Park property along many of the City's waterways and open spaces located within floodplains have been designated as natural floodplains. 
• Four Mile Run Park includes about 18 acres of dedicated wetlands in the Four Mile Run floodplain.
• Fort Williams Park has dedicated open space in a natural forested environment, as well as recently restored natural areas located in the Strawberry Run floodplain.
• Dora Kelley Park, Brook Valley Park and All Veterans Park contain parklands and dedicated natural areas located within the Holmes Run floodplain.
• Tarleton Park and Cameron Run Regional Park contain natural open space and parklands in the Cameron Run floodplain.

Benefits
• Reduce flood velocities and provide flood storage to reduce peak flows downstream by spreading over a large area.
• Create improved water quality and reduce the amount of sedimentation transported downstream by acting as a filter for stormwater runoff and flow.
• Reduce the frequency and duration of low flows of surface water by serving as a recharge area for groundwater.
• Provide habitat for diverse species of plants and animals, some of which can not live anywhere else. 
• Moderate water temperature, which reduces potential harm to aquatic plants and animals.

Hazards
• Alexandria is prone to flooding from heavy rainfall and tropical storms, creating overbank flooding from the Potomac River and its tributaries.
• In conjunction with development in low-lying areas and an overtaxed stormwater system, the tidal influence on the Potomac River can also contribute to flooding. Summer thunderstorms with high intensity-short duration rainfall are the most common flooding problem.
• The 100-year floodplain is the area that has a 1% chance of being flooded in any given year. Put another way, it has about a 26% chance of being flooded over the life of a 30-year mortgage. Smaller floods have a greater chance of occurring in any year and can create a significant flood hazard to people and property close to the channel. 

Flood Mitigation Maintenance
To mitigate flooding, the City conducts maintenance on storm drains and streams that become clogged with debris, soil erosion and overgrowth of vegetation. The City also investigates illegal dumping that can threaten the quality of waterways and contribute to flooding. 
• Report localized drainage problems to T&ES Maintenance at 703.746.4488. 
• Request maintenance service on storm drains or streams through Alex311. 
• Report illegal dumping to T&ES Stormwater Management Division at 703.746.6499.

Notable flooding events:
• Severe thunderstorms on Aug. 14, 2021
• Severe thunderstorms on Sept. 10, 2020
• Severe thunderstorms on July 23, 2020
• Severe thunderstorms on July 8, 2019
• Tropical Storm Lee on September 11, 2011 
• Significant storm event on June 25, 2006
• Hurricane Isabel on September 18, 2003
• Hurricane Agnes June 21 to 23, 1972

Alexandria is participating in a Flood Insurance Study being conducted by the Federal Emergency Management Agency (FEMA) to update the City’s current floodplain maps. Floodplain maps inform communities about local flood risk. The maps help set minimum floodplain standards, which helps communities build safely and resiliently, and they also determine the cost of flood insurance, which helps property owners financially protect themselves against flooding. A few FEMA resources are linked here:

What Flood Map Updates Mean for You

FEMA’s Flood Insurance Advocate Explains NFIP Basements (Video)

Defining a Property’s Unique Flood Risk (Video)

Flood risk changes over time due to weather patterns, land development, and erosion. 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. This effort is unrelated to recent flooding the city has experienced from flash flooding in July 2019 and, more recently, on July 23.  The storm on July 23 dropped 2.5 to 3 inches of rain in 30 minutes, creating a brief, extremely high-intensity event that caused significant flash flooding in many areas, including some not normally impacted by flooding. Visit the City’s Flooding and Drainage web page for Frequently Asked Questions about flooding, as well as more on planning and prioritization efforts for projects that will address flooding and drainage issues in less extreme cases.

FEMA map changes occur periodically, as the agency deems necessary—the maps in Alexandria were last changed in 2011. The City of Alexandria is a partner in this process, but FEMA develops the new maps and sets the process timeline. The new flood maps currently being developed by FEMA are scheduled to go into effect in Alexandria and neighboring jurisdictions in the Fall of 2022 (see timeline for implementation below). Click here for an interactive map to see the proposed changes (enter a property address to help orient the map).

Residents and businesses are encouraged to visit FEMA’s website to view the draft map changes and find both the current and proposed flood risk for their property. The City received copies of the new Preliminary Maps (below) and a new Preliminary Flood Insurance Study in September 2020. Before the new maps take effect in Fall 2022, residents will be invited to participate in a review and appeals process.

