FLOOD02665

• County: Larimer
• County: Weld
• Community: Larimer and Weld Counties
• Stream Name: Cache La Poudre River Basin
• Basin: South Platte
• Title: Special Study Cache La Poudre River Basin Volume II - Hydrology
• Date: 10/1/1981
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Floodplain Report/Masterplan

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EFFECT OF ROAD STRUCTURES

The preceding discharge-probability relationships for the Sheep

Draw basin were developed with and without the dams in place. Road

structures were assumed in place with culverts considered to be

unobstructed. The 100-year flood under existing conditions was also

modeled with roads removed to illustrate the effect of the road struc-

tures on discharge potential. The 100-year flood discharges with roads

and dams in place, with dams removed, and with both roads and dams

removed are shown in table 23. The removal of road structures in-

creases discharges somewhat. The removal of the dams would increase

discharges to a generally comparable degree.

Of the thirteen road structures and four dams that were modeled,

two roadway embankments were assumed to fail. County Road 25 over

Sheep Draw which has a 14-foot-by-6-foot concrete box culvert was

assumed to fail with the 500- and 100-year existing, projected

urbanized, and total urbanization conditions with and without dams; the

50-year total urbanization condition with and without dams; and the

10-year total urbanization condition without dams. County Road 25 also

has a 24-inch corrugated metal pipe located 2,200 feet south of Highway

34. This roadway was assumed to fail at this location for the 500-year

flood with existing and projected urbanized conditions without dams and

with the 500-, 100-, and 50-year total urbanized conditions with and

without dams. Failure of the road embankments was assumed to occur if

they were overtopped by more than 2 feet.

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