9676

• UCREFRP Catalog Number: 9676
• Author: U.S. Department of the Interior.
• Title: Preliminary Analysis
• USFW Year: 2001.
• USFW - Doc Type: Wayne N. Aspinall Unit Operations and the Draft Endangered Fish Flow Recommendations for the Gunnison and Colorado Rivers.
• Copyright Material: NO

Attachment A

RiverWare Hydrology Model Background

RiverWare is a software modeling tool developed by CADSWES (University of Colorado) for the Bureau
of Reclamation and the Tennessee Valley Authority for operation and planning studies of river basins and
river systems. A daily planning model of the Gunnison River was developed using the RiverWare
modeling software. The model includes the Gunnison River Basin from Blue Mesa Reservoir to the
confluence with the Colorado River. The modeling period runs from January 1975 through December
2000.

The model separates reservoir operations into 3 time periods: January-March, April-July, and August-
December. Basic daily inputs to the model are: historic Blue Mesa inflows, both actual and unregulated;
historic side inflows to Morrow Point and Crystal; Gunnison Tunnel diversions; and various downstream
gains computed from actual gage data. Other data provided as input to the model include forecasted
inflow and tunnel demands for each forecast period.

Forecast data, both reservoir inflow and tunnel demand, is for the current forecast period and can be input
on any day, generally on the first day of the month and then again on the fifteenth, if available. Forecast
data for the last month of the forecast period generally has to be adjusted (sometimes daily) to reflect that
as the end of a forecast period is approached, there is nearly 100 percent accuracy. The model determines
remaining forecasted inflow and demand by subtracting the int10ws or demands to date from the most
recent forecast data available. Remaining minimum canyon demands, which include trout spawning and
incubation flows. are computed at various times in the model since these demands are dependent upon
flOws that occur during the model run.

The flow recommendations are for a point at Whitewater on the river system about 80 miles downstream
of the Aspinall Unit. Flow recommendations vary on the type of water year forecast. Six different
recommended flow hydro graphs for this point on the river have been developed using the information
contained in the "Flow Recommendation to Benefit Endangered Fishes in the Colorado and Gunnison
Rivers", March 2001. This report identified a 2 day peak flow with shoulder flows and base flows under
different hydrologic conditions. Tributaries between the Aspinall Unit and the Whitewater gage
(measuring point) provide a portion of the recommended flow.

The Flow Recommendation Report indicates a peak flow should occur between May 15th and June 15th.
Preliminary analysis of tributary peak flows during May indicate that making peak releases from the
Aspinall Unit between May 20-22 would provide the best chance of matching the tributary peak and
reduce the volume of water released specifically for the recommended flows. An estimate of the unmet
portion ofthe recommended flow hydrograph for each year was computed outside the RiverWare Model
using estimated hydro graphs for the tributaries. The flow recommendation demand hydro graph was
input as a demand in the canyon immediately below the Aspinall Unit. The flow recommendation
demand hydro graph is included as a downstream demand on Aspinall and is included as part of the total
canyon demands. Because the demand hydro graph is based on estimated tributary hydrographs, the
recommended flow at Whitewater may be exceeded or not entirely met depending on the accuracy of the
projected tributary flows.

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