FLOOD10363 ‎(2)‎

• County: Gunnison
• Community: Gunnison County
• Stream Name: East River, Cement Creek, Alkali Creek, Ohio Creek
• Title: Gunnison County Flood Hydrology, Contract # W99-D-0018 Final Report
• Date: 11/1/2004
• Prepared For: US Army Corps of Engineers, CWCB and Gunnison County
• Prepared By: Tetra Tech, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Balanced 1 percent chance exceedence snowmelt hydrographs were developed for the following
locations for use in the reservoir operations model.

· Taylor River below Taylor Park Reservoir
· Taylor River at Almont
· Gunnison River at Almont
· Gunnison near Gunnison

The East River at A1mont data set (details in Chapter 5) was used to determine the snowmelt runoff
pattern event. The East River at Almont was chosen to develop the snowmelt runoff pattern since the
East River is unregulated and not affected by Taylor Park Reservoir operations. The five largest runoff
events for the East River at Almont, with peaks from 3,000 cfs to 4,000 cfs, were analyzed for use as a
pattern. The 1997 snowmelt runoff event was chosen as a typical snowmelt event and was utilized as the
snowmelt pattern.

The 1997 60-day snowmelt event for the East River at Almont lasted from May 9 to July 7. The pattern
hydrograph timeframe was determined by centering the 60-day period on maximum daily average flow of
3,010 cfs occurring on June 8. The pattern, as taken from the East River at A1mont data set, consists of
sixty 1-day average values. This time unit was found to cause large fluctuations in the model due to the
large volume entering the system at each time step. In order to eliminate the fluctuations, the time period
of the time step was set to 1 hour. The HEC-DSSVue program (Data Storage System Visual
Utility Engine, a program for viewing, editing, and manipulating time series data stored in HEC-DSS
database files) was used to process the pattern 1-day time step to create a pattern with a 1-hour time
step. The resulting snowmelt pattern hydrograph is shown in Figure 6.2.1.

Figure 6.2.1

Pattern Hydrograph for 1997 Snowmelt Runoff Event

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Date

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