Episodic atmospheric changes and their impact on the hydrography of coastal waters in Tanzania

A shift in the time of occurrence and duration of the rainy and dry seasons has been observed over Tanzania and the East African region in recent years. During 1998, El Nino rains produced substantial fresh water and sediment supply to the coastal zone. During that period, large sand bodies were deposited off river mouths and at stream entrances. Hydrographic measurements showed a persistent decrease in salinity and temperature of inshore waters indicating that coastal waters have been trapped along the shore. Such environmental changes could have negative effects on the biodiversity of the coastal zone. Based on beach profile measurements, the shoreline was predominantly eroding prior to the rains but accreted during the El-Nino rains. The tidal flats received a larger volume of sand. While the beach and tidal flats were receiving this supply of sand, river banks eroded as channels deepened and widened. In many instances, newly cut flood channels have remained semi-permanent serving as tidal inlets leading to tidal inundation of the low lying areas behind the beaches. These observations point to the significance of episodic events in maintaining or shaping the coastal zone.