Flood Action Alexandria
Flood Action Alexandria
Launched in 2021, Flood Action Alexandria is the City's comprehensive initiative to address flooding issues.
Join us in this story map to learn more about current flooding, significant causes of flooding, how Alexandria's history impacts today's flooding, what the city is doing to address flooding, and how you can help.
For more information, visit the Flood Action Alexandria website .
Current Flooding Issues
A river flood occurs when water levels rise over the top of riverbanks due to excessive rain from hurricanes or tropical storms, thunderstorms over the river's watershed for extended periods, persistent rainfall, and/or snowmelt. High tides often worsen river flooding.
A flash flood is caused by heavy or intense rainfall, generally less than six hours over a short period. Flash floods are usually characterized by raging torrents after heavy rains rip through streams, streets, or alleys. They can occur within minutes or a few hours of intense rainfall.
Sanitary sewer backups occur when rising ground water and inflow from stormwater gets into sanitary sewers through cracks and joints in pipes, roof downspouts, and holes in manhole lids. During heavy rainfall, sanitary sewers can surcharge and force water into basements.
Causes of Flooding
When land is converted from its natural state to farmland, lawns, roadways, and buildings, the ground cannot naturally absorb as much rainwater as it used to. Instead, the rainwater runs off these surfaces and can contribute to flooding. Before Alexandria was established, forests would have absorbed rainwater and slowly released it to natural waterways.
Some materials (such as asphalt and concrete) do not absorb rainwater. Such surfaces are referred to as impervious surfaces.
As more development occurs and more impervious surfaces are added to the environment, less rainwater is absorbed into the ground where it lands. This leads to more water running off impervious surfaces and can eventually cause flooding.
At a certain point, impervious surfaces can cause so much runoff that it results in flooding. During significant rain events, streams overtop their banks and enter the area adjacent to the stream channel known as the floodplain.
This was especially the case following early development patterns. Current (post-1992) development in Alexandria is required to retain rainwater on-site, which has reduced flooding impacts from impervious surfaces.
Did you know that significant portions of Alexandria are built on top of old stream beds and on filled-in areas of the Potomac River?
Before development, natural waterways in Alexandria collected rainwater, ultimately flowing into the Potomac River and Chesapeake Bay.
As Alexandria developed, natural streams and waterways were put in pipes and channels and buildings and roads were constructed in floodplains.
Many of these streams also became a source of stench and disease by carrying contaminated runoff from farms, houses, and roadways that encroached ever closer to stream banks.
Many waterways were buried in pipes to make more land available for development, control odors and reduce disease risk. These actions allowed some early development to occur on top of the streams.
The channelization and piping of streams eliminated natural floodplains and restricted the amount of water that could flow through the stream. However, the historic stream channels remain as features in the landscape where water naturally flows; therefore, buildings near these historic waterways are prone to experiencing flash floods and sanitary sewer backups.
With an increase in development, the City experienced more runoff and flooding.
To counteract flooding, an early drainage network of pipes, ditches and inlets collected stormwater and brought it to the Potomac River.
Some of the City's pipes are 50 to 100 years old. When those pipes were built, they were designed for less runoff because there was less development.
Today, these pipe systems are aging and undersized. They cannot handle the increased amount of runoff the City is experiencing from climate change and early development patterns. The infrastructure can leak and let groundwater in, which takes up space in the pipes, causing more frequent and intense flash flooding and sanitary sewer backups.
Warmer temperatures from climate change can result in water evaporating more rapidly into the air. This causes more intense rainfall during storm events. Climate change is also causing sea level rise, which results in the Potomac River's high tides reaching higher.
These factors affect Alexandria's drainage system, streams, and the Potomac River. More water means more flash floods, river flooding, and sanitary sewer backups.
Much of Alexandria's Potomac waterfront used to be comprised of natural bluffs, protecting the land from the ebb and flow of the Potomac River's tidal waters.
The Potomac River's natural bluffs were leveled as European settlement accelerated, making Alexandria's shoreline more vulnerable to tidal flooding and heavy rains.
