One of the low-impact features being used in this project is a green infrastructure item called infiltration swales. For this project, these will be constructed on either side of Dean Avenue, Auburn Avenue, Phillips Avenue, Adelpha Avenue, and Burton Avenue.
A swale is a low tract of land that is designed with different types of soils to slow and capture stormwater runoff by spreading it horizontally across the landscape. The soils that are used are specifically chosen, depending on the construction area, to help filter the stormwater.
During a rain event, the stormwater is captured by the infiltration swales and slowly filtered into the perforated HDPE pipe laid beneath the engineered soils. They will help relieve flooding by slowing the amount of water entering the system. Because of this, the project was able to be designed with smaller pipe sizes, leading to cost savings of thousands of dollars.
For this project, the infiltration swales will be constructed by excavating out the native soils alongside the roadways, laying the perforated HDPE pipe, then filling the swales back in with two types of engineered sand certified by the Michigan Department of Transportation.
Each infiltration swale will be constructed to capture and store water up to a depth of 18 inches. Once water within that infiltration swale exceeds that depth, catch basins within each area will route the extra water directly into the stormwater sewer system. Each basin is designed to capture and store stormwater runoff and meter it slowly into the storm sewer network.