Coastal Erosion at Mombasa Beaches Hydrodynamic and Morphological Interactions.

Abstract

Complex interactions of various natural processes together with anthropogenic activities on the beaches have encouraged coastal erosion along the Kenyan coast. Inadequate information on site-specific hydrodynamic and morphological and morphological interactions on the shores has encouraged mitigation measures which are ineffective and expensive to implement. Hydrodynamic and morphological parameters were measured both in field and laboratory. Hydrodynamic variables contributed significantly to the morphological variability which consequently accelerated beach erosion and shoreline instability. Nyali beach which was dominantly fine sand (0 2.62-2.83), moderately well sorted (0 0.564.75) and negatively skewed was characterised by low energy surging waves with high swash and low backwash velocity at high periodicity. Sediment composition was mainly quartz. Bamburi beach was of medium sized calcareous sand (0 2.79-1.84), moderately to poorly sorted sand (O 1.34-0.87) and negatively skewed. Hydrodynamic conditions were of high energy pluging waves and high backwash velocities. Wave energy contributed about 74.2% to the slope changes and about 83.0% to sediment distribution on the beaches. Generally steep shores of coarse sediments showed active erosion activities with a rate of retreat of about 0.15m/month to 0.22 m/month of the shoreline. It is recommended that measures be taken to dissipate wave energy before wave break on the shoreline and to develop effective legislation to protect the shoreline for sustainable planning utilisation and management of the marine ecosystem.