Today, rising sea levels and heavier rains resulting from climate change have made Alexandria even more vulnerable to flooding. These flooding impacts can be especially severe when higher tides and heavy rainfalls coincide.
History's Impact
Overview Timeline
The timeline below provides a glimpse of the topics, from Alexandria's early history to the present.
1600s and Prior
Early Settlement
1749
Establishment of the Town
1749 to 1800
Alexandria's Changing Waterfront
1800s to 1900s
Industrialization and Development | Hooffs Run | Four Mile Run | Developing Alexandria's Sewer System
Alexandria Today
1600s and Prior - Early Settlement
Like most of Eastern North America, Alexandria was forested before human habitation. Centuries before European colonization, the shores of the Potomac were home to several Native American tribes that lived in scattered villages and used the river for fishing and travel. The first documented European explorers reached the Chesapeake in 1588. The early settlers cleared land and farmed. This map from the time of John Smith provides a glimpse of Virginia in 1624.
This John Smith map from 1624 shows approximately where modern day Alexandria is located. The area is defined by small settlements, forests, and waterways, with little to no impervious surfaces to impede natural drainage systems.
1749: Establishment of the Town
European tobacco buyers and growers petitioned the General Assembly in Williamsburg to establish a town at the Hunting Creek Tobacco Warehouse on the Potomac River. The petition was approved. In 1749 the 60 acres of farmland immediately surrounding the tobacco warehouse were plotted out into individual lots, and the town of Alexandria was established on the natural cliffs overlooking a crescent-shaped bay.
This 1749 Plan of Alexandria, developed by George Washington, reflects the establishment of Old Town Alexandria. It also shows the small crescent-shaped bay it was located on, which is essential in the next section.
1749 to 1800: Alexandria's Changing Waterfront
A drawing of Alexandria from 1763, when it was situated on 15- to 20-foot bluffs above the Potomac River. Source: Alexandria Archaeology
Between 1760 and 1775, Alexandria’s waterfront was dominated by 15- to 20-foot high bluffs and four major piers extending into the Potomac River. The bluffs were topped by warehouses along Water Street (now Lee Street). This layout proved difficult for moving goods between ships and the warehouses. To solve this problem, by 1798 the town had leveled the cliffs and used the resulting fill to create new buildable land in the Potomac River. The new land in the bay became a mixture of piled earth, river sediment, timber, debris, and old shipwrecks. This land now sits in the Potomac River's floodplain.
Alexandria’s modern shoreline is mostly landfill; Lee Street was once called Water Street and ran along bluffs overlooking the Potomac River.
View of the Alexandria waterfront after the bluffs had been "pulled down" to fill and extend the shoreline.
Modifications to Alexandria’s waterfront continued through the 1800s. In many cases, the shoreline has been expanded further into the Potomac River and inland waterways. Use the interactive slider to explore how the shoreline and waterways shown in the 1798 Gilpin Plan compare to the City of Alexandria’s current shoreline.
1798 Gilpin Plan (left) and current topographic map (right).
1800s to 1900s: Industrialization & Development
Early development also led to dramatic alterations to Alexandria's waterways and substantial increases in impervious surfaces, resulting in more runoff. We will walk through changes to Hooffs Run and Four Mile Run as examples below, representing the historical issues that have shaped other watersheds in Alexandria, such as Holmes Run, Cameron Run, and Taylor Run.
Early Hooffs Run
Before the urbanization of Alexandria, Timber Branch and Hooffs Run (highlighted on the map) were once a continuous stream originating near present-day Braddock Heights. Before the mid-1800's, the run was navigable from Hunting Creek to Duke Street.
Hooffs Run has since been modified so extensively that it no longer connects to Timber Run.
Source: 1864 Hoffman & Brown map
Hooffs Run: 1850 to 1920
By 1900 development had occurred immediately adjacent to Hooffs Run.
The southern portion of Hooffs Run / Timber Branch was diverted in 1882. Parts of the creek trench south of Duke Street were then filled in by the Southern Railroad after 1890.
