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Coastal Vulnerability Index

KZN

Project Duration: Long Term

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Vulnerability relates to ones predisposition to be affected, or to be susceptible to damage. The CVI assesses the relative physical coastal vulnerability based on a set of coastal parameters which serve as indicators of 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. 

 

 

Need for this Coastal Vulnerability Assessment

  • Coastal regions around the world are increasingly becoming vulnerable to the effects of coastal erosion, extreme coastal storms and sea-level rise.
  • The March 2007 storm event in KZN resulted in significant damage to properties 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 vulnerability to future events of this nature?
  • What social, economic and ecological features are potentially vulnerable?

 

Interpretation of the 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.

 

Determining the Physical CVI

  • Five physical parameters were used:
    • Beach width - The wider the beach the more wave energy dissipates.
    • Dune width - Dune width gives an indication as to the sediment available which will buffer against erosion.
    • Distance to the 20m isobath - The greater the offshore distance to the 20m isobath the greater the dissipation of wave energy.
    • Percentage rocky outcrop - The higher the percentage the lower the erosion rate.
    • 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  100 - 150m 50 - 100m  < 50m 
 Dune width  > 150m 50 - 150m  25 - 50m  < 25m 
 Distance to the 20m bathy  > 4km 2 - 4km  1 - 2km  < 1km 
 Distance of veg behind back beach  > 600m 200 - 600m  100 - 200m  < 100m 
 Percentage outcrop  > 50% 20 - 50%  10 - 20%  < 10% 

 

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. 

 

 


Social, Economic and Ecological Components  
  • The primary concern relates to the 23% of coast classified as High Risk.
  • The CVI identified indicator features of social, economic & 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 Boat launch sites Subsistence fishing sites Marine protected areas Residential erven
Forest plantation Roads Fishing hot spots Subsistence harvesting sites Bird Sanctuary sites  
Sugar cane  Railway lines  Swimming beaches  Subsistence farming areas  Turtle nesting sites   
Commercial & industrial buildings  Lighthouses  Sports facilities    Estuary mouths   
Commercial farms    Coastal public property    Protected areas (terrestrial)   

 

 

References:

Palmer, B.J., Van der Elst, R., Mackay, F., Mather, A.A., Smith, A.M., Bundy, S.C., Thackeray, Z., Leuci, R., and Parak, O. 2011. Preliminary coastal vulnerability assessment for KwaZulu-Natal, South Africa. Journal of Coastal Research, 64.

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Acknowledgements

Bronwyn Goble

Rudy van der Elst

Fiona MacKay

Andrew Mather

Alan Smith

Simon Bundy

Zain Thackeray

Rio Leuci

Omar Parak