WSP01056

• File Number: 8200.766
• Description: Gunnison River General
• State: CO
• Basin: Gunnison
• Water Division: 4
• Date: 2/13/1992
• Author: Unknown
• Title: Gunnison River Basin Planning Model - Existing Model Review
• Water Supply Pro - Doc Type: Report/Study

Description of Existing Model

4

The minimum power release requirement was identified during the model calibration process
and subsequently verified by the USIlR Grand Junction office. The minimum is either a fiXed number or
is dctennincd by interpolation depending on reservoir contents. TIle contents and release ranges (all
expressed in acre-feel) used in this calculation are as follows:

,

Contems

Release

0-200.000
200,000-390.000
390.000-900.0UO

o
24,000-33,000
75,000

Blue Mesa storage rights. incorporating refill and net of inactive storage are set at 952.202 af; no
direct flow power rIghts are represented. The subordination of the Blue Mesa storage right to in-basin
junior depletions is effected by solving the model network in [wo steps. In the first step. the Blue Mesa
rights are administered in their correct priority vis-a-vis all upstream rights; in the second step, releases
from Blue Mesa are constrained to equal their first~s(ep values and the portion of the network above the
Blue Mesa outlet is re~sol...ed with Blue Mesa storage set junior to aU upstream rights except those sup-
porting transbasin diversions (if any). This two.step process essentially re.allocates Blue Mesa storage to
any upstream in-basin juniors that might have been called out by that storage.

Uncompahgre Project

Modeling of Uncompahgre Project operations includes Taylor Park storage and release, diver.
sion at the Gunnison Tunnel, administration of the Taylor Park Exchange, and diversions and return
009.'5 in the main Uncompahgre Valley canals. Taylor Park releases are determined from a combination
of inflow forecasts, instrcam flow targets. and seasonal storage targets. Depending on the month, the
model calculates the release defined by each of these methods and imposes the maximum of these as the
required release; practically speaking, the forecast. based releases and the instream flow targets
detennine the Taylor Park release most of the time.

I

The objee<ive of the forecast.based release is to fill Taylor Park without spilling by the end of
July maintaining a relatively conSlam now regime below the reservoir. Forecast.based releases are only
computed for the months of March through June. The release is calculated usmg the following equa-
tion:

release = (forecast + contents. capacity)/monthsleft

forecast is the projected inOow from the current date through July
contents is the active contems of Taylor Park at the beginning of the current month
caoacity is the active capacity of Taylor Park(106.200 acre-feet)
monthsleft is the number of months from the current date through July

.,

The instream flow targets are imposed in all months and mimic the CWCB instream flow decrees
for the Taylor River below the reservoir. During the months of October through April, the target is 50
cfs (3000 afper month); during May through September. the tar!(etls 100 cfs (6000 afper month).

The seasonal storage targets for Taylor Park were derived during the model calibration process
in an attempt to obtam bcaer correspondl"ncl' betwel'n llbsl'rved and modeled reservoir contents. 111e
targets used in the model are stated in terms of acre-fcC't of active capacity as follows:

.