Morphodynamics of the Manyema tidal delta at Kunduchi, Tanzania

Abstract

The prevailing northward longshore drift of beach sand on the northern part of Msasani Bay, north of Dar es Salaam, is interrupted at Kunduchi by the tidal flushing of Manyema Creek, a mangrove ecosystem partially developed for salt production. Shoreline changes around the creek mouth in recent decades have eroded coastal land and destroyed buildings, prompting stakeholders to construct protective groynes and revetments. Sand is transported across the delta by the interaction of two forcing processes – currents of water flushing the creek in response to tidal variation; and (generally) currents generated by wind-driven waves according to the monsoon season. Study of the sand morphology of the creek and delta platform together with time-series satellite imagery has permitted demarcation of the respective sand transport pathways and of morphodynamic changes on the delta over the last decade. The sand transport regime has promoted erosion of the shore to the south of the creek mouth and has led to a spasmodic delivery of sand to beaches north of the channel. Attempts to stabilise the shore around the creek mouth are described and their effectiveness evalutated.