For each subwatershed, we developed a 2D model to simulate runoff from a range of rainfall, including the 2-, 5-, 10-, 25-, 50- and 100-year events. The model simulates open channels up to and including those that receive runoff from 24-inch and larger storm sewers and enclosed stormwater system hydraulics starting at 24 inches or larger. The hydraulic models are used to estimate the water surface elevations and/or hydraulic grade line (HGL).
Using this data, we identified areas of flood risk and developed an improvement project to cost-effectively mitigate the flood risk. The project team will develop recommendations and define next steps for design criteria updates, considering hydrologic and hydraulic parameters, detention and stormwater best management practices (BMPs), green infrastructure requirements, general review processes for both planning and engineering, and applicability to both development and capital projects.
Throughout the project, our team has provided innovative suggestions in collaboration with the city staff to develop a streamlined data collection and stormwater modeling process. Through a series of modeling workshops, the city gained insight into model development, simulations and outlets. The collaboration empowered the city to make informed decisions, plan future phases, and evaluate various modeling processes for short- and long-term needs.
These subwatersheds represent a range of urban area land use with primarily inlet, pipe and street stormwater conveyance systems along with some open channel and ditch drainage. We utilized PC-SWMM 2D to model both the enclosed pipe system and overland flow paths and small open channels.
The PC-SWMM model employed a rain-on-grid 2D hydrology approach to simulate urban runoff. Radar rainfall data, adjusted with local rain gauges, were utilized to replicate two recent flood events accurately. The process compared model results with observed flood data. Subsequently, the validated model was employed to assess various rainfall scenarios, including different volumes, durations and frequencies. This evaluation aimed to define the current system’s level of service and identify the most cost-effective flood mitigation solution.
The 2D models identified stormwater improvement project needs within each subwatershed. The model results are compared to available area and neighborhood plans and other city-planned and/or -identified capital projects. This effort required interdepartmental coordination to understand how multiple infrastructure objectives could be addressed in identified stormwater improvement project areas. This process also assisted the city in identifying outside funding opportunities to pursue at a state and federal level. Finally, this project included development of a process to evaluate and prioritize identified stormwater improvement projects as part of the stormwater master plan update.