FLOOD10388 ‎(2)‎

• County: Statewide
• Stream Name: Gunnison River
• Title: Floodplain Information Report - Volume 3 - Gunnison River from Delta to the Confluence of the Colorado River
• Date: 5/1/1995
• Prepared For: Recovery Implementation Program for Endangered Fish Species in the Upper Colo
• Prepared By: CWCB
• Floodplain - Doc Type: Floodplain Report/Masterplan

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4.0 HYDRAULIC ANALYSIS

4.1 Base MaDDing

Base mapping selected for the delineation of the 50-year and IOO-year floodplains on the
Gunnison River consisted of 7.5 minute U.S.G.S. topographic quadrangle maps. A total of 11
quadrangle maps were used in compiling the base maps for the Gunnison River study reach. The
contour interval for the maps was either 20 or 40 feet (see Figure 8). Due to the small scale of
the base maps (1 "=2000'), the 50-year and IOO-year floodplain boundaries could not be shown
as separate in most cases.

4.2 Stream Reaches

Preliminary work on the floodplain mapping of the Gunnison River included dividing the entire
study into separate reaches. The reaches were classified by estimating stream floodplain widths.
The width classifications were refmed once cross-sections were plotted. The width classifications
selected are based on the distance from one side of the river to the other at a ground elevation
15 feet above the low water level. Those classifications are:

Broad
Medium
Narrow
Canyon

>0.5 mile wide;
0.2 - 0.5 mile wide;
0.1 - 0.2 mile wide;
<0.1 mile wide.

Based on these standards, there were 12 separate stream reaches classified for a total of 43.5 river
miles. That is an average of 3.6 miles per reach. These 12 stream reaches are listed in Table
4 and they are shown on Figure 6.

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