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FLOOD09590
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Last modified
1/26/2010 10:09:48 AM
Creation date
10/5/2006 4:28:51 AM
Metadata
Fields
Template:
Floodplain Documents
County
Arapahoe
Community
Aurora
Stream Name
Cherry Creek Lake
Basin
South Platte
Title
Hydrologic Improvement Assessment Cherry Creek Lake
Date
9/1/1993
Prepared For
State of Colorado
Prepared By
US Army Corps of Engineers
Floodplain - Doc Type
Project
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<br />for the first 8,500 feet and a 1.000-foot transition to a 45-foot bottom width <br />for the remaining 2,600 feet of the excavation, The spillway channel was <br />excavated into overburden with IV on 2H side slopes and int.o the Denver Formation <br />with IV on IH side slopes. All of the excavated material was placed in spoil <br />banks adjacent to both sides of the spillway, These spoil banks had 50-foot top <br />widths and side slopes of IV on 3H. The toe ':Jf the spoil banks was maintained <br />35 feet from the top edge of the excavation. The maximwn depth of cut was about <br />77 fe"et. It was intended that when the ultimat:e project design was implemented, <br />the spillway would be modified by placing an ungated ogee weir with a crest <br />elevation of 5623 feet m.s.l. and an 18-foot '.'ide notch to elevation 5598 feet <br />m. s .1. in the spillway. Inunediately downstream of the ogee structure, the <br />spillway invert base was to be excavated to elevation 5567 feet m, s .1, The <br />modifications were never made to the project as explained in the general <br />description section of this report. Plate 16 shows a plein, profile. and typical <br />sections of the spillway as designed without t:he spillway modifications, Since <br />construction of the spillway, the steep IV on IH side slopes in t.he Denver <br />Formation have weathered badly and sloughed off into the spillway channel. Due <br />to a combination of weathering and inadequate maintenance, the effective crest <br />of the spillway has been raised by about 11 feet to approximately elevation 5609 <br />feet m.s.l, The original spillway profile is plotted agaLnst spillway profiles <br />surveyed in 1975, 1980, and 1982, as shown on plate 17. <br /> <br />Tree growth and other vegetation have flourished wi thin the spillway and <br /> <br /> <br />runoff water collects in several depressed areas. The trees and ot:her heavy <br /> <br />vegetation have the potential for debris blockage which could drastically reduce <br /> <br /> <br />the spillway capacity. A contract was awarded in 1983 to remove the trees in the <br /> <br /> <br />invert of the spillway and 10 feet up the side slopes. This was accomplished in <br /> <br />December 1983, <br /> <br />OPERATION AND MAINTENANCE HISTORY <br /> <br />The basic responsibility for operation and maintenance of the Cherry Creek <br /> <br /> <br />Dam and Reservoir has been delegated by the District Engineer to the Area <br /> <br />13 <br />
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