9593

• UCREFRP Catalog Number: 9593
• Author: Tetra Tech Inc.
• Title: Concept Development Report Hartland Diversion Dam Fish Passage Structure Delta, Colorado.
• USFW Year: 2000.
• USFW - Doc Type: Grand Junction, CO.
• Copyright Material: NO

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TABLE 4.1 PEAK FLOWS FOR RETURN PERIODS ON THE GUNNISON RIVER AT DELTA. CO

Return Periods FIS Delta, CO
(years) AUQ. 19, 1991
10 13,500
50 18,700
100 21,200
500 26,700

4.2 Diversions and Returns
There are no significant diversions between the Delta gage and the Hartland diversion.
However, there are two ditches, which return to the Gunnison River immediately upstream of
the gage. These ditches are the Relief canal and Bona Fide ditch. The returns are not
monitored but are believed to return up to 20 to 30 cfs (Boyd 2000). For the purpose of this
analysis these returns are considered negligible.

4.3 Average Monthly Flows
Using gage information from 1976 through the end of 1999, the daily minimum, mean,
and maximum flows are calculated for each month. Exceedences for mean daily flows are also
determined. As previously discussed, April through August is the critical time for fish passage.
Results of the gage analysis are presented in Table 4.2.
Based on the analysis, the average spring runoff since 1976 occurs in late Mayor early
June. 30 days prior to the peak, average flows are approximately 3000 cfs. Average daily
flows in August are approximately 1200 cfs with a 50% exceedence of 1100 cfs. The 90%
exceedence for August is 350 cfs.
Flood flow-frequency curves for the Gunnison River are based on gage information
using log-Pearson Type III distribution for events that are not available from the FIS (USWRC
1981). These return periods and flows are presented in Table 4.3.

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