Addressing Inland Flooding: An Integrated Approach

The City of Alexandria, VA is highly urbanized with approximately 160,000 people living in 15.7 square miles. Approximately 48% of the land area is impervious. The City currently maintains over 200 miles of storm sewer and over 560 lane miles of roadways, and includes ~24 miles of streams.

The City has seen an increase in pluvial (inland) flooding, particularly over the last 3 years, which tracks an increase in high-intensity rain events hitting the Mid-Atlantic region. In 2016, the City completed a City-wide capacity analysis study to identify problem areas that would benefit from conveyance capacity upgrades as large scale capital improvements (CI) to address flooding on the watershed or sub-watershed scale. This planning work has led to the identification of the top 10 prioritized unique CI projects ranging in size from $10 million to $64 million. The detailed design and implementation of these 10 “Large Capacity” projects will be rolled out over the next 10 years.
In conjunction with this long-term planning, the City had been tracking an increase in Alex311 online reporting and phone calls and community groups reporting flooding events. Using this data, 19 distinct neighborhoods were identified for further “Neighborhood Engagement” and follow up action. This sparked the implementation of a parallel program to investigate the root causes of the flooding and develop solutions to provide more immediate relief to the neighborhoods most impacted by these flash flooding events.
The City hosted both in person and virtual community engagement sessions with each neighborhood where they  gathered firsthand accounts of the flooding being experienced at individual properties. With these insights, and data gathered through field visits and CCTV investigation into pipe conditions, connectivity, and diameters, the team was able to update the existing city-wide storm system models and identify four distinct work streams to start providing immediate relief: Large CI projects, Spot Projects, maintenance, private floodproofing (supported by a new City grant reimbursement program). These solutions are being designed to provide immediate improvements and to be incorporated into the long-term capital improvements.
This presentation provides an overview of the community neighborhood engagement, neighborhood investigations, solution development, and supporting state and federal grant application processes that have been implemented to make this undertaking a success.