FLOOD09522

• County: Logan
• Community: Sterling, Atwood
• Basin: South Platte
• Title: Pawnee Creek Flood Mitigation, City of Sterling, Town of Atwood and Logan County
• Date: 7/1/1999
• Prepared For: Logan County
• Prepared By: URS Greiner Woodward Clyde
• Floodplain - Doc Type: Flood Mitigation/Flood Warning/Watershed Restoration

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SECTIDNONE

Introduction

1.1 BACKGROUND

During the week of July 28, 1997, heavy rainfall in eastern Colorado, including the Pmmee
Creek watershed, saturated agricultural and range lands. The heavy rains caused significant
flooding in the communities of Fort Collins, Weldona, Atwood, and Sterling, Point rainfall
amounts of up to 15 inches in a 4- to 8-hour time period were reported in the upper watershed
areas of Pawnee Creek. On August I, 1997, President Clinton declared a major disaster in the
state of Colorado as a result of severe storms. heavy rains, flooding, mudslides, landslides, and
severe ground saturation. Three counties were initially declared eligible for Individual
Assistance, Public Assistance, and Hazard Mitigation Assistance and 10 more counties were
subsequently added. The incident period was from July 28, 1997 through August 12, 1997. This
designation allows Federal assistance funds to be used to minimize future flood hazard and the
cost of future damage. A substantial portion of the Federal financial assistance is provided by
Federal Emergency Management Agency (FEMA) pursuant to the authority of the Robert T.
Stafford Disaster Relief and Emergency Assistance Act, Public Law 93-288, as amended.

The City of Sterling (Sterling) and Logan County, located in eastern Colorado (Exhibit 1), have
applied to the State of Colorado for funding through the FEMA Hazard Mitigation Grant
Program (HMGP) for assistance under Presidential Disaster FEMA-1186-DR-CO. This
assistance would be used to reduce the potential for future flood damage as a result of flooding
along Pawnee Creek. The Council on Environmental Quality (CEQ) has developed regulations
to implement the National Environmental Policy Act (NEP A). These regulations are set forth in
Title 40, Code of the Federal Regulations (CFR) Parts 1500-1508, and require an investigation of
the potential environmental impacts of a proposed Federal action, and an evaluation of
alternatives as part of the environmental assessment process. The FEMA regulations that
establish agency-specific process for implementing NEP A are set forth in 44 CFR Subpart 10.
This Environmental Assessment (EA) was conducted in accordance ~ith both FEMA and CEQ
NEP A regulations.

1.2 HISTORY

Pawnee Creek is a left-bank tributary to the South Platte River and drains an area of about 645
square miles (Exhibit 2). The mouth of the creek is located about 5 miles southwest of Sterling
and about 1 mile northeast of the Town of Atwood (Atwood) in Logan County. The South Platte
River floodplain is broad and relatively flat. The channel capacity of Pawnee Creek within the
project area is quite small, less than 1,850 cubic feet per second (cfs), when compared to flows
that can be generated in the lower basin, in excess of 30,000 cfs during major precipitation
events. Presently, overbank flows of Pawnee Creek are prevented from flowing to the South
Platte River by embankments of Highway 6 and the Union Pacific Railroad (UPRR) track. The
embankments, which are located on the riverside of both towns, contribute to ponding of
floodwaters in Atwood and surrounding areas and directing the overflow into Sterling.

Major flood events on Pawnee Creek have occurred in 1935, 1965, and 1997. The worst flood,
which occurred in 1997, was estimated to be greater than a 100-year flood event in the upper

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