Cook Evaluation of Wyoming's New Depletions Plan

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which in turn could reduce natural flow use in Wyoming or Nebraska the same year. To the extent the reduction is to natural flow users who also have storage water available (whether in Grayrocks or on the main stem), the reduction in natural flow supply will be made up through additional storage releases, thereby delaying until later in that year or until a subsequent year a reduction in amount reaching the state line. • As per the discussion above, Wyoming will want to offset overruns on a year to year basis rather than let them accumulate. Conclusions: • To the extent that an overrun in subbasin 5 reduces spills from Grayrocks Reservoir, it could be a direct cause of reduced natural flow use by users in subbasin 3 who have no supplemental storage supplies. In that event, the downstream subbasin would experience either a reduction in its own overrun or an increase in its under run. To the extent the subbasin 5 overrun results in such an increased downstream under run, that increase in the under run should be allowed as a direct offset to the upstream overrun. For the same reason, however, the amount of the overrun that needs to be offset should be reduced only by normal conveyance losses from the upstream to the downstream subbasin, i.e. there should be no discounting in the amount after routing because of foregone diversions. Any such foregone diversions would have either contributed in equal amounts to the overrun in subbasin 5 or would have reduced the under run in subbasin 3. • To the extent that an overrun in subbasin 5 causes a reduction in spills from Grayrocks, it should be routed the same as water released from that reservoir per Attachment 1. • Allowing annual offsets would cause no significant harm to Nebraska or to the Program as long as the offset water crosses the state line in the same locations and in approximately the same proportions as would have crossed at those locations in the absence of the overrun. Baseline2, Subbasin 6 Overruns Assumptions: • Overruns in subbasin 6 do not contribute to under runs in any other subbasin • Overruns in subbasin 6 in the irrigation season or above Hawks Spring Reservoir in the non irrigation season have no adverse effect because there is normally no flow into the Platte from that subbasin during the irrigation season and none of the water stored in Hawks Springs reaches the state line at a later time. • Overruns in subbasin 6 below Hawks Springs Reservoir in the non irrigation season will affect flows at the state line in the non irrigation season. Conclusions: • Overruns in subbasin 6 should not be subject to offset from under runs in any other subbasin. • Overruns in subbasin 6 below Hawks Springs Reservoir and during the non- irrigation season are not subject to routing discounts except those relating to normal conveyance losses. 7