FLOOD05243

• County: Statewide
• Stream Name: White River
• Basin: Statewide
• Title: Floodplain Information Report Volume 2
• Date: 3/1/1995
• 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 Maooim!:

Base mapping selected for the delineation of the 50-year and 100-year floodplains on the White
River consisted of 7.5 minute V.S.O.s. topographic quadrangle maps. A total of 12 quadrangle
maps were 'used in compiling the base maps for the White 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 and 100-year flood plain boundaries could not be shown as separate in
most cases.

4.2 Stream Reaches

Preliminary work on the floodplain mapping of the White River included dividing the entire study
reach into separate stream 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 10 separate stream reaches classified for a total of 52 river
miles.. That is an average of 5.2 miles per reach. These 10 stream reaches are listed in Table
./ and they are shown on Figure 6.

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