WSP05425

• File Number: 8101
• Description: Arkansas River Basin Description
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 9/1/1962
• Author: High Plains SCD
• Title: Watershed Work Plan - Limon Watershed Protection Project - Elbert and Lincoln Counties - Colorado
• Water Supply Pro - Doc Type: Report/Study

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O~1777

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Principal spiUvlays are planned to be 3~-inch 1. D, reinforced
concrete pipe barrels with encasement and drop inlets. Entrances
of the drop inlets are set at the respective sediment pool elevations.
The drop inlets will be so designed as to control the principal
spillway peak discharges to the following respective maximums:
L-l = 63 c.fns.; L-2 = 32 c.f.s.; and L-3 = 32 c.f.s.

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Design criteria for emergency spillway capacities are in the
"Hydrology and Hydraulics'" section of this work plan,

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The three proposed floodwater-retarding structures are classified
as Class "c" based on the interpretation of Engineering Memorandum
SCS-27, revised. Capacities for sediment storage are provided to
contain the estimated sediment accumulation at the sites for the
next 50 years, The floodwater-retarding capacities are based on a
runoff of 2.5 inches, which exceeds the estimated flood event
having a frequency of occurrence of once in 100 years. There is
no permanent storage in these structures, A typical structure is
shovffi in Figure 2, Structure data for the three proposed structures
is listed in Table 3.

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Geologic Investiqations

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A preliminary geologic investigation was made at the proposed
floodwater-retarding site L-l, This investigation consisted of
drilling several test holes along the dam centerline with a power
auger, Bedrock at the dam site is the Pierre shale of Cretaceous
age. The valley bottom at the site is underlain by silty clay
alluvium with a maximum thickness of about 30 feet. In the
abutments the shale surface rises to within 5 to 10 feet of the
ground slirface.

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An inspection was made at proposed sites L-2 and L-3, and
geologic conditions at these sites appeared to be similar to those
at L-l. The foundation materials at all three sites appear to be
satisfactory for the type of structure proposed, The emergency
spillway will be excavated into shale or silty clay alluvium,
either of which should be relatively resistant to erosion.
Adequate amounts of satisfactory borrow material are available
within the reservoir areas.

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