Evaluation of Water Shortages in Agricultural Water Use in the Sangker River Basin, Cambodia

Abstract

The shortage of agricultural water in the Sangker River basin of Cambodia is becoming a severe problem, and the river flow seems to have decreased. The present study assesses the excess and deficiency of irrigation water resources in this river basin for agricultural production. The Soil and Water Assessment Tool (SWAT) is used to analyze the water balance at the main headwork in this river from 2014 to 2018. SWAT was used to estimate the available volume of stream water at the ungauged point of the Kang Hot headwork, and the model performance was evaluated at a gauged point downstream by the Nash–Sutcliffe efficiency (NSE). The model was calibrated manually and automatically by using data from 2007 to 2013. Furthermore, the flow rates in the two main irrigation canals were measured from June 2018 to October 2019 to obtain the actual irrigation water supply, and the evaluation was made by checking the difference between supplied water volume and irrigation water demand. The model output showed good agreement between observed and simulated monthly streamflow during the validation period (NSE = 0.69, RSR = 0.55). From the results of water balance analysis, water shortage rates exceeding 20% of the monthly water requirement occurred mostly between April and June from 2014 to 2017. Furthermore, there was excess water supply in 2018 because of abundant river flow that year. The actual irrigation water supply during the study period showed rates of water shortage of 52% and 41% in the left and right main canals, respectively, at the headwork. This study provides new insights for field technicians to consider irrigation planning for present and future water resources management and development for sustainable irrigation agriculture.