Hydrological assessment of Mitumba and Ngonya catchments in Kigoma region.

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University of Dar es Salaam
The study focused on the identification of the factors controlling the chemistry of water, the analysis of groundwater component of the total stream flow and the quantification of suspended stream sediment load. The study was conducted in two contrasting catchments of Ngonya and Mitumba having a total area of 12.63km2 located along the northern shoreline of Lake Tanganyika. Ca-Mg-HC03 hydrochemical facies is found to be dominant. Multivariate statistics including correlation and factor analyses show the water chemical character to be controlled by environmental factors. Dissolution of amphibole, biotite, iron sulphide, reduction of organic-rich matter influence the observed water chemical character in the two catchments. Though Ngonya catchment is an impacted catchment and Mitumba is a pristine one no marked differences in the chemical character of the water were detected. However, marked differences are shown by the groundwater component and suspended sediment discharges with Ngonya catchment having relatively low groundwater discharge and high suspended sediment load discharge, while Mitumba has high groundwater discharge and low sediment load discharge. Groundwater component of the total stream flow is estimated to be 65% and 70% for Ngonya and Mitumba respectively. The variation is due to difference in land use and is estimated using both hydrographic separation and chloride ion methods. The recession constants, 9.42x10-3 d-1 I for Ngonya and 9.6x10-3 d-1 for Mitumba suggest that groundwater is stored in small voids, fractures and fissures. This has also been observed at the point sources of the streams in the area. Suspended stream sediment load varies exponentially with stream flow; i.e., Qs=3.7765QW2.2859, r2=0.7712 for Mitumba and QS= 3.7522QW3 3302, r2=0.8495 for Ngonya catchment. Estimated suspended stream sediment load for Ngonya is 100 times that of Mitumba. It has been concluded that improper land use significantly affects the hydrology of a given area. It is then recommended that hydrological monitoring be conducted in the study area.
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Water quality, Purification, Groundwater, Hydrology, Mitumba and Ngonya Catchments, Kigoma region, Tanzania
Rubabwa, C. E. L. M. (2001). Hydrological assessment of Mitumba and Ngonya catchments in Kigoma region. Master dissertation, University of Dar es Salaam. Available at (