FS0018X Feasibility Study 11/01

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

Revised hydrology has since been prepared and will be used for future design efforts.
The new source for the Pawnee Creek hydrology is the report titled "Hydrologic /
Hydraulic Analysis of Flood Mitigation Alternative #5, Pawnee Creek Overflow, Logan
County, Colorado" which was prepared by URS Greiner Woodward Clyde for the
Federal Emergency Management Agency, Region VIII. A copy of this report is located
in Appendix 1.
Table 2. Peak Discharges Along Pawnee Creek Main Channel Under Existing
Conditions
Location 10-Year 50-Year 100-Year
(cfs) (cfs) (cfs)
*Mouth (South Platte River 100-Year Floodplain) 1517 2026 2226
*Upstream HWY 6 1517 2026 2226
*Upstream CR. 33 2945 5434 6645
*Upstream CR. 31 3264 6729 8611
* Split flows cause reduced discharge in the main channel
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 Appendix 2. 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 Appendix 3.
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:
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