National Capital Planning Commission | 401 9th Street, NW, Suite 500 North Lobby | Washington, DC 20004 | 202.482.7200 | www.ncpc.gov

JANUARY 2008

Report on Flooding and

Stormwaterin

Washington, DC

National Capital Planning Commission

Table of Contents

Anacostia River Potomac River

I. Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

II. Potomac River Flood Risk Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

Sea Level Rise

Washington’s Hidden Hydrology

June 2006 Flooding

Causes of the June 2006 Flooding

III. Existing and Proposed Flood Control Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

River Overbank Flooding Measures

National Mall Levee

Washington, DC Emergency Flood Procedures

Proposed National Mall Levee Improvement

Urban Drainage Flooding

Tidal Flooding Measures

Flooding Conclusions

IV. What is the Federal Role in Flood Prevention and Stormwater Control? . . . . . . . . .9

National Flood Control

FEMA 100-year Floodplain Maps

Executive Order for Floodplains

The National Environmental Protection Act

The Clean Water Act

Review of National Capital Planning Actions

V. What is the District of Columbia’s Role in 

Flood Prevention and Stormwater Control? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

District Stormwater Laws and Requirements

DC Floodplain Requirements

DC Clean Water Act Requirements

Anacostia Waterfront Initiative

DC Flood Emergency Plan

VI. Next Steps/Action Plan for Monumental Core . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

VII. Anacostia River Flood Risk Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

Anacostia River Hydrology and Geography

Anacostia River Flooding

Hurricane Isabel

VIII. Existing and Proposed Flood Control Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

Role of the Army Corps of Engineers

Anacostia River Flood Control Projects

Prince George’s County, Maryland Flood Control Project 

IX. Urbanization, Channelization, and Sedimentation Impacts . . . . . . . . . . . . . . . . . . .18

Impacts from Anacostia Tributaries on Flooding

Anacostia Sedimentation

Urban Drainage Flooding

Potential Impacts on Present and Proposed Waterfront Development

X. Restoration and Remediation Efforts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

Washington Navy Yard Storm Sewer Rehabilitation

Wetlands Restoration

XI. FEMA Floodplain Map Modernizations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21

Revised FEMA Floodplain Maps

XII. Next Steps/Action Plan for Anacostia River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Appendix A: Major Flood Events in Washington, DC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25

Appendix B: Information on Memorials Submitted to NCPC by NPS . . . . . . . . . . . . . . . . . . .26

Appendix C: Relevant Laws and Regulations for Flooding and Stormwater Management . . . .27

Appendix D: Acronyms and Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Appendix E: Potomac River Flood Stages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29

Appendix F: Aerial Maps of Flood Control Projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
National Capital Planning Commission

Report on Flooding and Stormwater in Washington, DC | Potomac River

Effects of flooding on 9th Street, NW in downtown Washington, DC in June 2006.
I. Executive Summary 

At the September 2006 National Capital Planning

Commission (NCPC) meeting, the Commission requested

additional information on flooding. This paper provides

the requested information and recommends the next steps

for reducing the risk of flooding.

GEOGRAPHICAL FLOODING RISK: The District’s

location at the confluence of the Potomac and Anacostia

Rivers, combined with three buried waterways, broad

floodplains, and relatively flat elevations, renders it highly

susceptible to periodic flooding. A large part of the

National Mall and adjacent areas were originally

underwater and were filled as L’Enfant’s plan was realized.

Urban development has increased impervious surfaces,

reduced vegetation coverage, and further exacerbated

flooding and stormwater runoff through the entire

watershed. This problem is especially acute in the National

Mall area given its downstream location.

NATIONAL MALL LEVEE: To keep water from the

Potomac and Anacostia River systems out of the

downtown business district, the Army Corps of Engineers

(ACOE) erected an earthen levee along the north side of

the mall, running from the Lincoln Memorial to the

Washington Monument. This flood control measure relies

upon temporary closures of several north-south streets,

which constitute gaps in the levee. To make the levee more

reliable, ACOE proposes making two of the temporary

closures permanent by extending the levee to meet the

higher topography to the north. To ensure the continued

flow of cross-mall vehicular traffic, the 17th Street closure

would remain temporary, but the barrier would be

redesigned to improve its effectiveness and ease of

assembly. Given the prominent location of the levee on

the Mall, ACOE’s improvement plan merits a careful

assessment by NCPC.

COMBINED SEWER SYSTEM: Downtown DC suffers

from inadequate storm sewer capacity making the area

especially susceptible to interior flooding. Flooding of the

magnitude experienced in June 2006 is costly and can be a

security threat if critical building systems are affected and

national historic and cultural resources are threatened.

While flooding in downtown DC is relatively infrequent,

the concentration of key federal agencies and the huge

federal, local, and private costs associated with recovering

from even periodic floods warrants a close examination of

cost-effective solutions. Moreover, future growth will

further strain the system’s already limited capacity.

REGULATIONS & RESPONSIBILITIES: Numerous

laws, policies, and executive orders are in place to reduce

property loss and environmental degradation caused by

flooding, but Washington, DC poses some unique

challenges. First, the division of responsibilities among

various federal and local authorities is not always clear or

uniform, and federal facilities in the business district must

rely on the local DC government to manage, regulate, and

otherwise control stormwater. Second, flooding in the

nation’s capital is particularly unacceptable given the

hazards it poses to the security of federal buildings and

our nation’s treasured historic resources.

POTENTIAL ACTION STEPS: There are a number of

strategies NCPC may consider to reduce flooding risks and

excess stormwater impacts. First, NCPC may review its

own agency’s guidelines and policies to increase the level of

scrutiny for proposals within or near the floodplains.

Second, NCPC may undertake a number of planning

initiatives and local and regional partnerships to further

evaluate flooding and stormwater issues and research new

and innovative measures for stormwater management.

Third, NCPC may encourage more proactive stormwater

management tactics to improve the water baseline and

ensure that future development does not exacerbate the

situation. No one solution can eliminate the potential

problem entirely, but a strategic combination, weighed by

the costs and benefits, could help minimize the risk by

lowering the frequency and magnitude of flooding that

does occur.

At the February 2007 National Capital Planning

Commission meeting, the Commission requested

additional information on flooding and stormwater in the

Anacostia River watershed. This paper provides the

requested information and recommends the next steps.

In general, Anacostia River flooding is less of a threat to

the Washington metropolitan region than Potomac River

flooding because of the far greater size and reach of the

Potomac watershed, and the volume of water carried by

the Potomac. However, the Anacostia watershed is far

more urbanized than the Potomac watershed and as a

result of increased impervious surfaces, channelization of

the tributaries, and wetlands destruction, even moderate

amounts of rainfall can cause localized stormwater issues.

Sedimentation of the Anacostia River is an ongoing

problem with much of the dirt and debris originating

upstream from Maryland communities. NCPC supports

the restoration of floodplain values and functions

whenever possible to mitigate the impact of stormwater

runoff resulting from increased development and

impervious surfaces.

A number of communities along the Anacostia River are

protected by levees. Over the past few years, the ACOE

inspected these levees and has required a number of

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National Capital Planning Commission
improvements to ensure that the communities behind the

levees are protected in the event of a storm. At the same

time, Federal Emergency Management Agency (FEMA)

has updated the floodplain maps for the District and

where the levee improvements have not been completed,

the proposed floodplain maps have been revised

accordingly. NCPC strongly supports levee improvements

and urges the ACOE to coordinate with staff early in the

design planning process. Further, NCPC urges FEMA to

ensure that floodplain maps for the National Capital

Region are updated in a timely manner.

In the past, Anacostia River flooding has been less

problematic as most of the waterfront is publicly-owned,

and a significant portion used as parkland. Recently

however, there have been a number of private and public

development proposals submitted for review and approval.

All new development is required to determine if they are

within a federally-mapped flood hazard area and if so,

obtain flood insurance and meet more stringent building

code requirements. Further, federal actions and approvals

within the floodplain must comply with Executive Order

11988 which was designed to minimize the impacts of

development on floodplains.

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II. Potomac River 

Flood Risk Overview

The District is susceptible to four different types of

flooding, three of which are caused by excess rainfall or

snowmelt, and one by the level of the tide.

J OVERBANK FLOODING

Overbank flooding occurs when the river channels receive

more rain than they can handle, or when the river channel

is blocked and does not permit the water to flow through.

J URBAN DRAINAGE FLOODING

Urban drainage flooding occurs when the sewer system

built to handle stormwater runoff is overloaded past its

design capacity.

J LEVEE-CAUSED FLOODING

Areas with levees can be inundated behind the levees

because they are relatively flat, and the levee serves as a

block to the water flowing to the river. Channels may be

built and/or pumps are installed to move the water past

the levee.

J TIDAL/STORM SURGE FLOODING

Tidal flooding occurs when there is an abnormal rise in

water level preceding a storm, usually a hurricane, due to

the combined effects of wind and low atmospheric

pressure. The Potomac, up to the base of Little Falls, is

tidal, which causes the river to rise and fall with ocean

tides. Normal tides have a mean range of three feet, but

have been known to surge as much as 12 feet in a

hurricane.

Major flooding in the Potomac basin occurred in 1889,

1936, 1937, 1942, and 1972. See Appendix A for detailed

flooding history in Washington, DC.

Sea Level Rise

Flooding in Washington is exacerbated with higher sea

levels. According to the U.S. Geological Survey (USGS),

Chesapeake Bay sea levels are forecast to rise

approximately one foot over 100 years.1 The American

Museum of Natural History forecasts that a rise in the

Potomac River of one foot, combined with a major

storm surge, would make the Jefferson Memorial an

island and flood the National Mall up to the Reflecting

Pool. Hurricane Isabel (2003) produced much more

severe flooding in the region than an unnamed August

1933 hurricane that was similar in its storm track, tidal

surge, maximum sustained wind speed, and minimum

pressure, possibly as a result of the relative sea rise of

one foot since 1933.

Washington’s Hidden Hydrology

Washington has historically had at least three major

streams––the Tiber Creek, James Creek, and Slash Run.

Tiber Creek2 was the largest stream system in Washington,

at one time draining––along with its tributaries––2,500

acres, or nearly 43 percent of the District. Tiber Creek ran

south, beginning near the Armed Forces Retirement

Home, through the site of Union Station. Near the East

Building of the National Gallery, it turned west and

roughly ran along Constitution Avenue for the length of

the National Mall. At the base of the White House lawn,

where it met the Potomac River, the Tiber was between

700 and 800 feet wide.

James Creek, in Southwest Washington, DC, formed near

where the Tiber turned west, and flowed southeast along

South Capitol Street, broadening into a marshy area and

into the Anacostia River near Fort McNair. Slash Run

was a tributary of Rock Creek and ran roughly south

down 18th Street, NW and entered Rock Creek near 23rd

Street, NW. 3

By the 1870s all three waterways were essentially open

sewers and were impounded. The DC Board of Public

Works embarked on a massive sewer construction program

by enclosing the creeks4

. Washington’s present-day

hydrologic problems have their roots in the burial of the

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1 The observed Chesapeake Bay sea level rate of increase is roughly twice the global average.

2 Local farmer Francis Pope is credited with renaming Goose Creek as Tiber Creek, a more grand designation to better suit his 400-acre farm that he dubbed “Rome.”

3 Note the historical points at which these waterways enter Washington’s Rivers; they indicate the critical points where the ACOE levee protects downtown DC from floodwaters.

4 Sadly, this massive sewer capital improvement system led the District into bankruptcy and caused Congress to take over control of the city. The city was run by a Board of

Commissioners appointed by the President until 1974, when, under the 1973 Home Rule Charter, the city elected a Mayor and City Council.