2023 Final Maps

On July 11, 2023, the Federal Emergency Management Administration (FEMA) published the FEMA Letter of Final Determination (July 11, 2023)  certifying FEMA’s new maps in Alexandria as the latest and best information on the FEMA delineated Special Flood Hazard Areas (SFHA), or the 1%-chance-per-year flood inundation zones (100-year floodplain). The new maps will become effective January 11, 2024. The City is required by FEMA to regulate any development in the SFHA to the new maps as of July 11, 2023. 

2023 Flood Insurance Rate Maps

Alexandria participates in the National Flood Insurance Program (NFIP). Because City engineers regularly inspect floodplains and stormwater management staff complete activities in 17 categories annually as part of the federal Community Rating System program, Alexandria residents are entitled to up to a 20% discount on flood insurance premiums. Residents with a preferred risk flood policy (PRP) can receive a reduction up to 5% on insurance premiums.

There are two types of coverage:

• Structural coverage covers everything that stays with a house when it’s sold, including cabinets, built-in appliances, and wall-to-wall carpeting. The maximum amount of structural coverage is $250,000 for residential policies and $500,000 for commercial policies.
• Contents coverage covers furniture and other personal possessions except money, valuable papers, etc. Renters may purchase contents coverage, even if the owner does not buy structural coverage. The maximum amount of contents coverage available for residential policies is $100,000 and $500,000 for commercial policies.

Local insurance agents are permitted to sell an NFIP flood insurance policy to everyone (residences and businesses) under the rules and standards set by the federal government. Any house or business in Alexandria can be covered by a flood insurance policy, and the average cost is less than $750 per year. Detached garages and other accessory buildings may also be covered under the policy for the main building on the lot. Check with your insurance provider for more details. 

Don’t wait until the next flood to buy insurance. There is a 30-day waiting period before the NFIP coverage goes into effect. For information on flood insurance, visit www.floodsmart.gov. 

The NFIP and the City of Alexandria require that if the cost of reconstruction, rehabilitation, additions or other improvements to a building equal or exceed 50% of the building’s market value, then the building must meet the same construction requirements as a new building. Substantially damaged buildings must be brought up to the same standards. This means that a residence damaged where the cost of repairs equals or exceeds 50% of the building’s value before it was damaged must be elevated above the base flood elevation (BFE).

Before proceeding with repairs or improvements to a damaged structure, contact the Department to Code Administration 703.746.4200.

Any development in the floodplain (not just the construction of buildings, but bringing in fill or storage of material) requires a permit. Our City's Zoning ordinance captures the requirements; however, you should first contact the Floodplain Administrator at 2900-B Business Center Drive, 703.746.6499, to find out exactly what is required.

Any illegal floodplain development should be reported to this office as well. Email stormwater@alexandriava.gov for Elevation Certificates of recent construction on file available to the public upon request. The Code Administration phone number is 703.746.4200 and the Floodplain Administrator at 703.746.6499.

• City's storm sewer system
  Following flooding in June 2006, the City of Alexandria launched a review of its storm sewer system to identify flooding areas and develop and prioritize solutions. The Storm Sewer Capacity Analysis (CASSCA) project was completed in February 2016.   
  City of Alexandria Storm Sewer Capacity Analysis  

• Which watershed do you live in?  
  Watershed Tool

• FEMA flood map updates questions & answers sheet
• Learn about FEMA's Risk Rating 2.0 which might impact your federal flood insurance rates
• CRS Community Certification
• Flood Hazard Mapping Fact Sheet  

Brian Rahal, P.E., CFM
Transportation & Environmental Services
2900B Business Center Drive
Alexandria, VA 22314
703.746.4057

Flood warnings are forecasts of impending storms and are broadcast to the public by the NOAA Weather Radio, commercial radio, TV stations, and local emergency agencies. Alexandria has developed a flood warning system to notify residents of impending floods. Warnings will be disseminated by local radio, including stations WTOP, and DC101, and local television stations including NBC4/WRC, FOX5/WTTG, ABC7/WJLA, and CBS9/WUSA. The flood warning system is intended to provide up to one half hour of advance warning of a flood hazard. By paying attention to weather alerts, you will have enough time to protect your property or evacuate. The National Weather Service local forecast office transmits flood advisories, watches and warnings on frequency 162.550 MHz. Anyone with a NOAA Weather Radio can receive this information. The Emergency Alert System (operated by the FCC in cooperation with FEMA and NOAA) allows the public to be notified via commercial radio, cable TV and broadcast TV of emergency messages from the National Weather Service or local civil authorities.