Integrated Urban Wet Weather Solutions Save Money and Provide More Benefits

Dense urban areas face unique stormwater challenges that require broader, more holistic wet weather solutions, especially in the face of climate changes. Applying an integrated urban wet weather approach can save millions of dollars, address both water quantity and quality issues, and create more visible tangible benefits back to the community. In many cities, the current stormwater design criteria result in solutions that are too costly, too big to construct, and may, in fact, worsen the situation when considering shorter more intense rainfall events caused by climate change. Furthermore, cities may be spending money on infrastructure that adversely impacts other infrastructure, causing more downstream impacts, or creating systems that are not resilient or sustainable long-term. With the current state of the practice 2D wet weather models, integrated wet weather solutions can be developed, refined, and tested across a range of stormwater events to obtain the most cost-effective, resilient solutions. Using this approach results in a system approach to capture, control, and convey stormwater in a way that optimizes existing systems, integrates more resilient green infrastructure solutions to store and slow down the runoff, constructs new systems that match conveyance requirements, and considers surface storage and overland flow paths to route water without damaging property. The use of 2D wet weather models provides the ability for a utility to demonstrate performance versus applying an outdated presumptive approach to meet an outdated design standard. In Kansas City, MO, integrated urban wet weather solutions were developed within two urban watersheds, resulting in cost-effective solutions that were supported by the public and the utility because the performance could be demonstrated through the use of 2D models; the solutions also provided multiple benefits. The first example is the Brookside watershed which is a historic single-family residential area with more dense commercial areas at the top and bottom of the watershed. Intense rainfall events cause flooding of streets, homes, and businesses. The previous solution developed over ten years ago was to construct a very large conveyance system to fully convey the 10-year, 24-hour rainfall event. This solution had an estimated cost of approximately $40 million which was not affordable, so nothing was done and flooding continued. Applying an integrated urban wet weather approach, a 2D model was developed. The model revealed that the flooding was actually caused by overland flow and that a system of collection areas, improved overland flow paths, storage, and smaller conveyance pipes could mitigate the flooding. This solution had an estimated cost of $28 million, saving the City almost $12 million. The second example is the Westport entertainment district, the oldest area in Kansas City. The Westport area experiences frequent and severe flooding, causing damage to parked cars and businesses. This area has been studied numerous times over the years but with a single focus on meeting a required level of service-not an integrated wet weather focus. Using an integrated wet weather focus and a 2D model, a range of storm events were evaluated to determine the best solution. The best solution was defined by the business stakeholders with the help of the 2D model to demonstrate the performance of the preferred solution using real rainfall data. Using real rainfall data with the 2D model resulted in the need for a system solution that utilized green infrastructure, underground storage, conveyance pipes, and real-time controls. This system approach resulted in not only a stormwater solution that will reduce future flooding but also a solution that invests in this entertainment district, creating a new multimodal corridor that will support parking, walking, and vehicular traffic. The solution also met the district's comprehensive plan and provided the opportunity for a forgotten neighborhood to be able to celebrate its history in a new park. The final design concept saved the City more than $30 million while creating more visible benefits and will reduce combined sewer overflows. This project is now moving forward as a progressive design-build project which will allow the City to meet an aggressive schedule for completion before the World Cup in 2026. This presentation will use these two case studies as examples of how to implement an integrated urban wet weather solution approach, the benefits of this approach, and outcomes and next steps. It is not easy to change firmly established stormwater design criteria in urban areas but through an integrated urban wet weather evaluation, more holistic cost-effective and resilient solutions can be achieved. As we look to the future, we cannot necessarily implement the solutions of the past to meet our new goals of creating cities that are more livable, sustainable, and resilient to changes in climate.