The mouth of the Tiber Creek showing that the White House south

lawn, Federal Triangle and Mall areas once were all under water.
natural drainage system. Areas in the city plagued by

chronic water problems can be located by the original

drainage system maps. In 1992, the DC Water Resources

Research Center reported that the gravelly deposits of the

old creek beds still act as conduits for water, with the result

that groundwater routinely infiltrates sewer pipes and

building foundations along the former waterways.

June 2006 Flooding

On June 19, 2006, a wet weather pattern started in

Washington. Soon thereafter, from June 25 through June

27, intense tropical downpours inundated the District. The

heaviest rainfall fell from early evening on Sunday, June 25,

through the early morning hours of June 26, with a total

recorded accumulation of 7.09 inches on June 25.

The extensive flooding shut down operations at four key

federal office buildings––IRS Headquarters, the Commerce

Department, the Justice Department, and the National

Archives. Several Smithsonian museums along Constitution

Avenue also closed their doors. The National Gallery of

Art closed due to a weather-related steam outage, and the

National Zoo banned cars because of flooding in the

parking lot. Rock Creek Parkway became impassable and

had to be closed when Rock Creek overflowed its banks

and flooded the road.

National Archives Building

Constitution Avenue flooded on Sunday evening, June 25.

Rainwater poured down the driveways of the 7th and 9th

street sides of the building and flooded the transformer

vaults and the subbasement areas. The two transformer

vaults were submerged in up to eight feet of water.

The freshly renovated (2004) William McGowan Theater,

located under the Constitution Avenue steps, was also

significant damaged. Flood water flowed down the

theater steps, submerging the stage and the first two rows

of seats. Electrical power went out immediately, but the

sprinkler and security systems remained operational.

Sump pumps continued to operate because of the

emergency generator, but they were overwhelmed and

had no place to pump the water. Fortunately, no original

records were affected by the flood.

IRS Headquarters Building

The IRS Building sustained the greatest amount of water

damage, most likely because it has the lowest elevation.

Rainfall flowing down Constitution Avenue spilled into the

moats surrounding the building. The IRS subbasement,

which holds all of the building’s electrical and maintenance

equipment such as electrical transformers, electrical

switchgears, and chillers, was submerged in over 20 feet of

water. Virtually all major building systems were affected

and most of the equipment either had to be extensively

rebuilt or replaced.

The basement flooded with five feet of water. The fitness

center, cafeterias, offices, systems furniture, carpet, ceiling

tiles, computer equipment and vehicles garaged in the

building were all destroyed.

Other Flooded Federal Buildings

The Smithsonian’s Natural History Museum, American

History Museum, the Smithsonian Institution Building and

the Castle also were closed. PEPCO shut off power to

those large government buildings because some basements

containing electrical switch gears were flooded, and the

buildings all share the same electricity network. The

National Gallery of Art also closed because flooding cut

off the building’s steam supply, which maintains air

humidity levels necessary to preserve the artwork.

Causes of the June 2006 Flooding

Shortly after the June flood, the General Service

Administration (GSA) retained an independent, private

consultant to ascertain its causes and to recommend

solutions to prevent future flooding. The study was

recently completed, although the results are not public.

GSA summarized the report so that we could include the

consultant’s initial findings here.

In short, after interviewing DC WASA, the GSA

consultant was unable to determine conclusively why the

Federal Triangle area flooded so badly and so quickly. DC

WASA was unable to provide an explanation as to why the

flooding occurred. In categorizing the rain event, the

consultant determined that over a 24-hour period the

rainfall was equivalent to the expected rainfall for a 50-year

storm event. However, over the most intense 6-hour

period of the storm, the rainfall was equal to a 200-year

storm. The capacity of the DC sewer system in the Federal

Triangle area is unknown, as it was constructed before

such standards were typically adopted.5 As a result, it would

be easy to conclude that the storm exceeded the capacity

4 National Capital Planning Commission

Report on Flooding and Stormwater in Washington, DC | Potomac River
of the sewer. However, the consultant noted that flooding

started before the rainfall should have exceeded the sewer’s

capacity. In addition, when the flooding dissipated, it also

did so at a speed greater than what would be expected.

Power outages caused the 12th Street pumping station to

be inoperable, but DC WASA concluded that while a fullyfunctioning pumping station would have offered some

relief, it would not have completely ameliorated the severe

flooding. The main pumping stations were operational

during the entire storm. The Potomac River remained

below flood stage during the entire storm, so backflow was

not a contributing cause to the interior flooding.

In summary, the flooding may have been caused by the

extreme intensity of the rainfall over a very short period of

time, but no one can be sure. The report to GSA includes

recommendations for future flood prevention at each of

the buildings that flooded. The report and these

recommendations are under consideration by GSA

management.

III. Existing and

Proposed Flood Control

Measures

River Overbank Flooding Measures

Washington, DC is particularly susceptible to overbank

flooding in Potomac Park, along the Tidal Basin, and over

the National Mall area up to the Reflecting Pool. These

areas have the lowest elevations in DC. Most of the area

with the highest risk of river overbank flooding is parkland

under the jurisdiction of the National Park Service (NPS).

National Mall Levee

As a result of the 1936 Great Flood in Washington,

Congress passed the Flood Control Act of 1936, which

authorized the ACOE to design a solution to overbank

flooding on the National Mall. In response, ACOE used

landfill from the Reflecting Pool to create a levee between

the Lincoln Memorial and the Washington Monument.

The project began operation in 1940 to protect against a

flood discharge of 700,000 cubic feet per second (cfs) on

the Potomac River.6

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5 Well after most of the sewers in downtown were constructed, DC WASA’s predecessor agency established a 15-year storm as the design standard for the system. New sewer

construction is designed to this 15-year standard.

6 It is estimated that the Potomac River’s discharge during the 1942 Great Flood was 450,000 cfs when the maximum flood stage was attained. The maximum discharge of record

for the Potomac River is 484,000 cfs, which occurred in March 1936. ACOE estimated that an overbank flood of 700,000 cfs has a larger percentage chance of annual occurrence

(two percent) than the 15.0-foot tide, which has less than a one percent change of annual occurrence. Consequently, Congress deemed that the ACOE Washington, DC flood

control measure (the levee) should be built to the 700,000 cfs design standard. According to USGS, the maximum tidal gauge height was recorded at 17.72 ft (DC MLW) on Oct.

17, 1942.

This ACOE map depicts the area of

Washington, DC protected by the

National Mall levee.
According to ACOE, a considerable portion of the levee

was removed during World War II for Navy Department

construction. Consequently, it is necessary to construct as

much as 1,500 feet of temporary levee in three segments

in the event of a major overbank flood to provide

protection to the height of the permanent works now in

place. See the map on page 5, which illustrates the areas

protected from flooding by the current levee when the

temporary closures are in place.

Washington flooded again in 1942. Congress then passed

the Flood Control Act of 1946, which authorized

improvements to the levee to restore the level of

protection and improve the levee’s operation. The levee’s

overall effectiveness depends on implementing the 1946

improvements; however, ACOE has not completed the

improvements because Congress has not funded them.

At present, the project is unable to provide the level of

protection it was designed to provide because in a flood

emergency the levee’s effectiveness relies on timely,

complete, and correct construction of the three

temporary barriers.

Washington, DC 

Emergency Flood Procedures

In the event of a storm, National Weather Service (NWS)

forecasts are posted on the Washington Area Warning

Alert System (WAWAS) and the National Oceanic and

Atmospheric Administration (NOAA) Weather Radio

whenever a Potomac River Stage of 7.0 feet mean low

water (MLW) or greater is predicted at the Wisconsin

Avenue gauge. Currently, the National Park Service (NPS)

is responsible for the 23rd Street and 17th Street

temporary closures in the National Mall levee.

23rd Street Closure: NPS is to construct the emergency

levee at 23rd Street when the Potomac River Stage of

19.0 MLW or greater is predicted at the Wisconsin

Avenue gauge.

17th Street Closure: NPS is to construct the temporary

levee at 17th Street. The 17th Street closure consists of

two structures constructed in two phases. Phase One is a

3-foot high jersey wall barrier with sandbags and plastic

sheathing and is triggered when the Potomac River is

projected to rise to flood levels over 10.4 feet MLW. Phase

One can be put into place relatively quickly, and provides

protection up to 15.42 feet MLW. Phase Two is a

temporary earth levee located 50-feet north of the Phase

One closure and should be initiated immediately after the

river exceeds elevation 11.42 feet MLW. Phase Two

construction is complex and requires significant

construction equipment and embankment material and has

the greatest potential for failure.

Fort McNair - The DC Emergency Management Agency

(EMA) is responsible for the Fort McNair sandbag closure

at P and Canal Streets when the Wisconsin Avenue river

stage exceeds 23-feet MLW.

Proposed National Mall Levee

Improvements

In 2000, ACOE proposed making the temporary closures

at 23rd Street and Fort McNair permanent to improve the

levee’s design and reliability. At 23rd Street, the Corps

proposed a 600-foot earth embankment with a maximum

height of 3 feet that would run along 23rd Street until it

met the existing embankment for the Route 50 ramp. The

topographic modifications would then complete the

protection line at 23rd Street. At Fort McNair, the Corps

proposed a permanent earth berm that would be 1.2 feet

high and extend for 570 feet.

The closure at 17th Street, NW remains temporary, but

will be redesigned to improve its reliability and minimize

the construction time needed during floods. Presently,

there are a number of options being considered. One

alternative is a “borrow pit.” The Corps would excavate a

portion of the Mall near 17th Street so that the hole could

be refilled with aggregate material. During a storm event,

NPS staff would excavate that specific location of fill and

use it to create an earthen dam across 17th Street. A

second alternative is an inflatable dam, known as an

aquadam [See below]. A third similar option is a

cofferdam, which is an A-frame structure that is erected

with a light-weight steel frame and covered with a plastic

membrane. [See below] Last, the Corps is considering a

“post and panel” temporary dam.

The Corps also proposes to fortify the portion of the

levee along the Reflecting Pool by eliminating low spots.

When all of the modifications are complete, the levee

would have less than a one percent chance of being

overtopped in any one year. The modifications will bring

the top of the existing levee along the Reflecting Pool

(between 23rd and 17th Streets) to a uniform elevation and

increase the level of freeboard7 protection provided.

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Report on Flooding and Stormwater in Washington, DC | Potomac River

7 “Freeboard” is the vertical distance between the normal maximum level of the water surface in a channel, reservoir, tank, canal, etc., and the top of the sides of a levee, dam,

etc. It is provided so that waves and other movements of the liquid will not overtop the confining structure.
ACOE is waiting for Congress to appropriate construction

funding for the project. The estimated total cost is $7

million; the project has received just over $3 million in prior

funding. ACOE estimates that without the levee closures a

major flood could cause more than $200 million in damages

to museums, memorials, and office buildings. The flood

control project requires NCPC review and approval.

ACOE has not yet completed final designs or construction

plans for the two permanent closures and the enhanced

17th Street temporary closure. However, given the levee’s

prominent location along the National Mall, staff believes

ACOE’s plans will warrant a close review to ensure that

the proposal does not adversely affect the National Mall

and its environs.

Urban Drainage Flooding

Urban drainage flooding is typically caused by sewer

overflows and thus is the responsibility of the DC

government.8 One-third of the District, including the

entire downtown business district, has a combined

sanitary and storm water system.9 In other words, a single

pipe carries both raw sewage and stormwater to the Blue

Plains treatment facility. When it rains, the combined

wastewater flow can easily exceed the capacity of the

combined sewer system and/or the treatment facility. 10

Two harmful things can occur if the capacity of the

system is exceeded.