Source: United States Geological Survey (USGS), 1900
The Hooffs Run Bridge was built in 1856 to allow the Orange and Alexandria Railroad to cross the run. This historic bridge is a significant bottleneck in the river and causes upstream flooding.
The Hooffs Run Bridge, built in 1856 (left) and a view of the Orange and Alexandria Railroad in 1863 with an arrow pointing to the Hooffs Run Bridge (right). Sources: National Archives and Alexandria Library, Special Collections.
Hooffs Run was the primary outlet for stormwater and sewage for the neighborhoods of Cottage Park, Braddock Heights, Rosemont and Union Station. Low-lying and poorly drained land along Hooffs Run frequently flooded, leaving stagnant water that bred mosquitos and contributed to spreading disease. The area was used as a City dump.
Amidst debates in the 1910s over municipal sewer needs, the Alexandria Gazette documented the unhygienic conditions and poor drainage in the Hooffs Run area:
Duke Street over Hooffs Run in 1923. Source: Alexandria Library - Special Collections
“On either side of Hooff’s Run are two low areas where drainage into the stream is intercepted. The water collected…offers a breeding place for the malaria as well as the common mosquitos.”
Source: Alexandria Gazette | 12 April, 1916
Hooffs Run: 1920 to 1950
Hooffs Run was mostly channelized by the 1930s to improve sanitation. Some of the stream segments were piped and covered by asphalt, green space, or concrete. Use the interactive slider below to see the underground piping of Hooffs Run (marked in red) and the increase in nearby development between 1927 (left) and 1949 (right).
Hooffs Run area in 1927 (left) and in 1949 (right). Hooffs Run can be seen in the center of each image, as an open waterway in 1927 and piped/covered by 1949. Source: City of Alexandria Imagery
Rosemont Flood. Source: Washington Times, September 3 1922
Due to the alterations of the channel and increased impervious area, flooding is not a new issue in the Hooffs Run Watershed. For instance, in 1922, “the worst rainstorm in 44 years” caused widespread flooding in the Washington, DC area, including the North Rosemont neighborhood of Alexandria.
Four Mile Run: 1900
Four Mile Run is another major drainage area in Alexandria. Four Mile Run's outlet was modified and channelized with the construction of railroads, as shown in this 1900 USGS map.
Four Mile Run: Early 1900s
The Four Mile Run area saw heavy development in the first half of the 20th century. Use the interactive slider below to compare two USGS topographic maps (one from 1900 on the left and one from 1956 on the right). This comparison shows the increase in development and infilling within the floodplain of Four Mile Run.
USGS topographic maps of the Four Mile Run area in 1900 (left) and 1956 (right).
Four Mile Run: 1927
Four Mile Run's floodplain and natural channel were relatively intact. The bay along the Potomac was still open.
Source: City of Alexandria
Four Mile Run: 1949
Infilling of the bay and floodplain began. Development accelerated to the west. Flooding issues arose in the Four Mile Run watershed, as seen in the photos below.
Source: City of Alexandria
Hume Springs, 1975. Source: Northern Virginia Regional Commission
Arlandia, 1972. Source: Alexandria Library
Arlandia, 1972. Source: Alexandria Library
Four Mile Run: 1995
Development continued, and the Army Corps of Engineers designed and installed a system of flood channels and levees. In 1995, the channel was armored with concrete and stone, and the floodplain was highly modified.
Source: City of Alexandria
Source: Alexandria Gazette, 12 Sep 1878
Developing Alexandria's Sewer System
Public health and flooding issues became a concern with more development and lack of proper drainage. The waterfront served as much as a sewer and dumping ground as it did a commercial district and a source of food. A newspaper description of the Yellow Fever outbreak in 1803 (which killed more than 200 Alexandrians and drove almost half of the population to seek safety in the countryside) provides a sense of the conditions along the waterfront.
