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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SEellONTWO

Alternatives Considered

· Construction of eleven 20-foot by 4-foot box culverts under the UPRR embankment

· Construction ofa 150-foot-Iong by 250-foot-wide flood channel from the UPRR
embankment to the South Platte River

. Installation of a siphon under the constructed flood channel for the Springdale Irrigation
Ditch

Photographs of the UPRR embankment and Highway 6 at Atwood are provided in Exhibit 4.

Pawnee Creek Improvements

Culverts, dikes, bridges, floodwalls, and flood channels would be sized to handle 8,200 cfs of
floodwater (projected 1 DO-year flood event) and would include the following project features:

· Construction ofa 300-foot floodwall on the north bank of Pawnee Creek downstream from
the UPRR bridge to protect a farmstead and associated livestock pens

· Construction of a 3,000-foot low-flowlflood-flow channel for Pawnee Creek from the UPRR
bridge to the South Platte River; removed fill material would be used during the construction
of the earthen levees

· Construction of earthen levees (1 to 5.5 feet high) along low-flow/flood-flow channel from
the UPRR bridge to the South Platte River; the north levee would be approximately 1,400
feet in length and the south levee would be approximately 1,500 feet in length

· Removal of fill material from under the UPRR bridge to open the entire span of the bridge;
removed fill material would be used during the construction of the earthen levees

· Construction oHour 20-foot by 8-foot box culverts to the southbound Highway 6 bridge and
coordinate replacement of the northbound bridge with CDOT

· Excavation of (lower) the Pawnee Creek channel approximately 1.5 feet from 100 feet
upstream of the Highway 6 bridge to 200 feet downstream of the UPRR bridge to increase
channel capacity; excavated material would be used during the construction of the earthen
levees

· Construction of concrete wing walls upstream and downstream of the two highway bridges
and placement of 30 linear feet of riprap upstream and downstream of the wing walls to
prevent erosion around the wing walls

. Construction of a 200-foot dike approximately 200 feet upstream from the Highway 6 bridge
to direct floodwater under the bridges

· Extension of the Springdale Irrigation Ditch siphon by approximately 80 feet to
accommodate the wider stream channel adjacent to the highway bridges

· Removal of the abandoned concrete irrigation ditch diversion structure downstream from the
UPRR bridge

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