infrastructure and property Moderate

High value urban development: Beachfronts, small craft harbours, residential homes, sewerage treatment works.

Regional impacts, loss of significant infrastructure and property High

Very High value urban development: Ports, desalination plants, nuclear power stations

Major disruption to the regional and national economy, failure of key national infrastructure

Very high

Bare soil Primarily beaches, easily eroded with no vegetation cover. Important resource in terms of coastal protection and amenity. Recovery from erosion can occur

Moderate

Cultivated land Fairly high economic value, expensive to re-establish Very high

Wetlands/seasonal water bodies

Inundation resulting from erosion of moderate impact, natural re-establishment will occur

Moderate

Herbaceous vegetation Can re-establish after erosion event Low

Indigenous Forest/ Thicket /Dense bush

If damaged, will take a long time to re-establish High

Co

asta

l flo

od

ing

risk

Low value urban development: Recreational facilities, car parks, board walks, temporary beach facilities

Minor inconvenience, alternative facilities in close proximity, short rebuild times

Low

Medium value urban development: Tidal pools, piers, recreational facilities, sewerage pump stations.

Local impacts, loss of infrastructure and property Moderate

High value urban development: Beachfronts, small craft harbours, residential homes, sewerage treatment works.

Regional impacts, loss of significant infrastructure and property High

Ports, desalination plants, nuclear power stations

Major disruption to the regional and national economy, failure of key national infrastructure

Very high

Bare soil Inundation has no impact Low/Mod

Cultivated land Of high value – saline water intrusion disastrous Very high

Wetlands/seasonal water bodies

Robust to inundation - limited impact if sustained Low

Herbaceous vegetation Coastal vegetation robust to temporary saline water inundation Low

Indigenous Forest/ Thicket /Dense bush

Moderate effect of flooding Moderate

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For this map, infrastructure located at rocky parts of the shore was considered to be at low risk.

Figure 8: Assessment of the sensitivity of coastal natural and urban infrastructure to coastal flooding and erosion.

4. Risk Assessment

Categories of risk likelihood were adopted in line with the wider SEA approach. The generic criteria of

different likelihood categories used are listed below, but as indicated should be regarded as relative

measures, rather than absolute.

Extremely unlikely = 1:10 000

Very unlikely = 1:100

Not likely = 1:20

Likely = 1:2

Very Likely = 1:1.

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Table 4 provides estimates (based on available information and expert judgement of the study team) of the

relevant likelihood of impacts occurring for the different production systems, with and without mitigation

measures. Table 5 provides a rating system for the consequences of coastal erosion and flooding. The

consequence terms make reference to:

The limit of acceptable change (e.g. specific shoreline retreat distances are referred to);

Resilience (e.g. the likelihood of natural beach recovery).

Table 4: Relative likelihood of drivers and the associate pressures impacting on coastal physical features and processes without and with mitigation (EU = extremely unlikely; VU = Very unlikely; NL = not likely, L= likely, VL = very likely)

IMPACT DRIVER PRESSURES

LIKELIHOOD OF IMPACT (EROSION)

LIKELIHOOD OF IMPACT (FLOODING)

Without mitigation

With mitigation

Without mitigation

With mitigation

ALT

ERA

TIO

N O

F C

OA

STA

L P

HY

SIC

AL

FEA

TUR

ES A

ND

P

RO

CES

SES


Hydrodynamic alteration VL NL L NL

Urban development

Hydrodynamic alteration L NL NL VU

Land transformation L VU

NL VU

Tourism activities Removal of coastal vegetation

L VU

NL VU

Table 5: Description of consequence levels used in the risk (of erosion and flooding) assessment for coastal physical features and processes

CONSEQUENCE RATING GENERAL DESCRIPTION

Slight (S)

Temporary local wetting of infrastructure (e.g. coastal carparks, roads, ablution facilities)

and/or natural vegetation, dries naturally with no permanent impact;

Local beach shoreline erosion close to but within the standard deviation of shoreline

fluctuations (typically within ±5-10 m within Saldanha Bay). Typically the beach is resilient

to such routine change and will recover on a seasonal basis.

