Coastline impacts of tropical cyclones and climate change on Mauritius.

Abstract

The tourism industry has grown to become the third pillar of the Mauritian economy, due mainly to its prestigious beaches. However, Mauritius is prone to severe tropical cyclones which can have detrimental impacts on its coastal environment and ultimately its economy. It is predicted that the frequency and intensity of these tropical cyclone will increase under the influence of climate change. This may accelerate the rate of coastal erosion as a result of rising sea level, tidal waves and storm surges. Prior to 2003, no preventive coastal management framework was available in Mauritius to address the impact of tropical cyclones. Since, various studies have recommended that wave prediction models be adopted to assess and quantify the amount of sediment transport resulting from tropical cyclones. In this research, the relative coastal erosion due to the predicted impact of climate change on tropical storm waves at Belle Mare beach in Mauritius was studied. This was achieved by, firstly, the generation of cyclone wind fields as the primary driving mechanism for the wave model using the MIKE 21 Cyclone Wind Generation model. This required cyclone parameters such as the cyclone tracks, maximum wind speeds and maximum pressures which were extracted from the “Australian Severe Weather” centre. Mike 21 SW model, a 2D-spectral numerical modelling software, was then used to generate cyclone-induced waves and surges. This required the creation of a regular grid defining the shoreline and bathymetry which was obtained from “NOAA data centre”. Based on the published expected effect of climate change on cyclones, the intensity of cyclone Davina (1999) was increased by 5%, 10% and 15% respectively. The resulting wave outputs for each scenario were applied in the XBeach model to assess and quantify the coastal erosion at Belle-Mare. The outputs from XBEACH revealed that the reef surrounding Mauritius reduces the cyclone wave height before it reaches the beach by some 85%. Despite the beneficial influence of the coral reefs on storm surge, the relative volume of sediment erosion resulting from the various intensified cyclone scenarios for Davina is significantly high; 15.36m3/m for a 5% cyclone intensification, 18.16m3/m for 10% and 21.45m3/m for 15%. XBEACH was found to produce reliable results in modelling processes in the coastal zone with accuracy. The implementation of vegetated dunes was proposed as a suitable and natural coastal defense measure at Belle Mare beach for environmental, aesthetical, socio-economic and financial reasons.