FLOOD10356

• Designation Number: 596
• County: Adams
• Stream Name: Comanche Creek, Wolf Creek
• Basin: South Platte
• Title: Floodplain Study - Comanche Creek and Wolf Creek - Technical Appendix
• Date: 5/1/2002
• Prepared By: McLaughlin Water Engineers, Ltd.
• Floodplain - Doc Type: Floodplain Report/Masterplan

06/2001 .
Urban Drainage and Flood Control District

R()..9

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DRAINAGE CRITERIA MANUAL (V. 1)

RUNOFF

TABLE RO-3 .
Recommended Percentage Imperviousness Values.
. .

Land Use or Percentage
Surface Characteristics Imoerviousness
Business:
Commercial areas 95
NeiQhborhood areas 85
Residential:
SinQIe-family *
Multi-unit (detached) .60
Multi-unit (attached) 75
Half-acre lot or laraer *
Aoartments 80
Industrial:
LiQht areas 80
Heavy areas ., 90
Parks, cemeteries 5
Plavarounds 10
Schools 50
Railroad yard areas 15
Undevelooed Areas:
Historic flow analvsis 2
Greenbelts, aariculturaJ 2
Off-site flow analysis 45
(when land use not defined)
Streets:
Pa~ed 100
Gravel (oacked) 40
Drive and walks 90
Roofs 90
Lawns, sandv soil 0
Lawns, clavev soil 0

* See Figures RO-3 through RQ-5 for percentage imperviousness.

Based in part on the data collected by the District since 1969, an empirical relationship between C and
the percentage imperviousness for various storm return periods was developed. Thus, values for C can
be determined using the following equations (Urbonas, Guo and Tucker 1990).

CA = KA + (1.3li3 - L44i2 + 1.135i - 0.12) for CA ~ 0, otherwise CA = 0

(RO-6)

CCD = KCD + (0.858e - 0.786i2 + 0.774i + 0.04)

(RO-7)

CB = (CA + CCD)/2

in which:

i =.% imperyiousness/100 expressed as a decimal (see Table RO-3)