First, excess stormwater causes untreated wastewater to

flow directly into nearby rivers. Such discharge of the

untreated stormwater is a violation of the Clean Water Act

and consequently, the District is under a consent decree to

construct storage tunnels to hold the excess untreated

water. The consent decree imposes a 20-year

implementation schedule for construction to be complete;

however, funding is a significant issue.11

The project is estimated to cost $1.9 billion and current

proposals provide that the entire cost be borne by the

ratepayer base. Presently, DC WASA’s storm-related

activities are funded solely through water and sewer fees.12

DC WASA estimates that to finance baseline capital

improvements and maintenance, in addition to the longterm plan for the combined sewer overflow (CSO), rates

would need to rise annually, with at least eight rate

increases above 10 percent per year for DC WASA to

raise sufficient capital. DC WASA has calculated that if it

receives 62 percent of the capital costs (approximately

$960 million) from external sources (e.g. the federal

government) that the agency would likely be able to keep

rate increases at no more than 8 percent per year.

Congress has made a number of dedicated

appropriations to DC WASA that currently amounts to

approximately $35 million.

Second, excess stormwater may be so great that that the

sewer system can not even collect it, and then it floods the

streets. The storage tunnel solution described above would

not prevent street flooding caused by excess rainfall

because the capacity of the sewers under the streets

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8 DC WASA sent comments to NCPC’s draft report, noting that “urban flooding can be caused by many factors including: improper grading; inadequate location, number or size of

catch basins; clogged catch basins; inadequate sewer capacity, and storms which exceed the design capacity of the system. Some of these are the responsibility of the DC

Government, while others are the responsibility of DC WASA or private landowners. Other factors are caused by nature and are not the responsibility of any entity.”

9 Combined sewer systems, introduced in 1855, were a vast improvement to the open cesspools originally used to convey wastewater, and are common in most older cities. As a

result, many cities still struggle with the attendant pollution from combined sewer overflows. 

10 Combined sewer overflows (CSOs) should occur only during wet weather. However, according to DC WASA’s overflow predictions, in an average year, less than 0.5” of rain can

cause more than 3 hours of untreated sewage to flow into the Anacostia River. Such an occurrence is predicted to occur more than 50 times in an average year.

11 The consent decree was entered March 23, 2005.

12 Typically, in other cities, the costs of municipal stormwater programs are funded through a combination of real property taxes, general revenues, and user fees.

The pictures above depict temporary dams, an inflatable dam (left) and a port-a-dam (right).
remains unchanged.13 The storage tunnel merely holds the

water for future treatment once it is in the system; not

increase the actual capacity of the old receiving sewer

tunnels.

One additional predicament is that when the river level

rises above the outfall pipes, water can back up into the

system and cause reverse flooding. This should be resolved

by the gates that DC WASA installed at the outfall pipes,

but there have been problems with the gates in the past

either being open during a storm or not functioning

completely. The tide gates at the outfall pipes specifically

prevent backflow of river water to Blue Plains Wastewater

Treatment Plant during high river levels. This protects the

plant against treating extraneous river water. However, tide

gates are not typically relied upon to protect life or

property during river floods.

In those situations, a positive means of shutting off flow is

used, such as sluice gates or stop logs. For example, in the

current ACOE Flood Emergency Manual for DC,

locations are identified where stop logs are to be inserted

in sewers to prevent backflow during river floods.

ACOE developed a map to illustrate the areas that would

experience street flooding in a storm event that produced

rainfall greater than what the sewer system could handle.

The ACOE map below delineates the flooded areas

corresponds almost exactly to the areas that flooded in

June 2006. Consequently, it appears that interior flooding is

a separate, persistent issue that needs a separate solution.

Tidal Flooding Measures

Washington is also susceptible to tidal flooding and tidal

surges. Tidal flooding in the Potomac River can be

caused by hurricane tidal surges that form in a number of

ways. The surges produce the highest water levels in the

upper Potomac when they coincide with the astronomical

high tide.

In 1955, a year after three successive hurricanes ravished

the northeastern seaboard, Congress directed ACOE to

evaluate cost effective structural measures to reduce the

human and property losses from future hurricanes. ACOE

prepared a report that evaluated the risk of tidal flooding

in the Washington, DC metropolitan area and concluded

that while the area was vulnerable to severe damage from

hurricanes, the relief from tidal flooding by structural

means could be accomplished by protective works needed

for overbank flooding control.

The report concluded that effective zoning was the most

important solution for reducing flood hazards:

The continuing encroachment on the tidal flats and floodplains of

the Potomac River in the Washington area has seriously reduced

the capacity of the stream to pass fluvial floods and absorb tidal

floods without losses. Zoning regulations to stem the encroachment

on the waterfronts and to establish future structures at safe

elevations are needed.

ACOE has not reevaluated Washington tidal flooding since

the original report, completed more than 50 years ago.

8 National Capital Planning Commission

Report on Flooding and Stormwater in Washington, DC | Potomac River

13For the Northeast Boundary area, the proposed CSO tunnels have a dual purpose: CSO control and

flood relief. The LTCP is designed to provide flood relief to known flood areas in Northeast Boundary.

1990 ACOE MAP SHOWING AREAS OF RESIDUAL FLOODING
Flooding Conclusions

The most frequent types of flooding in Washington, DC

are the consequences of river overflow and urban drainage

failures. Excess stormwater can trigger either type of

flooding, but they occur independently. Overbank flooding

is an easier risk to manage because fairly reliable warning

systems typically provide longer lead times before the

flooding begins. For example, the average rate of flood

crest travel time from Point of Rocks, MD to the

Wisconsin Avenue gauge is approximately 11 hours. Urban

drainage flooding, however, provides emergency workers

with less advance warning since the onset of urban

flooding is harder to pinpoint reliably, as illustrated by the

June 2006 flood.

A number of factors unique to DC make flood control

and stormwater management more vexing. First, while

many of the riparian areas in DC are parklands that retain

some of their natural floodplain functions, many priceless

monuments, museums, and national structures are located

in areas likely to flood. Many monuments are designed to

withstand intermittent flooding, but clean-up can be costly

and the impacts of repeated flooding may compound over

time. For other structures, flooding can be devastating and

irreversible, as would have been the case at the National

Archives if the agency had been unable to mitigate the

June 2006 flooding.

Second, the federal government is the largest developer,

tenant, and property owner in downtown DC. This

creates a significant federal interest in the cause and effect

of flooding.

Moreover, a significant amount of stormwater in this area

is routinely generated through runoff and de-watering at

federal facilities. The federal government may, over time,

be able to address some of the issues of peak period and

overall runoff through individual and coordinated design

and operational actions. These actions may also support

larger federal goals supporting green building and

environmental objectives.

Lastly, the responsibilities and jurisdiction for addressing

stormwater and flooding in the District, and specifically in

the downtown area, are complex. Many possible solutions,

whether structural changes to the sewer system, or using

low-impact development or green building design

strategies, are costly or beyond the ability of a single

jurisdiction to require. Therefore, developing coordinated

and comprehensive strategies will require coordination

between federal and local agencies alike.

IV. What is the Federal

Role in Flood Prevention

and Stormwater Control? 

The full panoply of floodplain laws, regulations, executive

orders, policies, and agency guidance, implemented over

the past 100 years on federal, state, and local levels, is

complex, comprehensive, and somewhat disjointed. [See

Appendix C for a chart of the relevant federal laws.] The

National Flood Insurance Program (NFIP), implemented

by FEMA, is the most well-known federal flooding statute.

The 100-year floodplain maps and the federally-mandated

and subsidized insurance program are the hallmark of

NFIP. However, there are a number of other federal

statutes and requirements that also play a role and these are

discussed in more detail below.

In addition to federal laws and regulations, the District has

its own responsibilities and rules. Some of the local rules

are federal requirements, such as the building regulations

for construction in a FEMA-designated floodplain, while

others, such as the Anacostia Waterfront Initiative’s

stormwater regulations, are entirely local requirements.

National Flood Control

NFIP is the key federal statute with regard to flooding.

Under NFIP the federal government accepts a significant

share of the responsibility for flood prevention, control,

emergency response, and property loss. The statute’s

underlying principle is that there should be development

restrictions within the floodplain for the dual purpose of

reducing flood damage losses and minimizing disruption

to the floodplain’s natural function of storing excess water

and draining water over land areas and into the floodway.14

NFIP directs FEMA to develop maps nationwide that

delineate the floodway and the floodplain.15 A Flood

Insurance Rate Map (FIRM) is the official map on which

FEMA has delineated both the special flood hazard areas

and the flood risk premium zones applicable to the

community. Structures built before the FIRM or before

1975, whichever is later, are eligible for flood insurance

with premiums that are reasonable, and if necessary,

federally-subsidized.16

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14“Floodway” means the regular channel of a river, stream, or other watercourse, plus the adjacent land areas that must be

reserved in order to discharge the base flood without cumulatively increasing the water surface elevation more than one foot.

15“Floodplain” means the low area of land surrounding water bodies that holds the overflow of water during a flood.

16“Consequently, NFIP is one of the largest domestic fiscal costs along with Social Security, Medicare and Medicaid.
Typically the maps are developed in conjunction with the

local government. Buildings within the floodplain must

obtain private flood insurance. Flood insurance eligibility is

based on communities adopting development restrictions

that meet minimum federal requirements.

FEMA 100-Year Floodplain Maps

An enduring problem nationwide is that the FEMA-issued

flood insurance maps are out-of-date. The District maps

are approximately 21-years old.

The DC Department of the Environment (DCDOE)

and FEMA are digitizing the 1985 DC floodplain maps.

Once the maps are complete, the agency will schedule a

public hearing and then they will be sent to the DC City

Council for adoption. The process that leads to final

adoption can last as long as a year. Once the maps are

adopted, new flood insurance requirements become

effective.

Development and impervious surface coverage within the

watershed has been sizeable, which could also easily

require a change in the delineation of the floodplain area.

In March 2005, the Maryland Department of the

Environment completed a study determining that:

In flat areas, structures located within several hundred feet

or more horizontally of the 100-year floodplain line may

also be at risk.17

However, the DC floodplain delineations will not be

revised to reflect any changes in sea level or development

in the watershed as part of the digitalization process. The

DC Flood Emergency Manual contains maps prepared by

the Corps delineating the area ACOE predicts will flood

for the 100-year storm. (See Corps map that is attached to

the report.) The inundated area is larger than the FIRM’s

100-year boundary, and more closely corresponds to the

FIRM’s 500-year floodplain line.

10 National Capital Planning Commission

Report on Flooding and Stormwater in Washington, DC | Potomac River

DC 1985 Flood Insurance Rate Map

ZONE A: Would flood in 100-year event ZONE B: Would flood in 500-year event

17Emphasis added.
Executive Order for Floodplains

In 1977, President Carter, faced with ever increasing flood

costs, issued Executive Order (EO) 11988 to hold federal

agencies to a higher standard than the NFIP rules.

Executive Order 11988 affirms that the federal

government should not encourage floodplain development

in all of its actions and funding mechanisms. The

President’s statement that accompanied the EO noted that

flood losses and adverse alteration to floodplains arise

mainly from “unwise land use practices.” Further, it states,

“Floodplain development ... is simply a bad Federal

investment and should be avoided.” The EO required all

executive branch agencies to develop compliance

procedures. As a result, on September 17, 1981, NCPC

adopted floodplain management procedures that apply to

all actions that “have the potential for adversely impacting

floodplains...or which are subject to potential harm by

location in floodplains.” According to the procedures, if

NCPC finds that an action meets the above test, then the

Commission is required to (1) identify the full range of

potential direct or indirect adverse impacts, and (2) identify

and evaluate practicable alternatives outside the floodplain

including the “no action” alternative. The procedures

require public notice for any plans, proposals, or actions in

floodplains followed by a 30-day review and comment

period. A Statement of Findings is required for all plans,

proposals, or actions in floodplains and must include why

the action is proposed to be in the floodplain; whether the

action conforms to applicable state and local floodplain

management standards; the list of alternatives considered,

a list of mitigation measures; and a map delineating the

proposal’s location and its relationship to its environs.

