Sea Level Rise and Flood Risk Assessment for a Select ...€¦ · ð•ð Managed retreat – retreat from or reduce development in coastal areas; and ð•ð Accommodation – modify

Department of Environmental Affairsand Development Planning

Final

May 2010

Sea Level Rise and Flood RiskAssessment for a Select Disaster Prone

Area Along the Western Cape Coast

Phase 3 Report: Eden DistrictMunicipality Sea Level Rise and Flood

Hazard Risk Assessment

REPORT TITLE : Phase 3 Report: Eden District MunicipalitySea Level Rise and Flood Hazard RiskAssessment

CLIENT : Provincial Government of the WesternCape Department of EnvironmentalAffairs and Development Planning:Strategic Environmental Management

PROJECT : Sea Level Rise and Flood RiskAssessment for a Select Disaster ProneArea Along the Western Cape Coast

AUTHORS : D. Blake

REPORT STATUS : Final

REPORT NUMBER : 769/3/1/2010

DATE : May 2010

APPROVED FOR :

S. Imrie D. BlakeProject Manager Task Leader

This report is to be referred to in bibliographies as:

Umvoto Africa. (2010). Sea Level Rise and Flood Risk Assessment for a Select DisasterProne Area Along the Western Cape Coast. Phase 3 Report: Eden District Municipality SeaLevel Rise and Flood Hazard Risk Assessment. Prepared by Umvoto Africa (Pty) Ltd for theProvincial Government of the Western Cape Department of Environmental Affairs andDevelopment Planning: Strategic Environmental Management (May 2010).

Phase 3: Eden DM Sea Level Rise and Flood Hazard Risk Assessment 2010

Executive Summary Page i

EXECUTIVE SUMMARY

INTRODUCTION

Umvoto Africa (Pty) Ltd was appointed by the Western Cape Department of EnvironmentalAffairs and Development Planning (DEA&DP): Strategic Environmental Management divisionto undertake a sea level rise and flood risk assessment for a select disaster prone area alongthe Western Cape coast, namely the portion of coastline covered by the Eden District (DM)Municipality, from Witsand to Nature’s Valley. The Western Cape DEA&DP required that aliterature assessment of current global and local understanding and knowledge with regardsto climate change and sea level rise be undertaken, in association with the development of asea level rise and flood inundation Geographic Information System model. Umvoto Africaproposed a three-phase work approach, namely: Phase 1 – Inception and Data Acquisition,Phase 2 – GIS Model Development and Phase 3 – Risk Assessment. This report describesthe coastal hazard risk assessment undertaken during Phase 3.

COASTAL HAZARD RISK ASSESSMENT METHODOLOGY

For this study, the Eden DM coastline was subdivided into 36 sections, termed Coastal ZoneManagement Units (CZMUs). The risk of each CZMU to three coastal hazards wasqualitatively assessed using a modified version of the rapid risk assessment methodologydescribed in Blake and Hartnady (2009). The three coastal hazard types that were selectedin order to undertake the Eden DM coastal risk assessment were sea level rise inducedcoastal erosion and inundation, groundwater contamination from saltwater intrusion (as aresult of sea level rise) and extreme coastal events (storm surges, estuarine flooding andtsunamis).

The risk of each CZMU to each specific hazard can be determined by using the classic riskequation, where Risk (R) = (Hazard (H) x Vulnerability (V)) / Coping Capacity (C). Hazard,vulnerability and coping capacity were in turn scored from 1 to 5 (with 1 representing verylow and 5 representing very high) for each CZMU for each hazard, allowing the risk to becalculated.

Hazard scores for each CZMU were calculated by determining the severity and probability ofeach specific hazard. Severity and hazard were both given a score out of 5 based. Theequation Hazard (H) = (Probability (P) + Severity (S)) / 2 was then used to calculate a finalhazard score out of 5.

Vulnerability (V) was divided into three types, namely social (So), environmental (En) andeconomic (Ec) vulnerability. Social vulnerability was based on the possible amount of humandeaths, economic vulnerability on the total approximate economic cost in Rands, andenvironmental vulnerability on the possible environmental damage to a specific ecosystem(i.e. whether sensitive/protected or not) that may result from a specified hazard or disaster.Each vulnerability type was scored out of 5 based on the variables, and a final vulnerabilityscore was calculated using the equation V = (En + Ec + So) / 3.

Coping capacity defines the resilience a community or area has to a disaster i.e. to whatextent will a community be affected by and how long it will take to recover from a disaster.Each CZMU was given a coping capacity score for each hazard, based on theimplementation of the various stages of the Hyogo Framework for Action (HFA): Priorities forAction (United Nations International Strategy for Disaster Reduction (UN/ISDR), 2005). TheHFA priority areas strive to reduce the impact of disasters through gender sensitive disasterpreparedness and risk reduction i.e. by increasing the coping capacity. Each HFA priorityarea was given a score out of 5, depending on whether there was none to very limited


Executive Summary Page ii

implementation (1), limited implementation (2), partially implemented (3), mainlyimplemented (4) and fully implemented (5). The final coping capacity was then calculatedusing the equation: C = (HFA1 + HFA2 + HFA3 + HFA4 + HFA5) / 5.

Full implementation of all the HFA priority areas will result in a CZMU having a high copingcapacity, ensuring that it is able to deal with coastal disasters. Little to no implementation ofthe HFA priority areas will result in coastal communities within the CZMU being highlyaffected by and taking a long period of time to recover from coastal disasters. The CZMUsalong the Eden DM coastline have low coping capacities, due to minor implementation of theHFA priority areas. HFA1 is the highest scoring priority area, due to the development ofnational, provincial, and in some cases (e.g. Hessequa LM) local coastal legislation, policiesand frameworks to deal with ICZM and coastal hazards. Little to no implementation of HFAs2 to 5 has occurred across the entire Eden DM coastline however.

The risk equation of R = H x V / C shows that coping capacity has a significant influence onthe final risk assessment, and hence the importance in developing coping capacitymechanisms to deal with disasters in order to reduce the final risk e.g. even if a specificCZMU had the highest H x V ranking possible of 25, a coping capacity of 5 (i.e. fullimplementation of all five HFA priority areas) would reduce the risk of the CZMU to thathazard or possible disaster to 5 (moderate risk).

COASTAL HAZARD RISK ASSESSMENT RESULTS

The majority of the Eden DM CZMUs are at a low to moderate risk to sea level rise inducedcoastal erosion and inundation (44% each). The regions most at risk include the Mossel Bayarea, Wilderness to Knysna area, and the Plettenberg Bay to Nature’s Valley area, while theCZMUs with a high risk ranking are Wilderness West (G4), Wilderness East (G5),Sedgefield-Swartvlei (K1) and Knysna (K6). The areas of moderate to high risk reflect lowgradient coastal areas, often with extensive beaches or large estuaries, in association withareas of development close to the shoreline.

The majority of the Eden DM CZMUs are at a moderate risk to groundwater contaminationfrom salt water intrusion related to sea level rise (69%). The CZMUs with the highest riskranking are Wilderness West (G4), Wilderness East (G5), Sedgefield-Swartvlei (K1), Knysna(K6) and Plettenberg Bay (B2). The majority of the Eden DM is comprised of hydraulicallyconductive and therefore vulnerable primary (Bredasdorp Group) and fractured quartzitic(Peninsula and Skurweberg Formation) aquifers, which are used to varying extents in mostCZMUs along the coastline for groundwater supply. Vulnerability and risk may increase overtime, due to possible future potable water shortages in the area as a result of climatechange, and the associated increased exploitation of groundwater resources.

The majority of the Eden DM CZMUs are at a moderate to high risk from extreme coastalevents such as large storm surges and tsunamis (44% and 42% respectively). The regionsat most risk include Stilbaai, the Mossel Bay area, Wilderness to Knysna area, and thePlettenberg Bay to Nature’s Valley area, while the CZMUs with a high risk ranking areStilbaai (H4), Mossel Bay (M4), Hartenbos (M5), Klein-Brakrivier (M6), Groot-Brakrivier (M7),Outeniquastrand (M8), Wilderness West (G4), Wilderness East (G5), Sedgefield-Swartvlei(K1), Walker’s Bay (K3), Knysna (K6), Plettenberg Bay (B2), Keurbooms-Bitou (B3),Keurboomstrand (B4) and Nature’s Valley (B6). The areas of moderate to high risk reflectexposed low gradient headland-adjacent or inlet/pocket bay beaches, in association withareas of high population and extensive development close to the shoreline.

The coastal risk hazard assessment for the Eden DM identifies 11 CZMUs that are at highrisk to all three coastal hazards, which are highlighted by the red CZMU names and redblocks in the Average Risk column. These results generally correspond to the towns


Executive Summary Page iii

identified by Hughes and Brundrit’s (1992) sea level rise vulnerability assessment for thesame section of coastline, namely Groot-Brakrivier, Wilderness, Stilbaai, Knysna,Keurbooms River, Sedgefield, Nature’s Valley, Klein-Brakrivier, Plettenberg Bay andHartenbos. Hughes and Brundrit (1992) used a different assessment methodology however,which focused on town infrastructure costs, and did not take into account social andenvironmental vulnerability, and coping capacity.

SEA LEVEL RISE ADAPTATION

There are three different options for sea level rise adaptation, namely (German AdvisoryCouncil on Global Change (WBGU), 2006):

Protection – protect the coastline from sea level rise by structures;

Managed retreat – retreat from or reduce development in coastal areas; and

Accommodation – modify land use and infrastructure to accommodate coastalhazards.

The best option for South African and Eden DM managers in particular is the “no-regrets”approach, as recommended to the City of Cape Town with regards to sea level rise(Cartwright et al., 2008). This involves a collective response, from both municipalities andlocal residents, where long term institutional, accommodation, retreat and soft protectiveapproaches are undertaken to understand and manage long term coastal evolution, insteadof haphazard, reactive hard protective approaches to specific extreme events. The no-regrets approach, which should be undertaken even if sea level rise does not occur as itforms good coastal management practice, includes (Cartwright et al., 2008):

no further land reclamation;

the development and management of healthy natural systems, i.e. the conservationand rehabilitation of wetlands, estuaries, kelp beds, dune cordons etc.;

decentralisation of strategic infrastructure, in order to ensure sea level rise does notaffect large areas;

maintenance of current sea walls, dolosse etc., but no development of new hardprotective structures, with other adaptation options being preferred;

insurance market correction i.e. incorporate sea level rise into long term economicalrisk assessments (which isn’t currently done), which will increase coastal premiumsand affect current coastal land owners in the short term, but will prevent further futureexcessive coastal development and reduce future liabilities;

develop coastal management capacity in municipalities and other local, regional andnational institutions;

build disaster management capabilities and incorporate the HFA priority areas into allfuture coastal planning and disaster management activities;

public (community and individual) and private (businesses and industry) coastaleducation drive in order to build an accountable and responsible coastal community,as well as increasing the resilience of coastal communities through povertyalleviation; and


Executive Summary Page iv

undertaking of detailed risk assessments, development of sustainable coastalmanagement plans (SCMPs), and the development of basic early warning systemse.g. combination of tidal information and storm forecasts to determine if there is anextreme storm surge hazard a few days prior to an actual event.

RECOMMENDATIONS

It is recommended that:

Eden District Municipality level:

o Employ the “no-regrets” approach in an ICZM framework along the Eden DMcoastline.

o The HFA Priorities for Action are integrated into all phases of planning, anddisaster risk reduction is made a necessity in municipal structures (if notalready incorporated in line with the Disaster Management Act (Act 57 of2002)), especially with respect to coastal zone hazards.

o Coastal Zone Management Strategies are developed for the remaining fourcoastal LMs of the Eden DM, namely Mossel Bay, George, Knysna and Bitou.

o CZMUs are identified and delineated for each LM (using the initial CZMUsdefined here as a working template if desired).

o Sustainable Coastal Management Plans should be developed for each CZMU,with the eleven high risk CZMUs identified in the risk assessment (Sedgefield-Swartvlei, Wilderness East, Wilderness West, Knysna, Plettenberg Bay,Hartenbos, Keurbooms-Bitou, Nature’s Valley, Klein-Brakrivier, Groot-Brakrivier, Walker’s Bay and Mossel Bay) receiving the highest priority.

o Detailed adaptation studies on each high risk CZMU are conducted, in orderto determine which best combination of methodologies should be developedto adapt to sea level rise induced hazards.

Conceptual studies:

o Begin to undertake architectural research into alternative housing technologye.g. lift houses, used in the Netherlands, Germany and flood prone areas ofthe United States of America. These new housing technologies take intoaccount rising water levels due to storm surges or floods, and can be used inhighly developed estuarine zones within the Knysna, Mossel Bay andPlettenberg Bay areas.


Table of Contents Page i

TABLE OF CONTENTS

Chapter Description Page

1. INTRODUCTION 1

1.1 Scope of work 1

1.2 Global and regional sea level rise 1

2. COASTAL HAZARD RISK ASSESSMENT METHODOLOGY 3

2.1 Coastal Zone Management Units 3

2.2 Hazard 5

2.3 Vulnerability 5

2.4 Coping capacity 7

2.5 Risk 9

3. COASTAL HAZARD RISK ASSESSMENT RESULTS 10

3.1 Sea level rise induced coastal erosion and inundation 10

3.2 Groundwater contamination 10

3.3 Extreme events 10

4. SEA LEVEL RISE ADAPTATION 18

5. RECOMMENDATIONS 20

6. REFERENCES 21


Table of Contents Page ii

LIST OF FIGURES

Figure 2-1 Initial delineated CZMUs for the Eden DM. 4Figure 3-1 SLR induced erosion/inundation risk assessment for the Eden DM. 12Figure 3-2 Groundwater contamination risk assessment for the Eden DM. 14Figure 3-3 Extreme event risk assessment for the Eden DM. 16

LIST OF TABLES

Table 2-1 Initial delineated CZMUs for the Eden DM. 3Table 2-2 Hazard scoring methodology for each hazard. 6Table 2-3 Vulnerability scoring methodology. 6Table 2-4 Key indicators for assessing coping capacity. 7Table 2-5 Risk scoring methodology. 9Table 2-6 Qualitative risk assessment, based on H x V and coping capacity score. 9Table 3-1 Number/percent of risk ranked CZMUs per coastal hazard. 10Table 3-2 SLR induced erosion/inundation risk assessment for the Eden DM. 11Table 3-3 Groundwater contamination risk assessment for the Eden DM. 13Table 3-4 Extreme event risk assessment for the Eden DM. 15Table 3-5 Summarised coastal hazard risk assessment scores. 17


Table of Contents Page iii

LIST OF ABBREVIATIONS

% - percent~ - approximatelyAR4 - Fourth Assessment ReportC - coping capacitycm - centimetreCCRC - Climate Change Research CentreCZMS - coastal zone management strategyCZMU - Coastal Zone Management UnitDM - District MunicipalityDRR - disaster risk reductionDP&R - disaster preparedness and responseDEA&DP - Department of Environmental Affairs and Development PlanningEc - economic vulnerabilityEn - environmental vulnerabilitye.g. - for exampleetc. - etceteraet al. - as well asGIS - Geographic Information SystemH - hazardHAT - Highest Astronomical TideHFA - Hyogo Framework for Actioni.e. - that isICZM - Integrated Coastal Zone ManagementIPCC - Intergovernmental Panel on Climate Changekm - kilometreKZN - KwaZulu-NatalLM - Local Municipalitym - metremm - millimetermamsl - metres above mean sea levelNo. - numberP - probabilityR - RandR - riskRA - risk assessmentS - severitySo - social vulnerabilitySLR - sea level riseSCMP - sustainable coastal management planUNSW - University of New South WalesUN/ISDR - United Nations International Strategy for Disaster ReductionV - vulnerabilityWBGU - German Advisory Council on Global Change


Page 1

1. INTRODUCTION

1.1 SCOPE OF WORK

Umvoto Africa (Pty) Ltd was appointed by the Western Cape Department of EnvironmentalAffairs and Development Planning (DEA&DP): Strategic Environmental Management divisionto undertake a sea level rise and flood risk assessment for a select disaster prone area alongthe Western Cape coast. The assessment area was defined as the southern Cape coastlinewithin the Eden District Municipality (DM), from the Breede River mouth at Witsand toNature’s Valley east of Plettenberg Bay. The Western Cape DEA&DP required that aliterature assessment of current global and local understanding and knowledge with regardsto climate change and sea level rise be undertaken, in association with the development of asea level rise and flood inundation Geographic Information System (GIS) model. UmvotoAfrica proposed a three-phase work approach, namely:

Phase 1 – Inception and Data Acquisition: Collection of GIS data to be used in thedevelopment of the sea level rise and flood inundation model; collection and review ofliterature on both the global and local aspects of climate and sea-level change, as well as allnational, provincial and local coastal legislation; and finalisation of the GIS and riskassessment model methodologies to be used.

