Transport and dispersion pattern of suspended particulate matter in estuaries of Tanzania: a case of Pangani estuary

The transport and dispersion pattern of Suspended Particulate Matter (SPM) in the Pangani estuary were investigated by employing in situ measurements, hydrodynamic modelling and satellite remote sensing methods. The sediment traps, refractometer, MIKE 21 model and MERIS FR were used for determining SPM fluxes, determination of salinity, simulating hydrodynamic regime and mapping the dispersion of SPM respectively. Based on the satellite image analysis, the distribution of SPM concentration in Pangani estuary is classified into three categories: area with high SPM (4.5 -15 g m-3), moderate SPM (4.5 to 1.5 g m-3) and low SPM (0-1.5 g m-3). The deposition of SPM fluxes increased exponentially on either side of the river mouth forming a parabolic curve with a minimum value occurring at about 3.3 km north/south of the central axis. The transport, dispersion and deposition of SPM in Pangani estuary are influenced by SE and NE monsoon wind pattern, waves, tidal currents and the Pangani River discharges. The River discharges and tidal currents influenced the salinity stratification, salinity intrusion and SPM input. The data on monthly river discharges positively correlated with SPM concentration. The highest fresh water discharges occurred during April – July, corresponding with highest input of SPM and salinity stratification and lowest extent of salinity intrusion. The locus of SPM deposition on the mouth of the estuary was influenced by the monsoonal seasonal changes, with preferential deposition on the northern side of the estuarine mouth. If the current trends of SPM deposition are left unabated, the preferential deposition of SPM on specific locations of the Estuary will pose considerable negative socio-economic and ecological impacts.