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Watershed Study and Improvements

Client: City of Superior, Wisconsin

Location: Superior, Wisconsin

Faxon Creek is an urban stream that collects stormwater from a variety of watershed types with varying degrees of development. Tributary areas have seen changes in both routing and land use. The stream itself has been piped for long sections and has numerous road crossings. This has changed the character of both the hydrology and hydraulics of the stream and cumulatively over a long period of time, has increased peak rates of runoff and flood elevations. Development adjacent to the stream is now affected on a recurrent basis by significant storm events and damage to the aging conveyance infrastructure is accelerating.

Flooding occurs in the Faxon watershed during every significant storm event. Wet weather flows routinely exceed the design capacities of the creek itself and several road and railroad crossings resulting in unacceptable flooding. In June 2012, a particularly large storm (about a 500-year event) caused widespread damage, including up to $20M in damage to the University of Wisconsin-Superior alone.

Donohue completed a stormwater management plan for the watershed, including development of an XP-SWMM 2D hydraulic and hydrologic model. The model was used to evaluate and recommend a series of improvement alternatives that, once implemented, will provide the desired level of protection from flooding. The recommended improvements include rehabilitation of existing infrastructure, conveyance capacity improvements, and stormwater detention/storage, sequenced in a manner from downstream to upstream that enables the City to provide the desired level of service as quickly and cost-effectively as possible.

Subsequently, Donohue worked with the City on the design and construction of two of the recommended stormwater improvement projects: The K-Street storm sewer rehabilitation and the Faxon Creek Culvert replacement at Hill Avenue. All of the Faxon Creek watershed drains through these two critical structures. 

The K-Street storm sewer, a 2,000-foot stretch of 10-foot diameter brick sewer, originates in Central Park and discharges into Lake Superior. This sewer was constructed in 1891 and was in poor condition. Over the years, wet weather flows have increased, and the declining structural condition of the pipe had significantly reduced its capacity while placing it at risk for structural failure. Donohue performed a thorough internal assessment of the condition of this pipe, then prepared plans and specifications to rehabilitate the pipe with a shotcrete liner. The smooth internal wall finish and removing several internal utility crossings resulted in a much-needed increase in pipe capacity.

The Faxon Creek Culvert Replacement at Hill Avenue involved replacing the Hill Avenue viaduct and culvert structure. In addition to being a retaining wall for Hill Avenue, the viaduct, constructed in 1930, also houses a 15-inch diameter gravity sewer interceptor. The project included HEC-RAS and XP-SWMM modeling of the stream and watershed in order to obtain regulatory permits, demolition of the viaduct and culvert, replacing the existing sanitary and storm sewers, construction of a new 10-foot x 12-foot culvert with headwalls and wing walls, and reconstructing several blocks of Hill Avenue to improve the vertical alignment and drainage.