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System (CIMIS). While the modified Penman-Monteith approach estimates evaporation from an open water body directly, parameter conversions are required to convert pan evaporation and CIMIS landsurface evaporation into open-water-body evaporation. We examined the net effect on financial performance using the System Advisor Model (SAM) and a sensitivity analysis that included estimates of three different solar PV structures at eight different sites along the California network of canals (Fig. 1). In our main results we considered CdTe semiconductor technology but also considered multicrystalline silicon in the sensitivity analysis. The three solar PV structures included a ground-mounted system (Fig. 2a), a steel-truss canal-spanning design that has been deployed in Gujarat, India 26 (Fig. 2b), and a suspension-cable canal-spanning design 27 that has been deployed in Punjab, India 28 (Fig. 2c). Our financial performance analysis includes NPV and levelized cost of energy (LCOE) comparisons of over-canal to ground-mounted designs. Our design comparisons considered enhanced PV performance due to evaporative cooling, and avoided costs for water and aquatic weed mitigation (Fig. 2d and 2e). ResultsHere, we present the results of our water savings, financial performance, and diesel engine retirement analysis. Water savingsEvaporation rates extracted to the locations of the canals and averaged annually are 1716, 1497, and 1570 mm y -1 for the modified Penman, pan evaporation, and CIMIS approaches, respectively. As expected, these estimates of evaporation from canal water surfaces are higher than estimates of evaporation from land surfaces due to the availability of water and surface energy balance. Our surface water evaporation estimates are 11% to 59% higher than California statewide potential evaporation from land surfaces 29,30 . Similarly, previous estimates of evaporation from water surfaces on lakes are generally larger than potential evaporation from land surfaces 31 .

This paper describes the development and application of a spreadsheet model to evaluate effects of water management on diversion modified flow regimes, enabling the exploration of novel ways to meet proposed environmental flow standards. Mill Creek, a northern California river with an altered flow regime that impacts aquatic species, was used as a case study. Test cases examined how water management alternatives, such as groundwater pumping, water rights transfers, and water exchange agreements, can improve environmental flow allocations given irrigation water demands. Four test cases include passage flows for Chinook salmon and steelhead trout, a minimum instream flow, 80% of natural flow, and a spring recession flow with functional flow components. The model identified late October as consistently water-scarce, even in wet years. These analyses suggest that fall shortages for fish migration could be eliminated through a water exchange agreement combined with use of wells. All cases except the minimum fish passage flow case required acquisition of the largest water rights to decrease environmental shortages by over 80%, with a substantial curtailment in irrigation.

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