Burnsville Minnesota Stormwater Risk Assessment, Resiliency Study, and Twin Lakes Flood Risk Reduction Improvement Project

Communities have extensive GIS data that can be used as input to storm sewer models. This presentation will walk through how communities can use this data to help plan, predict and mitigate flooding within their communities. The City of Burnsville (26.87 sq. mi.), like many communities throughout the Minnesota Minneapolis-St.Paul Metro, have a 1D City-Wide XPSWMM model. The City wanted to upgrade their 1D model into a 2D model to create a model with a higher accuracy for their complex storm sewer network. Burnsville was the first community within the Metro to develop a City-Wide 2D model. The 2D model allowed the City to have a better understanding of their flood risk that a traditional 1D model would not be able to identify (i.e. surface flow velocities, erosion susceptibility of overland flow areas, emergency overflow capacity issues in residential areas, and showing where overland flow conveyance points are most critical). The flood rasters and associated output data from the 2D model were then taken and integrated into a custom-built Resiliency Model evaluating the Consequence of Failure (CoF) versus the Likelihood of Failure (LoF) criteria, building on the techniques often used in water main and sanitary sewer asset management programs. The various CoF and LoF parameters were weighted based on input from City staff to determine the most critical aspects of their system such that the resiliency model would take these factors (weights) into account to determine which areas are the most critical to construct flood risk reduction projects. This approach removed any bias from the evaluation process allowing the City to develop a guiding document/living model the City can use for future planning & mitigation projects. All of the processes are fully dynamic allowing the 2D model and Resiliency Analysis to be rerun to re-prioritize the zones annually. Based on the outcome of the resiliency study, the city moved directly into constructing a large flood risk reduction project for a high-scoring area of the City's system. The Twin Lakes Flood Risk Reduction Project involved three major design components to alleviate flooding risk along a small chain of lakes. Given that these lakes drain to other flood-prone areas, at a minimum the project required that overall peak flows were maintained. The already-built city-wide 2D SWMM model allowed the design team to quickly develop the hydraulic design that reduced flooding in the Twin Lakes area and maintained downstream flows. Currently, evaluation of the next flood risk reduction project for a critical area is ongoing with design of that project expected to occur in 2022.