District Stormwater for a New Community: From Planning to Construction

Responding to the closure of the Ford Twin Cities Assembly Plant in Saint Paul, Minnesota, the Capitol Region Watershed District and the City of Saint Paul, with the assistance of Barr Engineering Co., developed a sustainable stormwater feasibility plan for redeveloping the 122-acre property (the development is now known as Highland Bridge) along the Mississippi River. Prior to development in the 1920s, the site contained an intermittent stream, Hidden Falls Creek, that fed a waterfall (of the same name), which was buried in a pipe to facilitate the construction of the assembly plant. The study developed master plan concepts for managing stormwater. A decision support framework was developed to help the compare two stormwater management options for the site-a conventional approach with distributed underground infrastructure and a district approach incorporating a green infrastructure corridor. Each option was evaluated against the city's goals for stormwater management, sustainability, redevelopment, creek restoration, and place-making. In addition to a traditional cost-benefit analysis, the study involved a life-cycle cost and impact assessment that monetized socioeconomic benefits. The team assessed factors such as water quality and quantity; flood risk reduction; recreation and property values; and water, carbon, and energy footprints, which revealed that a green infrastructure corridor more than doubled the value of the conventional approach. In 2018, the property was sold to a local developer, Ryan Companies, and work began to design and construct the district stormwater vision. The BMPs are connected as a district system treating public and private stormwater, placed in publicly- and privately-owned park spaces or right-of-way throughout the site to expand the public realm. The final BMPs include 5 large biofiltration basins, 5 underground storage and filtration systems, 2 large rate control ponds, and a re-imagined Hidden Falls Creek. The project reduces total suspended solids by 94%, total phosphorus by 75%, and peak discharges to the downstream waterfall and stream channel by 98% in the 2-year event. The project will also include pedestrian connections that provide continuous access approximately ½ mile through the site along the stormwater features to the existing waterfall, ultimately providing connections to the Mississippi River. Construction of the stormwater infrastructure was completed in 2020-2021. The innovative project approach came to fruition through years of collaboration of public & private partners.