All waterways and bodies of water are subject to flooding – a condition that occurs when the volume of water exceeds the capacity of the waterway channels or when tidal waters are pushed inland by coastal storms:
- Riverine or nontidal bodies of water are those that drain upland areas and are not influenced by coastal and tidal processes. In addition to rivers, nontidal bodies of water include streams and creeks and other small flowing waters. Flooding can also occur in localized low spots, even if the area is not adjacent to a body of water.
- Coastal flooding affects tidal bodies of water, including the tidal reaches of the Potomac River and the Patuxent River in Prince George’s County. The Potomac River is subject to tidal flooding along its entire length in the County, and the Patuxent River is subject to tidal flooding up to the confluence of Western Branch.
The Prince George's County Department of Environmental Resources (DER) recognizes and manages riverine flood hazard areas that are designated in two ways:
- Areas identified as vulnerable to flooding from the 1% annual chance flood (100-year floodplain) as shown on the County’s Flood Insurance Rate Map (FIRM) prepared by FEMA's National Flood Insurance Program (NFIP); and
- Other flood maps based on studies prepared by the County to evaluate the impact of future development. These maps often include areas not studied by the NFIP.
The first Flood Insurance Study and FIRM for the County were dated August 4, 1972 and prepared by the U.S. Department of Housing and Urban Development (a precursor agency to FEMA). Since that time, updates to the FRIM have been completed. The most recently revised and reprinted map panels are dated September 6, 1996. Also, note that FEMA published a preliminary county-wide FIRM for the County on September 30, 2010.
Starting in the 1980s, DER began to obtain State grants and use County funding to prepare more up-to-date watershed studies to delineate floodplains. The County's studies and maps, prepared with detailed base map data and detailed engineering models, account for future watershed development. They also are the basis for the State’s regulation of nontidal waterways. Watershed studies have been prepared for the following bodies of water:
- Piscataway Creek (April 1986);
- Henson Creek (April 1986);
- Western Branch of the Patuxent River (revised August 1991);
- Tinkers Creek (June 1979);
- Anacostia River (October 1993);
- Folly Branch (February 1995);
- Collington Branch (June 1985);
- Bald Hill Branch (April 1992);
- Southwest Branch (December 1992);
- Charles Branch (June 1991);
- Oxon Run (June 1991); and
- Beaverdam Creek (August 1995).
The figure below shows the extent of flooding as depicted on the latest FEMA FIRM. For more information on FEMA FIRM, how to locate your property on a FIRM, a description of the flood zones, and information on amendments or revisions to the FIRM, visit the section titled "Flood Insurance Rate Maps and Flood Insurance.
Flood Hazard History in Prince George’s County
Prince George's County has experienced some riverine and stream flooding in recent decades, although sound management of flood hazard areas and construction of flood control projects has reduced potential losses. Notable riverine and coastal flooding has occurred several times since 1933.
- August 1933 – This unnamed hurricane caused flooding along the Potomac River and throughout the Chesapeake Bay; the Livingston Bridge on Piscataway Creek also flooded.
- October 1954 – Hurricane Hazel raised water levels in the Potomac River Basin; statewide, the storm caused 6 deaths and an estimated $11.5 million in damage.
- August 1955 – Hurricane Connie caused riverine flooding that inundated a large commercial section of Upper Marlboro and flooded several buildings along Piscataway Creek; surge reached 4 feet above normal at the confluence of Patuxent River with Western Branch.
- August 1971 – Heavy rain and flooding.
- June 1972 – Tropical Storm Agnes; this storm of record brought high water levels along the Patuxent and Potomac River basins; statewide, it caused 19 deaths and $80 million in damage; in Prince George’s County, the storm caused more than $10 million in damage (see box).
- September 1975 – Hurricane Eloise; heavy rain and flooding; Prince George’s County was included in the major disaster declaration.
- September 1978 – Hurricane David; Prince George’s County was included in the major disaster declaration.
- November 1985 – Hurricane Juan affected the Potomac River Basin; Prince George’s County was included in the major disaster declaration.
- September 1996 – Hurricane Fran; remnants of this large storm caused flooding along the Potomac River Basin; Prince George's County was included in the major disaster declaration.
- September 2003 – Hurricane Isabel produced widespread wind damage, power outage, and localized flooding.
- June 2006 – Heavy rain and flooding.
- May 2008 – Heavy rain.
The Legacy of Tropical Storm Agnes
Leaving behind more than $10 million in damage in Prince George’s County and the City of Laurel, Tropical Storm Agnes moved through the area on June 21-22, 1972. Newspaper reports described the aftermath:
- $1 million in damage to public buildings, roads and bridges.
- Worst hit areas included along Chillum Road, Lewisdale, the Green Meadows subdivision in Hyattsville, Lakeland section of College Park, Brentwood, the Adelphi Mill area on Riggs Road, Oxon Run Drive, Tucker Road Bridge, and Water Street Bridge in Upper Marlboro.
- More than 1,800 people were served at shelters.
- Home foundations were braced with sandbags, propane gas tanks became detached, and basements were flooded.
- County personnel evaluated livability of damaged structures.
- WSSC reported erosion damage to some water supply mains; low-lying sewage collection and pump facilities were damaged.