Cook Evaluation of Wyoming's New Depletions Plan

• File Number: 8461.250
• Description: Water Issues
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 8/22/2005
• Author: Cook
• Title: Cook Evaluation of Wyoming's New Depletions Plan
• Water Supply Pro - Doc Type: Report/Study

• As per the Wyoming NDP, an under run in use below Guernsey (including the
Laramie subbasin) cannot be used to offset an overrun in this subbasin
because the below Guernsey subbasin is in Baseline 2.
• Wyoming wants to do what is necessary to offset any excess uses (overruns)
as soon as possible after they occur rather than let them accumulate until the
next allocation year when they would first cause a shortage of water for the
North Platte contractors and the corresponding reduction in state line flows
that will result from the reduced deliveries in that allocation year. Allowing
annual offsets would cause no significant harm to Nebraska or to the Program
as long as the offset water crosses the state line at the same locations and in
approximately the same proportions as would have crossed at those locations
in the absence of the overrun.
Conclusions:
To the extent that an overrun above Pathfinder is a direct cause of reduced
natural flow use in subbasin 2, the downstream subbasin would experience
either a reduction in its own overrun or an increase in its under run. Even
though not all the downstream under runs will result from upstream overruns,
it is acceptable to use a subbasin 2 under run as a direct offset to the upstream
subbasin 1 overrun in this baseline. 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 basin, i.e., there should be no discount in the
amount after routing because of foregone intervening diversions. Any such
foregone diversions would have either also contributed to the overrun in the
upper basin (and therefore would have themselves had to be offset) or would
have reduced the under run in the lower basin.
The practical effect of most overruns above Pathfinder will be to cause a
reduction in the future water supply for North Platte contractors in either
Wyoming or Nebraska. Therefore, any net overrun needs to be offset at or
ahove Whalen. Offsetting the net overrun at Whalen will cause such offsets to
cross the state line at the three crossing points in proportion to the reductions
in flow caused by the net overrun at those points.
For purposes of routing, the amount that does not reach Whalen because of
any net overrun in Baseline 1 that is caused by excess use in subbasin 1
should be reduced only by the conveyance losses from the point of use to
Pathfinder and the storage conveyance losses from Pathfinder to Whalen.
Wyoming should be allowed to offset the resulting reduced amounts at
Whalen on a year by year basis even though the impacts would have
otherwise not been experienced until the first allocation year thereafter.
Baseline 1, Under Runs Below Pathflnder (Subbasin 2)
Assumption:
? An under run below Pathfinder could result from either an overrun in subbasin
1 or from an inadequate water supply otherwise in subbasin 2
Conclusion:
• Regardless of the extent to which an under run in subbasin 2 results from an
overrun in subbasin 1, it is acceptable to allow such an under run to serve as
2