Phase 2 – GIS Model Development: Development of a sea level rise and flood inundationmodel, based on specific sea level rise scenarios that were determined from literature.

Phase 3 – Risk Assessment: Undertaking of a coastal zone hazard risk assessment foridentified Coastal Zone Management Units (CZMUs) within the Eden DM, based on a refinedrapid risk assessment methodology described by Blake and Hartnady (2009).

This report describes the coastal hazard risk assessment undertaken during Phase 3.Chapter 1 provides a brief overview of the literature review, and shoreline evolution, extremesea level and estuary flooding modelling conducted in the Phase 1 and 2 reportsrespectively. Chapter 2 describes the methodology used to undertake the coastal hazardrisk assessment. The results from coastal hazard risk assessment are described in Chapter3. Chapter 4 describes various adaptation methods that could be employed to reduce therisk to sea level rise induced hazards, while Chapter 5 concludes this report and providesrecommendations.

The Phase 1 report details the literature and current understanding with regards to sea levelrise both globally and regionally along the South African coastline, as well as the differentsets of national, regional and local South African policies that have been developed to dealwith future climate change induced coastal hazards. The Phase 2 report describes theshoreline evolution, extreme sea level and estuary flooding modelling that was undertakenalong the Eden DM coastline.

1.2 GLOBAL AND REGIONAL SEA LEVEL RISE

Due to the dynamic interaction of biophysical factors from both the Earth’s land surface andocean, and the high human population present, coastal areas are often at risk to natural andhuman-induced hazards. One such hazard, which is focused on in this study, is climatechange induced sea level rise. Sea level rise causes shoreline retreat through coastal


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erosion and dune migration, and coastal inundation and flooding through enhanced tidalreaches and an increase in the of frequency of storm surges (whose intensity may alsoincrease as a result of climate change). Rising sea levels can also cause groundwater andfresh coastal surface water contamination (with associated impacts on agriculture andaquaculture due to the decrease in soil and water quality), the loss of cultural andarchaeological resources, and the possible destruction of important coastal habitats suchwetlands, mangroves, estuaries etc.

Long term projections from coupled climate models are still uncertain with respects to globalmean sea level rise and regional variations, due to the relatively unknown dynamic responseof ice sheets to climate change, and the affects of regional climate circulation models(Cazenave et al., 2009). Tidal gauge and (since 1993) satellite altimetry measurementshave shown that sea level has risen 20 cm since 1870, with the rise during the 20th centurybeing approximately 17 cm (University of New South Wales (UNSW) Climate ChangeResearch Centre (CCRC), 2009). This rise of ~ 1.7 mm/year is an order of magnitudegreater than sea level rise during the last 2000 years (Church et al., 2008). Satellite altimetrymeasurements since 1993 have shown that sea level has risen by 3.4 mm/year since 1993.Current future predictions taking into account new ice sheet understanding are twice therange of the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report(AR4) projections, with an upper limit of sea level rise of 2 m expected by 2100 (Rahmstorf,2007, Vermeer and Rahmstorf, 2009 and the UNSW CCRC, 2009). Mather et al. (2009)recently conducted the first detailed analysis of all tide gauge sites along the southernAfrican coastline. The analysis shows that over the past 50 years, sea level rise along thesouthern African coastline has not been constant, varying between 0.42 mm/year (WestCoast) to 3.55 mm/year (East Coast) (with a rise of 1.57 mm/year along the southwesternand southern Cape coastline) (Mather et al., 2009).

Sea level rise is often felt most not via the gradual advance of mean sea level, but by theincreased frequency of storms and associated storm surge with the higher tidal regime andincreased wind regimes. The combination of cut off low generated storm surge systemsduring spring highs in February, March and September are responsible for the presenthighest sea levels along the southern and southwestern Cape coastline. A 30-year storm of+39 cm on a Highest Astronomical Tide (HAT) for Simons Town of 1.24 metres above meansea level (mamsl), which would be a 1:500 year event at present, could turn into a 1:30 yearevent by the end of the next decade with an additional 15 cm of sea level rise (Brundrit,2008). The 19th and 20th March 2007 storm along the KwaZulu-Natal (KZN) coastlineprovides a modern analogue for what damage such an event can cause, namely R1 billiondamage in this case (Smith et al., 2007 and Mather, 2008). By 2100, extreme sea levelevents of this nature may occur every 2 weeks on spring highs with the combination of asmall to moderate storm (Theron and Rossouw, 2008).

Extreme sea level, estuary flooding, shoreline and tidal reach evolution modelling has shownthat the Eden DM is vulnerable to coastal hazards induced by sea level rise. An extremestorm event with a swash run-up of 2.5 mamsl (sheltered or rocky coastlines), 4.5 mamsl(exposed or sandy coastlines) and 6.5 mamsl (headland and pocket bay beaches and sandyinlets), in association with estuary back flooding, would affect the major coastal towns alongthe Eden DM. This is a result of these towns being developed on low gradient coastal plainsor adjacent to estuaries, with development often damaging or removing natural protectivebarriers such as foredunes or estuary sand bars. Shoreline and tidal evolution modelling fora 2 m rise in sea level by 2100 has shown that the shoreline (especially along low gradientsandy coastlines) and lateral tidal reach may extend inland by a range of 20-100 m,depending on local coastal conditions. This gradual rise in sea level and slow coastalmovement can be adapted to, provided the coastal section isn’t highly developed and thereis space for both natural dune and development retreat.


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2. COASTAL HAZARD RISK ASSESSMENT METHODOLOGY

Rapid desktop risk assessments provide an excellent tool for identifying vulnerable and atrisk areas, and assisting the management of and adaptation to various hazards that theseareas may be subjected too. For this study, the Eden DM coastline was subdivided into 36sections, termed Coastal Zone Management Units (CZMUs). The risk of each CZMU to threecoastal hazards was qualitatively assessed using a modified version of the rapid riskassessment methodology described in Blake and Hartnady (2009). The three coastal hazardtypes that were selected in order to undertake the Eden DM coastal risk assessment were:

Sea level rise induced coastal erosion and inundation;

Groundwater contamination from saltwater intrusion (as a result of sea level rise); and

Extreme coastal events (storm surges, estuarine flooding and tsunamis).

The risk of each CZMU to each specific hazard can be determined by using the classic riskequation, where Risk (R) = (Hazard (H) x Vulnerability (V)) / Coping Capacity (C). Hazard,vulnerability and coping capacity were in turn scored from 1 to 5 (with 1 representing verylow and 5 representing very high) for each CZMU for each hazard, allowing the risk to becalculated.

