Shore Morphology and Sediment Characteristics South of Pangani River, Coastal Tanzania

Abstract

The shore morphology and nearshore sediments between the Pangani and Kipumbwi rivers were investigated to describe the shore and the reef platform sediments characteristics and also to update information on recent shoreline changes along the Tanzania mainland coast. The information gathered during this study comes from field observations, sediment sampling of the area and interviews with Pangani residents. The investigated area is a patch reef coast with narrow or no beaches and fossil reef terrace islands offshore, Pangani bay and estuary are among the most prominent shore features. Historical information indicates that, both the bay, and the estuary have undergone significant changes during the last 60 years. While the growth of the estuary has mainly been influenced by the reduced fresh water discharges, the bay has been mainly influenced by shore erosion induced by the high wave activity. The distribution of sediments on the sea bottom is mainly controlled by bathymetry, with sand (medium to coarse) dominating water depths less than 10 m and silt dominating depth greater than 15 m. Sediments in water between 10 and 15 m depth are dominated by fine sand/silt. The carbonate production in the investigated area is limited by the high influx of siliciclastic sediments from the Pangani, Kipumbwi and Ushongo Mabaoni depo-centres. While previous studies attribute the disappearance of Maziwi island to sea level rise, the present study considers the anthropogenic influence to be the major causative factor. Sea level is also considered to be one of the potential threats to the preservation of small islands such as the Maziwi, However, the present study believes that if indeed the vegetation on the island has been cleared as is reported, this action has hastened its disappearance.