As residents of Alexandria, we enjoy proximity to the Potomac River for its beauty and the benefit of recreation. But along with these benefits come natural hazards. Flooding is one of the most common risks to Virginia residents living in floodplains, and in Alexandria approximately 20% of the City is mapped as floodplain. 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 still create a significant flood hazard to people and property close to the channel.
Alexandria is prone to flooding from heavy rainfall and from tropical storms creating overbank flooding from the Potomac River and its tributaries (Backlick Run, Cameron Run, Four Mile Run, Holmes Run, Hooff's Run, Taylor Run, Timberbranch Run, Strawberry Run and Lucky Run). The most common local flooding problem is due to summer thunderstorms with high intensity-short duration rainfall. The tidal influence on the Potomac River in conjunction with development in low lying areas and an overtaxed stormwater system are also contributing factors to flooding.
For Alexandrians, the most notable recent flooding events were Hurricane Agnes June 21-23, 1972, Hurricane Isabel September 18, 2003, a major storm event June 25, 2006, Tropical Storm Lee on September 11, 2011, Severe Thunderstorms on July 8, 2019, and July 23, 2020.
Preliminary FEMA Maps Are Here
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.
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).
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 will receive 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.
Preliminary Maps (9/30/2020)
It is important for residents and business owners to know current flood risks if residences or businesses are in a FEMA 100-year floodplain, or property is susceptible to damage from any type of flooding that may occur. Residents and business owners can take steps to protect themselves and their property.
FEMA’s current schedule (a flood map change typically takes 36 months):
- Publish Preliminary Maps – September 2020
- FEMA Community Open House – TBD
- Public Review and Comment (Appeal) Period – 90 days in Summer 2021
- FEMA Issues Letter of Final Determination (LFD) – Spring 2022
- New Maps Become Effective – Fall 2022
The City will be conducting outreach on the update process and to discuss potential impacts to existing property and proposed redevelopment from FEMA’s Flood Insurance Study and re-mapping effort.
Flood Safety Measures
- Pay attention to evacuation orders. Listen to local radio or TV stations for forecasts and emergency warnings. Know about evacuation routes and nearby shelters and have plans for all family members on evacuation procedures and where to meet if you are separated during an emergency.
- Do not drive through flooded areas. During a flood, more people drown in their cars than anywhere else. Don’t drive around road barriers, the road or bridge may be washed out.
- Do not walk through flowing water. Flash flooding is the leading cause of weather-related deaths in the U.S. Currents can be deceptive; six inches of moving water can knock you off your feet in a strong current. If you walk through standing water, use a stick or pole to help you locate the ground.
- Stay away from power lines and electrical wires. Electrical currents can travel through water. Report downed power lines to Dominion Virginia Power at 1.888.667.3000.
- Have the power company turn off your electricity. Some appliances, like televisions, keep electrical charges even after they are unplugged. Don’t use appliances or motors that have gotten wet unless they have been taken apart, cleaned and dried.
- Look before you step. After a flood, the ground and floors may be covered with debris like broken bottles or nails. Floors and stairs that are covered with mud can be slippery
- Be alert for gas leaks. Use a flashlight to inspect damage. Don’t smoke or use candles, lanterns, or open flames unless you know the gas has been shut off and the area has been ventilated.
Flood Warning Procedures
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.
Property Protection Measures
There are several ways you can protect your property from flood damage before the flood occurs. If there is an imminent flood threat, you can take these emergency measures:
- Place sandbags or plastic sheeting in front of doorways and other low entry points
- Elevate furniture above flood protection levels
- Move valuables to a higher level
- Create floodway openings in non-habitable areas such as garage doors
- Seal off sewer lines to the dwelling to prevent backflow of sewer waters
You can also make permanent changes to protect a building from flood damage:
- Keep water away by regrading the lot
- Build a small floodwall or earthen berm. This can be helpful for some houses on slab foundations.