2.1 COASTAL ZONE MANAGEMENT UNITS

Integrated coastal zone management (ICZM) can often be complex, due to the variouscoastal habitats and types that can occur along a single stretch of coastline. Specific coastalunits are therefore delineated in order to assist in ICZM, as well as to ensure thatmanagement decisions taken at one section of coastline do not negatively affect anothersection e.g. the building of a seawall in one coastal area may cause erosion further along thecoastline, if the coastal section occurs within the same sedimentary cell. The City of CapeTown Coastal Zone Management Strategy (CZMS) (2003) delineated the coastline under itsjurisdiction into 43 sections, and termed them CZMUs. This delineation was based onbiophysical factors such as geology, geomorphology, habitat type, land use type e.g.residential development, harbour, power station etc., and administrative features. Thesesame variables were used to delineate CZMUs for the individual LMs of the Eden DM (seeTable 2-1 and Figure 2-1). The CZMUs defined here provide an initial, large-scale coastalsubdivision for each LM. As each LM develops its own CZMS, different CZMUs can bedelineated or defined according to that LM’s specific coastal management requirements.

Table 2-1 Initial delineated CZMUs for the Eden DM.

LM Hessequa Mossel Bay George Knysna BitouCZMU

No. H1 H2 H3 H4 H5 H6 M1 M2 M3 M4 M5 M6 M7 M8 M9 G1 G2 G3 G4 G5 G6 G7 K1 K2 K3 K4 K5 K6 K7 B1 B2 B3 B4 B5 B6 B7

CZMUName

Wits

and

Dui

wen

hoks

Jong

ensf

onte

inS

tilba

aiY

ster

vark

Gou

ritsm

ond

Vis

baai

Vle

esba

aiP

inna

cle

Poi

ntM

osse

l Bay

Har

tenb

osK

lein

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ier

Gro

ot-B

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rO

uten

iqua

stra

ndM

aalg

ate

Her

olds

Bay

Geo

rge

Vic

toria

Bay

Wild

erne

ss W

est

Wild

erne

ss E

ast

Kle

inkr

antz

Ger

icke

s P

oint

Sed

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rent

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eaK

nysn

aN

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incl

air-

Rob

berg

Ple

ttenb

erg

Bay

Keu

rboo

ms-

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asse

lot

Nat

ure'

s V

alle

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louk

rans


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Figure 2-1 Initial delineated CZMUs for the Eden DM (refer to Table 2-1 for CZMU names).


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2.2 HAZARD

Hazard scores for each CZMU were calculated by determining the severity and probability ofeach specific hazard. Severity and hazard were both given a score out of 5 based on Table2-2 below. The equation Hazard (H) = (Probability (P) + Severity (S)) / 2 was then used tocalculate a final hazard score out of 5.

For both sea level rise induced erosion and inundation, and groundwater contamination, aprobability score of 3 was given for all CZMUs. This is based on a high-end sea level riseprediction of 2 m by 2100 occurring gradually over the next 90 years, which could be seen asa slow onset 1:100 year event. The predicted increased frequency of extreme sea levelevents (with the exception of tsunamis) due to a higher sea level base and increased windregimes resulted in a probability score of 4 being given to all CZMUs for the extreme eventhazard.

The severity of each hazard is dependent on the geology and geomorphology of eachCZMU, with the scores defined in Table 2-2 below. Groundwater contamination refers to theincreased landward intrusion of highly saline seawater into freshwater aquifer systems, dueto a rise in sea level. Primary (unconsolidated sediment e.g. Bredasdorp Group) andfractured (faulted and folded quartzites and sandstones e.g. Peninsula and SkurwebergFormations of the Table Mountain Group) aquifers are generally more susceptible to allforms of contamination in comparison to regolith aquifers (weathered soil and regolith e.g.Bokkeveld and Kaaimans Groups, Cape Granite Suite), due to their higher hydraulicconductivity i.e. ability to transmit water. The extent of aquifer use (qualitatively determinedby the amount of National Groundwater Database registered boreholes within and in thevicinity of each CZMU) will also affect the severity of saltwater intrusion, as high groundwaterusage draws the freshwater-saltwater interface landwards and upwards, closer to the groundsurface. The severity of sea level rise induced erosion/inundation and extreme events canbe affected by various factors, including mean wave height, the amount of sea level rise, tidalrange, geomorphology, coastal slope and rates of accretion/erosion (Thieler and Hammar-Klose, 1999). The mean wave height, rate of sea level rise and tidal range is generally thesame along the Eden DM coastline, and the rates of accretion/erosion are unknown,therefore geomorphology and coastal slope were the two variables used to assess theseverity of both hazards. Low gradient sandy coastlines with no backing foredunes generallyexperience the greatest coastal erosion and inundation, with steep gradient rocky coastlinesexperiencing the least. Headland and inlet bay beaches usually experience the highestswash run-ups during extreme storm/sea level events, due to the headland geomorphologyand bathymetry often funneling wave energy directly towards the adjacent beaches.Sheltered sandy and steep rocky coastlines generally receive minor swash run-ups duringextreme storms etc, reducing the severity of the event.

2.3 VULNERABILITY

Vulnerability (V) was divided into three types, namely social (So), environmental (En) andeconomic (Ec) vulnerability. Social vulnerability was based on the possible amount of humandeaths, economic vulnerability on the total approximate economic cost in Rands, andenvironmental vulnerability on the possible environmental damage to a specific ecosystem(i.e. whether sensitive/protected or not) that may result from a specified hazard or disaster(see Table 2-3). Each vulnerability type was scored out of 5 based on the variables in Table2-3, and a final vulnerability score was calculated using the equation V = (En + Ec + So) / 3.

With the Eden DM’s and associated coastal LM’s 2009-2010 budget being approximatelyR 2.5 billion, each economic vulnerability score represents a percentage value of the budget


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increasing in factors of ten, ranging from 0.0004 % of the total budget (R 1 million – score of1) to 400 % of the total budget (R 10 billion – score of 5). An extreme coastal eventcomparable to the KZN March 2007 storm could cause damage worth half the total annualbudget of the Eden DM and five coastal LM’s combined. An extreme event in the form of avery large storm surge or tsunami would cause the highest loss of life, as well as the greatestinfrastructural and environmental damage, and hence the highest vulnerabilities areassociated with this hazard. Sea level rise induced coastal erosion and inundation is agradual process, and hence loss of human life is unlikely. Evolving shorelines can have ahigh economic and environmental cost over time however, as indicated in the riskassessment. Groundwater contamination may indirectly cause loss of life and affecteconomic activity, due to the destruction of possible future potable water resources.Environmental vulnerability is based on the sensitivity of the ecosystem in a regional sense.

Table 2-2 Hazard scoring methodology for each hazard.

Severity Probability

Score SLR induced erosion/ inundation

Groundwatercontamination Extreme events Frequency of return

1 Steep gradient rockycoastline

Unused regolithaquifer Steep rocky coastline Negligible

2

Steep gradient sandycoastline; low-

moderate gradientrocky coastline

Unusedprimary/fractured

aquifer; moderatelyused regolith aquifer

Sheltered sandycoastline; lowgradient rocky

coastline

1 : 1000 year event

3

Low gradient sandycoastline with steepbacking foredune or

cliffs

Moderately usedprimary/fractured

aquifer; highly usedregolith aquifer

Exposed sandycoastline 1 : 100 year event

4Low gradient sandycoastline with minorbacking foredune

Highly usedprimary/fractured

aquifer

Headland/inlet baybeach or low gradientcoastline with estuary

1 : 10 year event

5Very low gradient

sandy coastline withno backing foredune

Very highly usedprimary/fractured

aquifer

Head/inlet bay beachwith large estuary Yearly

Table 2-3 Vulnerability scoring methodology.