NCPC’s procedures also amend NCPC submission

guidelines for federal agency projects to require a copy of

the submitting agency’s Statement of Findings pursuant to

EO 11988 if the proposed project is within a floodplain.

In theory, the National Environmental Protection Act

(NEPA) environmental review can satisfy 

the EO’s requirements. However, to avoid floodplain

harm, the EO requires more affirmative action than

NEPA.

The National Environmental 

Protection Act

The NEPA also plays a role in flooding, floodplain

management, and stormwater control. NEPA requires

federal agencies to assess potential environmental impacts

before undertaking any federal building projects or site

changes that significantly affect the quality of the human

environment. The environmental review should discuss

whether any proposal would be affected by flooding, as

well as whether the proposed action would likely increase

flooding. Floodplain development is typically scrutinized

more closely for adverse impacts than development

outside the floodplain. Stormwater runoff and its

potential impacts are also likely to be part of an

environmental review assessment. In general, the

submitting agency is responsible for ensuring that a

thorough and comprehensive environmental assessment is

completed for each proposed action, and that alternatives

are considered, before final action is taken. However, as a

federal agency, NCPC has an independent obligation

under NEPA to assure this information is available before

it makes any decisions about a project. Moreover, when

analyzing the proposal and alternatives, federal agencies

must consider the direct or indirect consequences––that

is, connected, similar, and cumulative actions. These

actions should be incorporated into the description of the

proposal and alternatives.18

The Clean Water Act

The Clean Water Act (CWA) regulates stormwater

discharges from industrial activities (which include

construction activities and municipal sewer system

discharges) under the National Pollutant Discharge

Elimination System (NPDES) permit program. NPDES

regulates water quality. Municipal sewage system operators,

private developers, and the federal government are all

required to comply with the NPDES permitting program.19 

EPA administers the CWA and NPDES program and in

many instances delegates permitting authority to the

states. However, the District is not a delegated state and

EPA retains NPDES permitting authority with regard to

both construction activities and municipal sewer

discharge in DC.20 For construction, stormwater runoff is

regulated both during construction and after construction

is complete. Consequently, a developer in DC is required

to prepare a stormwater pollution prevention plan in

accordance with the EPA General Permit, submit the

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18 For an EIS, 40 CFR § 1502.16 which incorporates the definitions from 1508.7 and 1508.8 and for an ES, 1508.9(b) which also incorporates the definitions from 1508.7 and 1508.8.

Also, see generally NCPC Environmental Submission Guidelines Section 10 and Appendix B, Section 3(A).

19 The CWA specifically mandates that all departments or agencies of the executive, legislative, and judicial branches of the federal government comply with Federal, State,

interstate, or local stormwater regulations. Further, EO 12088, “Federal Compliance with Pollution Control Standards,” directs each executive agency to develop annual plans for

the control of pollution and to ensure that sufficient funds for compliance are requested from OMB in the agency budget.

20 In fact, the consent decree for the sewer storage tunnels was developed to settle an enforcement action brought by the United States against DC WASA because it is in violation

of the NPDES permit EPA issued to it.
plan to EPA, and file a notice of intent to start

construction. The stormwater plan governs runoff for

the period of construction and then for the building once

construction is complete.

Review of National 

Capital Planning Actions

Staff reviewed a number of executive director’s reports

and environmental documents prepared for projects in the

monumental core to better understand how flooding and

stormwater issues have been considered. While many, but

not all, of the documents do include information on

stormwater and flooding issues, the analyses have not

always been consistent in either the range of issues

reviewed, the scope of the evaluation, or the final

conclusions reached. Further, the analyses that we

reviewed focused on specific impacts to projects, and there

was typically little discussion on how development might

increase the likelihood of flooding. We have not identified

any documents discussing the cumulative impact of

development on stormwater and flooding in this area.

In addition, to assist our review, the National Park Service

provided details to NCPC on how a number of memorials

located within or near the floodplain have dealt with

potential flooding issues (See Appendix B). We also spoke

with a number of federal agencies regarding flooding and

stormwater, and found that all of the agencies were aware

of flooding and stormwater issues specific to their own

facilities. Many of the agencies expressed an interest in

better understanding how other agencies were addressing

flooding and stormwater, as well as looking more

comprehensively at the issue in the downtown area.

V. What is the District of

Columbia’s Role with

Regard to Flood Prevention

and Stormwater Control?

District Stormwater Laws 

and Requirements

In the District, stormwater management is a responsibility

shared jointly among four District agencies: the DC

Department of Health (DC DOH), the DC Water and

Sewer Authority (DC WASA),21 the DC Department of

Public Works (DC DPW),22 and the District Department

of Transportation (DDOT). Recently, DC DOH’s flood

and watershed responsibilities, including stormwater, were

transferred to the newly formed Department of the

Environment (DC DOE). In February 2007, DC DOE

will take over all responsibilities of managing the MS4

permit-related activities (described below) that DC WASA

previously handled.

DC DOE is responsible for monitoring water quality in

the Anacostia and Potomac Rivers. DC DOE is also

responsible for reviewing developers’ plans for compliance

with DC’s stormwater management and erosion and

sediment control regulations, monitoring implementation

with management plans through inspections, and

investigating illegal discharges to the sewers. Developers

cannot obtain a building permit from the Department of

Consumer and Regulatory Affairs (DCRA) until DC DOE

ascertains that the developer has complied with DC

stormwater rules. Construction activities that do not

disturb more than 5,000 square feet of land area are

exempt. Federal agencies follow the same procedure as

private entities to comply with DC’s stormwater rules.

Federal agencies, such as GSA, submit their stormwater

management plans to DCRA for DC DOE to review and

approve the plan, even though GSA does not ultimately

need a local building permit.

Stormwater plans must meet several requirements,

including an important directive that stormwater flow from

the site will not increase after development over the preconstruction baseline.

DC WASA is responsible for maintaining the District’s

sewer system, and cleaning the catch basins.

DC Floodplain Requirements

The District promulgated development regulations, known

as the DC Flood Hazard rules, for buildings proposed to

be constructed in a floodplain.23 These rules, mandated

by NFIP for a community to be eligible for federal flood

insurance, restrict uses, activities, and development in areas

subject to flooding (generally within the 100-year

floodplain). If development is permitted in an area likely to

flood, it must be flood-proofed. The Flood Hazard rules

are triggered when an applicant seeks a building permit in

the District.

12 National Capital Planning Commission

Report on Flooding and Stormwater in Washington, DC | Potomac River

21Unlike the other three agencies, DC WASA is an independent authority that was formed to assure that the money collected

for the purpose of maintaining the water and sewer system would not be transferred into the DC General Fund.

22DC DPW’s responsibility is primarily street sweeping, waste collection, litter control, and road repair.

23As approved by FEMA.
DC Clean Water Act Requirements 

The District is required to obtain two NPDES permits

for its stormwater discharge as a municipality: one for the

Municipal Separate Stormwater Sewer System (MS4)

which drains storm water from approximately two-thirds

of the city into the rivers, and one which covers the Blue

Plains Wastewater Treatment Plant and the combined

sewer system.

Anacostia Waterfront Initiative

The Anacostia Waterfront Corporation (AWC) had

proposed additional stormwater requirements that are

stringent and comprehensive. AWC proposed that any

development that receives AWC financing or is on AWCcontrolled property must adhere to stringent stormwater

guidelines, which require retention and on-site reuse of

stormwater. Since the initial publication of this report, the

AWC was absorbed into the District Office of Planning.

The federal government’s stance on the more stringent

guidelines has not yet been determined.

DC Flood Emergency Plan

Atypically, the ACOE developed the Flood Emergency

Plan for the District. Generally ACOE is responsible for

developing emergency flood plans for the dam structures;

while the local government entity is responsible for

developing a local flood emergency plan. The first DC

plan was developed in the late 70s and is revised

periodically. 24

ACOE is responsible for flood control measures

nationwide, and consequently has designed and provided

construction oversight of the National Mall levee since

Congress authorized it. FEMA recently asked ACOE to

certify the levee as the line of delineation for the 100-year

flood event. The significance of this certification is that

private development on the other side of the levee (in the

downtown district) would not need to obtain flood

insurance and would not need to meet the DC Flood

Hazard regulations.25 While ACOE has not responded

officially in writing, ACOE stated it will not certify the

levee to FEMA because it believes the temporary closures

do not sufficiently ameliorate the flooding risk. Once the

ACOE decision is transmitted in writing it is likely that

there will be increased pressure on Congress to fund the

permanent levee closures so that ACOE can certify the

levee and exempt private development from needing flood

insurance and flood-proofing requirements.

With or without the ACOE proposed modifications, urban

drainage flooding nonetheless remains an unmitigated

flooding risk.

VI. Next Steps/

Action Plan for

Monumental Core 

In short, our research led us to three key conclusions. First,

while the definitive cause of the June 2006 flooding may

not be determinable, the rainfall totals in Washington, DC,

were extraordinary and at times equal to a 200-year storm

event. However, even though the rainfall was much greater

than normal, it exposed our second finding––that flooding

poses a risk to the federal government in the Federal

Triangle and National Mall areas. Flooding is a risk to the

national cultural and historic resources in the area, a

financial risk for the property damage, and a security risk

given the concentration of key federal functions. Last, even

in amounts far below flood stage levels, stormwater

control is an ongoing issue for which there is not a longterm federal or local management plan in this important

area. NCPC could play a leadership role in the

development of such a plan, if the Commission chooses.

At a minimum, the Commission can consider revisions to

our project review procedures and adding stormwater

considerations to our relevant planning initiatives.

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24DC reviews the ACOE Flood Emergency Plan and may provide input to ACOE. 

25Recall that ACOE was criticized heavily for certifying the levees in New Orleans. Consequently, many of the homes that flooded after the levees failed did not have insurance

because it was not required. Certification deemed them “outside” the 100-year floodplain and they were believed to be safe from flooding because the levees would protect them.
VII. Anacostia River

Flood Risk Overview 

Anacostia River Hydrology 

and Geography

The Anacostia River originates in Bladensburg, Maryland,

where the Northwest and Northeast Branches meet, and

flows southward for 8.4 miles until it runs into the

Potomac River at Hains Point in Washington, DC. The

Anacostia is tidal from its headwaters, and has a 2.9-foot

average tide. It flows languidly toward the District, and

with a 0.22 percent average mainstem gradient it can take

more than 30 days for water to flow from Bladensburg to

the Potomac. As a result of the sluggish flow, sediment,

debris, and pollutants are not easily flushed downstream.

The Anacostia watershed is small and highly urban. The

watershed spans approximately 170 square miles in its

entirety (compared to the Potomac watershed which

covers 14,679 square miles), 120 miles of which are

located in Prince George’s and Montgomery counties, with

the remainder in the District of Columbia. The watershed

is home to more than 800,000 residents, and is one of the

most urbanized watersheds in the United States.

Urbanization and other impacts have altered the Anacostia

River and its tributary streams causing floods to be 10

times more frequent and summer flows much lower than

historical statistics. 26 

According to the ACOE, the federal government owns 17

percent of the land in the watershed. However, in the

District more than 90 percent of the river’s immediate

shoreline is in public ownership, with the National Park

Service (NPS), the Navy Department, the General Services

Administration (GSA), and the District as the major

landowners.

Historically, the Anacostia was broad, deep, and

meandering with thousands of acres of fully functional

freshwater tidal marshes. In 1790, Bladensburg was a

deepwater port receiving ocean-going vessels. But less than

100 years later, sediment from agricultural activities in the

surrounding area clogged the river channel and closed the

river to navigation.

