Optimum utilization of water resources in a run-of-the-river type irrigation project

Abstract

Service area achievement in a run-of-the-river type irrigation project depends upon the available flow which can be diverted from the river to the canal system through the headworks. But the available flow of the river varies from year to year~ If we can forecast the available flow ahead of time, it - will lead to proper planning and operational management of the project. This study was aimed at developing a methodology for optimum use of water in a run-of-the-river type irrigation project and to demonstrate of its usefulness by applying it to Manu River Project. A low flow prediction model of Manu river at Moulvibazar has been developed for forecasting the available flow before start of the irrigation season. The available flow can be better used if we consider various workable alternative strategies and select the one which gives the highest net return. The alternatives are: reducing the service area and applying the water at yield maximizing level; staggering of planting date to minimize the irrigation demand during the critical period; crop diversification; and deficit irrigation and water delivery according to crop sensitivity to water stress. The irrigation demand with the proposed cropping pattern of Manu River Project has been compared with the available flow (75 percent probable). The result shows that the available supply is v in deficit in most of the irrigation seasons. The dry period (November to April) flow of the Manu river during the period 1966-'85 has been divided into a number of categories. A linear programming model has been developed to determine the optimum acreages of different crops under the option of crop diversification The net returns from the above four alternatives have been calculated for each deficit flow category. Crop diversification was found to give the highest service area and net return among the four alternatives considered. The project management should consider that the lands having light textured soils are cultivated with other Rabi crops instead of Boro rice. The present status of water use in the Manu River Project has also been studied. Major constraints were the communication gap between the BWDB staff and water users, lack of extension personnel, absence of farmers' association, lack of field channel and lack of canal system in most fertile land. The project performance could be increased by providing' sufficient of extension workers to the project, forming farmers' effective association and constructing the field channels under Food for Works Programme. Such improvement works would encourage the farmers to irrigate the lands and improve the utilization of the existing facilities.