Social Economic EnvironmentalScore

No. deaths Cost (Rand)

1 0 - 10 0 - R1 million No sensitiveecosystem

2 10 - 100 R1 million -R10 million Sensitive ecosystem

3 100 - 1 000 R10 million -R100 million

Protectedecosystem

4 1 000 - 10 000 R100 million -R1 billion National Park

5 10 000 - 100 000 R1 billion -R10 billion

World Heritage orRAMSAR Site


Page 7

2.4 COPING CAPACITY

Coping capacity defines the resilience a community or area has to a disaster i.e. to whatextent will a community be affected by and how long it will take to recover from a disaster.Each CZMU was given a coping capacity score for each hazard, based on theimplementation of the various stages of the Hyogo Framework for Action (HFA): Priorities forAction (United Nations International Strategy for Disaster Reduction (UN/ISDR), 2005)(detailed in Table 2-4 below). The HFA priority areas strive to reduce the impact of disastersthrough gender sensitive disaster preparedness and risk reduction i.e. by increasing thecoping capacity. Each HFA priority area was given a score out of 5, depending on whetherthere was:

None to very limited implementation – 1 Limited implementation – 2 Partially implemented – 3 Mainly implemented – 4 Fully implemented – 5

The final coping capacity was then calculated using the equation:

C = (HFA1 + HFA2 + HFA3 + HFA4 + HFA5) / 5

Full implementation of all the HFA priority areas will result in a CZMU having a high copingcapacity, ensuring that it is able to deal with coastal disasters. Little to no implementation ofthe HFA priority areas will result in coastal communities within the CZMU being highlyaffected by and taking a long period of time to recover from coastal disasters. The CZMUsalong the Eden DM coastline have low coping capacities, due to minor implementation of theHFA priority areas. HFA1 (see Table 2-4) is the highest scoring priority area, due to thedevelopment of national, provincial, and in some cases (e.g. Hessequa LM) local coastallegislation, policies and frameworks to deal with ICZM and coastal hazards. Little to noimplementation of HFAs 2 to 5 has occurred across the entire Eden DM coastline however.

Table 2-4 Key indicators for assessing coping capacity based on the Hyogo Framework forAction (HFA) priority areas (UN/ISDR, 2005).

HFA PriorityAreas

Core Tasks for Disaster RiskReduction Key Indicators

Engage in multi-stakeholder dialogue toestablish foundations

Legal framework exists with explicit responsibilitiesdefined for all levels

Create or strengthen mechanisms forsystematic coordination

National multi-stakeholder platform

Assess and develop institutional basis National policy framework exists that requires plans andactivities at all levels

HFA 1Making DisasterRisk a Priority

Prioritize and allocate appropriate resources Dedicated adequate resources to implement plans at alllevels

Establish an initiative for country wide riskassessments (RA)

National RA based on H and V info/data and include RAfor key sectors

HFA 2Improving RiskInformation andEarly Warning Review availability of risk related info and

capacities for data collection and useSystems are in place to monitor, archive and disseminatedata on H and V


Page 8

HFA PriorityAreas

Core Tasks for Disaster RiskReduction Key Indicators

Assess capacities and strengthen earlywarning

Early warning in place for all major hazards

Develop communication and disseminationmechanisms

Early warnings reach and serve people at communitylevel

Develop a programme to raise awareness National awareness strategy exists that reaches allcommunities and people of all education

Include disaster risk reduction (DRR) ineducation system and research community

School curricula at all levels includes DRR elements andinstructors are trained in DRR at all levels

Develop DRR training for key sectors

HFA 3Building a cultureof safety andresilience

Enhance the compilation, dissemination anduse of DRR info

Environment: DRR is incorporated intoenvironmental and natural resourcemanagement

Environmental protection and natural resourcemanagement and climate change policies include DRRelements

Social needs: establish mechanisms forincreased resilience of the poor and mostvulnerable

Specific policies and plans are implemented to reducevulnerability of impoverished groups

Physical planning: establish measures toincorporate DRR in urban and land useplanning

Land-use development zoning, plans and building codesexist, include DRR elements and are strongly enforced

Structures: strengthen mechanisms forimproved building safety and protection ofcritical facilities

Long term national programme to protect schools, healthfacilities and critical infrastructure from common naturalhazards

Stimulate DRR activities in production andservice sector

Procedure in place to assess the DRR implications ofmajor infrastructure project proposals

Financial/economic instruments: createopportunities for Private sector involvement inDRR

HFA 4Reducing theRisks in KeySectors

Disaster Recovery: develop a recoveryplanning process that includes DRR

Develop a common understanding andactivities to support preparedness

Disaster preparedness and contingency plans at all levelswith regular training drills and rehearsals to test anddevelop disaster preparedness and response (DP&R)

Assess preparedness, capacities andreadiness

Independent assessment done and responsibilities forimplementing recommendations and resources scheduleassigned

All organisations, personnel and volunteers responsiblefor maintaining preparedness are equipped and trainedfor effective DP&R

Financial and contingency mechanisms are in place tosupport effective response and recovery

HFA 5StrengthenPreparedness forResponse

Strengthen planning and programming forresponse, recovery and review

Procedures are in place to document experience duringhazard events and disasters and to undertake post eventreviews


Page 9

2.5 RISK

The risk calculation, colour coding for the risk maps, and simplified conceptual spread of theranking is shown in below in Table 2-5 and Table 2-6 (the entire risk matrix is too large forthis document, containing ~ 2500 possible values compared to 70 shown in Table 2-6). Therisk calculation shows that coping capacity has a significant influence on the final riskassessment, and hence the importance in developing coping capacity mechanisms to dealwith disasters in order to reduce the final risk e.g. even if a specific CZMU had the highestH x V ranking possible of 25, a coping capacity of 5 (i.e. full implementation of all five HFApriority areas) would reduce the risk of the CZMU to that hazard or possible disaster to 5(moderate risk).

Table 2-5 Risk scoring methodology.

Score Risk Ranking0 - 1.5 Very Low

1.50 - 3 Low3.0 - 6 Moderate

6.0 - 15 High15.0 - 25 Very High

Table 2-6 Qualitative risk assessment, based on the hazard and vulnerability score (H x V) andcoping capacity score.

Coping Capacity (C)1 2 3 4 5

1 1.0 0.5 0.3 0.3 0.22 2.0 1.0 0.7 0.5 0.43 3.0 1.5 1.0 0.8 0.64 4.0 2.0 1.3 1.0 0.85 5.0 2.5 1.7 1.3 1.06 6.0 3.0 2.0 1.5 1.28 8.0 4.0 2.7 2.0 1.69 9.0 4.5 3.0 2.3 1.8

10 10.0 5.0 3.3 2.5 2.012 12.0 6.0 4.0 3.0 2.415 15.0 7.5 5.0 3.8 3.016 16.0 8.0 5.3 4.0 3.220 20.0 10.0 6.7 5.0 4.0

Haz

ard

x Vu

lner

abili

ty (H

x V

)

25 25.0 12.5 8.3 6.3 5.0


Page 10

3. COASTAL HAZARD RISK ASSESSMENT RESULTS

3.1 SEA LEVEL RISE INDUCED COASTAL EROSION AND INUNDATION

The majority of the Eden DM CZMUs are at a low to moderate risk to sea level rise inducedcoastal erosion and inundation (44% each; see Table 3-1, Table 3-2 and Figure 3-1). Theregions most at risk include the Mossel Bay area, Wilderness to Knysna area, and thePlettenberg Bay to Nature’s Valley area, while the CZMUs with a high risk ranking areWilderness West (G4), Wilderness East (G5), Sedgefield-Swartvlei (K1) and Knysna (K6).The areas of moderate to high risk reflect low gradient coastal areas, often with extensivebeaches or large estuaries, in association with areas of development close to the shoreline.

3.2 GROUNDWATER CONTAMINATION

The majority of the Eden DM CZMUs are at a moderate risk to groundwater contaminationfrom salt water intrusion related to sea level rise (69%; see Table 3-1, Table 3-3 and Figure3-2). The CZMUs with the highest risk ranking are Wilderness West (G4), Wilderness East(G5), Sedgefield-Swartvlei (K1), Knysna (K6) and Plettenberg Bay (B2). The majority of theEden DM is comprised of hydraulically conductive and therefore vulnerable primary(Bredasdorp Group) and fractured quartzitic (Peninsula and Skurweberg Formation) aquifers,which are used to varying extents in most CZMUs along the coastline for groundwatersupply. Vulnerability and risk may increase over time, due to possible future potable watershortages in the area as a result of climate change, and the associated increasedexploitation of groundwater resources.

