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

significant development. Projected urbanization represents year 2000

urbanization and is an intermediate level of development in that the

upstream half of the Fossil Creek basin is partially urbanized. Total

urbanization assumes the basin is urbanized except for the rugged area

west of, Taft Hill Road.

.

Existing and future urbanization are shown on plate 3. The land

use patterns were slightly altered to fit hydrologic subareas in the

SWMM model.

Any changes in these land,use projections and future urbanization

boundaries would change the hydrologic and hydraulic data presented in

this study.

The percent of imperviousness for each subcatchment was estimated

for exist'ng and projected urbanized conditions. Table 11 lists the

percent of imperviousness for each land use that was considered in the

model.

Table 11
Percent Imperviousness for Land Uses in the Fossil
Creek Basin

Land Use

Impervious Area
(percent)

Commercial
High Density Residential
Medium Density Residential
Low Density Residential
Agricultural '

90
52
40
30
5

DISCHARGE-PROBABILITY RELATIONSHIPS

FOSSIL CREEK

The 10-, 50-, 100-, and 500-year flood discharges for existing and

projected urban conditions for Fossil Creek are presented in table 12.

To show the maximum effect of urbanization, the 100-year flood was

computed with total urbanization.

.

30