FLOOD06791

• County: Hinsdale
• Community: Lake City
• Stream Name: Henson Creek
• Basin: Gunnison
• Title: Henson Creek Flood Control Improvements
• Date: 12/1/1985
• Prepared For: Lake City
• Prepared By: Westwater Engineering
• Floodplain - Doc Type: Project

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Tne San Juan Mountains in the study area are comprised primarily of
granitIc and volcanic rocks. Nu~erous rock outcrops are present. The
valley floors are comprised of alluvldl and c011u, .a. oeposlts or roc~s
from these sources. A thin layer of loam overlies the valley floor
deposits in some areas.
Characteristics of Different Reaches
The study reaches for Lake Fork of the Gunnison River and Henson Creek are
shown on Plate 1a. The lower reach of the Lake Fork of the
Gunnison River extends downstream approximately 2 miles from the confluence with
Henson Creek through the San Juan Ranch resort. The upper reach of detailed
study of the Lake Fork of the Gunnison River extends upstream approximately
0.7 miles from the confluence with Henson Creek to about 700 feet below Crooks
Falls. Approximate 100-year flood elevations have been estimated for the
700 foot stretch of river between the last upstream cross-section and Crooks
Falls. The Henson Creek reach extends about 0.33 miles upstream from its mouth
through the city limits. The Lake Fork was divided into two separate study reaches
since peak flows used in analYSis are different above and below the confluence
with Henson Creek.
The stream valley of the Lake Fork within the study reaches is generally
characterized by a relatively flat flood plain, 600 to 800 feet wide, situated
between steep, heavily wooded mountain slopes which rise to over 10,000 feet
on either side. The flood plain consists of alluvial deposits of boulders,
cobbles and sand with an overlying layer of topsoil. Occassional outcrops of
bedrock can be found along the stream channel. Vertical bluffs - 20 to 60 feet
high - border the Lake Fork on the northeast part of Town. The flood plain is
subject to erosion and extreme changes in the stream channels from floods.
Henson Creek emerges from the mountains through a narrow gorge onto the
Lake City flood plain. Both streams flow in well-defined channels within the
flood plain. The Lake Fork of the Gunnison has a tendency to meander, whereas
Henson Creek tends to be more confined to its existing channel (see Plates 16
through 24 for cross-sections of channels of both streams). Over the years,
the adjacent banks of both channels have been built up by the Town and County
in an attempt to control the location and reduce erosion potential from flood
flows. However, future floods will continue to exert pressure to shift stream
channels as they have in the past.

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