FLOOD02317

• County: Denver
• County: Arapahoe
• Community: Denver, Glendale, Arapahoe County
• Stream Name: Cherry Creek
• Basin: South Platte
• Title: Flood Hazard Area Delineation - Cherry Creek
• Date: 7/1/1976
• Prepared For: Denver / Glendale / Arapahoe County
• Prepared By: UDFCD
• Floodplain - Doc Type: Floodplain Report/Masterplan

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and dam removal, a flood on July 28, 1922, reached the
tops of the walls but did not spill over,

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Castlewood Dam failed on August 3, 1933, due to
heavy rains in the upper basin. When the dam burst, it
released 2,500 acre-feet of water causing the most
severe flood every recorded on Upper Cherry Creek.
Denver residents living along the creek were warned of
the impending flood, and many evacuated their homes.
The dam broke first at 12:10 A.M. along the east end,
then the center crumbled. Two walls of water came
through Denver - a three-foot wall at 5:40 A.M. and a
fifteen-foot wall at 6:18 A.M. The channel and the
concrete bridges held though the creek overflowed its
banks,

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Flood damages were estimated at $1,000,000 of
which $800,000 represented damages in Denver. It
took 2,500 men to clean up the flood debris,

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After this flood, city officials decided to built a
flood control dam at Kenwood, This dam was started
in 1935, It was an earth and rock fill dam which used
rock from Morrison, It was 4,000 feet long and had a
10,000 acre-foot capacity, In 1938, 600 WPA workers
began a $520,000 project to continue straightening and
rip rapping banks of Cherry Creek,

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In 1950, the U, S, Army Corps of Engineers
completed a much larger dam 1,000 feet upstream of
Kenwood Dam at a cost of $15,000,000, The capacity
of the new dam was 85,000 acre-feet and an

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emergency spillway was cut to Sand Creek. It was
built to handle a discharge of as much as 70,000 cfs
and is three miles long.

Since its construction, the Cherry Creek Dam is
estimated to have prevented $130,000,000 in damage
during the 1965 flood, While the South Platte and
other rivers flooded the city, the Cherry Creek
Reservoir impounded a flood which had a peak inflow
of 58,000 cfs and a volume of 16,000 acre-feet.

Presently, the dam is designed to release a
maximum of 8,100 cfs to Cherry Creek, whose present
capacity varies between 4,000 and 11,000 cfs, dependi-
ng on the obstructions in the creek bed.

HYDROLOGIC INFORMATION

a, Rainfall Data

Design rainfall values of the 100-year frequency
storm for the applicable townships and ranges
were taken from the tables given in RAINF ALL/-
RUNOFF INFORMATION.* These values were
weighted according to the basin area and a
composite rainfall was determined, The com-
posite rainfall values, which have been multiplied
by the appropriate factor to adjust for the
drainage basin area, are tabulated in Table 1.

*Urban Drainage and Flood Control District

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Table 1

100- Year Design Rainfall

Duration (hours)
Rainfall (inches)

2
2.79

3
3.16

4
3.86

24
4,55

1
2.20

b. Drainage Basin Areas

The drainage basin for Lower Cherry Creek was
determined from U.S,G.S. topographic maps and
divided into sub areas for use in the SWMM
program. The drainage basin and sub areas are
shown on Sheet 48 of the drawings.

c.

Runoff Coefficients

Runoff coefficients were determined by plotting
and measuring the various land use areas as
compiled from aerial photography and zoning
maps of the municipalities involved. The coeffi-
cients used herein are those for the future basin
conditions, The Future Land Use map is included
as Sheet 49 of the drawings.

d.

SWMM Calibration

The SWMM model was calibrated for the Cherry
Creek basin by computing the runoff for the May
6, 1973, storm and comparing the runoff with the
gaging record.