Moderate (M)

Temporary local flooding of low cost infrastructure (e.g. coastal carparks, roads, ablution

facilities) and/or natural vegetation, with limited permanent damage;

Local beach shoreline erosion greater than the standard deviation of shoreline fluctuations

(typically within ±5-10 m within Saldanha Bay) but less than the previous maximum

variation.

Erosion such that setback of infrastructure/property is 25% (in distance) less than

recommended minimum setback distances (~20 m on sheltered coasts within bays, ~40 m

on exposed coasts)

Total recovery of the beach is evident (temporary movement of sand offshore, to return

under constructive wave action) on a time scale of around 1 year.

Substantial (Sb)

Local flooding of property, infrastructure and/or natural vegetation with substantial permanent damage;

Local beach shoreline erosion greater than the previous measured maximum variation;

Erosion such that setback of infrastructure/property is 50% (in distance) less than

recommended minimum setback distances (~20 m on sheltered coasts within bays, ~40 m

on exposed coasts)

Total recovery of the beach within 1 year is not evident.

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CONSEQUENCE RATING GENERAL DESCRIPTION

Severe (Se)

Extensive flooding of property, infrastructure and/or natural vegetation with a regional impact;

Local beach shoreline erosion which is appears not to be recoverable;

Erosion such that setback of infrastructure/property is either damaged or requires

emergency protection (e.g. rock/sandbag placement)

Extreme (E)

Extensive flooding of property, infrastructure and/or natural vegetation with a national impact;

Local beach shoreline erosion which is clearly not recoverable;

Erosion such that severe damage to property occurs, before emergency protection can be

implemented successfully.

Based on the combination of likelihood and consequence ratings as indicated above, a matrix for the resulting

risk was developed (Table 6).

Table 6: Risk assessment look-up table showing the relationship between Likelihood x Consequence as Risk

CONSEQUENCE

Slight (S) Moderate

(M) Substantial (Sb) Severe (Se) Extreme (E)

LIK

ELIH

OO

D

Very Likely (VL) Very Low

(VL) Low (L) Moderate (M) High (H)

Very high

(VH)

Likely (L) VL L M H VH

Not likely (NL) VL L L M H

Very unlikely (VU) VL VL L M M

Extremely unlikely

(EU) VL VL VL L L

Very low risk: Extremely unlikely that the impact will have a consequence of any magnitude with close to zero effect on current ecosystem services

Low risk Very unlikely that impact will have a consequence of any discernible magnitude. Impact on ecosystem services is limited in extent (<1% of study area), short term in duration (<3 years)

Moderate risk Not likely that impact will have any serious consequence. Ecosystem services are impacted (<5% of study area) in the short-medium term (<10 years) but are well within their absorptive, adaptive and recuperative capacities.

High risk Likely materialisation of impact with serious consequences. Ecosystem services are substantially impaired (5-10% of study area) and medium-term in duration (10-20 years). Absorptive, adaptive and recuperative capacities are close to threshold

Very high risk Almost certain that the impact will cause some element of the system to collapse. Ecosystem services are degraded to the point of not being able to recover (>10% of study area) and long-term in duration (>30 years). Beyond the limits of acceptable change.

Table 7 and Table 8 provide the risk assessments for coastal erosion and coastal flooding. It is evident that

coastal erosion risks due to anthropogenic influences are generally very low or low, and moderate in only

two instances. Mitigation is effective in most cases, resulting in no risks higher than low. For coastal flooding

risk, anthropogenic influences are generally very low or low. Mitigation is effective in many cases.

