Freshwater and sediment discharge in Ungwana bay: the role of the Tana and Sabaki rivers

Abstract

The dy namics of sediment and freshwater discharge into Ungwana Bay b y the Tana and Sabaki Riv e r systems is still poorly understood. Most of the previous hydrological inv e stigations have focu sed on their upper catchments (Dunne and Ongwenyi, 1976; Ongwenyi, 1983; Ongwen yi, 1985). The present study shows that the interaction of the two river systems with the Indian Ocean is controlled not only by the intensity of river dischar ge, but also by the patterns of monsoon winds and astronomical tides. This st udy established that the exchange of terrigenous sediments as well as t hat of water between Tana and Sabaki estuaries and the Indian Oc ean portray both tidal and seasonal variations. The movement of the plumes wi thin Ungwana Bay was observed to shif t in response to changes in the direction and intensit y of the monsoon systems, which not only control climate in the region, but also influence the movement of wind-driven coastal oc ean currents (Johnson et al ., 1982; Brakel, 1984). In this study the dynamics of sediment and freshwater supply into Ungwana Bay will be highlighted.