During the past century, channel dredging and the

consequent wetlands “reclamation” significantly altered the

tidal river system’s morphology. A stone seawall was built

along much of the river’s edge creating a hard line between

the dredged river channel and the deposited fill material

behind the seawall.

Today, the hydrology of the Anacostia tributary system is

“flashy” (i.e., it has a quick flow response to rainfall) with

intense flow conditions even in moderate rainfall events.

Channelization of the Anacostia’s tributaries, along with

urbanization, results in higher runoff volumes that flow

quickly into the mainstem. Conversely, in dry weather, the

tidal river portion is sluggish, and water can languish for

100 to 110 days in drought periods. Average daily inflow

into the tidal river is approximately 138 cubic feet per

second (roughly 61,934 gallons per minute).

Anacostia River Flooding

In comparison to the Potomac River, there is less historical

flood data and river flow measurements for the Anacostia

River because the Anacostia is tidal for its entire length.

Due to the tidal effect on the Anacostia River’s water level,

the USGS can not collect stream flow data from the river’s

rise in the way that it is collected for a non-tidal river

channel. USGS is currently experimenting with new and

innovative ways to measure stream flow in tidal river

channels, such as using acoustics to measure velocity and

calculate stream flow on tidal rivers. However, these new

methods have not yet been implemented along the

Anacostia. Second, there are only three river gauges in the

entire Anacostia watershed, one for the Northeast Branch,

one for the Northwest Branch, and one in Watts Stream

(located 200 feet upstream from Minnesota Avenue). In

addition, USGS reports that the costs of their research and

data collection efforts are typically funded 50 percent by

the local jurisdiction, and the District has neither requested

nor funded research and data collection for the Anacostia

River to the extent that other local jurisdictions have

requested data for the Potomac River.

According to the USGS, another reason for extensive

research and data on the Potomac River is that the

Potomac is considered the “big gorilla” of the

Washington metropolitan region.27 Flooding along the

Anacostia River usually only occurs when the Potomac

floods and not independently. Potomac River flooding,

because of the far greater size and reach of its watershed

and stream volume, is a far greater threat to its

surrounding area. Therefore, it has been monitored more

closely in the past. Storm events that cause flooding

along the Potomac River will affect the Anacostia River

and cause flooding in the Anacostia watershed.

Therefore, research and monitoring of the Potomac

informs expected flooding on the Anacostia, making

Anacostia River monitoring somewhat redundant.

Moreover, during a storm, the flooding on the Anacostia

River will subside more quickly than along the 

Potomac River.

14 National Capital Planning Commission

Report on Flooding and Stormwater in Washington, DC | Anacostia River

26USGS “Effects of Urban Development on Floods,” Fact Sheet FS-076-03 November 2003.

27Phone interview with Dan Souder of USGS.
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A number of notable flooding incidents on the Anacostia

River correspond to Potomac River overbank flooding. In

August 1933, an unnamed hurricane hit Washington, DC,

causing the Anacostia River to rise over the seawall.

Intense storms in 1936 and 1942 flooded the Potomac

River and led Congress to pass the Flood Control Act that

authorized the National Mall levee. These same storms

also flooded the Anacostia River, as depicted in these

photos of a flooded Washington Navy Yard.

Hurricane Isabel

Hurricane Isabel had a notable impact on the Anacostia

shoreline when the river surged over the seawall and

flooded many historic buildings in the Navy Yard.

Hurricane Isabel’s storm surge produced higher than usual

tides along both the Potomac and Anacostia river

coastlines. According to the NPS, high waters on the

Anacostia River severely damaged 12 offices in the NPS

National Capital Park East’s headquarters and in the US

Park Police’s adjacent Anacostia Operations Facility.

In Prince George’s County, high waters closed three roads.

Fifteen buildings sustained major damage, and 53

additional buildings were flooded. When two of the largest

Maryland sewage treatment plants lost power, 96 million

gallons of sewage overflowed directly into the county’s

waterways, and presumably downstream into the District.

VIII. Existing and

Proposed Flood

Control Measures

Role of the Army Corps of Engineers

The ACOE has been involved with the Anacostia River for

more than a century. Past and present activities include

flood control, navigation, debris-removal, and aquatic

vegetation management.

In the late 19th century ACOE began channelization of

the river and seawall construction to aid navigation and

control flooding. Poor agricultural practices throughout the

upper watershed rendered the Bladensburg seaport

impassable and created extensive mud flats densely covered

with grasses that trapped sewage and other waste. The

Chief of Engineers attributed the prevalence of malarial

disease bordering the Anacostia to the mud flats. As a

result, Congress directed the ACOE to dredge the River

and deposit the sediment on the mud flats to reclaim the

land, provide sanitation, and promote navigation and

commerce. In 1902, ACOE dredged the tidal Anacostia

River up to the Anacostia Navy Yard, plus a smaller

channel upstream to the District line, and deposited the

dredged material on the flats below St. Elizabeths, creating

Poplar Point and much of the land currently occupied by

Bolling Air Force Base. Dredging continued through the

1920s, with the material held in place with a seawall.

ACOE estimates that from 1900 to 1960, their activities

destroyed approximately 2,600 acres of wetlands,28 99,000

linear feet of aquatic habitat, and 700 acres of bottomland

hardwood in the Anacostia watershed. Today, only 100

2898 percent of the tidal wetlands and 75 percent of the basin’s freshwater wetlands had been destroyed by 1987.

Eastern end of Washington Navy Yard during the October 1942 flood Washington Navy Yard during the October 1942 flood

Photos Courtesy of Naval Historical Center
acres of tidal emergent wetlands29 remain along the

Anacostia River between Bladensburg and Hains Point.

As we now know, channelizing the Anacostia (along with

its tributaries) increased the speed and volume of the water

during heavy rainfall. Increased riverflow, in combination

with a stone seawall which provided a conspicuous line of

demarcation between the river and the shore, as opposed

to the broad natural wetlands areas, probably increased the

severity of flood events from heavy rainfall. The ensuing

Anacostia floods of 1933, 1936, and 1942, along with

flooding in other areas of the country, helped build

support for a national legislative solution.

The Flood Control Act of 1950 authorized flood control

measures along the Anacostia that would afford

protection against a flood considerably greater than the

maximum flood of record, which occurred on August 23,

1933. In that flood, the maximum discharge of the

Northeast Branch was computed as 10,500 cfs and the

maximum discharge of the Northwest Branch was

computed as 8,000 cfs.30

ACOE built five levee systems, two in Maryland and three

in the District, as a result of the legislation. In Maryland,

there is a levee system on the Northeast Branch and one

on the Northwest Branch. Channel improvements also

were implemented along both branches, although the

navigation channel extends upstream only to Bladensburg.31

In the District, the National Mall levee, discussed in

Section II, protects the downtown monumental core from

Potomac and Anacostia river flooding. Specifically, the

portion of the levee in Fort McNair, which currently

requires a temporary closure at Canal and P streets, SW,

protects the downtown business area from flood waters

rising from the Anacostia. Fort McNair also is surrounded

by an ACOE-built seawall that is jointly maintained by the

Department of Defense and ACOE. In addition, there are

two levees on the east side of the Anacostia that protect

upland areas from Anacostia River flooding: the Potomac

Park levee and the US Naval Air Station levee.

Anacostia River Flood Control Projects

A two-section flood protection levee is located on the east

bank of the Anacostia River and extends approximately

1.84 miles from Poplar Point to the southwest corner of

the Navel District Washington Anacostia Annex. Most of

the levee is an earthen berm, however, approximately 1,200

feet is a concrete flood wall. There are also two stop-log

closures, four pump stations, and various gates on storm

drains and sewers. Aerial maps showing the location of the

flood control projects are attached to this.

This levee was authorized in 193632 and completed in 1944.

The levee was constructed under ACOE supervision using

Works Progress Administration (WPA) labor and

contractor equipment and materials. The Anacostia levee

system was designed to provide flood protection to the

Naval Air Station and Bolling Field from a Potomac River

flow of 600,000 cfs.33 The total project cost for the

National Mall levee and the Anacostia levee system was

$339,227. ACOE estimates that replacement of the levee

system located on Anacostia Naval Station and Bolling

AFB could reasonably be expected to exceed $20 million

in 2007.

As a result of new post-Katrina rules, ACOE has

documented a number of serious structural issues along

the entire length of the levee. Previously, ACOE would

merely downgrade a levee’s rating because of trees growing

in the earthen portion of any levee, however, because trees

were one of the major factors in the breach of New

Orleans’ levees, new ACOE criteria require that the levee

be deemed unacceptable. If a levee is deemed

unacceptable, FEMA can not consider it as protection

from a flood event, and the area within which private

property owners are required to obtain flood insurance

may increase accordingly. FEMA currently is modernizing

flood maps nationwide. In a number of locations,

including the District of Columbia, the new maps have

been adjusted to reflect that the ACOE has not certified

the levee.

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29Tidal wetlands are vegetated lands bordering, or lying beneath, tidal waters which are subject to regular or periodic tidal action. Emergent wetlands, commonly called marshes

and meadows, are dominated by herbaceous (non-woody) plants such as grasses, sedges, and forbs (broad-leaved plants) that “emerge” from the water while their roots remain

submerged.

30Given that there is no gauge on the Anacostia River, the maximum discharge was estimated as 15,000 cfs, or approximately 80 percent of the maximum discharge of the two

branches.

31The navigation channel is 80 feet wide and authorized to a depth of 8 feet but normally maintained at 5 feet, plus 1 foot allowable over-depth. This is considered adequate for

existing navigation. A few areas near Kingman Island have been dredged to a depth of 10-feet to supply fill material for the Kingman Island wetlands restoration project.

32Congress authorized the Anacostia portion of the levee in the same legislation as the National Mall levee in 1936.

33This flow is in excess of the flows expected during the 100 year flood on the Potomac River. Flood protection measures along the lower portion of the Anacostia are designed to a

protection level to account for forecasted flood stages on the Potomac as opposed to the flood stage on the Anacostia because the Potomac’s flooding abilities far exceed the

Anacostia’s.
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The upper portion of the levee that protects Poplar Point

is overgrown with mature trees and is in disrepair. The

levee is on NPS property; therefore NPS is responsible for

its maintenance and repair.34 NPS currently is working

with ACOE to remove the vegetation and trees. Once the

trees are removed NPS will need to back-fill the levee to

shore up the line of protection. The upper section is

relatively small compared to the entire length of the levee

system; however, both sections were designed to work

together as a system to keep Anacostia flood waters out

of the Naval Station and Bolling Air Force Base. This

portion of the levee is contained within the 150-acre

parcel to be transferred to the District of Columbia as a

result of the recently approved federal land transfer

legislation.35 NPS is working with ACOE to make the

necessary repairs before the land transfer is to take place.

NCPC would have review and approval authority over

these capital improvements.

The lower portion of the levee for the Anacostia Naval

Station and Bolling Air Force Base is an earth berm

approximately 11,600 linear feet long, with an elevation of

15 feet mean sea level. In addition to the earthen levee, this

flood protection system consists of approximately 1,200

linear feet of concrete flood wall, two stop log closures,

four pump stations and various gates on storm drains and

sewers. The concrete flood wall was designed with an

opening of 328 feet to allow seaplane access to a hanger

located just inside the line of protection on the Naval

Station. Originally, this opening in the line of protection

was to be closed by a portable dam system, but has since

been permanently closed with a concrete flood wall.

