WSP06472

• File Number: 8200.766
• Description: Gunnison River General Publications-Correspondence-Reports
• State: CO
• Basin: Gunnison
• Water Division: 4
• Date: 1/1/3000
• Author: Unknown
• Title: Summary Description and Review of Existing Gunnison Basin Model
• Water Supply Pro - Doc Type: Report/Study

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Description of EXisting Model

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The minimum power release requirement was identified during the model calibration process
and subsequently verified by the USBR Grand]unction office. The minimum is either a fixed number or
is determined by interpolation depending on reservoir contents. The contents and release ranges (all
expressed in acre. feet) used in this calculation are as follows:

. ~mn,+h- Contents

Release

0.200,000
200,000-390,000
390,000.900,000 .

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 two 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-step values and the portion of the network above the
Blue Mesa outlet is re-solved with Blue Mesa storage set junior to all 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
flows in the main Uncompahgre Valley canals. Taylor Park releases are determined from a combination
of inflow forecasts, instream flow targc.ts, and seasonal storage targets. Depending on the month, the
model calculates the release defined br 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
determine the Taylor Park release most of the time.

The objective of the forecast. based release is to fill Taylor Park without spilling by the end of
July maintaining a relatively constant flow regime below the reservoir. Forecast..based releases are only
computed for the months of March through June. The release is calculated using the following equa.
tion:

release ~ (forecast + contents. capacity)/monthsleft

forecast is the projected inflow from the current date through]uly
contents is the active contents of Taylor Park at the beginning of the current month
capadtv 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 target is 100 cfs (6000 afper month).

The seasonal storage targets for Taylor Park were derived during the model calibration process
in an attempt (0 obtain better correspondence between observed and modeled reservoir contents. The
targets used in the model are stated in terms of acre.feet of active capacity as follows: