Going Beyond the Modeling to Create Resilient, Sustainable, and Value-Driven Stormwater Solutions

Using the right tools for the job will help planners, reviewers, and regulators make informed decisions to create more resilient, sustainable, and value-driven stormwater solutions. The stormwater systems and watersheds of urbanized areas are more interconnected than most people understand. Urban stormwater systems direct flow through underground systems that often differ from the natural drainage paths. Stormwater flows on the surface when these systems surcharge, following the natural surface flow paths and sometimes contributing to adjacent stormwater systems. In addition, urbanization can lead to low areas that can only be drained by enclosed systems that were not designed to accommodate them. These single outlet systems have no redundant flow paths and frequently lead to deep flooding, impacting homes, businesses, and vehicles. More sophisticated tools, such as 2-dimensional (2D) modeling, allow for visualization of where overland flow paths occur. These visual outputs can help inform stakeholders' decisions on critical infrastructure, emergency planning, and future stormwater system improvements. In addition to understanding surface flow in urban areas, many standard hydrology and hydraulic methodologies, which are sometimes antiquated, can cause the overdesign of stormwater systems. Overdesign can be especially detrimental in older urban areas where urbanization has already overburdened the stormwater system. Following a more realistic and 'right-sized' design approach will help reduce the unintended consequences of overdesigning in these areas. These practical design approaches can also use more sophisticated hydrologic and hydraulic analyses to understand the problem clearly, providing the opportunity to create projects that provide the most value and community benefit. One aspect of this right-sized approach is understanding the 'knee' of the cost-benefit curve. This curve is created using the flood reduction cost for various rainfall events and plotting them against their probability of occurrence. This curve provides the point of diminishing returns for project value versus increasing cost, helping stakeholders and planners understand the current level of service for the stormwater system and how much benefit is realistically achievable. Many communities still use antiquated policies, criteria, and guidance that work in contradiction to creating more resilient and sustainable stormwater systems. Updating local policy and stormwater criteria may be necessary to accommodate these more resilient, sustainable, and value-driven design approaches. Another approach to more resilient stormwater criteria is to break up the watershed into areas with three goals: detention/retention, conveyance, and floodplain regulation. Detention/retention areas are typically farthest upstream and outside the influence of the existing stormwater systems. Conveyance areas generally are in the middle reaches of the watershed and are primarily influenced by the capacity of the stormwater system to convey flow. The floodplain regulation areas are at the downstream end of the watershed and are associated with FEMA regulatory streams. 2D modeling and other tools can be used to define these areas and allow for criteria and policies to be developed to address how these areas influence the flood risk in the watershed. Attendees will be presented with a summary of how antiquated design approaches can lead to overdesigned stormwater systems, how more sophisticated tools can provide more insight and understanding of stormwater challenges, and how they can be used to develop more practical solutions. Through example projects, attendees will have the opportunity to learn about how more sophisticated tools can be used to assess urban drainage challenges and create more resilient, sustainable, and value-driven solutions.