Flooding and Drainage
How to Protect Your Property
DETERMINE YOUR FLOOD RISK
The Federal Emergency Management Agency (FEMA) creates Flood Insurance Rate Maps (FIRMs) that show floodplain boundaries. As of 2011, approximately 20% of the City is mapped by FEMA in a floodplain. However, extremely high-intensity storms may cause flash flooding in areas that are not normally impacted, to include properties that may not be in a designated FEMA floodplain. Please visit the Flood Map page for more information on the FEMA flood maps.
PURCHASE FLOOD INSURANCE
Most homeowner’s insurance does not cover property damage from flooding but homeowners may purchase flood insurance through the National Flood Insurance Program (NFIP), even if your property is outside of a FEMA-designated floodplain. Alexandria participates in the NFIP’s Community Rating System (CRS) program, a voluntary incentive program that recognizes and encourages community floodplain management activities that exceed the minimum program requirements, and scores those activities to determine “classes” for those communities that participate. Recognized as a "Class 6" community, Alexandria homeowners are eligible to receive up to a 20% discount on flood insurance premiums.
FLOOD MITIGATION TECHNIQUES AND PRACTICES
Individuals interested in protecting their property from future floods have several options available. Some property owners can even be reimbursed for installing flood mitigation measures on properties impacted by flooding from recent flash flooding events, under the City's new Flood Mitigation Pilot Grant Program. The FEMA Homeowner’s Guide to Retrofitting is a great resource for homeowners who want to know how to protect their homes from flooding, and many products and services can be found to protect family and property. Common practices include:
- Floodproofing windows – Glass protection materials; fixed, translucent, water-tight covers; custom window wells and associated drains
- Floodproofing doorways – Flood gates or panels; flood socks: temporary quick dams and sandless sandbags; traditional sandbags
- Floodproofing basements – Battery-powered sump pumps; drain tiles below a basement floor; flood vents
- Floodproofing utilities – Elevating electrical outlets and switches, heating, ventilation, and air conditioning (HVAC) systems, and other appliances (indoors and outdoors); floodwalls, covers and shields for appliances
- Modifying topography – Surface grading; protective walls; impermeable soil materials
Preventative measures should be taken such as keeping your home’s gutters and drains cleared from debris and maintaining your home and appliance pipe system – even small pipes like the line to the ice maker in your fridge can cause major damage when compromised. Click here for information on floodproofing doorways and click here for more ideas from the U.S. Army Corps of Engineers publication on Local Flood Proofing Programs. Finally, in advance of a storm seek ways to minimize water intrusion such as sand bags and other measures.
CITY ASSISTANCE PROGRAM FOR SEWER BACKFLOW PREVENTION
The City of Alexandria offers financial assistance for sanitary sewer backflow prevention to help prevent sanitary sewer flows from backing up into the drains of your home during a flood.
Help Prevent Local Flooding
Not all storm drainage infrastructure is owned by the City. You can help prevent local flooding by keeping trash and other debris, like tree branches, away from storm drains and inlets. Utilize the Alex311 system to report storm sewer blockages or issues on public property.
Proactive City Operations and Maintenance
The City has about 185 miles of storm sewer pipe, about 13,500 storm structures, and about 26 miles of streams. City crews and contractors perform proactive maintenance on storm sewer infrastructure and in response to complaints to remove any blockages and to ensure that the storm sewer infrastructure is functioning as designed. Regular street sweeping of roadways is performed to aide in the removal of nutrients and pollutants from our local waterways while removing road debris to prevent it from entering the storm sewer system.
City Flooding and Drainage Projects
The increasing frequency of more intense storm events has created more frequent flooding and drainage issues. The City identifies flooding and drainage projects through resident complaints, analyses, and field observations. View an overview of capacity and spot projects presented to City Council. These include small to medium ‘Spot Improvement’ capital improvement program (CIP) projects to mitigate drainage issues. After identification and initial investigations, these projects often require work to identify CIP resources, perform onsite survey, complete design, secure right of entry (if applicable), and procure a construction contractor to perform the work. The City completed the initial Storm Sewer Capacity Analysis that identified problem areas and prioritized potential locations for large, multi-year CIP projects to address capacity issues. Please visit the Waterfront Plan Implementation page for more information on flood mitigation projects specific to the waterfront. To learn more about project funding, click here.
