FLOOD01307

• County: Logan
• Community: Sterling
• Title: Flood Impact Study Pawnee Creek Overflows
• Date: 11/23/1997
• Prepared For: Design Technics L.L.C.
• Prepared By: ICON Engineering, Inc.
• Floodplain - Doc Type: Flood Documentation Report

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ENGINEERING, INC 71066 South Alton Walj Englewood CO

6011C' Phone (303) C'C'1'060C' / Fax (303) C'C'1"4019

i November 24, 1997

Mr. Wayne Bethurum
Design Technics. L.L.c.
P.O, Box 408
Sterling, Colorado 80751

RE:

Design Technics Subdivision Flood Impact Study

Dear Wayne:

ICON Engineering, Inc. (ICON), has completed a second hydraulic analysis to determine
potential flood impacts to your property in Sterling, Colorado caused by the Pawnee Creek
Overflows. Enclosed with this letter for your review is the following information:

I. All of the HEC-2 models prepared as a part of the updated analysis.

2, A map presenting the results of the analysis.

3. Plots of the cross-sections used in the analysis.

4. A print of the final grading plan for phase I of your subdivision.

As you know the Colorado Water Conservation Board (CWCB) intends to rescind their approval
of our original floodplain study dated February 3, 1997 because the flood which occurred on July
31, 1997 impacted your property differently than our first analysis anticipated.

Our first analysis estimates that most of your subdivision is in a Zone X shallow floodplain
during a 100-year storm event. Our study indicated that the shallow flooding is caused by a
low point along the Sterling No. I ditch which allows storm water to overtop the ditch
embankment and sheet flow through your subdivision.

A flood event similar to the July 30th event occurred in June of 1965 and, as you know, the
flooding on July 30th took a different flow path in the area upstream of your subdivision
causing different flooding conditions throughout your property, We have spoken with the
CWCB regarding the recent flood (July 1997) because representatives from the CWCB
observed the flooding and are in the process of preparing a report describing the impacts of this
flood event. Based on observations by the CWCB, the Pawnee overflows drained north along
the west side of U.S. Highway 6 and across your planned subdivision rather than flowing into
Sterling north of the Sterling No I Ditch. The CWCB's documentation of this study is not
available at this time.