FLOOD09522

• County: Logan
• Community: Sterling, Atwood
• Basin: South Platte
• Title: Pawnee Creek Flood Mitigation, City of Sterling, Town of Atwood and Logan County
• Date: 7/1/1999
• Prepared For: Logan County
• Prepared By: URS Greiner Woodward Clyde
• Floodplain - Doc Type: Flood Mitigation/Flood Warning/Watershed Restoration

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SECTIONTWO

alternatives Considered

The President's CEQ has developed regulations for the preparation of environmental impact
documents in compliance with NEPA. The CEQ requires an investigation and evaluation of
practicable alternatives as part of the environmental assessment process.

Sterling and Logan COUllty, in conjunction \\ith the Colorado Water Conservation Board, held a
series of public meetings to solicit input from the local commUllity regarding the type of flood
control project that would be acceptable to the community. The meetings were held in December
1997 and January 1998. The meetings in December were designed to obtain input from farmers,
urban residents, and business owners. During the January meeting, the refined alternatives were
presented to the commUllity for comments. There was general agreement in the meetings that for
a proposed alternative to be supported by the overall community, it would need to provide
benefits to Sterling, Atwood, and to agricultural lands flooded by Pawnee Creek. Input from the
commUllity at these meetings helped to determine which alternatives would be dismissed and
which alternatives would be retained for further evaluation.

2.1 ALTERNATIVES ANALYZED AND DISMISSED

2.1.1 Flood Control Levees

This alternative, identified as Alternative 2 in the applicant's Flood Hazard Mitigation Feasibility
Study, would restrict the 100-year flood flows from overflowing into the overbank floodplain
near where Pawnee Creek crosses Highway 6, would provide protection to agricultural lands, and
would provide protection to Sterling (rCON 1998). This alternative included the construction of
a system of flood control levees that would follow the north bank of Pawnee Creek, beginning
upstream of COUllty Road (CR) 29 and continuing east to Highway 6. The conveyance capacity
of the bridge for the southboUlld lanes of Highway 6 would be increased by adding four 20-foot
by 8- foot concrete box culverts west of the existing bridge. The existing timber bridge for the
northbound lanes of Highway 6 would be replaced by the Colorado Department of Transporta-
tion (COOT) and the span of the new bridge would have the capacity to pass the 100-year flood
flows. Fill material presently beneath the UPRR bridge would be removed to open the entire
span. A second system of levees and a floodwall would be constructed to convey storm water
from the UPRR bridge downstream to the 100-year floodplain of the South Platte River. When
compared to other alternatives, this alternative required the construction of more levees on agri-
cultural land. Additionally, if a flood of greater than the 100-year design flood occurred, levees
constructed upstream of the Highway 6 bridges with the required 3-foot freeboard could increase
the level of flooding in Atwood (ICON 1998). Due to negative impacts associated with the large
amoUllt of agricultural lands that would be required for the flood control facilities and the
potential for greater flood damage in Atwood, this alternative was eliminated from consideration.

2.1.2 Upstream Flood Control Reservoirs

This alternative, identified as Alternative 3 in the applicant's Flood Hazard Mitigation Feasibility
Study, is a series of upstream flood control detention dams. With this alternative, seven
detention structures would be constructed in the upper watershed to temporarily store

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