Irrigation efficiency and water-saving potential considering reuse of return flow

Abstract

Irrigation efficiency (IE) and water-saving potential (WSP) are two fundamental parameters for assessing water use and management in irrigation systems. A new calculation method was proposed herein to accurately estimate the IE and WSP in irrigation systems. The proposed method considers the reuse of return flow. A modified Soil and Water Assessment Tool (SWAT) was used to simulate hydrological processes under various water-saving scenarios for the Yangshudang (YSD) watershed within the Zhanghe Irrigation System (ZIS) in Hubei Province, China. The dry year of 2010 was chosen as a study case. Based on simulation results, the traditional irrigation efficiency (IE0) and water-saving potential (WSP0) as well as the irrigation efficiency taking into account the reuse of return flow (IEr) and water-saving potential considering the reuse of return flow (WSPr) were calculated for various scenarios. The relationships between the two IE indicators and the cause thereof, as well as the two WSP values, were analyzed and explored. The results showed that both IE and WSP were improved with the enhancement of water saving. As long as there was the reuse of return flow, IEr must be greater than IE0. Moreover, in terms of water-saving approaches that improved the reuse rate of return flow, WSPr was determined to be greater than WSP0, thereby suggesting that the traditional method underestimated the WSP. However, for water-saving approaches that reduced the reuse rate of return flow, WSPr was determined to be less than WSP0, which suggested that the traditional method overestimated the WSP. The relationship between WSP0 and WSPr was attributed to the fact that WSPr was calculated by subtracting the amount of the water saved by the reuse of return flow on the basis of WSP0, and this difference can be either positive or negative. Therefore, the managers of irrigation systems should use IEr as the actual IE but not IE0, and use WSPr instead of WSP0 to evaluate the actual WSP.