WSP07002

• File Number: 8449
• Description: Platte River Studies
• State: CO
• Basin: South Platte
• Date: 2/1/1991
• Author: City of Greeley
• Title: Feasibility Study for Rehabilitation of Hourglass Dam and Reservoir Vol. 1
• Water Supply Pro - Doc Type: Publication

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flowing water. The outlet control gates were operated at the time of our visit. and appeared
to be functioning adequately. The discharge channel downstream of the energy dissipator
appeared to be functioning well. There were no signs of significant sloughing or undercutting
of the energy dlssipator. (Note: The Slate Engineer's Inspection report of July 30, 1985
indicates that the Interior of the outlet conduit had been inspected in November of the previous
year, and appeared to be in good condition.)

5.2.4 SPILLWAYS

The service spillway for Hourglass Reservoir is a side channel spillway located in the feeder
ditch which comes from Comanche Reservoir. This spillway Is lined with riprap and appears
to be in good cond~ion, with no undercutting, movements of riprap. or erosion. The emergency
spillway for Hourglass Reservoir is an unlined earth-cut channel at the exlreme righl end of Ihe
embankment The unlined spillway does not show any signiflcanl erosion or sloughing of the
side slopes. The reservoir operational records indicate that the emergency spillway has not
been used.

5,2,5 SUMMARY OF DEFICIENCIES

Based on our reconnaissance and the review of historical information, several areas of
deficiencies have been noted. Seepage problems have been noted In both abutments of the
main embankment at the downstream toe, downstream of Ihe dam along the discharge channel,
at the downstream toe of the dike at about Station 114+00, and the Corps of Engineers
inspection from 1980 reported seepage exiting the morainal ridge 300 to 400 feet downstream
of the embankment The seepage hlslory of the reservoir indicates that the embankment and
foundation materials are highly pervious. Continued. uncontrolled seepage could lead 10 material
migration and loss of embankment stability,

Several areas of the embankment appear to be susceptible to erosion damage, Only the central
part of the main embankment Is covered with riprap on the upslream face, The remaining
portions of the upslream face of the main embankment show minor erosion damage in the form
of small wave scarps. In the past, the leII groin of the downstream face of the main
embankmenl has eroded badly. The repairs which were made were nol permanent and the
potenlial for erosion of the downstream face still exists. The emergency spillway is unlined. and
the left side is formed by an apparently uncompacted dike. In the event that the emergency

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