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1907 . Discussions'with the District revealed that no attempt has been made to deter- mine the irrigation requirement for any year. In addition, there is no evidence that the District has I imited the headgate diversion based on an irrigation requirement. A comparison of 1985 headgate diversions (only year with suitable irrigated acreage data) with the irrigation requirement computed using methodo- logy of the 1961 Study shows that the 1985 headgate diversion exceeded the require- ment by 14,210 acre-feet.~ To gain insight into the impact of excess diversion, the previously described Baseline study (lH and lR) and variation studies 5H and 5R were modified to reflect assumed increases in headgate diversion. This included established cri- teria for calculating return flow from diversions in excess of ideal requirement as described in the 1961 Study. Several runs were made, each reflecting an incremental increase in headgate diversion (above ideal). Excess diversion increments ranged from .1 to 1 foot of addit i ona I \'/ater per acre. When an increment resu Ited in a negat i ve effect on John Marti n Reservoi r i nfl ow, no analysis was done of the higher increments. This range of excess diversions represents an increase in headgate diversion requirement of from 1,972 to 19,717 acre-feet per year{example - 19,717 acres X 0.1 foot per acre). In order to simulate a more realistic water management pro- cedure, excess di vers ions were allowed to occur on ly in those years of above normal water supply. . The modified Baseline study shows the direct effects of the excess diversions. The modified 5H and 5R show the cumulative effects of excess diversions, transfer of water out of the Mode I decree and wi nter storage under joi nt use decree. . i/ I t must be noted that 1985 is not with i n the study peri od and the first year that Model lands were back to full irrigation. the example of effect of excess diversions,.it is appropriate. that 1985 is HOI'/ever, for I I I I I I I I I I I A few of the key resu It s of this analysis are displayed below: Effect of Excess Diversion on Baseline Study IHIlR Foot/Acre of Excess Diversion Item Baseline 0.1 0.2 0.3 0.4 0.5 1.0 (Units 1000 Acft.) Total Bypass/Spill 13.6 13.3 13.0 12.6 12.4 12.2 11.0 Total Return Flow 17.3 17.7 18.0 18.2 18.6 18.9 20.3 Total Irrigation Shortage 11.5 11.8 12.1 12.3 12.6 12.9 14.0 Net Effect on J.M. inflow compared to historic Model reservoir operation (IH) 1.0 0.8 0.7 0.5 0.3 0.2 -0.7 Net Effect on J.M. i nfl ow compared to rehabilitated Model Operation (IR) 3.3 3.2 3.0 2.8 2.7 2.6 1.7 44