FLOOD03304

• County: Statewide
• Community: State of Colorado
• Stream Name: All
• Basin: Statewide
• Title: Colorado Flood Hydrology Manual
• Date: 1/1/1995
• Prepared For: State of Colorado
• Prepared By: CWCB
• Floodplain - Doc Type: Educational/Technical/Reference Information

6. COLORADO URBAN HYDROGRAPH PROCEDURE (CUHP) (From Yiessrnan, Lewis,
Knapp)

The Colorado Urban Hydrograph Procedure provides 5-minule synthetic unit
hydrographs for use in the Denver metropolitan area. It is based on Snyder's method and
is considered applicable to watersheds in the size range from 90 acres to 10 square miles,
with "regular" shapes (length = 4 times width). it was developed in the early 1980s and
modified in 1984 to reflect refinements from early applications. In its pre-1984 form, the
Synder/cUHP C, and Cp values are:

Ct - 7.81
- p~.7li

(IY-15)

Cp = 0.89 C,O.46

(IY-16)

Where p. is the percent imperviousness. These regression equations were developed for
p. > 30%, using data for 96 storms over 19 IJrban watersheds. The given equations apply
to normal watersheds conditions and need to be adjusted for steep, flat, or sewered
basins. If an urban area is fully sewered, the calculated C, from Eq. (IY-15) is decreased
10%. If sparsely sewered, a 10% increase is made. If the average slope, S of the lower
80% of the main water course is flat (less than 0.01 Wit) the C, value becomes:

C,

3.12
p~. 78 SO.2

(IY-17)

and for steep areas (S>0.025 ftIft):

C,

3. 75
F"'.; 78 So. 2

(IY-18)

The Cp coefficient is determined from Eq. (IY-16) and adjusted to 10% up or down for fully
or sparsely sewered conditions, respectively.

For CUHP applications equations for widths of the unit hydrograph are:

l-\o = 500 A
Qp

(IY-19)

Colorado Flood
Hydrology Manual

7-44

a=w=r