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Natural
History of the Anacostia Watershed: Hydrology There are three major drainage areas comprising the Anacostia watershed: the Northwest Branch, the Northeast Branch, and the tidal drainage. The Northwest and Northeast branches are free-flowing (nontidal) streams, and their confluence forms the tidal Anacostia River in the vicinity of Bladensburg, Maryland. The tidal drainage area consists of the tidal river and its floodplain, as well as small Coastal Plain streams that flow directly to the tidal river; most of these streams are enclosed in storm sewer systems. The tidal reach of the Anacostia River is 8.4 miles (13.5 kilometers) in length from the confluence of the Northwest and Northeast branches downstream to the Potomac River. The river joins the Potomac approximately 108 miles (174 kilometers) upstream of the Chesapeake Bay. A total of 3,208 acres of wetlands remain in the Anacostia, comprising just under three percent of the total watershed area. A majority of this acreage is located in the Coastal Plain portion; that is the eastern two-thirds, of the watershed. Palustrine wetlands make up more than three-quarters of the total wetland acreage in the Anacostia watershed, with the remainder as riverine (20%) and lacustrine (4%). It is estimated that more than 4,000 acres of nontidal wetlands have been lost from the Anacostia watershed due to both the suburban sprawl of the last five decades and earlier urban development and agricultural activity; this represents greater than 60% of the historical nontidal wetland acreage. More than 90% of the nontidal wetland acreage loss has occurred from the Coastal Plain portion of the watershed and has been concentrated in the lower reaches of the Northwest Branch, the Northeast Branch and Lower Beaverdam Creek subwatersheds. The loss of tidal wetlands in the watershed has been even more extensive than that observed for nontidal wetlands. The Army Corps of Engineers estimates that approximately 2,500 acres of tidal emergent wetlands have been destroyed in the Anacostia between Bladensburg and the confluence with the Potomac River. Even with the restoration of Kenilworth Marsh (representing approximately 32 acres), less than 100 acres of tidal emergent wetlands currently exist. Moreover, the total area of remaining tidal wetlands is approximately 180 acres (non-open water), constituting an overall loss of more than 90% of the originally-occurring tidal wetlands from the watershed.
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