FLOOD09536

• County: Larimer
• Community: Fort Collins
• Stream Name: Douglas Reservoir
• Basin: South Platte
• Title: Hydrology Study for Douglas Reservoir
• Date: 9/6/1977
• Prepared For: Larimer County
• Prepared By: M.W. Bittinger
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Composite Soil Numbers

Note A: For full PMP flood the SCS records were used in soil classifi-

cation and the areas were planimetered and results compiled.

The sheets of calculations have been eliminated due to the

huge volume of work involved.

Note B: For the thunderstorm computations the table on page 544, Design

of Small Dams, Bureau of Reclamation was used.

The results are:

Large Area Small Area
PMP 78 86
Assum. "Au 78 86
Thunderstorm 73 73
Assum. itA" 82 81

Time of Concentration
Large Area Small Area
Time (15 Min.) (1 Hr) (6 Hr) (15 Min.) (1 Hr) (6 Hr)
Time of Concentration 4.5 Hr 3.5 Hr 3.5 Hr 3.22 Hr 3.22 Hr 3.22 Hr
Time of Peak 2.8 Hr 2.6 Hr 5.6 Hr 2.1 Hr 2.4 Hr 4.9 Hr
Time to End 7.5 Hr 6.9 Hr 15.0 Hr 5.5 Hr 6.5 Hr 13.2 Hr
Incremental Flow qp 7566 cfs 8148 cfs 3783 cfs 1245 cfs 10.56 cfs 520 cfs

SU1IlIllary

PMP l1aximum Precipitation = 21.2" )
Zone 1/4 ) Figure 15
Zone C Figure 18
Direct Runoff Reduction .84 Large area.
Direct Runoff Reduction .80 Small area.
Minimum Retention = .12"

Assumption IIA"
Factor for reduction to "A" flood = 3.7

;>k IV, BITTiNGER -AND ASSGCIATES. INC.

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