FLOOD03582

• County: Adams
• Community: Westminster
• Stream Name: Big Dry Creek and Tributaries
• Basin: South Platte
• Title: Final Hydrologic Analysis Report for Big Dry Creek and Tributaries
• Date: 1/1/1984
• Prepared For: Westminster
• Prepared By: MSM Consultants, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

-
-

2.5 Impervious Calculation

.

The percent of imperviousness for each sub-bas in was

determined from a recent aerial photograph of the study

.

area (Reference 11). A land use map (Sheet 2) located

at the back of the Appendix was developed from the

aerial photograph of the study area.

Typical

.

impervious values were assigned to each land use and

are listed in Table 2.

These values were obtained

from current UD&FCD drainage criteria. For a sub-basin

.

consisting of more than one land use designation, a

compos i te value was determined. The impervious values
for each sub-basin are listed in the Appendix.

.

TABLE 2

PERCENT UlPERVIOUS VALUES

.

Land Use Percent Imperviousness
Single Family Residential
Normal Density (4.4 D.U./Ac) 40%
Low Density (1.6 D.U./Ac) 30%
Multi-Family Residential 60%
Commercial and Industrial 80%
Open Space 5%

.

2.6

Stream Routings

.

For the stream routing analysis, a typical stream

cross-section for each sub-basin was determined for use

.

in the Hodified PuIs routing method. The HEC-l program

.