9469

• UCREFRP Catalog Number: 9469
• Author: Colorado Water Conservation Board.
• Title: Floodplain Information Report\
• USFW Year: 1995.
• Copyright Material: NO

' 3.0 HYDROLOGIC ANALYSIS
3.1 Existing Data
For locations where detailed existing hydrologic analyses were available, those analyses were used
' to obtain peak 50-year and 100-year flows.
Published floodplain studies prepared by FEMA for Delta, Colorado provided 50-year and 100-
' year flows at the upstream limit of this study. The floodplain study for Grand Junction provided
50-year and 100-year flows at the downstream limit of the study.
3.2 New H~gic Information
Hydrologic analyses of the 50-year and 100-year flood flows for the remainder of the hydrologic
points along the study reaches of the Gunnison River were accomplished by interpolation of the
known flow values. The peak flows per square mile for the 50-year and the 100-year frequencies
were virtually the same at both the upstream end of the study and the downstream end of the
study. Using the relationship of flow per square mile from the known values, the flow values
for the selected hydrologic locations on the Gunnison which did not already have a detailed
floodplain study were calculated. The drainage areas at those points were simply multiplied by
' the flow per square mile. The flow per square mile selected from the existing data is 3.3 cubic
feet per second per square mile (cfs/miz) for the 50-year flow and 3.7 cfs/mil for the 100-year
' flow. Because the flow/drainage area relationship was so constant throughout the study reach,
no regression equation had to be computed.
' 3.3 Hydrologic Findings
Table 3 shows the results of this analysis in tabular form.

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