Cook Evaluation of Wyoming's New Depletions Plan

Home Browse Search

• Because this subbasin extends to the state line, routing is unnecessary. However, offsets need to cross the state line in the same locations and in approximately the same proportions as would have crossed at those locations had the overrun not occurred. Baseline 2, Subbasin 4 Overruns Assumptions: • An overrun in this subbasin will have the effect of (1) reducing starage in Wheatland Reservoir; (2) reducing storage in Grayrocks Reservoir; and/or (3), to the extent it would reduce spills from Grayrocks Reservoir, reducing 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 the Laramie Basin or on the mainstem), 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 noted earlier and under the conditions described earlier, Wyoming will want to offset any such overruns on a year to year basis rather than let them accumulate. • As with overruns in Baseline 1, Wyoming will want to offset them as soon as possible rather than let them accumulate. Conclusions: Normally, an overrun in subbasin 4 will have little or no effect at the state line because it will either cause an under run in subbasin 5 or will be absorbed by Grayrocks reservoir. Therefore, while overruns in subbasin 4 may adversely affect Wyoming users in subbasin 5, they typically will not affect flows at the state line. Only to the extent that an overrun in subbasin 4 reduces spills from Grayrocks will it be a direct cause of reduced natural flow use by users in subbasin 3. It is only under those conditions that a net overrun from subbasins 4 and 5 needs to be offset. If those conditions occur, any such net overrun could be offset by an underrun in subbasin 3. Routing should be through the use of normal conveyance losses only, i.e. there should be no discounting in the amount after routing because of foregone diversions. Any such foregone diversions would have either contributed to the overrun in subbasin 4 or would have reduced the under run in subbasin 3 or 5. The amount of the overrun that needs to be offset, if any, should be reduced only by normal conveyance losses to the state line. 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. Baseline 2, Subbasin 5 Overruns Assumptions: • An overrun in this subbasin will have the effect of (1) reducing starage in Grayrocks Reservoir; and/or (2) reducing the spill from Grayrocks Reservoir 6