FLOOD01592

• Designation Number: 248
• County: Hinsdale
• Community: Lake City
• Stream Name: Lake Fork of the Gunnison River and Henson Creek
• Title: Floodplain Information Report - Lake Fork of the Gunnison River and Henson Creek, Lake City, Colorado
• Date: 10/1/1985
• Designation Date: 1/1/1986
• Floodplain - Doc Type: Floodplain Report/Masterplan

Cralnage BaSins and CharacterlSt!CS
;he JDper 1rainage basi1s or Henson Creek and the Lake Fork Of the
Gunnison are similar in area ana physical characteristics. Henson
Creek has a drainage area of 'l1.Q S!luarerniles. The Lake Fort or tne
GunnIson has a drainage area of 146.8 sQuar~ miles above the mouth or
Henson Creek. Henson Creek flows primarily in an easterly direction with
tributaries coming in from the ~rth and south. The Lake Fork of the
Gunnison initially flows easterly in the upper half ane in the lower half
it takes a long, 90Q bend northward before entering Lake City.
The following information on the Lake Fork of the Gunnison was
taken from reference ~2.
Mean8asinElevatlon-l1.500ft. Land Use:

ChannelSlope-.396
Channel Length-23.7m1.
Basin Length - 13.8 rni.
Basinlolidth-B.3mi.
Channel Aspect-74Q
Basin Aspect 550
Henson Creek has a similar elevation, topography and land use.

Forest - 66%
Agrlcultur€' 0
Rang€' 28%
Water 0
Urban 1'1;

T~e San Juan Mountair.s In the study area are comprised primarily of
granitic and volcanic rocks. Numerous rock outcrops are present. The
valley floors are cornpri sed of allu~ I ai and co llu'! i a: sepos i ts or rockS
fram these sa~rces. A thin layer of loam o~er:ies 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 la. 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 Ri~er extends upstream approximately
D.7milesfromtheconfluence'ilithHensonCreektoabout700feet 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 upstreal1lfrom 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.
Tne 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
~n either side. The flood plain consists of aliuvial 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 _ oorderthe Lake Fork on the northeast part of Town. T~ 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. 80th streams flow tn well-defined channels within the
flOOd plaln. Tile Lake Fork of the Gunni>on has" t.:;nd;;ncy to "1;;Jn;:::~)'". ;;herCJ;
~enson 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 bullt up by the Town and County
in an atte~pt to control t~e location and reduce erosion potential from flood
flows. Howe~,"r, future floods ~i 11 conti nu€ to exert pressure to shi ft stream
channelS as they ha~e in the zast.

Elevations in the study area range from over 14,000 feet in the
western headwaters to 8670 feet at Lake City. Topography, particuldrly
In tne side bdsins andhNdwaters. is very rugged and steep. Trltlutar:es
may drop 3,000 to 4.COO feet over 3 to 4 miles. The main valleys of the
Lake Fork and Henson Creek have a more gentle gradient belOW 10,000 feet.
Three types of vegetation zones are present in the study area: Alpine,
Sub~alpine and Montane. Grasses and sedges grow in the tundra zone
above tree line. The trees are comprised primarily of spruce, fir and
aspen. with sorne cottonwoods in the valley floor. In the lower areas,
there are some irrigated pastures and sagebrush meadows.
Approximately 300 acre feet of irrigation water are diverted annually
on the Lake Fork above Lake City. The Lake Fork also flows through Lake
SanCristobal.anatural1akecreatedbyalargernudslideintheearly
1900s. '~hICh attenuates its flows. There are no dl versions or dams of
significance on Hensen Creek.

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