Summary of Abstract Submission

Abstract Submission No. IO50-03-0001PresentationPoster

DYNAMICS OF THE TURBIDITY MAXIMUM ZONE IN A SHALLOW, WELL-FLUSHED ESTUARY IN KENYA

Dr. Johnson U. Kitheka*1

1 South Eastern Kenya University, Kenya

ABSTRACT :

The spatial-temporal variability and the behavior of the Estuarine Turbidity Maximum (ETM) zone in the shallow, ephemeral, well-flushed Sabaki estuary located in the northern region of the Kenya coast, were studied during a period of moderate river discharge. The estuary is one of the most turbid estuaries along the Indian Ocean coast of East Africa, characterized by high sediment input and high suspended matter (SPM) concentrations. The estuary is completely flushed after every tidal cycle and experiences high salinity and SPM concentrations gradients at high water (HW). The SPM concentrations in the ETM zone varied significantly depending on the river sediment input and phase of the semi-diurnal tide, but were on average 50% greater than the river SPM concentrations. The ETM was located up-estuary during periods when river runoff was around the average and further down-estuary during periods of low river runoff, due to different sediment settling rates. While gravitational circulation tended to cause accumulation of mud in a null zone located below the freshwater- saltwater interface, causing formation of an ETM zone, the ETM was separated from the salt-limit. This separation was attributed to the time lag in the tidally-driven resuspension of bottom mud and subsequent tidally-driven advection of turbid water up-estuary during the flood period. The relatively low current velocities combined with high horizontal and vertical gradient in eddy diffusivity in the central region of the estuary, tended to favour rapid settling of flocculated sediments, leading to the formation of an ETM. The ETM zone is located in the region in which inter-tidal mudflats are located and it is postulated that the formation of the intertidal mudflats are related to the ETM dynamics. The study concludes that rapid settling through non-turbulent pycnocline is the dominant mechanism responsible for the formation of the Sabaki estuary ETM.