FLOOD01349

• County: Arapahoe
• Stream Name: Cherry Creek
• Title: Engineering Division Technical Report Cherry Creek Watershed
• Date: 12/1/1991
• Prepared For: Arapahoe County
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Flood Documentation Report

discharges are increased 25 and 50 percent while the total
volume is held constant. The unit hydrograph and hydrographs
peaked 25 and 50 percent are shown in Figure 4. The IDF
results for the 25 and 50 percent peaked unit hydrographs are
presented in Table 4 and the inflow and outflow hydrographs
and reservoir water surface elevations are shown in Figures 7
and 8. The HEC-1 input data file is shown in Figure 10.

Table 3
IDF Rainfall and Runoff
cherry Creek Basin above cherry Creek Reservoir

Time
(hours)
1-12
12-24
24-36
36-37
37-38
38-39
39-40
40-41
41-42
42-43
43-44
44-45
45-46
46-47
47-48
48-60
60-72

Rainfall
Cinches)
0.39
0.87
3.87
0.38
0.63
0.92
1. 33
2.00
2.92
7.83
2.25
1.50
1. 00
0.75
0.62
1. 38
0.58
29.22

Loss
(inches)
0.39
0.87
3.87
0.38
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
1. 38
0.58
12.97

Runoff
(inches)
o.
o.
o.
O.
0.13
0.42
0.83
1. 50
2.42
7.33
1. 75
1. 00
0.50
0.25
0.12
O.
o.
16.25

5. Reservoir Routinq
a. Methodology. Using HE.C-.1, reservoir storage and
outflow was determined by recelvlng upstream inflows and
routing these inflows through the reservoir according to the
Modified PuIs routing method. This method uses a storage
volume versus elevation relationship and an outflow capacity
versus elevation relationship. The area capacity curve used
for Cherry Creek reservoir was developed from 1975 surveys of
the lake. The spillway rating curve for the existing
spillway was taken from "Design Memorandum No. CC-ll,
Spillway Performance Review, South Platte River, Cherry Creek
Lake, Colorado," dated January 1985.

b. Assumptions. The initial pool level in the Cherry
Creek reservoir routing was a half full flood control pool,
elevation 5,579.0 ft-m. s .1., since the outlet works can be
used to draw down a full flood control pool to half full

8