Cumulative Effect Report on Plan for Future Depletions (2)

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i rights as assumed in the CPFD (i.e., South Platte flow development assumed to occur at 5% in April, 40% in May, 50% in June, and 5% in July). The call records used in this analysis are from the records of the Colorado State Engineer's Office. The initially assumed % water supply source mix by region of the CPFD, Paragraph B, was for the period 1998 through 2002. As listed in Figure 2, the weighted % of time for a July 1, 1997 water right to be in-priority is 53% for 1998- 2002 versus 33% for 1998-2006. Figure 2 shows the analysis for adjusting the % water supply from native South Platte flow development by region. Colorado proposes for the Initial Reporting Period of two years to use an average for the 1998 through 2006 period for the % of time that a July l, 1997 priority water right would be available for diversion. The analysis adjusts the initially assumed % of native South Platte flow development by region by the ratio of % time between the 1998-2006 period (33%) to the 1998-2002 period (53%) that a July 1, 1997 water right would be in-priority--that ratio being 33% / 53% or 62%. The results of this analysis changes the % water supply from native South Platte flow development from 10°/o to 6.2% for the North region, 15% to 9.3% for the Central region, and 10% to 6.2% for the South region. If the drought continues, Colorado in the future will propose adjusting this percent even more to reflect the lack of native water for junior water rights by using a more recent period average only such as 2003-2006 or some other rolling average to determine monthly water availability by call records. With these adjustments downward for the % water supply from native South Platte flow development, Colorado proposes that there is a corresponding increase in % water supply from water reuse. Colorado has begun a data collection effort with the major municipal water providers to better define the °/o water source mixes from the six categories of water sources. Initial indications from major providers is that water reuse is increasing along with in-basin agricultural conversions. Note that the water reuse sources have a net depletive effect for all months while in- basin agricultural conversions have a net accretive effect for all months as shown in Figure 1. Figure 3 is similar to Figure 1 but the analysis has been redone using the adjusted % water supply for the source of native South Platte flow development and the source of water reuse. Table 3 lists a total of 26,882 acre-feet of net accretions for the winter months of October through April and lists a total of net depletions in May and June of 2,713 acre-feet. At the bottom of Figure 3 is the modified % water supply source mix by region. The transit loss assumptions used in this modified analysis of Figure 3 are the same as those used for the original analysis in Figure 1 and as approved in the CPFD in Paragraph C. The transit loss assumptions in the CPFD in Paragraph C are based on the administrative losses assigned by the Colorado State Engineer for routing reservoir releases downriver (i.e., protected flows). Colorado is sttidying new transit loss factors that better reflect the physical situation of water flowing downriver subject to rediversion and subsequent return flows (i.e., unprotected flows). The Water Conservation and Water Supply Study dated December 1999 of the Platte River Research Cooperative Agreement contained Appendix D written by the Water Management Coinmittee, which dealt with monthly loss factors as related to water being diverted by canals. Accretions and depletions from new water related activities would be diverted by downstream canals as such water flows from the Front Range downriver to the Colorado-Nebraska Stateline. The % diversion loss factors listed in Appendix D are gross values where lagged groundwater and surface water returns are not considered as noted in Appendix D, which can result from diversions 2