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Table 7: Coastal Erosion Risk Assessment of relevant drivers and pressures on coastal physical features and processes (VL = Very low; L = low; M = Moderate; High = High; VH = Very high). Likelihood and Consequence ratings as per

Table 4 and Table 5 respectively)

IMPACT DRIVER PRESSURE SENSITIVITY WITHOUT MITIGATION WITH MITIGATION LIKELIHOOD CONSEQUENCE RISK LIKELIHOOD CONSEQUENCE RISK

CO

AST

AL

PH

YSIC

AL

FEA

TUR

ES A

ND

P

RO

CESS

ES



Low VL S VL VU S VL

Moderate L M L VU M VL

High NL Sb L EU Sb VL

Very high VU Se M EU Se L

Urban development


Low VL S VL NL S VL

Moderate NL S VL VU S VL

High NL S VL VU S VL

Very high VU M VL EU M VL

Land transformation.

Low L M M NL M L

Moderate NL M L VU M L

High NL Sb L VU Sb L

Very high EU Se L EU Se L

Tourism Removal of coastal vegetation

Low L S VL VU S VL

Moderate NL S VL EU S VL

High VU M VL EU M VL

Very high EU Sb VL EU Sb VL

Table 8: Coastal Flooding Risk Assessment of relevant drivers and pressures on coastal physical features and processes (VL = Very low; L = low; M = Moderate; High = High; VH = Very high). Likelihood and Consequence ratings as per

Table 4 and Table 5 respectively)

IMPACT DRIVER PRESSURE SENSITIVITY WITHOUT MITIGATION WITH MITIGATION LIKELIHOOD CONSEQUENCE RISK LIKELIHOOD CONSEQUENCE RISK

CO

AST

AL

PH

YSIC

AL

FEA

TUR

ES A

ND

P

RO

CESS

ES



Low NL S VL VU S VL Moderate VU M VL EU M VL High VU Sb L EU Sb VL

Very high EU Se L EU Se L

Urban development


Low VU S VL EU S VL Moderate VU M VL EU M VL High EU Sb VL EU Sb VL Very high EU Se L EU Se L

Land transformation

Low NL S VL VU S VL Moderate VU M L EU M VL High VU Sb L EU Sb VL Very high EU Se L EU Se L


Low VU S VL EU S VL Moderate EU M VL EU M VL High EU Sb VL EU Sb VL Very high EU Se L EU Se L

5. Best practice mitigation, monitoring and limits of acceptable change

Recommended best-practice mitigation efforts, considerations for appropriate monitoring systems, as well

as limits of acceptable change relevant for various drivers, and the relevant pressures are presented in

Table 9. To provide ecological and socio-economic risk maps, the information in Table 9 needs to be

geographically translated using the sensitivity maps.

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Table 9 provides an overall risk score associated with each of the drivers, for different ecological and socio-

economic sensitivity rating in the environment (Table 1).

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Table 9: Best Practice mitigation, suitable monitoring system and acceptable limits of change linked to risks from drivers and pressures relevant to coastal physical features and processes

IMPACT DRIVER PRESSURE BEST PRACTICE MITIGATION BEST VARIABLES AND SUITABLE SYSTEMS FOR

MONITORING

CO

AST

AL

PH

YSIC

AL

FEA

TUR

ES A

ND

PR

OC

ESSE

S



Redesign of breakwaters /channels /berth pockets to minimise changes to waves that induce erosion.

Strategic dredging to alter wave heights/directions to minimise changes to waves that induce erosion.

Landward retreat of infrastructure, buildings, where practical.

Beach sand nourishment/recharge. Sand can potentially be sourced from accreting shores.

Cross-sectional volume and width of the foredune and beach – from beach topography survey (lidar or conventional survey – 2 to 4 times a year)

Condition of the dune and associated vegetation cover (by inspection by a suitably qualified dune botanist - annual)

Adequate beach (or dune) height on the seaward side of a development or vulnerable area - from beach topography survey (lidar or conventional survey – 2 to 4 times a year)

Urban development


Redesign of stormwater discharge, featuring retention ponds and/or scour protection, and/or pipelines discharging beyond the shoreline.

