FLOOD06183

• County: Douglas
• Community: Denver, Douglas County
• Stream Name: Dad Clark Gulch
• Basin: South Platte
• Title: Flood Hazard Area Delineation
• Date: 5/1/1981
• Prepared For: Denver, Douglas County
• Prepared By: UDFCD
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Time
(Min. )

DE5IGN

% of
I-Hr. Depth

5
10
15
20
25
30
35
40
45
50
55
60

1
2
4
8
15
25
14
8
5
5
4
4

I-Hr. De pt h = 2. 56 in.

TABLE 1
100-YEAR RAINFALL PATTERN

Depth
(In. )

.03
.05
.10
.20
.38
.64
.36
.20
.13
.13
.10
.10

Time
(Min.)

65
70
75
80
85
90
95
100
105
110
115
120

the rel at ions shown in Figure 1 and the equat ion:

Ct = Kt

(L L )0.14
ca
50.22

% of
I-Hr. Depth

In this equation L is the basin length (mi), Lca is the distance from
the outlet to the centroid of the basin (mi) and 5 is the basin slope
(ftlft). The values of L, Land 5 were determined from a topographic
ca
map for each of the subareas used in the study. As ment ioned earl ier, the
basin slope values used in this analysis ignore the existing check dams
which have been placed in the flood plain by previous land owners since
these check dams are not considered permanent structures. The percent
imperviousness needed for finding Kt and Cp was estimated using a
composite building density versus percent imperviousness for Arapahoe
County shown in Figure 2. The housing density was determined from the
proposed development plan for Highlands Ranch which includes the Dad Clark
Gulch drainage area. For development such as commercial business, in-
dustrial or school sites, or for areas of housing densities greater than 5
units per acre, percent imperviousness was estimated by analyzing indi-
vidual site plans for such areas and/or similar existing developments ,in
Arapahoe County. The imperv iousness ranged from 5 percent for open space
to 75 percent for community centers and industrial parks.

Depth
(In.)

4
2
2
2
2
2
1
1
1
1
1
1

.10
.05
.05
.05
.05
.05
.03
.03
.03
.03
.03
.03

2-Hr. Depth = 2.95 in.

The entire basin was divided into 13 sub-basins or subareas so that Q's
could be determined at a number of locations. These subareas are identi-
fied on the Basin Boundary Map found in the Appendix of this report (sheet
1 of 23 of the drawings). The physical characteristics and hydrograph
parameters for each of these subareas as well as the entire basin are
tabulated in Table 2. The CUHP computer program was used to find the peak Q
(IOO-year, future development) at the downstream end of each of the 13
subareas. The Q at a point was computed by 1 umping in succesion all the
contributing areas into singular subareas. The Q100 values calculated

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