Hydrodynamic Modelling on Transport, Dispersion and Deposition of Suspended Particulate Matter in Pangani Estuary, Tanzania

Abstract

The present study was formulated with the aim of using MIKE 21 software in studying the hydrodynamic regime of the Pangani estuary. Water level, river discharge and wind drag force were used as hydrodynamic forcing factors during the model set up. The data set for the model (i.e. water level, tidal current winds and river discharge) were collected in Pangani estuary during the field campaigns conducted from December 2010 and August 2011. The results indicated that the tidal currents were relatively sluggish (0–0.05 m/s) in the beginning of model simulation. The ebb currents were established from 2 to 7 hours; originating from the inner part of the estuary tended to flow radially (Eastwards, North-wards and Southwards) soon after reaching the river mouth. The radial flow pattern of the ebb tidal currents seemed to be influenced by the funnel shape of the estuary. The flood tidal currents were established after 7 hours. The flood tidal phase started earlier on the southern part of the river mouth compared to the northern and tended to become more intensive on the northern part than on the southern part of the estuary. The currents pattern observed were influencing the transport and deposition of Suspended Particulate Matter (SPM). The maximum deposition of SPM preferentially occurred about 3 km north and south of the estuary mouth and the minimum deposition occurred in the middle of the estuary mouth. The deposition of SPM was highest during the southeast monsoon relative to the northeast monsoon. Approximately 872.6 kg/m 2 /year of SPM were brought into the estuary. This implies that, in the long term, the SPM deposition along the river mouth will significantly change the Pangani hydrodynamic regime, from its present condition. Also infilling of navigational channel and alteration of the ecosystems is imminent. Urgent actions are required to minimize the generation of SPM within the Pangani river basin.