Near the Anacostia naval facility, ACOE officials observed

trees growing into the sides of the levees. To date, Navy

officials have removed all of the vegetation and trees and

are beginning to address the more significant issues with

the seawall along their property. During the 1996 flood and

during Hurricane Isabel in 2003 under-seepage36 was

observed at the flood walls. ACOE’s inspection of the

walls is incomplete, but ACOE is working with the Naval

Station. Inspectors also found that stormwater drainpipes

could pose a problem during a flood if water from the

river were to back-up to the other side of the levee. ACOE

suggested that gates be added to the stormwater drain

pipes so water could flow only in one direction. The Naval

District has informed ACOE that they will look into this

recommendation. The Navy expects to undertake the

necessary structural levee repair work in the near future.

NCPC would have review and approval authority over

these capital improvements.

The jurisdiction and ownership of the very top segment of

the levee that runs under the Frederick Douglass Bridge

(South Capitol Street) is unclear. ACOE cited trees on the

levee and the lack of a gate to seal a gap in the levee

during storms. A seawall along this stretch also needs

maintenance. It is unclear under whose jurisdiction this

parcel falls and which entity ultimately has responsibility

for repairs and maintenance. However, ACOE stated that

it is probably in the best interest of the Naval District to

maintain this portion of the levee as it is designed to

protect their facility from Anacostia floodwaters.

Prince George’s County, Maryland, 

Flood Control Project

ACOE also designed and constructed flood protection

measures upstream in Prince George’s County, Maryland.

The Anacostia Local Flood Protection and Navigation

Project was completed in the 1950s. To manage drainage

on the land-side of the levees and protect against leveecaused flooding, ACOE installed four pumping stations.

Prince George’s County operates and maintains the

pumping stations, and in coordination with the Corps,

conducts an annual inspection of the levees, floodway

channel, and pumping stations.

In 1993, the Maryland Department of Natural Resources

(MDNR), Water Management Division, completed a

watershed study for the Prince George’s County portion of

the Anacostia. The study identified 2,500 flood-prone

structures located behind the existing levee system and

more important, found that the existing levee system does

not meet FEMA’s current safety criteria. The study

determined that the levee should be raised approximately

two to five feet to meet FEMA’s criteria. It is unclear if this

work has been completed; no one in either the state or

county offices is familiar with the study or its

recommendations.

Additionally, MDNR provided funding to Prince George’s

County to install an automatic flood warning system for

the lower half of the Anacostia watershed. The system,

completed in 2003, electronically monitors rain and stream

level information at 19 sites strategically located

throughout the watershed. The system automatically

transmits the information to the Prince George’s County

Public Safety and Communications Office to warn of

possible flooding. In the event of a major flood or other

flood-related hazard, individuals registered in the system

are notified via phone, fax, e-mail, or pager. Unfortunately,

34Levees typically fall into three categories. (1) They can be built and maintained by ACOE. (2) They can be built by the ACOE and transferred to a local owner to operate and

maintain. (3) Non-federal levee projects can be built by a local community. The latter two categories, if properly maintained and operated by the owner, are eligible for federal

rehabilitation assistance. In the case of the National Mall levee and the Poplar Point levee, ACOE built the levees, but NPS is expected to maintain them.

35The legislation requires the District to complete a land-use plan for Poplar Point that identifies a minimum of 70 acres, including wetlands, to be maintained in perpetuity as a park.

36Under-seepage occurs when levees are built on pervious foundations. Seepage beneath the levee (under-seepage) during floods can produce pressure and flow conditions

capable of initiating subsurface erosion leading to levee failure.
this notification system is not connected in any way to the

District to provide early warning notification for flooding

downstream. However, the National Weather Service

would notify the District in the event any of the gauges

indicated flooding was possible.

On February 1, 2007, ACOE deemed the Anacostia levees

in Prince George’s County unacceptable because of trees.

ACOE claimed that the dozens of trees growing on or

near the levees might cause the levee to fail if an uprooted

tree should pull apart the earthen barriers. This

determination surprised county officials because the trees

had been growing on and along the levee for years, and

some trees even pre-dated the levees.

Because there were so many sizeable trees to remove and

the work could not be completed before the ground froze

for the winter, Prince George’s County decided to remove

the trees in two phases. First, contractors cut the trees

down to a stump flush to ground level. With that phase

complete, County contractors will remove the root balls

and repair and reconstruct the earthen levee where

necessary. Prince George’s County officials also reported

that ACOE guidelines were revised a number of times

delaying the contract process and tree removal.

According to Prince George’s County staff, the Anacostia

Watershed Society planted many of the trees and was

understandably upset when the trees were removed. Just as

many local environmentalists and residents found the treeloss distressing, many communities nationwide have had to

implement the new ACOE tree policy and face significant

tree removal to retain ACOE levee certification. In

Sacramento, 5,100 mature trees were removed as a result

of the new levee maintenance policy.

ACOE levee certification is particularly important given

that FEMA is in the midst of a nationwide floodplain map

modernization initiative. If ACOE does not certify a levee

to FEMA, the revised floodplain maps must indicate the

potential 100-year flood as if the levee did not exist. This

is discussed in more detail in the next section.

At the same time that Prince George’s County is repairing

the levees to ACOE standards, county officials have also

embarked on flood control improvements, both physical

and technical. For example, the Edmondson Flood

Control Pumping Station upgraded its capacity by 300

percent to ensure sufficient capacity in the event of a

flood. The County is also updating floodplain information

for all of their watersheds using GIS-based hydrologic and

hydraulic models.

IX. Urbanization,

Channelization, and

Sedimentation Impacts

Impacts from Anacostia 

Tributaries on Flooding

Significant alterations of the Anacostia tributaries from

channelization, floodplain loss, and urbanization increase

flooding risks in the entire watershed. In general, these

alterations cause flashy storm flows with a low base flow

between storm events. Urbanization increases impervious

surfaces, which causes the storm flow to have higher peaks

and greater volumes. Greater stream flow, in combination

with channel modifications, increasingly deepens the

stream channels, and cuts the stream off from the

floodplain and its flood-mitigating functions. The

increased flow and the deeper channel within the

tributaries have an even greater capability to mobilize

stream sediment and reduce or eliminate river bed features

that help dissipate flow energy and slow the water down.

However, because the Anacostia River is flatter in elevation

than the Potomac River, alterations to its tributaries that

cause sediment to become waterborne are a more

significant problem. The sediment remains in the

Anacostia River’s streambed rather than washing further

downstream, and, therefore, increases the flooding risk in

the surrounding communities.

According to the USGS, the frequency with which daily

discharge exceeded 1,000 cfs on the Northeast Branch of

the Anacostia increased from once or twice a year during

the 1940s and 1950s (about the same time the Anacostia

River was channelized, the levees constructed, and the

wetlands filled) to as much as six times per year in the

1990s. Thus, in recent years the Anacostia River has had to

carry much greater volumes of water more frequently than

in the past.

Anacostia Sedimentation

Sedimentation is a great cause for concern. The existing

levees were designed to protect Anacostia from a 100-year

storm event. However, ACOE’s baseline assumptions were

for a deeper river channel with less sedimentation then

exists today. ACOE has not completed a full Anacostia

assessment since the 1950s, and the Anacostia has not

been dredged for years. Near the town of Bladensburg, the

Anacostia River is frequently more riverbed than river, with

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no more than a trickle of water. Present-day river

conditions are far removed from the 40-foot-deep shipping

channel it once was. Over the years, the riverbed has been

silted in with dirt and debris carried by stormwater runoff

from Montgomery and Prince George’s counties.

Sedimentation of the stream channel means that the

riverbed can only contain a small volume of water. Rainfall

or river flow displaced by the sedimentation will flood over

the top of the riverbank. In other words, even moderate

rainfall has the potential to cause overbank flooding

because the excess stormwater can not be conveyed

downstream in the river channel.

In January 2007, ACOE released a report on its

investigation of the June 2006 flooding of Cameron Run

in Virginia. The report concluded that channel

sedimentation considerably affected flood levels. The

report found that in the 25 years or so since the FEMA

flood maps were last updated, between five to six feet of

sediment accumulated in the Cameron Run Channel. As a

result, flooding in the Huntington neighborhood was up to

two feet higher than it would have been. It was estimated

that much of the sediment originated from the

development of Fairfax County upstream from the

flooded neighborhoods. It is reasonable to assume that

given the Anacostia’s propensity for sedimentation, and the

significant upstream development in Prince George’s

County, that sedimentation in the Anacostia would likely

result in higher flood levels in a storm event than previous

events would indicate.

There are two solutions to directly deal with the increased

flooding risks resulting from sedimentation. First, ACOE

or the relevant local municipalities could conduct a field

investigation and model various storm simulations. This

would determine if the existing levees provide a sufficient

amount of protection (typically the levee would protect

against a 100-year storm event) given the current level of

sedimentation in the Anacostia River. These models

could also determine which improvements, such as

increasing the height of the levees, might be necessary to

provide communities behind the levees with a sufficient

amount of protection.

Second, dredging can remove sediment from the riverbed

of the Anacostia and restore the deeper channel. The

Navy supports a recommendation to dredge the Anacostia

because existing sedimentation prevents larger naval ships

from coming up the Anacostia. As a result, the Navy

incurs steep docking fees for its ships at a private port in

Alexandria when their ships are in town. However,

dredging is not a straightforward solution. It is expensive

under ideal circumstances and very difficult to complete

when a disposal site is needed for any contaminated

sediment spoils, which is likely from the river areas

surrounding Poplar Point and the Navy Yard. Additionally,

ACOE favors dredging projects that are part of a larger

ecosystem restoration project so that uncontaminated soils

can be used for wetlands creation.

Urban Drainage Flooding

Urban drainage flooding is typically caused when the sewer

system’s capacity is exceeded. While one-third of the

District, including the entire downtown business district,

has a combined sanitary and stormwater system, most of

the area east of the Anacostia has separate sewers.

Separate systems have two independent piping systems:

one system for sanitary sewage and one system for

stormwater. Separate systems for stormwater and sanitary

sewage can’t ensure that an area will not flood, but the

additional sewer capacity can help mitigate heavy rainfall. A

portion of the District along the west side of the

Anacostia River falls within the combined sewer area.

Presumably this area would be more susceptible to

flooding from excess stormwater. However, there have not

been reports of urban drainage flooding in this area.

Potential Impacts on Recent and

Proposed Waterfront Development

Until recently, there has been little development along the

Anacostia riverfront within the District as most of the

waterfront is publicly owned. In the last few years,

however, development pressure has increased substantially

throughout the District, especially along the waterfront. In

addition, a number of land development transactions have

led to more waterfront land slated for private development.

This increased development pressure and concurrent

interest in areas along the Anacostia Riverfront warrants

further attention.

The Yards is one recent development proposed along the

Anacostia River. GSA granted Forest City the opportunity

to redevelop a 42-acre riverfront property site with mixeduse redevelopment including 2,800 residential units, 1.8

million square feet (SF) of office space, up to 300,000 SF

of retail space, and a riverfront public park. The Yards

mostly avoided developing within the 100-year floodplain

by proposing to raise the site’s elevation above floodplain

levels. This is a common and permissible development

technique that is employed as a means of avoiding the

costly construction, insurance, and regulatory requirements

typically associated with building in a floodplain. Raising

the site’s base elevation helps protect the site by keeping

water out that would otherwise have inundated the site in a
storm. It is important to note that while this methodology

is both customary and allowable, elevating the base

elevation by placing fill within the floodplain can make

flooding impacts worse elsewhere in the watershed,

particularly from the cumulative impacts when a number

of projects in the same watershed use this means.

Poplar Point is another prominent site slated for

development. Congress authorized the site to be

transferred from NPS to the District, and the Mayor’s

Office has been considering a number of development

proposals for the site. While no specific development

proposal has been selected for the site, because the 100-

year floodplain extends over much of the site, it is likely

that any proposed development would raise the elevation

of the site above the base flood elevation to avoid

additional costs. Again, it is unlikely that this methodology

would result in greater flooding impacts within the

immediate area; however, staff would recommend that

District planners consider the potential floodplain impacts

when the site plans are submitted for review and approval.

