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GD0206 . assumption was allocated to downstream canals in accordance with the priority if said canals were receiving less than the estimated irrigation water requirement for that time period adjusted for on-farm efficiencies. As was done in the Series II runs also, the historical pumping was assumed to have taken place. The remaining irrigation requirement adjusted for on-farm efficiency was used to determine the amount of canal water required to be delivered at the farm headgate, Series III-B runs. This run was the same as the Series III-A run except that the farm irrigation efficiency was brought up to a 75 percent level. Adjustment of ditch diversions and allocation of water saved was done the same as described for Series III-A, . Series IV runs--varying ground-water pumping The purpose of the Series IV runs was to evaluate the sensitivity of irrigation water-use efficiency in the reach to changes in use of ground water, The input data for the Series IV run was the same as the final Series I run with the exception of the amount of ground water pumped. In the Series IV runs, it was assumed that sufficient ground water was pumped under each canal system to meet the irrigation water requirements not satisfied by historical diversions. Under this assumption the ground-water reservoir was being used as a supplemental supply, pulled upon heaviest during drought years and released during years of good surface-water supplies. Series V runs--combinations The purpose of the Series V runs was to evaluate the sensitivity of irrigation water-use efficiency in the reach to combinations of changes in canal seepage, on-farm efficiency and ground-water pumping. The combinations tested were: Series V-A run. Combination of Series II-B, III-A and IV runs. Series V-B run. Combination of assumptions of Series II-B, III-B and IV runs. . -49-