ABOUT THE PROJECT
The original scope of the preliminary
design required determining the most efficient option for a flood-risk
reduction project for providing permanent flood protection for
the neighborhood to an elevation of 907 feet, or a river flood stage of
40.4 feet. The project also needed to reduce the impacts to the adjacent
landowners.
After the flood of 2011, the scope of the project was expanded to
provide the neighborhood with a permanent flood protection system to be
built to certifiable standards. These standards changed many aspects of
the project, most notably, the protection level and the increased area
of permanent acquisition.
The protection level was then increased from the 907 feet elevation
to 910 feet to accommodate the minimum elevation required for a
certified earthen levee. The footing design was increased to accommodate
the construction of structural floodwalls in the future to produce a
final flood protection elevation of 913 feet. Ultimately, the Rose Creek
Flood Mitigation project consists of 1,300 linear feet of earthen
levees, 1,900 linear feet of structural flood walls, and an internal
drainage system that includes two future stormwater pumping stations.
The project also includes securing permanent easements on 16 properties
along the project corridor. The project design uses the USACE design
standards that will enable it to meet FEMA certification requirements.
Water surface elevations were well-documented in the channel from
past major flood events between 1997 and 2009, which assisted the
modeling efforts. During major flooding events like the one that
occurred in 1997, overflows from other conveyance systems, such as the
Wild Rice River tributary to the Red River, exceeded their individual
capacities and caused the excess to flow into neighboring systems, such
as Drain 27 and Drain 53, which supply Rose Coulee.
Therefore, modeling of spring events was determined to be unnecessary
because of excessively high river stages from the Red River that backup
through the drain system of Rose Coulee. Using the existing US Army
Corps of Engineers (USACE) HEC-RAS model for the Fargo Southside Flood
Study interior watershed model developed by another firm, an analysis
was performed to calculate water surface elevations along Rose Coulee
for normal free flow through the culvert structure at University Drive.
This analysis was performed to determine the impacts of design
components for the proposed levee system on the existing water surface
profile of Rose Coulee. Analyses were specifically made for a proposed
box culvert installation to remedy instability issues regarding raising
the earthen levee along Rose Coulee. The analysis was performed using a
range of flood discharges varying in excesses to determine the
feasibility of the proposed box as a solution to mitigate geotechnical
issues concerning the design and to accommodate the certification
requirements for the proposed levee system.
