Development of decisions support system for integrated water management of lake Victoria basin

In this study a monthly lake water balance developed by some and Plinton (194) for the period 1925-1990 and extended by Okuja (2000) to include the period 1991-1998 is modified and used. The observed and estimated net basin supplies show that the behaviour of the lake is in response to the rainfall over the lake. It is observed that for periods with higher rainfall, the higher are the net basin supplies and consequently the higher are the levels. The impact of varying annual water demand on the lake was done using the lake water balance for two different scenarios. Firstly, the water demand for four probable irrigation scenarios were used while the second is that of the lake regions of Tanzania . comprising the municipal and irrigation water demand. It was found that irrigation 3%, 5%, 8% and 10% of the total area of the basin would reduce the like level/lake inflow by 9mm, 65mm, 264mm and 33 mm respectively. The corresponding reductions in the lake outflows are 2.4mm, 4.5mm,, 7.4mm and 9.9mm. in the second scenario the existing annual water demand of the lake regions of Tanzania reduces the lake level lake inflow and lake outflow by 12 mm and 0.04 mm respectively while the corresponding reductions for the annual potential water demand are 52mm and 0.44 mm. various trade-off curves have been produced under natural outflow and energy optimization regulation options, which show the impact of annual water demand on the hydropower generation at Owen Falls Dam. The Kagera sugar Irrigation Scheme is found to have no significant impact on the Kagera River flows at Kyaka ferry. The maximum monthly abstraction of 3.45ms and 5.33m3/s for existing and potential irrigation scenarios occur in June while the monthly river flow ranges between 180m3/s and 253m3/s.