KWAZULU WAZULU-NATAL COASTAL VULNERABILITY INDEX. Summary Guide

Transcription

1 KWAZULU WAZULU-NATAL COASTAL VULNERABILITY INDEX Summary Guide Prepared by the Oceanographic Research Institute (ORI) for the Department of Agriculture and Environmental Affairs (DAEA)

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3 BACKGROUND Introduction KwaZulu-Natal (KZN) experienced first-hand the effects of extreme weather events in As a result there was a need to have a better understanding of the coast s vulnerability to the risks posed by such events and related coastal erosion impacts. A Coastal Vulnerability Index (CVI) was developed whereby small sections of the coast were ranked, based on their relative degree of vulnerability as: Risk, Moderate Risk or High Risk. Vulnerability is defined as the inherent risk of the coastal zone, relating to its predisposition to be affected, or to be susceptible to damage from events (Kumar et al., ). The CVI assessment is based on remote sensing data, processed by means of GIS methodology. The CVI assesses the relative physical coastal vulnerability based on a set of physical coastal parameters which serve as indicators of risk or vulnerability. This assessment also tries to address social, economic and ecological factors by identifying indicators and assessing them in relation to the findings of the CVI to determine which populations and associated infrastructure are potentially at risk. An interactive viewer has been developed to simplify and facilitate the interpretation of the CVI. The viewer is a guideline for managers of the coastal zone, in light of coastal vulnerability and risk from coastal erosion and extreme storm events. Need for Vulnerability Assessments Coastal regions around the world are increasingly becoming vulnerable to the effects of coastal erosion, extreme coastal storms and sea-level rise. 1 Kumar, T.S., Mahendra, R.S., Nayak, S., Radhakrishnan, K. and Sahu, K C., Coastal Vulnerability Assessment for Orissa State, East Coast of India, Journal of Coastal Research, 26 (3), Prepared by the Oceanographic Research Institute (ORI) for the Department of Agriculture and Environmental Affairs (DAEA) 1

4 Need for this Assessment The March 2007 storm event in KZN resulted in significant damage to property and infrastructure costing millions of rands. Climate change predictions are that the east coast of South Africa will be subjected to increased frequency and intensity of storms. Aim of this Assessment Which sections of coast are at the highest physical risk to future events of this nature? What social, economic and ecological features are potentially vulnerable? o Done through an assessment of relative coastal vulnerability for the KZN coast. COASTAL VULNERABILITY INDEX (CVI) Determining the Physical CVI Five physical parameters were used: o Beach width - The wider the beach the more wave energy dissipates. o Dune width - Dune width gives an indication as to the sediment available which will buffer against erosion. o Distance to the 20m isobath - The greater the offshore distance to the 20m isobath the greater the dissipation of wave energy. o Percentage rocky outcrop - The higher the percentage the lower the erosion rate. o Width of vegetation behind the back beach - The more the vegetation, the greater the buffer against erosion. Data was extracted from aerial imagery and converted into a grid of 50x50m cells along the littoral active zone. Sites of known erosion were captured as a separate dataset. These results were used to inform vulnerability thresholds. Each cell was rated per parameter - in terms of its individual vulnerability based on predefined thresholds. Scoring ranged between 1 and 4 per parameter. Physical Parameter Extremely Low (1) Low (2) Moderate (3) High (4) Beach width > 150m m m < 50m Dune width > 150m m 25-50m < 25m Distance to 20m bathy > 4km 2-4km 1-2km < 1km Distance of veg behind back beach > 600m m m < 100m Percentage outcrop > 50% 20-50% 10-20% < 10% Prepared by the Oceanographic Research Institute (ORI) for the Department of Agriculture and Environmental Affairs (DAEA)

5 Rating of Indicators Beach width, dune width and distance to the 20m isobath were considered to be the critical indicators. Cells which scored High on all these three paramaters were weighted in order to highlight the compounded risk. Due to the dynamic nature of estuaries, estuarine areas (to the 5m contour) were also weighted to highlight the sensitivity of these areas. In addition, areas of known historical erosion were considered critical and also weighted. Based on the scoring and weighting each point received a total vulnerability score (out of 32), as outlined below. Determination of CVI Scores Distribution of CVI scores for the coast and erosion sites were used to inform ranking Grouping of CVI scores for the coast based on distribution

6 Social, Economic and Ecological Components The primary concern relates to the 23% of KZN s coast classified as High Risk. The CVI identified indicator features of social, economic and ecological importance. It assessed where features are in relation to cells of High Risk. Features located in or across the littoral active zone are at relatively higher risk if all, or a proportion, fall directly within a cell of High Risk. Economic & commercial activities Strategic infrastructure Recreational areas Subsistence sites Ecological important areas Residential properties Dune mining Piers # # Subsistence fishing Boat launch sites sites # Forest plantation Roads Fishing hot spots # Subsistence harvesting sites # Marine Protected Areas # Bird sanctuary sites # Residential erven Sugar cane Railway lines Swimming beaches # Subsistence farming areas Turtle nesting sites # Commercial & industrial buildings Lighthouses Sports facilities Estuary mouths # Commercial farms # within the coastal zone Coastal Public Property Protected areas (terrestrial) Percentage social, economic and ecological components at risk Prepared by the Oceanographic Research Institute (ORI) for the Department of Agriculture and Environmental Affairs (DAEA)

7 INTERPRETATION OF CVI Risk Lowest risk category - likelihood of impact or damage is lower. Physical parameters are in good condition. If developments in these areas are approved they may increase the vulnerability of these areas. New developments should be set-back appropriately so as to maintain the natural functioning of the coast. Moderate Risk Sites are at higher risk than areas of Risk, but lower than areas of High Risk. Likelihood of sites being damaged is higher. Retreat and defence should be explored for existing infrastructure. New developments should be set-back sufficiently or alternative sites should be considered. High Risk These sites are considered to be the most susceptible to the effects of erosion, sea-level rise or extreme events. Existing developments have a high likelihood of being damaged. It is recommended that the options of retreat and defence be explored. New developments should be set-back sufficiently to ensure that they are not damaged. Alternatively, new sites for the development should be considered.

8 MANAGEMENT INTERVENTIONS There is a need to determine the best management options depending on the feature s nature, value, lifespan and potential impact if lost: o Retreat/Remove; o Do nothing; or o Defend ( hold the line ). Retreat/Remove Remove infrastructure that is in a hazard zone and therefore vulnerable to damage. The problem with this option is that for much of the coast there is little space for retreat, particularly in urban areas. Do Nothing Leave and let natural processes occur. The problem with this option is that public infrastructure and access roads often have to be defended. Defend Defend is most often employed. Choice of hard engineering or soft engineering options. Protection and maintenance related. Vegetation and geobags = soft engineering, a good option. Example of vegetation recovery Prepared by the Oceanographic Research Institute (ORI) for the Department of Agriculture and Environmental Affairs (DAEA)

9 For more information contact: The Coastal and Biodiversity Management Unit KwaZulu-Natal Department of Agriculture and Environmental Affairs Private Bag X9059 Pietermaritzburg 3200 SOUTH AFRICA Tel: +27 (0) /8 or Prepared by for