An 1878 Alexandria Gazette article shows how Alexandria's waterways were associated with disease:
"...fill up the cove there, and pile it with warehouses and dwellings that receive the sewerage from the hills above, and give it no outlet; for that was the condition which surrounded the newly filled cove between Fishtown and Pioneer Mills in 1803. Even then the poison of the disease was spent mainly on the newly made ground, the bulk of the cases occurring below Water street, and none beyond royal street."
To address some of the early flooding and sanitation issues discussed above, Alexandria began to install sewer infrastructure to manage waste and stormwater as early as 1870. This map series shows the installation of part of the sewer system from 1896 through 1914.
In 1896, the City’s first engineer reported that 22.6% of the city’s streets were unpaved dirt, and there were only four sewers.
By 1902 there were 3.5 miles of sewer: 57% were terra cotta pipes, and 38% were larger brick barrel sewers.
By 1907 there were 7.1 miles of sewer: 73% were of terra cotta pipes and 20% were brick barrel sewers.
A significant addition to the sewer system by 1907 was one of the first storm sewers in the city (shown in green). The storm sewer collected flow from King Street and West Street and discharged into Hooffs Run. This pipe's subsequent expansion can be seen in the 1914 map.
By 1914 the sewer system was 10.3 miles long. The increasing prevalence of sewer pipes decreased the need for privies, which were eliminated in the early 1900's.
Source, Jason Tercha, 2017, “Report on the Early History of the Alexandria, Virginia Sewerage System.”
Source: Alexandria Gazette | 18 Sep 1912
Introducing separate storm sewers resulted in large amounts of water being quickly conveyed to natural waterways. Whereas water in the past would take many hours or days to infiltrate and slowly enter streams, pipes reduced that time to minutes and hours, causing larger volumes of water to enter waterways and causing them to flood. In this 1912 article, note how much water is piped to Hooffs Run.
Alexandria Today
Today, nearly all of Alexandria is serviced by a network of stormwater, sanitary, and combined sewers that is made up of about 200 miles of pipe. The City also has about 25 miles of streams. While inspection and upgrades are made to this system every year as needed, some original pipes placed 50 to 100 years ago remain in use. These older pipes, often terracotta, brick, or corrugated metal, may leak and allow groundwater in. Stormwater pipes, inlets, and outfalls are sized for the level of development present when they were built, so that older pipes were often installed under older requirements or were not upgraded with additional development that occurred prior to current standards.
Within areas with older communities like Del Ray and Rosemont, and adjacent areas in the Hooffs Run and Four Mile Run watersheds, there may be undersized portions of the storm sewer drainage system can be overwhelmed by and more intense storms caused by climate change and cause flash flooding that impacts the community. Higher tides in Old Town can cause flooding even during sunny days as stormwater runoff from upstream areas swells the Potomac River. The City recognizes the importance of accelerating upgrades to the drainage system. Continue scrolling to "What is the City Doing?" to learn about current and upcoming projects.
What is the City Doing?
Flood Action Alexandria is committed to addressing flooding challenges through a multi-faceted approach.
Flood Mitigation Projects and Dashboard
Each year, the City allocates tens of millions of dollars towards the planning, design, and construction of flood mitigation projects through the Capital Improvements Program. The City continues to pursue flood mitigation projects to address existing issues identified through resident complaints, engineering analyses, and field observations. The City works with engineering and construction professionals to design and construct the mitigation projects, always with community input and engagement.
The master project schedule is also available for detailed project timelines.
RiverRenew
The City is supporting Alex Renew on a major stormwater pollution control initiative called RiverRenew . This key project involves construction of an underground storage tunnel beneath the Potomac River to reduce the overflow of combined stormwater and sanitary sewage into the Potomac River during rain events.
Stormwater Regulations
The City has required stormwater management in new development and redevelopment activities dating back to the 1990s. Stormwater quality requirements in the City were implemented in 1992 under the Chesapeake Bay Act for development activities disturbing land with an area of 2,500 square feet or greater, as incorporated into Article XIII of the zoning ordinance. These stormwater quality requirements implemented via the City’s Bay ordinance are more stringent than the state law. Stormwater quality requirements are detailed in section 13-109 of the City’s zoning ordinance, which can be found here . To meet these requirements, stormwater best management practices (BMP’s) are used to treat pollutants from stormwater runoff.