The Commission also will have an opportunity to review

any proposed development for the site and will need to

apply the NCPC floodplain guidelines in its review.

X. Restoration and

Remediation Efforts

Below is a short summary of some recent federal efforts

along the Anacostia River to restore water quality. This

summary is not all encompassing and does not include all

the remediation efforts that have been undertaken.

Instead it is intended to illustrate efforts to restore the

river’s natural flood control characteristics and other

ecological functions.

Washington Navy Yard 

Storm Sewer Rehabilitation

The Washington Navy Yard, established in 1799, is the

nation’s oldest naval shore facility. The Navy Yard’s

industrial operations ended in the 1960s; however, the

former military activities left behind hazardous waste. The

Navy has undertaken numerous cleanups to remediate

environmental damage at the Navy Yard. In particular,

sewer remediation and innovative stormwater management

techniques have helped reduce a small portion of the

stormwater pollution that ends up in the Anacostia River.

In March 1998, to settle a civil lawsuit alleging that

contaminated stormwater from the Navy Yard contributed

to Anacostia River pollution, the Navy agreed to specific

cleanup actions, including storm sewer cleaning and

rehabilitation. One of the remedial actions was the

rehabilitation of nearly six miles of stormwater and

sanitary sewer pipes.

During Phase One, 20,000 linear feet of storm sewer lines

were cleaned and inspected with video cameras. About 30

percent of the sewer lines were crushed or obstructed.

During Phase Two, storm sewer lines were repaired,

renovated, or replaced, as needed. When possible, the

Navy renovated existing pipes by placing a new impervious

liner inside them, which eliminates groundwater seepage

into the pipes and allows more efficient stormwater flow

within the pipes. More than 50 percent of the pipes were

too damaged for lining and had to be replaced.

Last, the Navy installed a number of small-scale,

sustainable stormwater management structures (known as

Low-Impact Development or LID). LID reduces

stormwater pollutants from being discharged into the

Anacostia River. In heavy storms, LID also helps control

the peak stormwater velocity and volume in the storm

sewer system. The Navy Yard LID measures are often

cited as a notable local effort to reduce Anacostia

stormwater pollution.

Wetlands Restoration

Progress is also being made in wetland creation and

restoration. Wetlands restoration confers many

environmental benefits, such as providing a new wildlife

and waterfowl habitat, and beautifying the shoreline.

Wetlands are not only beautiful, they are functional and

help mitigate the impacts of heavy rainfall. They help

prevent flooding, flush out stormwater pollutants, and

improve water quality.

More than 100 acres of wetlands have been reclaimed or

created in the Anacostia basin. In 1993, ACOE

reconstructed approximately 30 acres of freshwater tidal

marshes in the Kenilworth Marsh area near the last

remaining stand of original tidal marshes. Adjacent to this

wetland is the Kenilworth Aquatic Garden, operated by

NPS. The District and ACOE are restoring a 46-acre marsh

near Kingman Lake. Immediately upstream from the New

York Avenue Bridge, approximately 20 acres of wetlands

are being created and 30 acres of freshwater wetland sites

have been identified for the Northeast Branch.

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Unfortunately, while there is widespread support for

additional wetlands creation in the District, it is unlikely to

happen until a solution can be found for the originally

migrant, and now permanent, Canadian geese population

that was responsible for eating half of the newly installed

wetland plants at the Kingman Marsh wetland restoration

project near Robert F. Kennedy Stadium. The geese

previously stopped temporarily in the District en route

either north or south but recently stopped migrating to

take advantage of the plentiful food and lack of natural

predators in the District. Local and federal agencies do not

have a management strategy for the geese, and lethal

control is likely to be unpopular. This past July, NPS held a

public scoping meeting for the Anacostia Park Wetlands

Restoration Plan to develop resident geese management

strategies on NPS wetlands. Until the environmental

review is complete and a resident geese management

strategy selected, wetlands restoration in the District is

likely to be put on hold.

The Anacostia East Wetland Mitigation Project is located

on Maryland National Capital Park and Planning

Commission (M-NCPPC) property near Bladensburg. Just

upstream from the Washington, DC, border, approximately

55 acres along the Anacostia River’s eastern shore are

being transformed into a tidal wetland. The project

includes a series of aquatic zones that will provide a fish

habitat and promote the growth of various wetland plant

species. Approximately 25 acres of the restoration project

is a mitigation site for the Woodrow Wilson Bridge

Replacement Project. The two-year contract was awarded

in March 2007.

In Poplar Point, wetlands have developed in several areas

since the Architect of the Capitol’s nursery activities

ceased, and stormwater has been allowed to collect in

topographically low areas.37 Presently, there are four

federally mapped wetland areas on the site. As part of the

redevelopment of Poplar Point, the District plans to

restore wetlands more fully and bring Stickfoot Creek,

which is currently submerged through a drainage pipe,

back to the surface.38

XI. FEMA Floodplain

Map Modernizations

FEMA develops maps nationwide that delineate floodways

and the floodplains.39A Flood Insurance Rate Map (FIRM)

is the official map on which FEMA has delineated both

the special flood hazard areas and the flood risk premium

zones applicable to a community. Buildings within the 

100-year floodplain must obtain flood insurance and meet

more stringent building codes. Buildings within the 

100- to 500-year floodplain are not required to obtain

flood insurance, but may do so at a preferred risk-rate.

In the District, FEMA develops the maps in conjunction

with the District Department of the Environment

(DDOE). Like most communities nationwide, the District

floodplain maps, last revised in 1985, are outdated. Over

the past few years at the urging of Congress, FEMA has

embarked on a substantial initiative to update the maps

nationwide. The map modernization process took on

increased urgency after Hurricane Katrina when the levees

in New Orleans failed. Numerous property owners

sustained damage to their homes but did not have flood

insurance to cover their financial losses. In the past, the

floodplain did not extend to the landward side of the

levees because the assumption was that the levee would

hold the floodwater back. Due to the New Orleans levee

failure, FEMA required ACOE to inspect all levees. If a

levee is deemed insufficient to withstand a storm event,

FEMA will delineate the floodplain area without benefit of

the levee’s protection.

37Excess stormwater previously was pumped from the site when it was in operation as a nursery.

38Stickfoot Sewer runs under the eastern portion of the site and conveys both stormwater and Stickfoot Creek from areas south of the site to the Anacostia River.

39“Floodplain” is the low area of land surrounding water bodies that holds the water overflow during a flood.
REVISED FEMA FLOODPLAIN MAPS

On September 26, 2007, FEMA published notice in the

Federal Register for a 90-day public review and comment

period on proposed revised floodplain maps for the

District. The proposed maps are significantly different

from the existing maps largely because the ACOE has not

certified any of the levees in the District. The lack of

ACOE certification requires FEMA to note the location of

the levees on the map but to treat them as if they do not

exist for purposes of mapping where the floodwater would

inundate for a 100-year storm. (See map on page 23.)

Consequently, most of the monumental core area is within

the 100-year floodplain because the proposed maps

assume that floodwaters from the Potomac and Anacostia

rivers would flood the downtown area via 17th Street, NW,

and near Fort McNair. Similarly, areas east of the

Anacostia River beyond the existing levee structures are

within the 100-year floodplain because ACOE did not

certify the Poplar Point and Naval District levees.

As we noted earlier, the impact of being within the 100-

year floodplain is two-fold. First, all private development

must secure flood insurance. Second, all new public and

private development must comply with more stringent

building codes designed to protect the structures from

flood damage. The federal government has an additional

requirement to comply with Executive Order 11988, which

was implemented to reduce the potential impact of federal

decisions on floodplains, and requires federal agencies to

consider alternative actions outside of the floodplain

where possible.

There are a number of large federal installations near the

Anacostia River that are within the proposed 100-year

floodplain, including Bolling Air Force Base, the Navy

Yard, Fort McNair, and much of the NPS riverfront

parkland. Fortunately, the proposed floodplain designation

should not adversely impact any of these facilities or their

day-to-day operations. Representatives from the Navy Yard

and Bolling report that due to past flooding, numerous

procedures and measures are already in place to handle

overbank flooding. Existing precautions include, but are

not limited to, prohibiting critical equipment on ground

floor locations and keeping sufficient pumps on hand at all

times to ensure that operations are only minimally affected

in a flood event. Many NPS properties, such as the FDR

Memorial, have been designed to withstand periodic river

flooding because of their location in the floodplain, on the

river-side of the levee.

These riverfront installations are unlikely to be impacted by

the proposed broader 100-year floodplain designations

because they have either been designed or retrofitted to

accommodate occasional flooding. However, numerous

federal headquarters, offices, museums, and other

important federal facilities within the monumental core are

within the proposed enlarged 100-year floodplain as a

result of the ACOE failure to certify the levee along the

National Mall. The impacts on these federal facilities are

less obvious. The flood insurance requirement would not

affect federally owned buildings because the federal

government is self-insured. However, federal agencies

seeking to renew office leases, or agencies that need to

procure new leased space may face higher rents because

private building owners will need to obtain flood insurance

that previously was not required.

New federal construction may also be more costly because

all new development, private and public, will have to

adhere to more stringent building requirements if the

property falls within the expanded floodplain. Building

modernizations also may cost more as GSA likely will

consider such additional renovation measures as moving

key building operations equipment from basement areas to

avoid the risk of flooding. Last, all federal agencies,

including NCPC, will need to comply with EO 11988

which requires federal agencies to consider the impact of

their decisions on the 100-year floodplain. Among other

considerations, EO 11988 requires that agencies consider

potential alternatives to locations within the floodplain.

FEMA and DDOE have been collecting public comments

through January 3, 2008 on the accuracy of the maps.

Members of the public can protest the map delineations if

they believe they are based on erroneous data. Presumably,

because the repairs to the east of the Anacostia levees are

almost complete, ACOE might be able to certify their line

of protection and have FEMA revise the maps before they

are made final. However, because the design of the

improvements to the National Mall levee has not started

and Congress has yet to appropriate the funds for the

improvements, it is unlikely that ACOE will be able to

certify the National Mall levee before the maps are

finalized. Consequently, it is very likely that the maps will

proceed with an extensive floodplain covering much of the

monumental core.

22 National Capital Planning Commission

Report on Flooding and Stormwater in Washington, DC | Anacostia River
XII. Next Steps/Action

Plan for Anacostia River

Based on our research, NCPC has taken the following

actions. First, staff has submitted a comment letter to

FEMA and the District Department of the Environment

(DDOE) on the proposed flood map revisions that makes

four requests. (1) NCPC requests that DDOE and FEMA

confirm, in writing and by public notice, the reasons for

the proposed map revisions. (2) NCPC urges DDOE and

FEMA to provide increased and creative public notice to

property owners affected by the map revisions because

most property and building owners would not expect to be

within the 100-year floodplain. (3) NCPC urges FEMA

and DDOE to determine an expedited process to update

the flood maps as soon as the National Mall and Anacostia

levee improvements are complete as it is unacceptable for

the maps to remain incorrect if the next round of map

revisions will not occur for another 25 years. (4) NCPC

urges FEMA and DDOE to continue to research whether

urbanization within the Anacostia and Potomac

watersheds, and expected sea level increases, would warrant

further map revisions. In addition, staff recommends that

the Commission encourage FEMA to consider whether

Anacostia River sedimentation will alter the floodplain

delineations because the reduced capacity of the river

channel could cause higher flood levels.

