16 Case Study: Enhancing Infiltration at Elmwood Park Omaha, Nebraska The city of Omaha completed the Elmwood Park project in combination with a neighborhood sewer separation project to help reduce combined sewer overflows while providing an amenity in a residential neighborhood. The city’s Public Works Department collaborated with the Parks, Recreation, and Public Property Department to construct several new storm sewers that divert stormwater from approximately 30 acres of the existing combined sewer system to the nearby Elmwood Park. Infiltration and treatment of that stormwater is provided by dry detention ponds, bioretention gardens with native plantings, and a series of grade-control slotted weirs that allow water to pass after reaching a certain depth. The system is designed to handle flows from a 100year storm—a significant improvement over the previous combined sewer’s inability to handle flows from a 10-year storm. The project removes a large volume of flow from the overburdened sewer system, and the diversion project enabled city designers to install smaller gray infrastructure upgrades in the downstream portions of the system due to the reduced demand. The park is a highly visible and wellused recreational facility, and the diversion project has become a visual focal point that is enjoyed by residents who watch the water cascade through the weirs during a rain storm. Carefully selected vegetation enhances the park’s visual appearance. The final project cost was $1.2 million, and city officials estimate $550,000 in savings over a traditional gray infrastructure solution to combined sewer overflows. The project eliminated the need to upgrade existing gray infrastructure in downstream areas at additional cost. Officials also say that the system is working well and requires minimal maintenance. Figure 8. Top: view from the bottom of the system which is planted with a variety of deep-rooted native plants. Bottom: conditions before the project. (Source: City of Omaha Stormwater and CSO Programs)
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