Lower South Platte River Study

• Contractor Name: Colorado Water Conservation Board
• Loan Projects - Doc Type: Feasibility Study

Lower South Platte River Study
Colorado Water Conservation Board
' December 2001
Cottonwood Creek
The proposed Cottonwood Creek Reservoir site is located about 24 miles upstream
of the Nebraska State line on the Lower South Platte River, 6.2 miles northwest of
Sedgwick, Colorado. The site is within a broad valley with an incised meander at the
bottom, moderately steep abutments, and Brule bedrock outcrops exposed near the
' proposed axis. Bedrock is expected to be relatively shallow along the dam axis.
Cottonwood Creek and one of its tributaries run directly through the reservoir site,
and there are wetland areas present on the site according to USFWS mapping. The
' reservoir would be created by a zoned embankment with a height of 60 feet and a
crest length of 2,600 feet. The storage volume and normal maximum pool elevation
would be 4,000 acre-feet and 3,760 acre-feet, respectively. One source of water to
fill the reservoir would be by pumping water from Julesburg Reservoir. The
contributing drainage area to the reservoir is 8.7 square miles. It would be necessary
' to relocate a road running along the south side of the reservoir, and there are several
buildings located near the proposed site. The land for the proposed reservoir site is
privately owned. The total cost to build the reservoir is estimated to be$7,150,000,
por$1,790 per acre-foot of storage.
Johnson
' The proposed Johnson Reservoir site is located about 27 miles upstream of the
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' Nebraska State line on the Lower South Platte River, 5.7 miles northeast of Crook,
Colorado. The proposed site is located within a broad valley with moderately steep
abutments. There are several cemented sandstone erosional remnants near the dam
' axis alignment. About half of the proposed reservoir basin area is located on state-
owned lands according to BLM land use mapping, with the remainder being
privately owned. There are no buildings on the reservoir site. The dam would be a
zoned embankment with a height of 70 feet and a crest length of 4,300 feet. The
reservoir would have a storage capacity of 10,600 acre-feet with a normal maximum
pool at Elevation 3790. The reservoir could be filled from the North Sterling Outlet
' Canal or by pumping water from the Harmony Ditch. The contributing drainage
area to the reservoir is estimated to be 4.2 square miles. USFWS wetlands
' delineation mapping and field observations indicate the presence of wetlands in the
potential reservoir basin. The wetlands appear to be isolated and may not be
jurisdictional because of their isolation from waters of the U.S. The total cost to
build the reservoir would be $11,820,000, while the cost per acre-foot of storage
would be $1,120.
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GEI Consultants, Inc. 4-12 01002 Dec 2001 Lower South Platte River Study