FS0018X Feasibility study

• Contract/PO #: FS0018X
• Contractor Name: Sterling, City of
• Contract Type: Loan
• Water District: 0
• County: Logan
• Loan Projects - Doc Type: Feasibility Study

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URS Greiner Woodward Clyde for the Federal Emergency Management Agency, Region VIII. A copy
of this report is located in the Appendix.

Table 2. Peak Discharges Along Pawnee Creek Main Channel Under Existing Conditions

50:'Yean
. (cf$~'~;;1'1i
2026
2026
5434
6729

1 OO;Year;;
'(~fs) >\
2226
2226
6645
8611

1 O-'Yem:;..'
(e,fs)'''
1517
1517
2945
3264

V. FIELD REPORTS

On July 30th, 1997, an intense rainstorm occurred in the Pawnee Creek basin. Personnel from the
CWCB were informed of the storm and traveled to Sterling before floodwaters began moving into the
city limits. Their observations and subsequent analysis and evaluation of the flood is summarized in a
report titled, "Pawnee Creek, Logan County, Colorado, Flood of July 1997" and located in the
Appendix. The CWCB also authorized the preparation of an overview report of the 1997 flood season
for the entire state. A document titled "Colorado's 1997 Flood Season in Review" was published in
August 1998 and prepared by Riverside Technology, Inc. The portion of this document that pertains to
Logan County is located in the Appendix.

VI. ALTERNATIVE EVALUATION

Based on a review of the existing reports and discussions with the project sponsors and local citizens,
six alternative improvement projects were selected for further study. A conceptual design of all of the
proposed projects was completed in sufficient detail to determine relative construction quantities, cost
estimates, and expected benefits. Approximate locations of the alternatives are shown on Figure 8.
Each Alternative, with the exception of the "No Action" Alternative, protects varying lengths of the
area surrounding the lower portions of Pawnee Creek, and the Pawnee Creek overflow. Common to
each alternative (except for Alternative No. 1 the "No Action" Alternative), but not discussed in detail
are flood warning systems and maintenance programs. The alternatives studied are as follows:

Alternative No.1: "No Action" alternative. A series of seven public meetings with landowners and
concerned citizens were held between December 1997 and January 1998. This alternative was
uniformly not acceptable given the past series of serious flood events and subsequent damages.

Alternative No.2: This alternative will restrict the 100-year flood flows from overflowing into the
left overbank floodplain near where the Pawnee Creek crosses HWY 6. Protection would be provided
to agricultural lands and the City of Sterling. This alternative was the recommended alternative from
the "City of Sterling Drainage and Flood Control Implementation Plan" dated June 1997. This
alternative is shown on Figure 9 and consists of a system of flood control levees. In general, the levees
would follow along the north side of Pawnee Creek beginning upstream of CR. 29 and continuing east
to HWY 6. Since the levees would be designed for the 100-year storm, they would be required to have
3 feet of freeboard by FEMA. The existing bridges at HWY 6 would be improved to convey the 100-
year discharge under the bridges. For the southbound lanes, the existing concrete bridge would be

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