- If your house is on a crawlspace, a low floodwall, berm or “wet floodproofing” may help. Wet floodproofing means moving all items subject to flood damage out of harm’s way so water can flow into the crawlspace without causing problems.
- Make the walls waterproof and put watertight closures over doors. This is called “dry floodproofing.”
- If floodwaters go over the first floor, you can raise the building above flood protection levels.
- Electrical panel boxes, furnaces, water heaters, washers and dryers should be elevated or relocated to a location less likely to be flooded.
The City’s Engineering Department can help you determine which of these methods is most appropriate for your home, and you will need a permit to make permanent retrofits to your building. If you are interested in elevating your home above the flood level, grant funding may be available to cover up to 75% of the cost. More information can be found in Homeowners’ Guide to Retrofitting: Six Ways to Protect Your House from Flooding. Available at www.fema.gov/rebuild/mat/fema312.shtm.
Most homeowners’ insurance policies do not cover a property for flood damage. Since Alexandria participates in the National Flood Insurance Program (NFIP), local insurance agents are permitted to sell everyone (residences and businesses) an NFIP flood insurance policy under the rules and standards set by the federal government. You can purchase an NFIP flood insurance policy, which is separate from your homeowners’ insurance. Any house or business in Alexandria can be covered by a flood insurance policy. The average cost of a flood insurance policy is less than $750 per year. Detached garages and other accessory buildings are covered under the policy for the main building on the lot. There are two types of coverage you can purchase:
- 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.
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 more detailed information on flood insurance you can go to www.floodsmart.gov. Alexandria is a class 6 CRS (Community Rating System) community, thus entitling its citizens with a standard flood policy up to a 20 % discount on their insurance premiums. Those citizens with a preferred risk flood polices (PRP) are receiving a 5% discount on their insurance premiums.
Floodplain Development Permit Requirements
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. Our Code Administration office, Room 4200 of City Hall, has 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.
Substantial Improvement/Damage Requirements
The NFIP and the City of Alexandria requires that if the cost of reconstruction, rehabilitation, additions, or other improvements to a building equals or exceeds 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.
Drainage System Maintenance
The City’s drainage system, including storm drains and streams, is designed to carry away water during a storm and helps prevent floods. Dumping debris, soils erosion, and overgrowth of vegetation can compromise the drainage system. When this happens, flooding occurs more frequently and reaches higher elevations, subjecting otherwise safe properties to unnecessary damage. Dumping waste down storm drains or into streams or other bodies of water is not only bad for the environment, but it is illegal. To keep our drainage systems functioning, do not dump or throw anything into ditches, storm drains, streams or rivers. Keep grass clippings and other debris out of storm drains. This will prevent clogging and loss of stormwater storage capacity.
If you see localized drainage problems call T&ES Maintenance at 703.746.4488. If you see dumping into storm drains, streams, ditches or rivers call T&ES Stormwater Management Division at 703.746.6499.
Natural and Beneficial Functions
In their natural, undeveloped state, floodplains play an important role in flooding. They allow flood waters to spread over a large area, reducing flood velocities and providing flood storage to reduce peak flows downstream. Natural floodplains and its vegetation act as a filter for runoff and flow creating improved water quality, reducing the amount of sedimentation transported downstream, and minimizing the impurities in the sedimentation. Floodplains can be recharge areas for groundwater and reduce the frequency and duration of low flows of surface water. They provide habitat for diverse species of plants and animals, some of which cannot live anywhere else. Floodplains are particularly important as breeding and feeding grounds. Natural floodplains also moderate water temperature, reducing potential harm to aquatic plants and animals.
The City of Alexandria has designated City park property along many of the City’s waterways and has several areas preserved as open space or park areas located within the floodplains that provide natural and beneficial functions. Four Mile Run Park includes approximately 18-acres of dedicated wetlands in the Four Mile Run floodplain. Fort Williams Park contains 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 contains natural open space and park lands in the Cameron Run floodplain.
