FLOOD03140

• County: Denver
• Community: Aurora, Denver
• Stream Name: Westerly Creek
• Basin: South Platte
• Title: Flood Hazard Area Delineation
• Date: 1/1/1977
• Prepared For: Aurora, Denver
• Prepared By: UDFCD
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

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7

Table 2

Drainage Basin Parameters

Rainfall Data

The drainage basin parameters used in this study for nine

subareas are listed in the following table. Subareas are

Storm Frequency

Rainfall Depth (inches)

shown on Drawing No.3.

2-year

1.19

2-year frequency

1.0 inch/hour

0.5 inch/hour

Table 3
Drainage Basin Parameters
Future Average
Subarea Area Length L Imperviousness Slope Ct C
e." p
(sq mile) (mile) (mile) (%) (%)
1 2.21 1. 67 0.89 60 2.0 0.20 0.54
2 0.43 0.66 0.49 40 2.0 0.24 0.60
3 0.97 1.71 0.49 40 1.0 0.24 0.60
4 1.16 1. 74 0.89 60 1.0 0.20 0.54
5 3.12 1. 95 1. 27 45 0.9 0.23 0.59
6 3.90 2.63 1. 91 50 0.8 0.22 0.57
7 0.86 1. 46 0.81 40 0.8 0.24 0.60
8 2.51 2.46 1.12 50 1.0 0.28 0.48
9 2.42 1. 38 1. 00 50 0.6 0.28 0.48
Note: Definition of syrnbols.- refer to the "Urban
Storm Drainage Criteria Manual" of Urban
Drainage and Flood Control District

10-year

1.60*

100-year

3.11

SPF

5.63

Losses

We have applied the following loss factors from the Colorado

Urban Hydrograph Procedure in computing flood runoff:

1. Infiltration Losses:

First 1/2 Hour

Second 1/2 Hour

10-year frequency
and greater

0.5 inch/hour

0.5 inch/hour

2. Detention and Depression Storage:

Impervious area

0.1 inch total

Pervious area

0.3 inch total

3. Residual Loss (Impervious Area):

5 percent of incremental rainfall minus Detention
and Depression Storage

Floodflows and Design Hydrographs
The floodflows at various locations were determined by unit

* The rainfall depth of the 10-year storm is 2.29 inches in

hydrograph, storm runoff and flood routing procedures. The

the Rainfall/Runoff Information. It was modifed to 1.60

unit hydrograph and the storm runoff were determined according

inches as suggested by the Corps of Engineers, Omaha District,

to the Colorado Urban H~aph Procedure. The Modified Puis

while developing the Report on Drainage Master Plan for

Method was used to define flood discharges at specified

Westerly Creek, Camp Dresser & McKee, Inc., January, 1976

locations with consideration of storage effects. Corps of