FLOOD02883

• Designation Number: 266
• County: Broomfield
• Community: Broomfield
• Stream Name: Quail Creek & Tributaries & McKay Lake Basin
• Basin: South Platte
• Title: Flood Hazard Area Delineation - Quail Creek and Tributaries and McKay Lake Basin, Broomfield, Westminster
• Date: 7/1/1986
• Designation Date: 11/1/1986
• Floodplain - Doc Type: Floodplain Report/Masterplan

Rainfall
Rainfall data were obtained for the 10- and 100-year storms from the "Flood Hazard
Area Delineation (FHAD) - Broomfield Area" study by Wright-McLaughlin Engineers,
June 1979 (Reference 4). The rainfall data from this study had been developed
using Volume III of the NOAA "Precipitation-Frequency Atlas of the Western United
States" (Reference 5). The rainfall hyetographs for the various storm frequen-
cies are shown in Table 2.

.30
.60
.69
.78
1.32
1.86
3.24
4.62
2.97
1.32
1.05
.78
.63
.48
.39
.30
.27
.24
.24
.24
.21
.18
.18
.18

.48
.96
1.02
1.08
1.98
2.88
5.04
7.20
4.65
2.10
1.62
1.14
.81
.48
.42
.36
.33
.30
.30
.30
.30
.30
.28
.24

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

HYDROLOGIC ANALYSES

TABLE 2
QUAIL CREEK AND McKAY LAKE BASINS
RAINFALL HYETOGRAPHS (inches/hour)

Introduction
Hydrologic model 1 ing was used to develop the runoff estimates from the Quail
Creek and McKay Lake basins because historic stream flow measurements were not
available. The UDSWM2 program was used to determine the runoff hydrographs in
various conveyance elements along the drainageways. UDSWM2 (Reference 1) is the
name assigned by the Urban Drainage and Flood Control District (UDFCD) to the
Runoff Block of the Environmental Protection Agency's, Storm Water Management
Model (SWMM) program (Version 2) as modified by UDFCD and the Missouri River
Division of the U.S. Army Corps of Engineers (Reference 2). In an effort to make
the results of the UDSWM2 program more representative of rainfall/runoff data
collected within the UDFCD, the model was calibrated against the Colorado Urban
Hydrograph Procedure (CUHP) (Reference 3). Frequency discharges were developed
for each of the drainageways in this study for the 10- and 100-year storm events
using the UDSWM2 model.

UDSWM2 Model
The procedure for developing the mathematical abstraction of the actual drainage
basin is to divide the major basin into subcatchments that drain to conveyance
elements, then connect these conveyance elements to create a model of the drainage
system. Figure 1 shows the subcatchments, conveyance elements and various design
points for the Quail Creek and McKay Lake watersheds.

Time
(min)

5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
115
120

10-Year

100-Year

The coefficients and parameters necessary to characterize hydraulic properties of
the subcatchment areas include the surface area, width, ground slope, roughness
coefficient, surface retention depth, infiltration rate, and percent impervious-
ness. The subcatchment parameters used for the Quail Creek basin are shown on

..