Retaining walls provide a storm water management solution in community park
Village of Kimberly, Wisconsin, residents pinpointed a neighboring field as the origin of cyclical flooding and erosion that affected the homeowners’ properties as well as the surrounding roadways. During rain events and seasonal snowmelt, water accumulated in the residents’ yards and caused spillage over roadways, making travel hazardous. The vacant neighborhood field suffered from nutrient depleted topsoil caused by frequent rainfall and years of erosion, so much so it could no longer absorb accumulating storm water. With nowhere to go, the storm water spread into the surrounding area where it would collect and remain for multiple days until eventually evaporating or soaking into the ground. Tired of the endless cycle of property repairs and flooded roadways, residents gathered to present their concerns to village officials and request a resolution.
The Village of Kimberly took action and established an ad-hoc committee to focus on the issue at hand. Committee representatives contacted McMahon Associates Inc., a regional engineering firm that specializes in providing storm water solutions, to assist with the project. Assigned engineers were tasked with finding a cost-effective, long-term solution that could be implemented in a relatively short amount of time to meet the residents’ needs and to prevent further storm water damage. Once onsite, project leaders evaluated the lot and located the primary flooding issues.
Finding a Solution
In the early spring of 2016, McMahon Associates Inc. presented village committee members and officials with the firm’s proposed engineering plan for the empty lot. The plan called for the creation of a 143.5-acre multipurpose park that consisted of a four-acre manmade pond with fountain features, two storm water management ponds and more than one mile of walking trails. To prevent future erosion, an expansive serpentine-shaped retaining wall would be constructed along the manmade pond to hold back the earth, accommodate elevation changes and preserve the pond’s shell over time. The original plan was approved with the use of traditional-sized segmental retaining wall units. Upon further consideration, project engineers re-evaluated the use of traditional-sized SRW units and realized they would exceed budgetary restrictions and push back timeline expectations. The plan was revisited, and an alternative was found in the use of oversize Rib Rock Landscape Block manufactured by County Materials.
Rib Rock units are larger in size and weight, measuring approximately 2’ x 4’ x 2’ and weighing more than 1,800 pounds each, compared to traditional-sized retaining wall units, which range in dimensions and typically weigh between 30 to 100 pounds each. Working with greater square-footage units allows more wall area to be covered with the use of less materials. Not only would the overall cost be reduced, but the installation time would be as well. Project engineers also considered climatic conditions and the impacts of a pond application. Being in central Wisconsin, the park’s pond would be prone to freezing temperatures and temperature fluctuations. Engineers considered the possibility for water freezing and thawing between the joints and ice expanding or shrinking, possibly causing traditional size wall units to shift in a pond application like this. However, by constructing the perimeter pond wall with Rib Rock units, the structural integrity of the wall is enhanced by the units’ substantial weight, built-in interlock and fewer joints to reduce freezing and thawing affects. Once presented with the benefits of using Rib Rock, the project committee agreed to move forward.
Constructing a Community Asset
With the finalized project plans in hand, the engineers began site excavation and removed earth to form the shell of both the manmade fountain pond and the two storm water management ponds. Next, a drainage system was installed to connect the new ponds to each other and to existing parts of the structure. For the storm water management ponds to be effective, they required access to where the water flows and there needed to be adequate space within the system to allow fluctuating volumes of water to pass through. Storm water management ponds must be excavated deep enough to maintain a desired water level while accommodating heavy rainfall. Using outlets, these ponds would be able to control the water passing through, which is essential to prevent flooding and erosion. To preserve the manmade pond’s shell and protect the drainage system, a serpentine-shaped retaining wall was built along its perimeter. Because the pond is in contact with the retaining wall units, it required geogrid and site-specific engineering. The wall’s structural integrity was maximized by compacting base materials to the proper density per industry standards. Once the base was prepped and unit installation began, geogrid, a non-biodegradable reinforcement mesh, was also laid the length of the wall at specified layers for added soil reinforcement and engineered stability. Geogrid emulates a natural root system by holding the soil in place to prevent movement and erosion.
As the project engineers predicted, the larger wall units expedited installation. Because the pond is located below ground level, fencing was installed in the top Rib Rock units to enhance safety features of the park. Once the retaining wall was completed, recreational elements were added to the park. A paved walking trail was laid around the pond’s perimeter and throughout the park. Garden beds line the segments of the trail, adding to the park’s aesthetic appeal. Lastly, a lighted fountain was installed in the manmade pond to complete the focal point.
Following one year of construction, Memorial Park opened to the community during the spring of 2017. The park’s namesake originated from the World War I and World War II Memorial that is placed within a prominent park garden bed. Since the storm water management system’s installation, it has proven effective and residential flooding and erosion has dissipated. Residents are pleased with the implemented solution and enjoy the park’s recreational features. The addition of the multipurpose park increased the perceived and actual value of neighboring homes, which homeowners are satisfied with. In 2018, one year after the project’s completion, village officials approved the installation of the park’s latest feature, a lighted gazebo. The gazebo, constructed by Kimberly High School students in technical education courses, was installed near the retaining wall overlooking the fountain pond. Memorial Park has proven to be a valuable asset now and for years to come.