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
Julesburg Reservoir Enlargement
Julesburg Dam and Reservoir are owned by the Julesburg Irrigation District. The
reservoir is off-channel and is supplied by the Harmony Ditch, which diverts water
from the South Platte River. Decreed storage is 22,700 acre-feet (April 7, 1904 filing
No. 1377) at Gage Height 24.0, which corresponds to Elevation 3707. The nominal
dam crest is at Elevation 3715. The 1,400-acre reservoir is formed by five
embankment dams. The dams are numbered from west to east, with Dam No. 1
located at the southwest edge of the reservoir. Dams No. 1A, 2, and 3 are located on
' the side of the reservoir, and Dams No. 4, 4 (Dike), and 5 located on the west edge of
reservoir. Dam No. 4 incorporates the reservoir outlet works, which discharge to the
Highline Canal. Dam No. 5 incorporates the emergency spillway. Descriptions of
the dams are provided in the following paragraphs. These descriptions are from a
1998 report by W.W. Wheeler& Associates and Kumar&Associates on enlarging
' Julesburg Reservoir(Wheeler-Kumar Report, 1998). Significant wetlands have
developed around the reservoir and below the dams.
Dam1
Dam 1 is an approximately 2,500-foot-long earthen embankment. The upstream
slope of the embankment is approximately 2.8:1 (horizontal:vertical) for a height of
12 feet, below which there is a considerable silted area with a significantly flatter
slope. The downstream slope varies between 1.7 to 2.6:1.
Considerable seepage has been observed downstream of Dam 1. The seepage is in
' the form of point discharges at a few locations and seepage exiting at the interface of
the overburden and bedrock. Small gullies have been formed by point discharge
flows. Slope stability analyses performed indicate an adequate factor of safety for
this embankment if the seepage level on the downstream slope is below Elevation
3690. Seepage above this elevation has not been observed.
Dam 2
Dam 2 is approximately 1,700 feet long and is the tallest of the Julesburg Reservoir
embankments, with a maximum height of 65 feet and a crest width of approximately
20 feet. The upstream face of the dam is paved with concrete for slope protection,
' and includes a 3-foot-high concrete parapet wall for wave runup protection. The
upstream slope of the dam varies from 1.5 to 1.7:1. The downstream slope of the
' dam is non-uniform, varying in slope from 1.5:1 at the abutments to approximately
2.5:1 at the maximum section. A stabilizing berm constructed at the base of the
downstream slope in 1992 is 20 feet wide at the top and has a slope of 3:1.
GEI Consultants, Inc. 4-6 01002 Dec 2001 Lower South Platte River Study