3.3 EXTREME EVENTS

The majority of the Eden DM CZMUs are at a moderate to high risk from extreme coastalevents such as large storm surges and tsunamis (44% and 42% respectively; see Table 3-1,Table 3-4 and Figure 3-3). The regions at most risk include Stilbaai, the Mossel Bay area,Wilderness to Knysna area, and the Plettenberg Bay to Nature’s Valley area, while theCZMUs with a high risk ranking are Stilbaai (H4), Mossel Bay (M4), Hartenbos (M5), Klein-Brakrivier (M6), Groot-Brakrivier (M7), Outeniquastrand (M8), Wilderness West (G4),Wilderness East (G5), Sedgefield-Swartvlei (K1), Walker’s Bay (K3), Knysna (K6),Plettenberg Bay (B2), Keurbooms-Bitou (B3), Keurboomstrand (B4) and Nature’s Valley(B6). The areas of moderate to high risk reflect exposed low gradient headland-adjacent orinlet/pocket bay beaches, in association with areas of high population and extensivedevelopment close to the shoreline.

Table 3-1 Number/percent of risk ranked CZMUs per coastal hazard.

SLR induced coastalerosion/inundation

Groundwatercontamination Extreme eventsScore Risk Ranking

No. % No. % No. %0 - 1.5 Very Low 0 0 0 0 0 0

1.50 - 3 Low 16 44 6 17 5 143.0 - 6 Moderate 16 44 25 69 16 44

6.0 - 15 High 4 11 5 14 15 4215.0 - 25 Very High 0 0 0 0 0 0


Page 11

Table 3-2 Risk assessment for the Eden DM with respects to sea level rise induced coastalerosion and inundation (refer to Table 2-5 for risk ranking values).

Hazard Vulnerability Coping Capacity RiskLocalMunicipality

CZMUCode CZMU Name

P S H Ec So En V HFA1 HFA2 HFA3 HFA4 HFA5 C RH1 Witsand 3 3 3.0 3 1 2 2.0 4 1 1 2 1 1.8 3.3H2 Duiwenhoks 3 2 2.5 1 1 2 1.3 4 1 1 2 1 1.8 1.9H3 Jongensfontein 3 1 2.0 2 1 3 2.0 4 1 1 2 1 1.8 2.2H4 Stilbaai 3 3 3.0 3 1 2 2.0 4 1 1 2 1 1.8 3.3H5 Ystervark 3 2 2.5 1 1 2 1.3 4 1 1 2 1 1.8 1.9H

esse

qua

H6 Gouritsmond 3 2 2.5 2 1 2 1.7 3 1 1 2 1 1.6 2.6M1 Visbaai 3 3 3.0 1 1 2 1.3 3 1 1 1 1 1.4 2.9M2 Vleesbaai 3 4 3.5 2 1 2 1.7 3 1 1 1 1 1.4 4.2M3 Pinnacle Point 3 1 2.0 3 1 2 2.0 3 1 1 1 1 1.4 2.9M4 Mossel Bay 3 3 3.0 4 1 2 2.3 3 1 1 1 1 1.4 5.0M5 Hartenbos 3 4 3.5 4 1 2 2.3 3 1 1 1 1 1.4 5.8M6 Klein-Brakrivier 3 4 3.5 4 1 2 2.3 3 1 1 1 1 1.4 5.8M7 Groot-Brakrivier 3 4 3.5 4 1 2 2.3 3 1 1 1 1 1.4 5.8M8 Outeniquastrand 3 4 3.5 3 1 2 2.0 3 1 1 1 1 1.4 5.0

Mos

sel B

ay

M9 Maalgate 3 1 2.0 1 1 2 1.3 3 1 1 1 1 1.4 1.9G1 Herolds Bay 3 1 2.0 3 1 2 2.0 3 1 1 1 1 1.4 2.9G2 George 3 1 2.0 2 1 2 1.7 3 1 1 1 1 1.4 2.4G3 Victoria Bay 3 1 2.0 3 1 2 2.0 3 1 1 1 1 1.4 2.9G4 Wilderness West 3 4 3.5 4 1 5 2.3 3 1 1 1 1 1.4 8.3G5 Wilderness East 3 4 3.5 4 1 5 3.0 3 1 1 1 1 1.4 8.3G6 Kleinkrantz 3 3 3.0 3 1 2 2.0 3 1 1 1 1 1.4 4.3

Geo

rge

G7 Gerickes Point 3 2 2.5 1 1 2 1.3 3 1 1 1 1 1.4 2.4K1 Sedgefield-Swartvlei 3 3 3.0 4 1 4 3.0 3 1 1 1 1 1.4 6.4K2 Goukamma 3 2 2.5 1 1 4 2.0 3 1 1 1 1 1.4 3.6K3 Walker's Bay 3 2 2.5 3 1 4 2.7 3 1 1 1 1 1.4 4.8K4 Buffelsbaai 3 2 2.5 1 1 4 2.0 3 1 1 1 1 1.4 3.6K5 Brenton-On-Sea 3 1 2.0 1 1 2 1.3 3 1 1 1 1 1.4 1.9K6 Knysna 3 4 3.5 4 1 3 2.7 3 1 1 1 1 1.4 6.7

Kny

sna

K7 Noetzie 3 1 2.0 1 1 3 1.7 3 1 1 1 1 1.4 2.4B1 Sinclair-Robberg 3 1 2.0 1 1 3 1.7 3 1 1 1 1 1.4 2.4B2 Plettenberg Bay 3 4 3.5 4 1 2 2.3 3 1 1 1 1 1.4 5.8B3 Keurbooms-Bitou 3 4 3.5 4 1 2 2.3 3 1 1 1 1 1.4 5.8B4 Keurboomsstrand 3 3 3.0 3 1 2 2.0 3 1 1 1 1 1.4 4.3B5 De Vasselot 3 1 2.0 1 1 4 2.0 3 1 1 1 1 1.4 2.9B6 Nature's Valley 3 3 3.0 3 1 4 2.7 3 1 1 1 1 1.4 5.7

Bito

u

B7 Bloukrans 3 1 2.0 1 1 4 2.0 3 1 1 1 1 1.4 2.9


Page 12

Figure 3-1 Risk assessment for the Eden DM with respects to sea level rise induced coastalerosion and inundation (refer to Table 2-5 for risk ranking values).


Page 13

Table 3-3 Risk assessment for the Eden DM with respects to groundwater contamination (referto Table 2-5 for risk ranking values).


CZMUCode CZMU Name

P S H Ec So En V HFA1 HFA2 HFA3 HFA4 HFA5 C R

H1 Witsand 3 2 2.5 2 2 2 2.0 4 1 1 2 1 1.8 2.8H2 Duiwenhoks 3 3 3.0 1 2 2 1.7 4 1 1 2 1 1.8 2.8H3 Jongensfontein 3 3 3.0 1 2 3 2.0 4 1 1 2 1 1.8 3.3H4 Stilbaai 3 5 4.0 2 3 2 2.3 4 1 1 2 1 1.8 5.2H5 Ystervark 3 5 4.0 2 3 2 2.3 4 1 1 2 1 1.8 5.2H

esse

qua


Mos

sel B

ay


Geo

rge


Kny

sna


Bito

u

B7 Bloukrans 3 2 2.5 1 1 4 2.0 3 1 1 1 1 1.4 3.6


Page 14

Figure 3-2 Risk assessment for the Eden DM with respects to groundwater contamination (referto Table 2-5 for risk ranking values).


Page 15

Table 3-4 Risk assessment for the Eden DM with respects to extreme events (refer to Table 2-5for risk ranking values).


CZMUCode CZMU Name

P S H Ec So En V HFA1 HFA2 HFA3 HFA4 HFA5 C R

H1 Witsand 4 5 4.5 3 2 2 2.3 4 1 1 2 1 1.8 5.8H2 Duiwenhoks 4 3 3.5 1 2 2 1.7 4 1 1 2 1 1.8 3.2H3 Jongensfontein 4 2 3.0 2 1 3 2.0 4 1 1 2 1 1.8 3.3H4 Stilbaai 4 5 4.5 3 3 2 2.7 4 1 1 2 1 1.8 6.7H5 Ystervark 4 2 3.0 1 1 2 1.3 4 1 1 2 1 1.8 2.2H

esse

qua


Mos

sel B

ay


Geo

rge


Kny

sna


Bito

u

B7 Bloukrans 4 1 2.5 1 1 4 2.0 3 1 1 1 1 1.4 3.6


Page 16

Figure 3-3 Risk assessment for the Eden DM with respects to extreme events (refer to Table 2-5for risk ranking values).


