Clarification of Water Use under the Complicated Irrigation System and its Modeling in the Boribo-Bamnak River Basin, Cambodia

Abstract

Effective, equitable, and sustainable management of water resources in river basins requires clarification of the current river basin situation and potential water use and water balance challenges. This study performs a water balance calculation involving an analysis of the appropriate water distribution of the Boribo-Bamnak River basin in Cambodia. This river basin covers the Boribo and Bamnak basins, both of which are interlinked by the Bamnak headworks. Together, this constitutes an integrated irrigation and drainage system. The Soil and Water Assessment Tool (SWAT) model was used to simulate rainfall-runoff in the Boribo-Bamnak basin over a study period of nine years (2010-2018), whereupon a simulated daily streamflow was applied to the water balance computation in the river basin according to the water distribution ratio at Bamnak headworks. The SWAT model yielded NSE, PBIAS, and RSR values of 0.55, 9.70, respectively, and 0.67 for model calibration. It also obtained values of 0.51, 3.70, and 0.70 for model validation of the three quantitative statistics, NSE, PBIAS, and RSR. The results of the calculated water balance indicate that although the Bamnak and Boribo Rivers have abundant water in the wet season, they have faced water shortages in the dry season during every year of the study period except 2016. Irrigation safety during the dry season is always low (approximately 10%). Attaining a desirable safety level of 80% in all existing irrigation areas would require additional water resources of approximately 6.0 × 10⁶ m³ for the Boribo River basin and 10⁷ m³ for the Bamnak River basin. In light of the above findings, this study provides recommendations for coordination strategies to improve water resource management and development plans in the river basin.