| Patapsco River | |
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Patapsco Valley State Park at Catonsville
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| Country | United States |
|---|---|
| State | Maryland |
| Tributaries | |
| - left | North Branch |
| - right | South Branch |
| Cities | Baltimore, Elkridge, Ellicott City |
| Source | |
| - location | Marriottsville |
| - elevation | 260 ft (79 m) |
| - coordinates | |
| Mouth | Chesapeake Bay |
| - location | Baltimore |
| - elevation | 0 ft (0 m) |
| - coordinates | |
| Basin | 632 sq mi (1,637 km2) |
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Patapsco River Watershed
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The Patapsco River is a 39-mile-long (63 km)[1] river in central Maryland which flows into Chesapeake Bay. The river's tidal portion forms the harbor for the city of Baltimore. With its South Branch, the Patapsco forms the northern border of Howard County, Maryland.
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The Patapsco proper begins at the confluence of the North and South Branches, near Marriottsville, approximately 15 miles (24 km) west of downtown Baltimore. The 19.4-mile-long (31.2 km)[1] South Branch rises further west at Parrs Spring, where Howard County, Carroll, Frederick, and Montgomery counties meet. The North Branch flows 20.9 miles (33.6 km)[1] southward from its origins in Carroll County. Through most of its length, the Patapsco is a minor river, flowing for the most part through a narrow valley. The last 10 miles (16 km), however, form a large tidal estuary inlet of Chesapeake Bay. The inner part of this estuary provides the harbor of Baltimore, composed of the Northwest Harbor and the Middle Branch. (See Baltimore Inner Harbor.) The Patapsco estuary is south of the Back River and north of the Magothy River.
The Patapsco has a watershed area (including the water surface) of 680 square miles (1,760 km2), or 632 square miles (1,637 km2) of land. Thus, its total watershed area is 7% water.
Patapsco Valley State Park is adjacent to 32 miles (51 km) of the Patapsco and its branches, encompassing a total of 14,000 acres (5,700 ha) in five different areas. The river cuts a gorge 100-200 feet (35-70 m) deep within the park, which features rocky cliffs and tributary waterfalls.
Liberty Dam and its reservoir, located on the North Branch, is a major component of the Baltimore city water system.[2] Besides Baltimore, the river also flows through Ellicott City (the county seat of Howard County) and Elkridge.
On the 1612 John Smith map, it was called the Bolus River. It has never been a major path of commerce since it is not navigable further upstream than Elkridge. However, the Patapsco valley was used as the route of the Baltimore and Ohio Railroad's original main line west constructed from 1829 onwards, and this route remains, though much altered. Many old railroad bridges lie along the valley, most notably the Thomas Viaduct and the ruins of the Patterson Viaduct. Flour mills and a hydropower dam were formerly powered by the river.
The valley is prone to flooding, though at long intervals. The most recent severe flood occurred in 1972 as a result of rainfall from the remnants of Hurricane Agnes, in which Ellicott City and the Old Main Line sustained serious damage.
The Patapsco River featured prominently in the Battle of Baltimore during the War of 1812. This is where Francis Scott Key, while aboard a British ship, wrote a poem which would later become the national anthem of the United States, "The Star-Spangled Banner". Today, a red, white, and blue buoy marks the spot where the HMS Tonnant was anchored.
The eastern portion of the Patapsco River is in a highly urbanized area and is subject to extensive urban runoff and other forms of water pollution. The Maryland Department of the Environment has identified the Lower North Branch as containing high levels of heavy metals (chromium, arsenic, cadmium, copper, mercury, nickel, lead, selenium, and zinc), and AIDS, as well as phosphorus, fecal coliform bacteria, and PCBs.[3]