Page 17

The coastal risk hazard assessment for the Eden DM identifies 11 CZMUs that are at highrisk to all three coastal hazards, which are highlighted by the red CZMU names and redblocks in the Average Risk column in Table 3-5. These results generally correspond to thetowns identified by Hughes and Brundrit’s (1992) sea level rise vulnerability assessment forthe same section of coastline, namely Groot-Brakrivier, Wilderness, Stilbaai, Knysna,Keurbooms River, Sedgefield, Nature’s Valley, Klein-Brakrivier, Plettenberg Bay andHartenbos. Hughes and Brundrit (1992) used a different assessment methodology however,which focused on town infrastructure costs, and did not take into account social andenvironmental vulnerability, and coping capacity.

Table 3-5 Summarised coastal hazard risk assessment scores and highest risk CZMUs.

CZMUCode CZMU Name

SLR InducedErosion andInundation

GroundwaterContamination

ExtremeEvents Average Risk

K1 Sedgefield-Swartvlei 6.4 9.5 9.5 8.5G5 Wilderness East 8.3 6.5 9.2 8.0G4 Wilderness West 8.3 6.5 9.2 8.0K6 Knysna 6.7 7.5 9.5 7.9B2 Plettenberg Bay 5.8 6.7 9.6 7.4M5 Hartenbos 5.8 5.7 9.6 7.1B3 Keurbooms-Bitou 5.8 5.7 9.6 7.1B6 Nature's Valley 5.7 4.8 9.6 6.7M6 Klein-Brakrivier 5.8 5.0 8.6 6.5M7 Groot-Brakrivier 5.8 5.0 8.6 6.5K3 Walker's Bay 4.8 4.8 9.6 6.4M4 Mossel Bay 5.0 4.8 8.6 6.1B4 Keurboomsstrand 4.3 4.3 6.7 5.1M8 Outeniquastrand 5.0 3.6 6.7 5.1H4 Stilbaai 3.3 5.2 6.7 5.1K2 Goukamma 3.6 5.7 5.0 4.8M2 Vleesbaai 4.2 4.2 5.7 4.7G6 Kleinkrantz 4.3 3.6 5.8 4.6K4 Buffelsbaai 3.6 4.3 5.0 4.3G1 Herolds Bay 2.9 3.6 5.8 4.1G3 Victoria Bay 2.9 3.6 5.8 4.1H1 Witsand 3.3 2.8 5.8 4.0M1 Visbaai 2.9 4.2 3.8 3.6G2 George 2.4 5.0 3.0 3.5K7 Noetzie 2.4 3.6 4.2 3.4M3 Pinnacle Point 2.9 3.6 3.6 3.3B5 De Vasselot 2.9 3.6 3.6 3.3B7 Bloukrans 2.9 3.6 3.6 3.3H6 Gouritsmond 2.6 3.6 3.3 3.2H5 Ystervark 1.9 5.2 2.2 3.1H3 Jongensfontein 2.2 3.3 3.3 3.0B1 Sinclair-Robberg 2.4 3.0 3.0 2.8G7 Gerickes Point 2.4 2.4 3.3 2.7H2 Duiwenhoks 1.9 2.8 3.2 2.6K5 Brenton-On-Sea 1.9 3.0 2.4 2.4M9 Maalgate 1.9 2.4 2.4 2.2


Page 18

4. SEA LEVEL RISE ADAPTATION

There are three different options for sea level rise adaptation, namely (German AdvisoryCouncil on Global Change (WBGU), 2006):

Protection – protect the coastline from sea level rise by structures;

Managed retreat – retreat from or reduce development in coastal areas; and

Accommodation – modify land use and infrastructure to accommodate coastalhazards.

Shoreline protection can be in the form of engineering or hard structures, orbiological/geomorphic or soft structures. Hard structures include sea walls, dykes, dolosse,groynes, gabions and offshore reefs. Hard structures are often very expensive protectiveoptions with regards to construction and maintenance, are aesthetically unpleasing and canform a hazard to bathers and other beach users (Breetzke et al., 2008). They also often onlyhave a positive effect at the exact site (although they can exacerbate the effects of sea levelrise on site in some cases), and can cause changes in and increased stress uponneighbouring ecological and littoral systems e.g. triggering or acceleration of erosion due thedisruption of longshore sediment transport, and the reduction of wetlands on the landwardside of the barrier due to reduced water inflow (WBGU, 2006).

Soft protective structures can either be biological e.g. the conservation, rehabilitation andprotections of wetlands, mangroves, kelp beds and dune vegetation, or geomorphological innature e.g. dune cordons and offshore sedimentary bars, geofabric bags, and beachnourishment, water pump and beach drainage systems. Soft structures (especially naturalsystems) are often more cost effective and offer better protection than hard structures,although they are difficult to implement and also require continuous maintenance (Breetzkeet al., 2008). Soft structures have a reduced safety hazard, are more flexible and usuallyallow for the continuation of natural processes. Human developed soft structures have to beimplemented properly in order for them to be effective however e.g. beach nourishmentrequires sand of the right size grade to be used (finer beach sediment can erode quicker andlarge rocks or rubble can develop into a hazard to beach users), while drainage systems canhasten salt water intrusion into coastal aquifers.

Managed retreat is often not possible in highly urbanised environments, and this is especiallythe case in coastal towns and cities along the Eden DM coastline, where little to no retreatspace exists presently due to extensive coastal development. Coastal setback lines providea system of employing managed retreat, and the methodology is currently being developedfor parts of the Western Cape coastline. Institutionalised retreat, although the best option todeal with sea level rise in most cases, may require compensation if relocation of settlementsis to take place. Accommodation in the form of modified land use can take place byconverting inundated coastal land to fish farms or commercial marinas and waterfronts, orcultivating grain varieties resistant to increased salinity for example (WBGU, 2006).Infrastructure modifications can include raised or floating buildings, water tight sealed lowerlevels and canalised developments (WBGU, 2006). Both managed retreat andaccommodation options require planners to understand both short-term coastal processes(days to years in length) and long-term coastal evolution (50 to 100 year changes) however,and coastal specialists should be used to assist in coastal planning decisions in the future(Pethick, 2001). Breetzke et al. (2008) and Cartwright et al. (2008) provide a detailedoverview of the various adaptation and mitigation strategies that can be employed withregards to coastal hazards.


Page 19

A combination of all three strategies and the principles of ICZM have proved the best meansto adapt to sea level rise e.g. the development of protective measures where there are highunmovable populations or critical infrastructure, allowing for coastal retreat in undevelopedareas, and land use conversion of newly flooded areas. South Africa has little to no adaptivecapacity unfortunately, with the ability to halt climate change and sea level rise on a largeregional scale virtually non-existent (Theron and Rossouw, 2008). Municipalities are notsucceeding in addressing the issues of coastal erosion and sea level rise, and they oftenstruggle to communicate their plans and visions not only to communities, but their own staffas well (Mather, 2008). This often results sea level rise just becoming another issue pusheddown the list of municipal worries, resulting in negative perceptions of readiness of themunicipality to respond extreme events being inherent in the local population’s mindset(Mather, 2008).

