Ecological and engineering importance of the Bet el Ras beach-sandstone

Abstract

A unique sandstone known as the Bet el Ras sandstone, supposedly of Holocene age, occurs profusely along the western coast of Unguja but more extensive at its locality area, Bet el Ras, where it forms a rocky shore. The sandstone has been blasted in the past for construction of the sea wall that fronts the Zanzibar Town, and stands to be blasted further for renovation works. From the results of the survey made, it is clear that the sandstone is ecologically and environmentally important such that its total removal will lead to loss of a habitat as well as enhance coastal erosion and sediment input in the littoral zone thereby impacting on the ecology of the associated flora and fauna. Since none of the fauna species is endemic and due to its engineering importance, selective extraction may be considered such that extraction of the sandstone be done in steps and cavities be refilled as well. A thin veneer may also be left close to the land as protection against erosion. This will also minimize sediment input in the littoral zone that would otherwise have affected the community structure.