FS0018X Feasibility Study 11/01

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

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 15 ,
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 expanded by adding 4 cells of
20' wide X 8' tall RCBs to the south of the existing bridge. The existing timber bridge
along the northbound lanes would be replaced. The CDOT currently has plans to replace
the timber bridge within the next 3 to 5 years. In the summer of 1996, the UPRR/BNRR
replaced their bridge located just downstream of HWY 6 for structural reasons. Design of
the new railroad bridge was such that the new bridge will ultimately convey the 100-year
peak discharge. Since the proposed bridge improvements would allow more flow
downstream of HWY 6, a second system of levees and a floodwall are proposed to
confine storm water downstream of the highway to the 100-year floodplain of the South
Platte River. The estimated project cost of the proposed improvements along Pawnee
Creek is $1,135,500. This cost does not include the new bridge at HWY 6 by CDOT or
the newly constructed railroad crossing by UPRR.
These proposed improvements would eliminate the Pawnee Creek overflows from
draining into the City. The overflows are estimated to be about 5,000 cfs during the 100-
year storm. Eliminating these overflows removes a substantial amount of land and many
structures from the floodplain in both Logan County and the City of Sterling.
Alternative No. 3. This alternative is a series of upstream flood control reservoirs as
presented in the report entitled "Flood Plain Management Study, Pawnee Creek and 2' •ti ,„
Logan Creek, Colorado" dated April 1992. This alternative will store floodwaters in
detention structures in the upper watershed. General location of the reservoirs is shown
on Figure 10.
16