Monitoring and modelling approaches for quantitative assessment of irrigation return flows in a command

Irrigation is one of the major consumers of fresh water but crops consume only a small part of supplied water and huge quantities emerge downstream as rejuvenated flow and recharge groundwater. The assessment of these flows is cumbersome due to dependence on multiple factors; hence a fixed percentage is assumed by government agencies for designing downstream projects. Three different modeling and measurement techniques, i.e., water balance, isotopic analyses, and hydrological modeling were used to compute surface and sub-surface components of irrigation return flow in an irrigation project (Sanjay Sagar Project with the capacity of 82 MCM and 9863 ha command area) situated in the hard rock region of Central India. The water balance analysis confirmed that a major portion ranging from 12.3 to 35.9%, with an average of 22.9% of supplied water to the command reached the Bah River as regenerated flow, while 1.9–16% with an average of 10.2% of supplied water reached the groundwater body as recharge. The isotopic analysis yielded qualitative insights into the proportional influence of irrigation water on open wells and bore wells in the range of 81% and 9%, respectively. The outcomes of the SWAT model demonstrated that within Sanjay Sagar's command, irrigation led to approximately 27.8% of regenerated flow and 8.9% of recharge from applied irrigation.