THIENSVILLE, WI - For nearly 50 years, the downtown area of the Village of Thiensville, located in Ozaukee County, Wisconsin, had been plagued with constant flooding. The flooding repeatedly affected 10 residential and 30 commercial properties when Pigeon Creek overtopped its banks during heavy rainfall. Having experienced six major flood events since 1973, four of which resulted in a federal disaster declaration, Thiensville decided to do something about the creek. They came up with a project that not only remedied some of the problems, but also received an award for Excellence in Project Design or Implementation from the Wisconsin Association for Floodplain, Stormwater and Coastal Managers as well as “Top Project” by Storm Water Solutions magazine.
“We had a storm in1985 and previous to that there were several storms in the early 70s and 80s that flooded downtown Thiensville,” said Mike Campbell, project engineer. “As the consulting engineer, I identified major restrictions that had been placed in the creek, a lot of man-made obstacles.” Noteworthy obstacles included: a floodplain that had been filled in (downtown area); placement of two undersized, lengthy culverts; and construction of a dam upstream in the neighboring city of Mequon (which was also an obstruction to fish passage).
The Village of Thiensville applied for a Pre-Disaster Mitigation grant in 2003. The grant was awarded in 2006 and totaled $2,308,620. The Federal Emergency Management Agency (FEMA) provided 75 percent ($1,731,460) of the project cost. The project was administered by Wisconsin Emergency Management. The Village Board amended the Tax Incremental Financing District to assist with the remaining funds needed to defray project costs.
The flood mitigation project was executed in three phases.
Phase One: Easements were obtained to detain stormwater in an open space area upstream in the neighboring city of Mequon. A plate was installed on the upper half of an existing outlet culvert that controls the culvert’s outflow, causing flood storage during high water events.
Phase Two: Two restricting undersized culverts, which allowed roadway passage from a parking lot to a commercial building, were removed and replaced by a 50-foot clear span bridge.
Phase Three: The high flow channel of the creek was widened from its previous width of 10 to 20 feet, in some areas, to 60 feet to increase the capacity of the creek. A meandering 25- foot wide low flow channel, which is rock-lined, was created for fish passage. Invasive trees were removed and replaced with native species. Wetland and prairie plants were added along the creek’s bank to prevent erosion.
According to Andrew LaFond, Director of Public Works, the Village has had three flood events in 2010 that would have normally caused road closures and property damage in the downtown area. That did not occur due partly to the successful completion of the project.