FLOOD07213

• Designation Number: 85
• County: Adams
• County: Arapahoe
• County: Douglas
• Community: Denver Metro Region
• Stream Name: Weir Gulch Tributaries
• Basin: South Platte
• Title: Flood Hazard Area Delineation - Weir Gulch Tributaries, 1st Avenue and Dakota Avenue - Lakewood and Denver, CO
• Date: 7/1/1977
• Designation Date: 11/1/1977
• Floodplain - Doc Type: Floodplain Report/Masterplan

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off from the rainfall data:

Flood Flows and Design Hydrographs
For every subbasin listed in Table 2 above, a design hydrograph was calculated
in accordance with the Colorado Urban Hydrograph Procedure using the computer
program developed by Leonard Rice Consulting Water Engineers. The subbasin

1. Infiltration:

Frequency

Second 1/2 Hour
To End of Storm

Fi rst 1/2 Ho_ur

1.0 inch/hour
.5 inch/hour

5-Year
10-Year and Greater

.5 inchlhour
.5 inchlhour

hydrographs were routed downstream to the next design point by estimating
the lag time as the travel time based on one half of the design peak flow.
The Puls Method was used to calculate discharges at locations where storage

2. Detention and Depression Storage:

Impervious Area - .05 inch total
Pervious Area - .3 inch total

had a significant effect. The peak discharges which are inflow peaks at the

3. Residual Loss for Impervious Areas:
5 percent of i I1crementa 1 ra i nfa 11 mi nus Detenti on and Depress i on Storage

design point are listed in Table 3 for each design year freq uency .
TABLE 3
fEAK DISCHARGE AND FREQUENCY
5-Year 10- Year 50-Year 100-Year
Loca ti on cfs cfs cfs cfs
S-l (INCL S-B) 220 500 760 840
S-2 240 410 560 630
S-3 60 110 160 180
0-1 190 310 420 470
0-2 140 230 320 350
0-3 70 130 190 220
0-4 135 190 240 260

Drainage Basin Parameters
Each of the two main basins is divided into subbasins. Designations and design
points are S-l, S-2, and S-3 for the 1st Avenue Tributary, and 0-1,0-2,0-3,
and 0-4 for the Dakota Avenue Tributary. Locations are shown on Sheet No.1
of the drawings. Percent of imperviousness was calculated by using a typical
residentially developed block, calculating the imperviousness and estimating
the percentage of developed and undeveloped area. Commercial and undeveloped
areas were estimated separately.

For location of design points, see Drawing No.1

HYDRAULICS

The HEC-2 computer program as developed by the Corps of Engineers was used to

calculate the water surface profile for the 10 and 100-year floods. In 10ca-

TABLE 2
DRAINAGE BASIN PARAMETERS3

Area
(Sq. r1iles)
.68
.64
.19

Future
Length L Avg. Slope Imperviousness Ct l
(Miles) ca Percent Percent
1. 78 .66 1.5 35 .49- .64
2.13 .95 1.5 37 .47 .63
1. 20 .41 1.5 25 .63 .72

and overland flow was determined by defining head-discharge relations for each

culvert using Engineering Circulars No.5 and 10 as published by the U.S. De-

tions where the results from the HEC-2 program needed clarification, the slope-

Subbasin
S-l
S-2
S-3
Total 1st
Ave. Basin- 1.51

0-1 .17
0-2 .19
0-3 .23
0-4 .13
Tota 1 Dakota..--
Ave. Basin- .72

area method was used. The capacity of culverts and the division between culvert

.68
.64
.78
.47

partment of Commerce, Bureau of Public Roads. The Puls method of routing was
applied where reservoir storage affected the water surface. Digitized cross-
sections and mapping, 1"=100' with 2 feet contours, was provided by the Urban

.69
.53
.73
.61

1.0
1.5
1.5
1.5

.35
.26
.45
.30

30
35
20
85

.55
.49
.75
.24

Drainage and Flood Control District. The conditions of the channel and flood

3The symbols used in this table are defined in the "Urban Storm Drainage Cdteria
Manual" .