The best option for South African and Eden DM managers in particular is the “no-regrets”approach, as recommended to the City of Cape Town with regards to sea level rise(Cartwright et al., 2008). This involves a collective response, from both municipalities andlocal residents, where long term institutional, accommodation, retreat and soft protectiveapproaches are undertaken to understand and manage long term coastal evolution, insteadof haphazard, reactive hard protective approaches to specific extreme events. The no-regrets approach, which should be undertaken even if sea level rise does not occur as itforms good coastal management practice, includes (Cartwright et al., 2008):

no further land reclamation;

the development and management of healthy natural systems, i.e. the conservationand rehabilitation of wetlands, estuaries, kelp beds, dune cordons etc.;

decentralisation of strategic infrastructure, in order to ensure sea level rise does notaffect large areas;

maintenance of current sea walls, dolosse etc., but no development of new hardprotective structures, with other adaptation options being preferred;

insurance market correction i.e. incorporate sea level rise into long term economicalrisk assessments (which isn’t currently done), which will increase coastal premiumsand affect current coastal land owners in the short term, but will prevent further futureexcessive coastal development and reduce future liabilities;

develop coastal management capacity in municipalities and other local, regional andnational institutions;

build disaster management capabilities and incorporate the HFA priority areas into allfuture coastal planning and disaster management activities;

public (community and individual) and private (businesses and industry) coastaleducation drive in order to build an accountable and responsible coastal community,as well as increasing the resilience of coastal communities through povertyalleviation; and

undertaking of detailed risk assessments, development of sustainable coastalmanagement plans (SCMPs), and the development of basic early warning systemse.g. combination of tidal information and storm forecasts to determine if there is anextreme storm surge hazard a few days prior to an actual event.


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5. RECOMMENDATIONS

A coastal hazard risk assessment of the Eden DM has indicated that the identified CZMUsare at most risk to extreme coastal events, followed by groundwater contamination and thenslow onset erosion and inundation caused by sea level rise. The eleven highest risk CZMUsto all three hazards are Sedgefield-Swartvlei, Wilderness East, Wilderness West, Knysna,Plettenberg Bay, Hartenbos, Keurbooms-Bitou, Nature’s Valley, Klein-Brakrivier, Groot-Brakrivier, Walker’s Bay and Mossel Bay. It is recommended that:

Eden District Municipality level:

o Employ the “no-regrets” approach in an ICZM framework along the Eden DMcoastline.

o The HFA Priorities for Action are integrated into all phases of planning, anddisaster risk reduction is made a necessity in municipal structures (if notalready incorporated in line with the Disaster Management Act (Act 57 of2002)), especially with respect to coastal zone hazards.

o CZMSs are developed for the remaining four coastal LMs of the Eden DM,namely Mossel Bay, George, Knysna and Bitou.

o CZMUs are identified and delineated for each LM (using the initial CZMUsdefined here as a working template if desired).

o SCMPs should be developed for each CZMU, with the eleven high riskCZMUs identified in the risk assessment (Sedgefield-Swartvlei, WildernessEast, Wilderness West, Knysna, Plettenberg Bay, Hartenbos, Keurbooms-Bitou, Nature’s Valley, Klein-Brakrivier, Groot-Brakrivier, Walker’s Bay andMossel Bay) receiving the highest priority.

o Detailed adaptation studies on each high risk CZMU are conducted, in orderto determine which best combination of methodologies should be developedto adapt to sea level rise induced hazards.

Conceptual studies:

o Begin to undertake architectural research into alternative housing technologye.g. lift houses, used in the Netherlands, Germany and flood prone areas ofthe United States of America. These new housing technologies take intoaccount rising water levels due to storm surges or floods, and can be used inhighly developed estuarine zones within the Knysna, Mossel Bay andPlettenberg Bay areas.


Page 21

6. REFERENCES

Blake, D. and Hartnady, C. J. H. (2009). City of Cape Town Disaster Risk Assessment –Coastal zone hazards. Prepared by Umvoto Africa (Pty) Ltd. in associated withAurecon for the City of Cape Town Disaster Risk Assessment, City of Cape Town(June 2009), 34pp.

Breetzke, T., Parak, O., Celliers, L., Mather, A. A. and Colenbrander, D. (2008). “Living withcoastal erosion”: The KwaZulu-Natal best practice response strategy. InternationalConference on Impact Assessment 2008, Perth, 9 pp.

Brundrit, G. B. (1995). Trends of southern African sea level: statistical analysis andinterpretation. South African Journal of Marine Science, 16, 9-17.

Brundrit, G. B. (2008). Global climate change and adaptation – A sea-level rise riskassessment. Phase one: Sea-level rise model. Prepared for the City of Cape Town byLaquaR Consultants CC, 36 pp.

Cartwright, A., Brundrit, G. B. and Fairhurst, L. (2008). Global climate change and adaptation– A sea-level rise risk assessment. Phase four: Adaptation and risk mitigationmeasures for the City of Cape Town. Prepared for the City of Cape Town by LaquaRConsultants CC, 42 pp.

Cazenave, A., Chambers, D. P., Cipollini, P., Fu, L. L., Hurell, J. W., Merrifield, M, Nerem, S.,Plag, H. P., Shum, C. K. and Willis, J. (2009). Sea level rise: regional and globaltrends. OceanObs2009, 21-25 September 2009, Italy.

Church, J. A., White, N. J., Aarup, T., Wilsong, W. S., Woodworth, P. L., Domingues, C. M.,Hunter, J. R. and Lambeck, K. (2008). Understanding global sea levels: past, presentand future. Sustainability Science, 3, 9-22.

City of Cape Town. (2003). Coastal Zone Management Strategy. City of Cape Town, CapeTown, 24 pp.

German Advisory Council on Global Change (WBGU). (2006). The future oceans – Warmingup, rising high, turning sour. WBGU, Berlin, Germany, 110pp.

Hughes, P. and Brundrit, G. B. (1992). An index to assess South Africa’s vulnerability to sea-level rise. South African Journal of Science, 88, 308-311.

Hughes, P., Brundrit, G. B. and Shillington, F. A. (1991). South African sea-levelmeasurements in the global context of sea-level rise. South African Journal of Science,87, 447-453.

Intergovernmental Panel on Climate Change (IPCC). (2007). Climate change 2007: Thephysical science basis. Contribution of Working Group I to the Fourth AssessmentReport of the Intergovernmental Panel on Climate Change. Cambridge UniversityPress, Cambridge, United Kingdom.

Mather, A. A. (2007). Linear and nonlinear sea-level changes at Durban, South Africa. SouthAfrican Journal of Science, 103, 509-512.


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Mather, A. A. (2008). Coastal erosion and sea level rise. IMIESA (Institute of MunicipalEngineering of Southern Africa journal), March 2008, 49-70.

Pethick, J. (2001). Coastal management and sea-level rise. Catena, 42, 307-322.

Rahmstorf, S. (2007). A semi-empirical approach to projecting future sea-level rise. Science,315 (19 January), 368-370.

Smith, A. M., Guastella, L. A., Bundy, S. C. and Mather, A. A. (2007). Combined marinestorm and Saros spring high tide erosion events along the KwaZulu-Natal coast inMarch 2007. South African Journal of Science, 103, 274-276.

Theron, A. K. and Rossouw, M. (2008). Analysis of potential coastal zone climate changeimpacts and possible response options in the southern African region. Science Realand Relevant: 2nd CSIR Biennial Conference, CSIR International Convention CentrePretoria, 17-18 November 2008, 10pp.

Thieler, E. R. and Hammar-Klose, E. S. (1999). National assessment of coastal vulnerabilityto sea-level rise: Preliminary results of the U. S. Gulf of Mexico Coast. U. S. GeologicalSurvey Open-File Report 00-179.

United Nations International Strategy for Disaster Reduction (UN/ISDR). (2005). HyogoFramework for Action 2005-2015: Building the Resilience of Nations and Communitiesto Disasters. UN/ISDR, World Conference on Disaster Reduction, January 2005,Hyogo, Japan, 22 pp.

University of New South Wales (UNSW) Climate Change Research Centre (CCRC). (2009).The Copenhagen Diagnosis: Updating the world on the latest climate science. UNSWCRCC, Sydney, Australia, 60pp.

Vermeer, M. and Rahmstorf, S. (2009). Global sea level linked to global temperature.Proceedings of the National Academy of Sciences, 106 (51), 21527-21532.

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Sea Level Rise and Flood Risk Assessment for a Select ...€¦ · ð•ð Managed retreat – retreat from or reduce development in coastal areas; and ð•ð Accommodation – modify