Cross-sectional volume and width of the foredune and beach – from beach topography survey (lidar or conventional survey – 2 to 4 times a year)


Adequate beach (or dune) height on the seaward side of a development or vulnerable area - from beach topography survey (lidar or conventional survey – 2 to 4 times a year)

Coastal engineer inspection of the condition of stormwater discharges to ensure optimal functioning, particularly scour protection.

Land transformation

Relocation of (or avoiding of) infrastructure situated within coastal sediment transport corridors/pathways;

Artificial re-establishment of coastal aeolian sediment transport pathways if necessary, e.g. trucking sand (costly)

Cross-sectional volume and width of the foredune and beach – from beach topography survey (lidar or conventional survey – 2 to 4 times a year) to assess dune change with time;

Aerial/satellite image analysis to identify and monitor windblown sand corridor evolution (annual).


Timeous construction of boardwalks and/or prevention of pedestrians at sites that suddenly become popular (e.g. as a result of watersport trends)


If relevant to check, cross-sectional volume and width of the foredune and beach – from beach topography survey (lidar or conventional survey – 2 to 4 times a year)

If relevant, adequate beach (or dune) height on the seaward side of a development or vulnerable area - from beach topography survey (lidar or conventional survey – 2 to 4 times a year)

6. Conclusions and Recommendations

The primary drivers in relation to coastal physical processes are:

20

Port development: Previous modelling has demonstrated that both dredging and reclamation (with

associated revetments) can cause moderate beach erosion which manifests on a time scale of decades.

This is generally mitigatable, at least in part, by altering the configuration and slopes of dredged

channels and reclamation edging, where practical. Beach protection measures and/or sand supply is a

less likely but possible mitigation;

Urban development impacts on sand corridors/sources: This can block sand transport corridors and/or

sequestrate sand in dunes or beaches which may serves as erosion and/or flood protection. This can

be avoided by careful planning with knowledge of the sand transport environment and can be

mitigated to some extent at considerable cost (by artificially moving sand);

Urban development storm water discharges: Localised beach scour is generally recovered naturally,

but can induce/attract the formation of rip current cells which, in turn, result in localised erosion. This

can be mitigated by appropriate storm water discharge design, featuring retention ponds and/or scour

protection and/or pipelines discharging beyond the shoreline.

Unmanaged recreational access through coastal vegetation. This can be mitigated through the prompt

construction of boardwalks and/or prevention of pedestrians at sites that suddenly become popular.

Monitoring is key to the early identification of potential impacts, allowing for them to be timeously mitigated.

The following is recommended:

Regular (2 to 4 times a year) topography surveys (conventional or Lidar) of wave-exposed sandy coasts,

and of coasts bordered by urban development, where erosion issues are possible and/or are known to

have occurred recently. These should aim to add to existing date (e.g. targeting beach profile locations

previously measured);

Periodic (annual or post-event) assessment of beaches, dunes, and sand transport corridors (and/or

evolving corridors) by means of high resolution stereo satellite imagery and/or LiDAR, with ground

truthing observations if necessary. The purpose of the assessment is to identify changes in sand

volumes in these corridors over time.

21

7. References

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for the Saldanha Bay Water Quality Forum Trust

CEM Coastal Engineering Manual (2006) Types and Functions of Coastal Structures EM 1110-2-1100 (Part VI)

Engelbrecht, F. 2019. Green Book – Detailed Projections of Future Climate Change over South Africa.

Technical report, Pretoria: CSIR.

IPCC-5 (2013). Church, J.A., P.U. Clark, A. Cazenave, J.M. Gregory, S. Jevrejeva, A. Levermann, M.A. Merrifield,

G.A. Milne, R.S. Nerem, P.D. Nunn, A.J. Payne, W.T. Pfeffer, D. Stammer and A.S. Unnikrishnan, 2013:

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Mather, AA, Garland, GG & Stretch, DD (2009). Southern African sea levels: Corrections, Influences and

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