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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expanded by adding 4 cells of20' 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 UPRRJBNRR 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 lOO-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 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.

Alternative No.4: This alternative will collect the Pawnee Creek overflow and divert these flows
directly to the South Platte River in the general vicinity of the Cemetery just south of Sterling. This
alternative consists of construction of a berm having an approximate height of 5 feet to the north and
west of the Riverside Cemetery. This berm would collect and prevent flows from the Pawnee
overflow from entering the City along the HWY 6!Railroad embankments. Included in the alternative
is lowering of CR. 24, construction of a channel with a concrete floodwall, a closure structure for
HWY 6, construction of box culverts under the railroad, a siphon for the Sterling No.1 Ditch, and
construction of a trapezoidal channel to the South Platte River. This alternative is shown on Figure 11.

Alternative No.5: The proposed alternative will provide a conveyance structure at Town of Atwood,
increasing the bridge capacities at the mainstem of Pawnee Creek, channel cleaning, (debris removal)
and stabilization measures upstream ofHWY 6 to CR 29, and the project features of Alternative No.4.
This alternative consists of construction of Alternative No.4, along with modifications and new HWY
6 bridges, channel and levee improvements downstream of the UPRR at Town of Atwood. Flows in
excess of the design event on the mainstem would thus necessitate providing the project features at the
Riverside Cemetery. Alternative No.5 would decrease the severity o( the 100-year flood event in the
area west of HWY 6 between the Pawnee Creek Bridge and the Cemetery, but would not eliminate all
overflows. In addition, this alternative would provide flood benefits to the community of Atwood.
This alternative is shown on Figure 12.

Alternative No.6: This alternative provides a drainage floodway upstream of the Town of Atwood
that diverts Pawnee Creek to the south, along CR. 29 directly to the South Platte River. The floodway
would be sized for the 100-year storm peak flow and would handle a discharge equal to the July 1997
flood event at that location. This alternative would require crossings for the Pawnee Irrigation Ditch,
and both HWY 6 and the UPRR. This alternative is shown on Figure 13.

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