FLOOD02445

• County: Hinsdale
• Community: Lake City
• Stream Name: Henson Creek
• Basin: Gunnison
• Title: Technical Addendum Floodplain Information Report Lake Fork of Gunnison River
• Date: 10/1/1985
• Prepared For: Lake City
• Prepared By: Westwater Engineering
• Floodplain - Doc Type: Floodplain Report/Masterplan

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CHAPTER IV
HYDROLOGIC ANALYSIS

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Flood Characteristics
Most of the annual flood flows on Henson Creek and the lake Fork of the
Gunnison within the study area result from rapid springtime melting of the
snow pack in the high mountain basins, which comprise the majority of the
drainage area for both streams. According to availa?le stream flow records,
peak flows occur primarily from May through early July. Snow melt may
occasionally be augmented by rain. Stream flows from snowmelt runoff are
characterized by sustained periods of high flow and marked daily fluctuation.

Periods of thunderstorm activity normally occur during the summer months
after the high runoff has receeded. Cloudbursts are normally localized and
only occasionally produce high flows in the stream. A review of available
runoff records indicate only one summertime peak flow (outside the normal
runoff period).

Methods of Analysis
A hydrologic analysis was carried out to establish peak discharge frequency
relationships for floods of 10-, 50-, 100-, and SOO-year recurrence intervals
for the Lake Fork of the Gunnison and Henson Creek in the study area,

Streamflow records are available for 9 years on Henson Creek (1918 - 1937)
and for 14 years on the lake Fork of the Gunnison (1918 - 1937). The gauging
station on the Lake Fork is located % mile upstream of the Henson Creek confluence.
The gauging station on Henson Creek is located 1~ miles above its mouth.

Peak flows calculated from the on stream records were compared to fifteen
other gauging and study sites in nearby similar basins. These fifteen sites
were chosen for the comparison because of the high correlation between
basin characteristics such as slope, precipitation, elevation, size and
vegetation. Table 1 lists basin characteristics of these streams. Peak flows
from six of these'stations are from the U.S.G.S. Open File Report 84-137
(reference 2 ) and were determined using Log-Pearson Type III analysis as
outlined by the Water Resources Council. Peak flows for these six stations
are listed in Table 2. Peak flows from the remaining nine sites are from
.~ recent flood insurance or flood plain reports and may include heavier weighting
~ on preCipitation analysis than the U.S.G.S. flows. Table 3 shows the peak
~ discharges from these streams.

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