Since that time, stormwater management systems that have been designed with these stringent requirements and have proven to be more resilient during large storm events than older systems. In addition, new development and redevelopment in the city are required to meet water quantity management requirements. Stormwater quantity management requires that the rate of runoff from development sites be at or below pre-construction conditions. This requirement can be met by providing onsite detention, deploying green infrastructure, and/or removing existing impervious area. In addition to water quality and quantity management, storm sewer capacity requirements are more stringent in the City of Alexandria compared to the industry standard and neighboring localities.
Storm sewer pipes are based on capacity for a 10-year storm event, which is consistent with Virginia state requirements. However, the rainfall intensities used in Alexandria are higher when compared to precipitation intensity data from the National Oceanic and Atmospheric Administration (NOAA). Therefore, City of Alexandria rainfall intensities are more protective when applied to storm sewer design. These rainfall intensities are determined using rainfall intensity – duration – frequency (IDF) curves. These IDF curves set out the level of rainfall that must be used for City of Alexandria storm sewer design and can be found here . Designing to these higher intensities result in larger pipes, which convey more flow for a given storm event. Because of the water quality and water quantity stormwater management requirements, and because of the stringent storm sewer system design requirements, recent new development and re-development projects have not experienced the kinds of flash flooding impacts that have affected the older parts of Alexandria.
Incentive Programs
The City provides monetary incentives for property owners to protect against the impacts of flooding through the following programs:
Flood Mitigation Pilot Grant Program : Property owners can receive a matching reimbursement grant from the City to install practices on their properties to reduce flooding impacts. To learn about eligibility requirements and how to apply, click here.
Stormwater Utility Fee Credit Program: The City encourages property owners to reduce their stormwater utility fee on a bi-annual basis through the use of best management practices (BMPs) such as the installation of raingardens and green infrastructure or installing dry floodproofing measures on private properties, which collectively improves water quality and helps reduce runoff and flooding. See the Stormwater Utility Fee Credit Manual for more information on eligibility, requirements, and benefits of this program.
Backflow Preventer Assistance Program: This program offers reimburses homeowners for up to 50 percent of the cost of installing a backflow preventer device by a licensed plumbing contractor, up to a maximum of $2,000. The program is open to all City of Alexandria homeowners. See – City Assistance Program for Sewer Backflow Prevention for more information.
What is Your Role?
You can make a difference, both in your own home and in our City.
Stay Informed
Visit the Flood Action Alexandria website for information on the City of Alexandria's flooding programs. You can also sign up for City of Alexandria's digital newsletter (opt-in to “Flood Action Alexandria”), educate yourself on crucial flooding terms , and view a Q&A that answers some common flooding questions. View all of these resources on the Flood Action Alexandria Community Engagement page.
Assess your flood risk using the interactive FloodFactor tool and review upcoming changes to Federal Emergency Management Agency (FEMA) flood zones in Fall 2022. Additional information on the upcoming FEMA flood changes is in this Q&A .
Alexandria, Virginia | Flood Factor
Report Issues
If you experience flooding that is an immediate danger to yourself or others, always call 911. To report non-emergency issues, use the link below to report a flooding issue or dial 311 and follow the prompts. Hearing directly from residents helps the City identify problems that may go unnoticed.
Be Prepared
If your property is at risk, take steps to mitigate flooding impacts on your home by reviewing some flood emergency basics and learning about common flood mitigation practices .
If you install a flood mitigation practice, you may qualify for financial assistance under the City of Alexandria's Flood Mitigation Pilot Grant Program . For quick reference on eligibility and how to apply, see this Q&A sheet.
You may also be eligible for stormwater utility fee credits if you install certain stormwater management practices, such as rain barrels or a permeable pavement system. See the Stormwater Utility Fee Credit Manual for more information on eligibility, requirements, and benefits of this program.