CITY OF ALEXANDRIA STORM SEWER CAPACITY ANALYSIS (CASSCA)
In 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. As a high-level conceptual planning exercise, the storm sewer system was modeled to predict potential capacity issues for the City’ current design standard which is a 10-year storm. While the City’s design standard is consistent with or more protective than some of the City’s neighboring jurisdictions, the July 8, 2019, and the July 23, 2020, storms were more intense than this design standard, with the July 23 event about 30 times more intense.
Out of the 83 "problem areas" in the City’s eight watersheds, the top two watersheds were Hooff’s Run and Four Mile Run, with 23 "problem areas" each. More detailed planning and analysis will take place to assess the overall implementation feasibility (including construction) prior to full design of these large-scale capital projects.
The City compares the modeled "problem areas" from the CASSCA project to (1) actual reports of flooding, drainage, and capacity issues during calendar year 2018 (one of the wettest years on record), (2) the July 8, 2019, regional flash flood, (3) the July 23, 2020, localized flash flood, and (4) the September 10, 2020, localized flash flood to help determine the most appropriate areas for improvements. The CASSCA project recommended more than $40 million in storm sewer capacity investments (in 2016 dollars) in Hooff’s Run and Four Mile Run alone to bring the current storm sewers to the current design standard. In fiscal year 2021, the City's CIP has allocated $19 million towards storm sewer capacity improvements.
SPOT IMPROVEMENT PROJECTS
Spot improvement projects are small capital projects managed by Transportation & Environmental Services Stormwater Management Division (T&ES SWM) to help address localized flooding and drainage issues. Spot improvement projects support the increased functionality of the City’s storm sewer system which is comprised of hundreds of miles of underground pipes, culverts, inlets, grates, manholes, and “flap gates” or “check valves”. Click here to learn more about spot improvement projects.
CAPITAL IMPROVEMENT PROGRAM | STORM SEWER CAPACITY IMPROVEMENTS
The City’s Capital Improvement Program (CIP) outlines the large infrastructure projects to be undertaken across City departments during a 10-year time horizon. The list of Capital Projects is updated annually during the budgeting process undertaken by the Mayor, City Council, and City Manager’s Office in coordination with all City departments. Eleven priority storm sewer capacity improvement projects have been identified here for FY2022 - FY2031. Click here to learn more about stormwater capacity projects.
STREAM AND CHANNEL MAINTENANCE
The City performs maintenance to streams and channels throughout the city to preserve their capacity to carry 100-year floodwaters, and for repairs to erosion damage, stream corridor degradation, stabilization/restoration in Holmes Run and Cameron Run watersheds, including smaller tributaries to these streams. The increasing frequency of intense storm events will require increasing funding for sediment and vegetation removal to ensure the conveyance capacity of these waterways as climate resiliency and adaption measures consistent with the City’s Climate Emergency Declaration. Click here to learn more.
FOUR MILE RUN LEVEE PROJECT
The City of Alexandria must maintain the structural integrity and the flow capacity of Four Mile Run channel through routine maintenance practices. Associated with the channel is a levee and floodwall system that was construction back in the 1970’s to mitigate flooding. City staff and in coordination with the U.S. Army Corps of Engineers to identify areas to address as ongoing maintenance in accordance with the City’s Operations and Maintenance program.
Transportation and Environmental Services routinely removes vegetation along the levee from the I-395 bridge to just downstream of the Mt. Vernon Avenue bridge at Four Mile Run Park. This maintenance work involves removing and cutting vegetation flush to the levee, which is part of the maintenance of the levee. Other maintenance includes inspection and maintenance of the infrastructure and removal of accumulated sediment that builds up in the channel over time. The City is currently working with Arlington County on the design and construction effort to remove sediment from the Four Mile Run channel. Click here to learn more.
2020 HOOFF’S RUN INSPECTION AND CLEANING PROJECT
In June of 2020, the city hired a contractor, Red Zone Robotics, to inspect and survey approximately 7,000 feet of the Hooff’s Run Culvert which conveys stormwater from a significant portion of Northridge, Del Ray, and Rosemont. The survey identified overall debris levels in the range of 5% with isolated sections of pipe having debris accumulation of approximately 15-20%. An overview of the report can be found here.
Beginning in November of 2020 through mid-2021, the Hooffs Run Culvert from E. Maple to Duke Street will be cleaned of the debris that was identified. It is anticipated that there will be additional maintenance activity within these areas from contractors equipment.