FLOOD02894

• Designation Number: 456
• County: Logan
• Community: Sterling
• Stream Name: Pawnee Creek
• Basin: South Platte
• Title: Floodplain Anaylsis - Pawnee Creek Overflows, Sterling
• Date: 2/1/1997
• Designation Date: 5/1/1997
• Floodplain - Doc Type: Floodplain Report/Masterplan

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ICON ENGINEERING, INC.

3131 South Vaughn Way, Suite 428. Aurora. Colorado 800 14

P~one [phone]

FAX [phone]

February 3, 1997

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Mr. Wayne Bethururn /
Design Technics, L.L.c. I"
1'.0, Box 408
Sterling, Colorado 80751

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RE: Floodplain Analysis, Pawnee Creek Ovel'flow~1

Dear Wayne:

ICON Engineering, Inc, has com;Jleted a floodplain study for the Pawnee Creek Overflows from
Iris Drive to County Road 24 in Logan County and the City of Sterling, Colorado, The resulting
floodplain is presented on Sheet] 01'2, which is enclosed with this letter for you use.

As a part of our analysis we reviewed the following two studies which were completed earlier to
address the Pawnee Creek overflows:

1. Floodplain Information and Drainage Plart fQL~mLD'~ek and the Pa\Vllee ,Qyj;Ifl9-'Y.J!l
Sterling. Colorado. Charles F, Leaf and Resource Consultants, May 1983; and

2. Flood Plain Management Studv. Pawnee _CredL-in.._1.Qg~.l!!ltL-CoDJQIiLdJ2. Soil
Conservation Service (SCS). April 1992.

The first study investigated the overflows from the South Platte River through the City of
Sterling to Iris Drive. Detailed hydrology was completed as a part of this study. This hydrology
was adopted by the Federal Emergency Management Agency (FEMA) and llsed in their Flood
Insurance Study dated September 29, 1989. According to this hydrology, the Pawnee Creek
overflows are equal to 5,000 cubic feet per second (cfs) during the lOO-year storm.

The second study investigated the overflows from the point where they leave the banks of
Pawnee Creek north to County Road 29. Detailed hydrology was also completed for this study
and the reported peak discharge during the 100-year storm fer the Pawnee Creek Overflows is
4,242 cfs.

Neither of the two previous studies delineated the floodplain between County Road 29 and Iris
Drive. The purpose of this study is to delineate the floodplain in this area and evaluate the
potential impacts to the proposed Design Techniques Subdivision_ Since this area is currently
regulated by FEMA, the accepted flow of 5,000 cfs was used for our analysis.