Browsing by Author "Magangi, Wilkister"

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    Investigation of the impact of irrigation abstraction on the river systems in the Lake Victoria basin in Kenya.
    (University of Dar es Salaam, 2001) Magangi, Wilkister
    The impact of irrigation water abstraction in Nzoia and Nyando catchments in the Lake Victoria basin is investigated using the Penman-Monteith method to estimate the irrigation requirement and then compare the resulting river flow with the mean river flow. It is noticed that the abstraction leads to reduced river flow and reduced levels in the swamp at the outlet of the Nzoia river basins. In the case of Nzoia catchment the swamp geometry and outlet were estimated and used to carry out water balance calculations over the swamp. The total inflow into the swamp was then estimated by correcting the inflow for irrigation water abstraction. Comparison was carried out between the total amount of inflow into the swamp with and without irrigation, and the swamp outflows. In the case of Nyando, river flow was routed through ten cross sections between the last gauging station (1GD03) and the swamp using the Muskingum-Cunge method. The volumes of spilled water were analyzed and the reduction of these was investigated. It was found that irrigation impact by volume in Nzoia was highest (63% of mean river flow will be abstracted) upstream of gauging station 1DD01, while in Nyando 100% abstraction would occur. It was also found that the volume of irrigation water abstraction would increase from 6.5 m3/s to 15 m3/s for Nzoia and from 2.1 m3/s to 3.55 m3/s in Nyando. There is insignificant effect in the outflow and depth of storage of the swamp in Nyando and significant impact in Nzoia from irrigation water abstraction and this may consequently affect lake levels.