NCPC also continues to support strongly ACOEproposed improvements to the National Mall levee as a

critical measure to protect the National Mall and its

environs, the art and artifacts housed in the Smithsonian

buildings and the National Archives, and critical federal

functions in the monumental core. Any modifications

would require NCPC review, and, due to the levee’s

location, any improvements would need to be developed

carefully to protect the historic, cultural, and aesthetic

attributes of the National Mall. The letter indicates that

NCPC staff encourages ACOE to schedule consultation

meetings about the proposed levee improvements as early

in the design process as possible.

NCPC staff will continue to coordinate with other federal

agencies and organizations to understand the potential

short- and long-term impacts of the revised floodplain

maps and provide assistance, when necessary, to comply

with federal rules and policies. This approach is consistent

with agency policy outlined in the Comprehensive Plan for the

Nation’s Capital: Federal Elements, which states that federal

actions in the region should support the restoration of

floodplain values and functions whenever possible.

23

Report on Flooding and Stormwater in Washington, DC | Anacostia River

National Capital Planning Commission

DC 2007 Preliminary Flood Insurance Rate Map

ZONE A: Would flood in 100-year event 

ZONE B: Would flood in 500-year event

Potomac River

Washington Channel

Tidal Basin

25

Report on Flooding and Stormwater in Washington, DC | Appendix A

National Capital Planning Commission

APPENDIX A: Major Flood Events in Washington, DC

Flood Year Hurricane Name Flooding Elevation*/ Comments Recurrence

Peak Discharge Interval

(Years)

1889 Potomac crested at 12.5’ above flood stage 50->100

1933 Unnamed +11.0’ LWD Most destructive hurricane on record for 

Chesapeake Bay and DC

Storm surge highest of record on Bay and Potomac;

superimposed on astronomical high tide

1936 28.10 Thick Ice, snowmelt and intense rainfall runoff 90

484,000 cfs –– Little Falls

1937 23.30 Huge storm over entire northeast

40,100 cfs

1942 25.88 Floodwaters reach the Lincoln Memorial steps

394,200 cfs Rainfall 6.27”

Rainfall 10-15” to west

1954 Hazel +8.7’ LWD Second most destructive storm 25 to >100

Storm surge of 5.6’ imposed on

astronomical high tide

1955 Connie +6.6’ LWD Tidal surge of 5.6’ on astronomical low tide 5 to 10

Would have reached +10’ LWD if superimposed

on high tide

1955 Diane +7.0’ LWD Surge approximately 4.5’

Heavy rainfall increased damage and flooding after

Diane passed through the area

1972 Agnes 22.03 Greatest Maryland flood 50 to >100

359,000 cfs –– Little Falls More death and property damage in Maryland than DC

1996 19.29 Potomac rose 85’ in 48 hours 30

317,000 cfs –– Little Falls Fifth largest flood in DC

2001 7” rain fell on DC

2003 Isabel Washington Harbor Flood gates raised, Levee closed

Potomac above flood stage

June 2006 86,2000 cfs (6/29/06) Short period of excessive rainfall 1.5

* Flood Stage at the Wisconsin Avenue gauge is 10.0 feet. Sea Level Conversion (SLC) at this gauge is 37.95.

To convert to sea level, add the SLC to the river stage to determine if a property is in danger of flooding.
MEMORIAL NPS COMMENTARY

Background Before West Potomac Park was completed the topography of

lower Northwest DC formed the shoreline. Higher ground

elevations were present at the Naval Hospital site, Square 63 and

Square 88, but the squares east of 21st Street were low and

subject to tidal action. The architectural walls that separate the

garden forecourt to the Federal Reserve, Interior South and the

Pan American Union Annex buildings built between 1931 and

1945 are set at elevations between 21.40 and 23.75. Elevation

19.1 represents the level of the 250 year storm event. 

Korean War Veterans Memorial The civil engineering analysis by ACOE determined that the

memorial (based on the November 1985, DC Federal

Emergency Management Agency Map, Panel Number 11001-

0015B) is located outside the limits of the 100-year floodplain,

but within the 500-year flood. No significant site modifications

were required. There is a mechanical room with an area way

entrance whose top elevation is between 13.5 and 14.5 that

would be below the 15.6 foot 100-year event. This space will be

protected by a temporary barrier of sand bags in the event of a

100-year event.

Franklin Delano Roosevelt Memorial The granite walls of the memorial are built to elevation 19.5 and

at critical equipment areas to elevation 22.50 and elevation 22.95.

The park grounds around the memorial are between elevation 8.5

and 12.0 and subject to a 100-year event of elevation 15.6. The

Entry Building at the FDR Memorial has a floor elevation of

approximately 11.0 and is managed to be cleared in the advance

of predicted flooding.

World War II Memorial The centerline of the memorial on 17th Street, SW is at elevation

8.7 feet, while the original Rainbow Pool was at elevation 5.6 feet,

and is subject to impact by a 100-year storm event elevation of

15.6 feet. The location of the memorial just outside the existing

levee’s protection area was noted in a May 1998 Environmental

Assessment. The memorial was designed to withstand the

impacts of flooding so that significant property damage and

potential environmental impacts would not occur. The equipment

room of the WW II Memorial is designed to be sealed from flood

waters, while the memorial itself can be flooded and

subsequently flushed of debris and deposited sediments. 

Vietnam Veterans Memorial The memorial is protected by the National Mall levee. 

APPENDIX B: Information on Memorials Submitted to NCPC by National Park Service 

26 National Capital Planning Commission

Report on Flooding and Stormwater in Washington, DC | Appendix B
APPENDIX C: Relevant Laws and Regulations for Flooding and Stormwater Management

27

Report on Flooding and Stormwater in Washington, DC | Appendix C

National Capital Planning Commission

Federal Laws/ Federal Agency

Responsibilities Overview NCPC NPS FEMA ACOE GSA

National Flood

Insurance

Program (NFIP)

EO11988–

Floodplains

NEPA

Clean Water Act

Miscellaneous

Considerations

FBMA has implementation

responsibility

Other federal agencies must

evaluate actions in 100-year

floodplain

Federal agencies should

avoid floodplain

development––agencies must

evaluate actions in

floodplains to disclose if

action will occur in a

floodplain, and if so, what

alternatives were considered

to avoid adverse effects and

incompatible development.

Agencies must conduct an

Environmental Assessment or

Environmental Impact

Statement for any proposed

action that may significantly

affect the human

environment; disclose

unavoidable adverse impacts;

and consider alternatives

Regulates stormwater

discharges from construction

activities and sewer system

discharges

Must evaluate any

action in floodplain,

disclose impacts,

consider alternatives

NCPC’s NEPA

submission

guidelines require

discussion of

environmental

impacts of proposal

& alternatives on

floodplains, flooding

and stormwater

impacts

While not directly

from NFIP, NPS

implements temporary

flood control closures

on the Mall at 17th

and 23rd Street

Must evaluate any

action in floodplain,

disclose impacts,

consider alternatives

NPS must evaluate

environmental impact

of its actions and

alternatives on

floodplains, flooding,

and stormwater

impacts

As developer and

property owner must

comply with CWA

Costs from flooding

impacts on memorials

borne by NPS

Develops DC FIRM,

approves DC Flood

Hazard Rules,

works with DC

Emergency

Management.

Must evaluate any

action in

floodplain, disclose

impacts, consider

alternatives

Called to action

when federal

disaster area

declared

Designed and

constructed

National Mall

levee

Must evaluate any

action in

floodplain,

disclose impacts,

consider

alternatives

Must evaluate

environmental

impacts of flood

control measures

and alternatives

on floodplains,

flooding, and

stormwater

impacts

Must evaluate any

action in floodplain,

disclose impacts,

consider

alternatives

GSA must evaluate

environmental

impacts of its

actions and

alternatives on

floodplains,

flooding, and

stormwater impacts

As developer and

building owner

must comply with

CWA

As landlord,

responsible for

such flood clean-up

and prevention
100-year flood A flood that has a 1-percent chance of being equaled or exceeded in any given

year. A base flood may also be referred to as a 100-year storm and the area

inundated during the base flood is sometimes called the 100-year floodplain.

ACOE U.S. Army Corps Engineers

AWC Anacostia Waterfront Corporation

cfs cubic feet per second - the common unit of measure for the flow of a river

CSO combined sewer overflow - what happens when an excess of stormwater and / or

sewage exceeds the systems capacity and flows without treatment into the rivers

CWA Clean Water Act

DC DOE DC Department of the Environment

DC DOH DC Department of Health

DC DPW DC Department of Public Works

DC EMA DC Emergency Management Agency

DCRA Department of Consumer and Regulatory Affairs

DC WASA DC Water and Sewer Authority

DDOT DC Department of Transportation

EPA U.S. Environmental Protection Agency

EO Executive Order

FCIP Federal Capital Improvement Plan, prepared by NCPC

FEMA Federal Emergency Management Agency

FIRM Flood Insurance Rate Map - prepared by FEMA, required by NFIP, shows 

100-year and 500-year floodplain

GSA General Service Administration

LEED Leadership in Energy and Environmental Design - the green building system of

the U.S. Green Building Council

LTCP Long Term Control Plan

MLW Mean low water- the average height of the low tides over a 19-year period 

MOU Memorandum of Understanding

MS4 Permit Municipal Separate Stormwater System Permit, required by CWA for municipal

stormwater systems

NEPA National Environmental Protection Act

NFIP National Flood Insurance Program

NOAA National Oceanic and Atmospheric Administration

NPDES National Pollutant Discharge Elimination System

NPS National Park Service

NWS National Weather Service

OMB Office of Management and Budget

USGS U.S. Geological Survey 

WAWAS Washington Area Warning Alert System

28 National Capital Planning Commission

Report on Flooding and Stormwater in Washington, DC | Appendix D

Appendix D: Acronyms and Abbreviations
24.1 Water begins to inundate Constitution Avenue near the Lincoln Memorial at the low spot on

Henry Bacon Drive. 

22.2 Water begins to reach the Pentagon East parking area. 

20.5 Water begins to inundate the north end of the North-South runway at Reagan National

Airport. 

19.0 Water begins to flood the south end of the North-South runway at Reagan National Airport. 

17.0 Water approaches the Southeast end of the Northwest-Southeast runway at Reagan

National Airport. 

16.7 Water begins to inundate the Kennedy Center for Performing Arts at Rock Creek and

Potomac Parkway. 

16.0 Water approaches low spots of the 14th Street Bridge approach on the DC side of the river.

Water also reaches George Washington Memorial Parkway south of Reagan National Airport

near Four Mile Run. 

15.0 Water inundates portions of Maine Avenue. 

13.7 Water approaches East Potomac Park at the railroad bridge. 

13.0 Wisconsin Avenue and K Street are flooded. 

12.0 The parking lot at the foot of Wisconsin Avenue in Georgetown floods. 

11.0 There are no longer tidal effects. The river will rise to crest then fall, not seeing the

separate high and low tides again until the water drops below 11 feet. 

10.5 Water approaches Independence Avenue at 17th Street and the George Washington

Memorial Parkway at the railroad bridge north or Reagan National Airport. 

10.0 Water approaches K Street in Georgetown near Washington Harbor. 

7.0 Water begins to inundate Washington Harbor. 

6.0 Water reaches bulkhead along Washington Harbor. 

29

Report on Flooding and Stormwater in Washington, DC | Appendix E

National Capital Planning Commission

APPENDIX E: Flood Stages for the Potomac River from USGS
30 National Capital Planning Commission

Report on Flooding and Stormwater in Washington, DC | Appendix F

APPENDIX F: Aerial Maps of Flood Control Projects

Figure 1
31

Report on Flooding and Stormwater in Washington, DC | Appendix F

National Capital Planning Commission

APPENDIX F: Aerial Maps of Flood Control Projects

Figure 2
National Capital Planning Commission | 401 9th Street, NW, Suite 500 North Lobby | Washington, DC 20004 | 202.482.7200 | www.ncpc.gov