The risks, management and adaptation to sea level rise and coastal erosion along the Southern and Eastern African Coastline.

Abstract

Sea level rise and coastal erosion are two processes which may result in major problems for coastal cities around the world. This is particularly true for Southern and Eastern African cities as they struggle to meet their developmental challenges in addition to sea level rise and coastal erosion. This thesis focuses on three main areas, the analysis of the rates of sea level from tide gauges in the region, the extent of wave run-up on the beach and the development of a simple technical and management framework that managers can apply to assess coastal hazards. The rates of sea level rise in the region vary, Zanzibar, Tanzania reflects a falling sea level at -3:64 plus minus 1:62 mm per year while the highest rate of sea level rise at Diego Garcia, British Indian Ocean Territories is +4:35 plus minus 7:61 mm per year. The rate of sea level rise are dependent on the complex interactions of vertical crustal movements, barometric pressure changes, and the warm Agulhas and cooler Benguela currents. Wave run-up is an indicator of the hazard zone. A number of international wave run-up models were assessed for use in this region and were found to be unsuitable. A new wave run-up model was developed which uses the bathymetric profile as opposed to the beach slope in predicting wave run-up. This model uses the equation Rx H0 = C S2=3, where Rx is the wave run-up height above Still Water Level, H0 is the significant wave height at the closure depth, C is dimensionless coefficient where median values are described by C ' 7:5, S is a representative nearshore slope (S = (hc=xh)). hc is the closure depth and xh the horizontal distance from the waters edge to the closure depth. An assessment of the impacts of sea level rise and wave run-up was undertaken based on a detailed case study of the Durban coastline. The results were incorporated into a standalone freeware viewer tool enabling this information to be accessible to planners, decision makers and the general public. The research has identifed several types of shoreline that are vulnerable to coastal erosion, sea level rise and extreme wave events. Recommendations as to what adaptation measures could be undertaken for the different beach types are proposed. With this information coastal managers and decision makers charged with managing shorelines can take the first step in understanding and adapting into the future.