Application of SIRMOD to Evaluate Potential Tailwater Reduction from Improved Irrigation Management

The SIRMOD surface irrigation simulation, evaluation, and design software developed at Utah State University was applied to evaluate potential increases to irrigation performance from improved irrigation management within the Imperial Irrigation District of Southern California (IID). This study was conducted as part of a planning effort to develop strategies to satisfy the Colorado River Quantification Settlement Agreement and Related Agreements (QSA), which call for IID to generate more than 300,000 acre-feet annually through a combination of District and voluntary on-farm efficiency conservation savings. Potential irrigation management performance increases were evaluated by calibrating the SIRMOD model for 34 selected border and furrow irrigation events for which delivery and tailwater hydrographs were measured. These events occurred at fields distributed throughout the Valley representing a range of crops, soils, run lengths, and tailwater production (surface runoff). For each event, simulations were conducted to identify potential reductions in tailwater resulting from different combinations of inflow rate and cutoff time. Simulations were constrained to minimize reductions in irrigation adequacy. Simulation results were detuned to represent practical, attainable performance based on an estimate of uncertainty in the soil moisture deficit prior to irrigation on the planning of an irrigation delivery.