Assessment of Shoreline Changes in the Period 1969-2010 in Watamuarea, Kenya

Abstract

Watamu coastlineis a major attraction site for tourist and also a source of income for the local people. However, the shoreline has been changing due to erosion. This study sought to find the trend of shoreline changes, and the factors attributed to the changes. Aerial photographs of 1969 and 1989 and a recent satellite image of 2010 were used to digitize the shoreline.The Digital Shoreline Analysis System (DSAS) in ArcGIS environment was used to create transects and statistical analyses for the shoreline.Several GPS points were taken in October 2013 and 2014 during ground truthing following the High Water Mark (HWM). The 9.8 km long Watamu shoreline was divided in-to 245 transects with 40 meter spacing in order to calculate the change rates. The rates of shoreline change were calculated using the End Point Rate (EPR), Net Shoreline Movement (NSM), and Weighted Linear Regression (WLR) statistic in DSAS. In addition, Focused Group Discussion (FGD)and key informants interview were conducted with curio sellers, boat operators, fishermen, safari sellers, and longtime residents and hoteliers in order to get information about the drivers of shoreline change.The analysis from WLR indicated a mean of -0.89 m/year where 69.7% of transects fall under erosion and 30.2% accretion. The result from EPR and NSM revealed mean shoreline change of - 0.7m/year and -30.3m/period respectively from1969 to 2010 with negative signs indicating erosion. Both EPR and NSM results showed out of 245 transects 158 or 64.4% experienced erosion and 87 transects or 35.5% accretion in the 41 year study period.Shoreline erosion was mainly attributed to anthropogenic factors. These include construction near the High Water Mark, defensive structures and sea walls, and destruction of vegetation along the beach. Therefore, it will be advantageous if all institutions and stakeholders with responsibilities for such coastal areas to work in collaboration so as to keep the coastline and its marine life and resources from further damage and erosion.