FLOOD10043

• County: Larimer
• Community: Fort Collins
• Stream Name: Fossil Creek
• Basin: South Platte
• Title: Documentation for Selection of Manning's Roughness Coefficient for Fossil Creek Master Drainageway Planning Study
• Date: 12/1/1981
• Prepared For: Larimer County
• Prepared By: Simons Li & Associates Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Table 1. Criteria Used for the Selection of Manning's Roughness
Coefficient, n I and the Source of the Information.

I

Average n

Source

Description of Flow Conditions

I

Natural Streams

I

Minor Streams on Plain

1. Clean, straight, full stage, no rifts
or deep pools

.030

I

2. Same as 1, but more stones and weeds

.035

I

3. Clean, winding, some pools and shoals

.040

4. Same as 3, but some weeds and stones

.045

I

5. Same as 4, lower stages, more ineffec-
tive slopes and sections

.048

I

6. Good stand any grass (flow depth
.7 to 1.5 ft)

I

a. 12 inches
b. 24 inches

.070
.100

I

7. Good stand any grass (flow depth
3 to 4 ft)

I

a. 12 inches
b. 24 inches

.035
.035

Floodplains

I

8. Pasture, no brush

I

a. short grass
b. high grass

.030
.035

9. Cultivated areas

I

a. no crop
b. mature row crops
c. mature field crop

.030
.035
.040

I

(1)

(1)

(1)

(1)

(1)

(2)
(2)

(2)
(2)

(1)
(1)

(1)
(1)
(1)

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(1) Open-Channel Hydraulics, V.T. Chow, McGraw-Hill Book Company, 1959.
(2) Larimer County Storm-Water Management Manual. Resource Consultants,
Inc., Fort Collins, Colorado, 1979.

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