Flood Zone Information
Alexandria’s low elevation and its proximity to the Potomac River make it susceptible to flooding. Nearly every year, and sometimes several times throughout the year during periods of heavy rain, hurricanes or quick snow melts, residential and commercial properties are threatened with the potential of tidal and wind-driven flooding from the Potomac River and/or low-land flooding, particularly in neighborhoods around Four Mile Run. We encourage residents and business owners to plan for flooding as part of their emergency preparedness planning.
The City of Alexandria has detailed, digital flood hazard maps available. These maps, also known as Flood Insurance Rate Maps (FIRMs), reflect current flood risks, replacing maps that date back to 1991. As a result, you and other property owners throughout the city will have up-to-date reliable information about your flood risk on a property-by-property basis.
Storm Sewer Capacity AnalysisIn February 2016, the City finalized a summary report of the City of Alexandria Storm Sewer Capacity Analysis (CASSCA) project, the purpose of which was to analyze the storm sewer system, identify problem flooding areas, and develop and prioritize solutions. The City conducted the study in response to flooding in June of 2006. The City is working on the design and construction of large capital projects based on this analysis, which identified problem flooding areas and prioritized potential projects to alleviate storm sewer capacity issues.
Frequently Asked Questions (FAQ)
How will these changes affect you?
If your parcel is located in a Special Flood Hazard Area (SFHA), and shown as Zone A or AE on the FIRM and if you have a mortgage from a federally-regulated lender and the building(s) on this parcel are within the SFHA, then by federal law, your lender must require you to carry flood insurance when these flood maps become effective. Flood insurance is available through the National Flood Insurance Program (NFIP), a federally underwritten program provided by nearly 100 insurance companies and written through licensed insurance agents. Contact your insurance agent to learn about lower-cost “grandfathering” options offered by the NFIP for properties being mapped into higher-risk areas for the first time.
FEMA's NFIP Grandfathering Rules:
If you do not have a mortgage, it is still recommended that you purchase flood insurance. According to FEMA, over the life of a 30-year loan, there is about a three times greater chance of having a flood in your home than having a fire. And most homeowner's insurance policies do not provide coverage for damage due to flooding. For more information on flood insurance, visit the National Flood Insurance Program’s website, www.floodsmart.gov.
The new maps help promote public safety.
These flood hazard maps are important tools used in the effort to protect lives and properties in Alexandria. By showing the extent to which areas of the city and individual properties are at risk for flooding, the flood maps help business owners and residents make more informed decisions about personal safety and financially protecting their property. These maps also allow community planners, local officials, engineers, builders and others to make determinations about where and how new structures and developments should be built.
If you feel there has been an error, you can file a protest or appeal.
If you feel your property or your building(s) are physically out of the floodplain, FEMA provides an opportunity for you to have the insurance requirement removed by applying for a Letter of Map Amendment (LOMA) that lenders/underwriters accept.
When did the maps become effective?
FEMA issued a Letter of Final Determination on December 16, 2010. On or before the effective date of the new maps, an ordinance approving the new Digital Flood Insurance Rate Map was be adopted. The maps became effective on June 16, 2011.
Here’s where to go for more information.
Digital copies of the Flood Insurance Rate Maps (FIRMs) are available below and may also be viewed at the FEMA National Flood Hazard layer viewer . Paper copies of the maps are also available at the City’s main libraries.
- Flood Hazard Mapping Fact Sheet
- 2011 Flood Insurance Rate Maps (all maps in a single file : 29 MB)
To locate the floodplain near your property on these maps:
1. Click on "2011 Flood Index Map" below to view the index map.
2. Locate and make note of the map number (ex: 5155190009E) that corresponds to your property location.
3. Come back to this page and click on the noted map number below to view that map (adobe PDF): 2011 Flood Index Map
The FEMA Flood Maps are also available for viewing at all Alexandria Public Libraries: alexlibraryva.org
For more information, please contact:
Brian Rahal, P.E., CFM
Transportation & Environmental Services
2900B Business Center Drive
Alexandria, VA 22314