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Boundary Channel is a channel off the Potomac River in Washington, D.C. The channel begins at the northwestern tip of Columbia Island extends southward between Columbia Island and the Virginia shoreline. It curves around the southern tip of Columbia Island before heading northeast to exit into the Potomac River. At the southwestern tip of Columbia Island, the Boundary Channel widens into the manmade Pentagon Lagoon. ==History of Boundary Channel== Columbia Island is in part natural, and in part man-made. About 1818, Analostan Island (now known as Theodore Roosevelt Island) was largely rock and quite close to the D.C. shoreline. Due to deforestation and increased agricultural use upstream, the river eroded much of the northern bank of the Potomac River and widened the gap between Analostan Island and the shore. Simultaneously, large deposits of silt built up around Analostan Island. By 1838, Analostan had almost doubled in length toward the south. By 1884, the new southern part of Analostan Island was defined and built up, and supported a well-established wetland. Gradually, however, the river eroded the center of Analostan Island, severing Columbia Island from its parent body.〔Office of Conservation, Interpretation, and Use, p. 48-49; Moore and Jackson, p. 91.〕 Between 1911 and 1922, the Potomac River was repeatedly dredged by the United States Army Corps of Engineers to deepen the channel and alleviate flooding. Dredging widened the distance between Analostan/Theodore Roosevelt Island and Columbia Island (so that the "Virginia Channel" west of Analostan/Roosevelt Island would not flood easily). Dredged material was piled high on Columbia Island, helping to build it higher, lengthen and broaden it, and give it its current shape.〔 The new island received its name about 1918 from an unnamed engineer working for the District of Columbia.〔Secrest, Meryle. "Park Named for Mrs. Johnson." ''Washington Post.'' November 13, 1968.〕 An anonymous Corps of Engineers officer named the waterway between Columbia Island and Virginia the "Boundary Channel".〔(Corps of Engineers, p. 533. ) Accessed 2013-05-07.〕 Boundary Channel was further defined in the late 1920s. In 1925, Congress authorized construction of the Arlington Memorial Bridge across the Potomac River. Preliminary designs for the bridge showed it terminating on Columbia Island,〔"Island to Be Remade in New Bridge Plans." ''Washington Post.'' April 15, 1925.〕 which necessitated additional expansion of the island. The Corps of Engineers had already planned to continue dredging the Potomac River and enlarge Columbia Island, so on April 1, 1925, Secretary of War John W. Weeks ordered the expenditure of $114,500 to dredge the river between the Highway Bridge and the Lincoln Memorial. The dredged material was dumped on Columbia Island.〔"Potomac Channel to Be Dredged for Flood Prevention." ''Washington Post.'' April 2, 1925.〕 By June 30, 1927, dredging of the Potomac River and the reshaping of Columbia Island was largely finished.〔Office of Public Buildings and Public Parks of the National Capital, 1927, p. 20.〕 Boundary Channel marks the original Virginia shoreline.〔Moore, p. 91.〕 It separates Columbia Island to the east from Virginia in the west and south, and is roughly a mile long. The channel is part of the Potomac River.〔"Oil Is Spilled Into Channel From Ft. Myer." ''Washington Post.'' June 14, 1977.〕 In 1936, Boundary Channel was in width and in depth.〔''Severin v. United States'', 86 Ct. Cl. 53, 56 (1937).〕 No lagoon existed at this time. Broundary Channel was changed again after ground was broken for The Pentagon on September 11, 1941. The Pentagon was being built on land just south of the Boundary Channel. But the ground to the northwest, north, northeast, and east of the building site was so low that, for a time, the Corps of Engineers considered building a levee to protect it from floods. But General Brehon B. Somervell, the Army officer in charge of the Pentagon's construction, decided instead to raise the ground by at least to or more above the average water level. Boundary Channel was dredged and slightly widened in order to help provide this fill material.〔Vogel, p. 133.〕 Due to silting and other issues, Boundary Channel is approximately wide as of 2013 (although the width varies). It is also quite shallow.〔(National Oceanic and Atmospheric Administration. ''United States Coast Pilot. Vol. 3: Atlantic Coast: Sandy Hook, NJ to Cape Henry, VA.'' 46th ed. Washington, D.C.: u.S. Government Printing Office, 2013, p. 291. ) Accessed 2013-05-07.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Boundary Channel」の詳細全文を読む スポンサード リンク
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