Shoreline Change in the Kunduchi Beach Area, Tanzania

Sammanfattning: Coastal erosion is a global problem affecting almost every country in the world having a coastline. This problem is expected to accelerate in the future due to the global warming, which most likely will cause a sea level rise and increase the number of storm events around the globe. The effect from the erosion costs 700 million US dollars each year for the US alone and will increase in the future with the accelerating coastal erosion. The money used for minimizing the effects from the erosion, in a poor country like Tanzania, could instead be used to increase the living and health standards in the country. Kunduchi and the studied coastal stretch of 23 km are situated north of Dar es Salaam in Tanzania on the African east coast. In the 1980´s it was reported about severe erosion in the area. Erosion, resulting in a retreating shoreline, over hundreds of meters on several locations, and the collapse of the Africana Hotel. The setback of the beach has lead to that many of the hotel and house owners have applied different methods of shore protection. Resulting in the building of groins and seawalls, without any expertise, to protect their properties. The purpose of the study is to clarify and quantify the governing sediment transport processes in the area, quantify the historical shoreline movement, and propose suitable mitigation measures to reduce the impact of the erosion. In the present study the theory behind the beach dynamics in the area is studied along with general theories about sediment transport and shoreline formations. An extensive field visit was carried out during July and August 2007 with field measurements of beach profiles and sediment samples. A synoptical study was made of the coastal stretch, which led to an area description. Besides this, visits were made to different organisations and authorities with connection to the area and the current problem. Results from the analysis indicate that the governing transport process in the area is longshore transport. By a numerical analysis the main transport direction along the coast is determined to be north. Further, the shoreline change analysis shows accretion along the shoreline between 1953 and 1981, followed by severe erosion from 1981 until 2005. During 2005 to 2007 there has been accretion that almost has restored the shoreline position. Groins and seawalls have been used as the major mitigation measures in the past. The future recommendation is to utilize beach nourishment instead. Sand can probably be taken from the harbour basin in Dar es Salaam, which would both benefit the repeatedly dredged harbour as well as the Kunduchi beach area. Another recommendation for the future beach management in the area is to start a cooperation between the dwellers in the area, hotel owners, the municipality and the government. The shore protection law should be implemented, which states that no structure should be build within 60 m of the highest shoreline.