7997

• UCREFRP Catalog Number: 7997
• Author: Nash, L. L. and P. H. Gleick.
• Title: The Colorado River Basin and Climatic Change, The Sensitivity of Streamflow and Water Supply to Variations in Temperature and Precipitation.
• USFW Year: 1993.
• USFW - Doc Type: EPA 230-R-93-009,
• Copyright Material: NO

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constraints of this study, it was not possible to study all of the Upper Colorado River sub-basins. Yet by

studying smaller, detailed sub-basin models, only limited information on the entire basin could be gel'lerated.

Thus, we used the composite Two-elevation model to obtain an overview of the impacts on the entire upper

basin. The Two-elevation model has an additional advantage of being highly correlated with streamflow

nodes in the CRSS water-supply model.

All three sub-basins are high-elevation, snowmelt-driven watersheds, with no significant rainfall

showing up in the average hydrograph. Streamflow measurements for the White River model come from

the USGS gauging station located 2.5 miles east of Meeker at an elevation of 6300 feet. The drainage area

of the White River covers approximately 770 square miles. The period of record for the White River dates

from 1909. Mean annual discharge computed over the period 1949-1983 is about 435 thousand acre-feet

(tat). East River measurements are made at the Almont station, which has an elevation of 8006 feet. The

period of record dates from October, 1934. Streamflow measurements for the Animas River are made at

an elevation of 6502 feet at the station of Durango. Records date from 1912. In all cases, monthly and

annual streamflow records are classified as "good".7 Streamflow into Lake Powell, which is used to calibrate

the Two-elevation model, is calculated by the Bureau of Reclamation based on reservoir outflow, changes

in reservoir storages, and evaporative losses, and is checked against the combined flows of three upstream

USGS gauging stations (the Colorado River at Cisco, the Green River at Green River [Utah], and the San

Juan River at Bluff).

As stated above, the NWSRFS is a forecasting model that was developed for the short-term

forecasting of streamflows. For this purpose snow-pack conditions, daily observations of temperature and

7 USGS classifications are defined as follows:
Excellent -- 95% of daily discharges are within 5% of their true value.
Good -- discharges are within 10% of their true value.
Fair -- discharges are within 15% of their true value.
Poor -- discharges do not fall within 15% of their true value.

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