FLOOD09102

• County: Logan
• Community: Sterling
• Basin: South Patte
• Title: Sterling Flood Control Interceptor Channel Project
• Date: 4/1/2002
• Prepared For: Sterling
• Prepared By: URS
• Floodplain - Doc Type: Project

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SlmOITHREE AUected Environments and Environmental Consequences

South Platte River would not result in a significant change in the base flood elevation (BFE) of
the river (Enserro 2002).

Potential effects of Alternative 2 on water quality in Pawnee Creek would be limited to increased
total suspended solids (TSS) (turbidity) during construction of the channels, roads, bridges etc.
The contractor would be required to employ sediment control procedures, which would reduce
the amount of sediment entering Pawnee Creek and the South Platte River. Effects on water
quality related to this alternative would be minor and short-term.

An NPDES Construction Storm Water Discharge Permit would also need to be obtained from the
Colorado Department of Public Health and Environment with this alternative.

3.9.3 Alternative 3 - Improve Routing of Pawnee Creek Flood Flows

The facilities at Riverside Cemetery would increase flood depths upstream of Highway 6 by
approximately 0.1 to 0.4 feet due to the construction oflevees, floodwall, and road closure
system (URS Greiner Woodward Clyde 1999b). This increase would primarily occur within and
immediately adjacent to the constructed conveyance system. This alternative would prevent
flood flows up to the 100-year flood event from entering Sterling and, thus, significantly
decreasing the potential for flood damage within the city.

Even for flood events which exceed the design event, this alternative would substantially reduce
flooding in Sterling. In addition to less flow, the duration of flooding would be reduced. With
this alternative, flows in the South Plate River between the channel's outfall and Sterling could
be increased by up to 5,000 cfs. Preliminary evaluation indicated that this discharge into the
South Platte River would not result in a significant change in the BFE of the river (Enserro
2002).

Potential effects of Alternative 3 on water quality in Pawnee Creek would be limited to increased
TSS (turbidity) during construction of levees, channels, roads, etc. The contractor would be
required to employ sediment control procedures, which would reduce the amount of sediment
entering Pawnee Creek and the South Platte River. Effects on water quality related to this
alternative would be minor and short term.

An NPDES Construction Storm Water Discharge Permit would also need to be obtained from the
Colorado Department of Public Health and Environment with this alternative.

3.10 BIOLOGICAL RESOURCES

3.10.1 Wetlands (E.O.11990)

E.O. 11990, entitled Protection of Wetlands, requires federal agencies to take action to minimize
the loss of wetlands. Activities disturbing jurisdictional wetlands or other waters of the United
States under Section 404 of the Clean Water Act require a permit from the United States Army
Corps of Engineers (USACE). Depending on the type of project and potential impacts, either an
individual 404 Permit or a Nationwide General Permit could be required. If the proposed action

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