Assessment of future water demands in Pangani River Basin.

Effective management of a river basin is crucial in ensuring sustainability and eliminating conflicts between different water users. Usually, available water in a basin cannot satisfy all demands, and consequently restrictions have to be implemented for the benefit of all. Therefore, quantifying water demands of different users in a river basin is an important aspect of river basin management. Irrigation water demands are estimated using the Penman Monteith approach. The approach is incorporated in the F.A.O program for irrigation management and planning known as CROPWAT. Penman Monteith calculates Potential evapotranspiration, which after multiplication with the appropriate crop coefficient results into the crop water requirement. If rainfall is zero, then crop water requirement is effectively equal to irrigation requirement. Results of Penman Monteith were compared with that of pan evaporation, which gave the expected trend. In Pangani river basin, the estimated present demand for irrigation and, domestic and industrial is 25.46 cumecs. Power generation downstream requires a minimum firm flow of 24 cumecs and maximum of 45 cumecs at Hale (station 1d17). The average annual discharge at 1d17 is 36.82 cumecs, which means that the maximum flow required for power generation cannot be met for almost half of the year. The estimated future demand of about 11 more cumecs for irrigation and, domestic and industrial will have to compromise further with power generation downstream if no measures are taken to control the situation. As domestic and industrial water requirement constitute a small percent of the whole, irrigation is the major threat to power generation as all irrigation schemes are located upstream of the power plants. Therefore implementation of the recommendations proposed, which are, promoting use of ground water for irrigation, adopting more economical cropping pattern and construction of small dams to store water during rain season is important in alleviating the water conflicts in Pangani river basin.