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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SECTIONTHREE Anected Environments and Environmental Consequences

Potential effects of Alternative 2 on water quality in Pawnee Creek would be limited to increased
total suspended solids (TSS) (turbidity) during construction oflevees, 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.

Since the alternative involves construction activities within "waters of the United States," a
Section 404 pern1it from the U.S. Army Corps of Engineers (USACE) would be required.

3.9.3 Alternative 3 . Pawnee Creek Overflow Cutoff

With Alternative 3, flood control facilities would only be constructed at Riverside Cemetery and
the effects of this alternative are the same as discussed for this location in Alternative 2. Flood
depths upstream of Highway 6 would be increased by approximately 0.1 to 0.4 feet due to the
construction of levees, floodwall, and the road closure system (URS Greiner Woodward Clyde
1999). This increase would primarily occur within and immediately adjacent to the constructed
conveyance system. Alternative 3 would prevent flood flows up to the 100-year flood event
from entering Sterling and, thus, decrease the potential for flood damage within the city. Even
for flood events which exceed the design event, Alternative 3 would greatly assist in minimizing
flooding in Sterling. Additional flood protection would not be provided for Atwood or
agricultural lands with this alternative.

Potential effects of Alternative 3 on water quality would be the same as those discussed for
Alternative 2.

A Section 404 permit from the USACE is not anticipated for this alternative because
construction would not occur in "waters of the United States".

3.10 BIOLOGICAL RESOURCES

3.10.1 Wetlands

Executive Order 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 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 would affect more than
500 feet of a stream, more than 3 acres of wetlands, or the stream flow is greater than 5 cfs, an
individual permit would be required (R. Flecher, USACE, personnel communication, 1999). If
the proposed project would affect resources less than those listed above, a General Permit 26
would be required. General Permit 26 is presently being revised by the USACE and the
proposed project would need to be under construction by September 15, 1999, for the existing
rules to apply. After that date the more restrictive revised rules would apply (R. Flecher,
US ACE, personnel communication, 1999).

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