Efficient Water Use in Run‐of‐the‐River Irrigation

Abstract

Irrigation water demand, crop yield and water allocation models were developed and applied to a Philippine run‐of‐the‐river irrigation project. Dry season water supply hydrographs were classified into four levels of availability from high (I) to low (IV). These levels were correlated with the October stream flow volume to provide a prediction of dry season supply. Project net annual benefits could be increased for all four dry season water supply hydrograph levels by growing an upland crop (soybean) and rice, instead of only rice, providing that costs were less than $90/ha for additional drainage facilities. Net benefits for all rice were greater for reduced area planted, but fully irrigated when the available dry season water supply was lower than average as compared to planting the total area with inadequate irrigation. The irrigation system water demand model was calibrated to match actual diversions for the 1977‐78 dry season. The project irrigation efficiency, combined effects of conveyance and application, was determined to be 41%. Thus, a savings in available water supply could be realized by increased system efficiency both from physical modifications as well as from improved management.