City-Wide Storm Drainage System Evaluations and Improvements Mitigate Flooding

In the wake of the storm, the Norwalk Department of Public Works collected debris from residents totaling 39 tons of garbage and five tons of scrap metal. The destruction was graver than that caused by Hurricane Sandy nine years earlier, which caused damage to 1,320 properties in the city due in large part to storm surge averaging five feet. Such storms not only damage private properties, but render roads impassable, interfere with public safety services, and jeopardize utility infrastructure. City officials knew something had to be done to improve resiliency and mitigate flooding in their community.

Woodard & Curran has partnered with the city of Norwalk to develop a comprehensive flood mitigation strategy to inform capital improvement decision making. Woodard & Curran conducted field investigations to have a thorough understanding of the existing storm drainage system, its condition, and potential limitations of the aging infrastructure. The data collected in the field substantiated recommendations to the city for both short- and long-term initiatives. The field investigation also helped the city identify pragmatic ways to explain the increased flood risks associated with more intense, frequent rainfall events in conjunction with sea level rise impacting the city’s shorelines and taxing existing drainage system capacity. Our team of experts helped create an extensive engagement program, leveraging social media and public meetings to garner support from community members.

Woodard & Curran is supporting the city through implementation of several short-term planning, design, and construction activities to address the storm drainage system. This includes help in obtaining local, state, and federal permits for removing sediment and vegetation as part of a dredging program in drainage channels, streams, and ponds. Our team also identified an opportunity to integrate additional stormwater drainage pipe into a planned roadway project being executed by the Connecticut Department of Transportation. Woodard & Curran is also supporting the city with planning, design and construction of water and sewer projects that intersect drainage system improvements. Woodard & Curran designs ensure the alternative recommendations do not negatively impact sewer and water system.

Woodard & Curran’s innovative approach to understand, analyze, and mitigate urban flooding utilizes the development of comprehensive one-dimensional (1D) and two-dimensional (2D) “living” models. These models generate straightforward visualizations to help city officials understand the flood vulnerability and flood mitigation measures needed for priority watersheds. The detailed hydrologic/hydraulic models help identify existing hydraulic deficiencies in the watersheds and evaluate flood risks to public infrastructure and private properties. The results of the modeling provided the basis for alternatives analysis that identify potential mitigation measures that could reduce the frequency, extent, and duration of flooding in historically inundated areas.

One such effort is focused on flood hazard and mitigation for a 0.6-square-mile watershed in the Dreamy Hollow neighborhood, comprised of 7.8 miles of storm drain piping and six culvert/bridges. This aspect of project work included a downstream impact analysis, expanding on the Betts Pond Brook Watershed model by adding more than 3.2 miles of streams. This step provided assurances that work done in would not negatively impact other areas in the city. As a result, Woodard & Curran designed and developed a bid package for drainage system improvements to mitigate flooding in this neighborhood. Our team also provided construction management for the project. When a slow-moving front dropped more than 10 inches of rain in a 24-hour period on August 18, 2024, this project proved successful with several dozen homes protected from flooding.