Operational losses and environmental flow recovery in a multi-irrigation districts river Basin, evidence from Iran’s arid central plateau

This study introduces a systematic technical–environmental appraisal framework that links off-farm operation to environmental flow recovery (EFR) potential in watersheds containing multiple irrigation districts (IDs)The analysis focuses on the surface-water distribution infrastructure within the IDs and, specifically, on off-farm agricultural water management. It considers interconnected open-canal networks, a manual operating system, and the associated standard operating procedures (SOPs). The framework is demonstrated in Iran’s arid central plateau, where six IDs operate in a basin with a long record of environmental water-rights violations linked to agricultural withdrawals. To quantify operational losses, integrated hydraulic–operational models were developed by coupling an integrator–delay hydraulic simulation model with IDs’ SOP logic. The models were calibrated and verified for all six IDs. The technical assessment indicates that daily water losses caused by operational failures and inefficiencies vary markedly across operating conditions. Under normal to severe shortage scenarios, these losses account for 6.5–17.3% and 21.5–31.1% of the supplied surface water, respectively. To estimate the EFR recovery potential, the study applied an flow-duration-curve (FDC)-shifting approach together with the Global Environmental Flow Calculator (GEFC). Under the best-case scenario, 61 MCM yr⁻¹ can be recovered from operational losses and returned to the river, which corresponds to 45.16% of the flow deficit required to satisfy class F. Even under the most severe shortage scenario, 13 MCM yr⁻¹ (9.63% of the class F deficit) remains recoverable. Overall, the proposed framework is transferable to similar multi-ID watersheds and provides technical evidence to support licensing decisions for off-farm system automation, enabling basin authorities, licensing agencies, and irrigation-district managers to audit operational losses, define diversion-reduction targets at diversion dams, and operationalize compliance monitoring for environmental-flow releases.