FEMA Preliminary Flood Zone Maps Released For Alexandria

ALEXANDRIA, VA — On Wednesday, FEMA released preliminary flood zone maps for the City of Alexandria. Flood zone maps show the projected flood risk of properties to determine who needs flood insurance as well as the cost of flood insurance. There will be a review and appeals process before the new flood zone maps are expected to take effect in fall 2022.

Alexandria is one of the participating localities in FEMA's Flood Insurance Study to update the flood zone maps. According to Mayor Justin Wilson's October newsletter, flood maps were last updated in 2011 and expanded the flood zones in the Old Town, Rosemont and Arlandria neighborhoods. Currently, around 20 percent of the city is mapped as floodplain.

"Flood risk changes over time due to weather patterns, land development, and erosion," reads a statement on the city's flood map web page. "The changes are likely to affect some residential and commercial property owners, who may need to obtain coverage under a new flood insurance policy or alter existing policies."

The estimated review schedule calls for a 90-month public review and comment period in summer 2021. FEMA could issue a letter of final determination in spring 2022 and make the maps effective that fall.

Residents can view the proposed flood zone maps by searching for the City of Alexandria on FEMA's preliminary maps web page.

The FEMA process is separate from any efforts the city may take to address recent flooding events on July 8, 2019 and July 23 and Sept. 10, 2020. The July 23 storm produced 2.5 inches to 3 inches of rain within 30 minutes, causing flash flooding in areas that may or may not be normally impacted by flooding. The Sept. 10 storm produced 2.5 to 4 inches with rates up to 3 inches per hour, while the July 8, 2019 storm was a flash flooding event with a regional impact.

A key problem is that the city's design standard for stormwater infrastructure is a "10-year storm," which produces 2.28 inches of rain over an hour or 4.81 inches over 24 hours. There are older neighborhoods of the city that don't even meet that "10-year-storm" standard. For that reason, city officials are looking into bolstering infrastructure investments and maintenance, as well as providing more financial and technical assistance to residents and considering development standard reform.

Heavy rainfall makes Alexandria vulnerable to flooding for a number of reasons. Overbank flooding can occur from the Potomac River and tributaries such as Cameron Run, Four Mile Run, Holmes Run and Hooff's Run, while other contributing factors include the tides of the Potomac River, an overwhelmed stormwater system amid high-intensity rainfall, and development in low-lying areas. Aside from the three flooding events in the last 14 months, major flooding events in Alexandria included Hurricane Agnes on June 21 to 23, 1972, Hurricane Isabel on Sept. 18, 2003, a major storm event on June 25, 2006, and Tropical Storm Lee on Sept. 11, 2011.

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