| Abstract from DBPedia | A meander is one of a series of regular sinuous curves in the channel of a river or other watercourse. It is produced as a watercourse erodes the sediments of an outer, concave bank (cut bank) and deposits sediments on an inner, convex bank which is typically a point bar. The result of this coupled erosion and sedimentation is the formation of a sinuous course as the channel migrates back and forth across the axis of a floodplain. The zone within which a meandering stream periodically shifts its channel is known as a meander belt. It typically ranges from 15 to 18 times the width of the channel. Over time, meanders migrate downstream, sometimes in such a short time as to create civil engineering challenges for local municipalities attempting to maintain stable roads and bridges. The degree of meandering of the channel of a river, stream, or other watercourse is measured by its sinuosity. The sinuosity of a watercourse is the ratio of the length of the channel to the straight line down-valley distance. Streams or rivers with a single channel and sinuosities of 1.5 or more are defined as meandering streams or rivers.蛇行（だこう、英: meandering）とは、蛇が這う姿のように曲がりくねって進むことを指す。また、川や気流が曲がりながら流れることを指す。 川の流れがカーブの内側となる場所は、流れが遅く、土砂が堆積されるが、外側となる場所では、流れが急で、水深も深い。 川は地形の低い場所に水を流すため、自然状態では通常蛇行する。なお、ドイツの流体力学者は「蛇行の原因は河川の断面方向にある二つの螺旋流である」と著書 "Das sensible Chaos. Strömendes Formenschaffen in Wasser und Luft "（原著1962年刊。日本語題：カオスの自然学）の中で述べている。また、蛇行は洪水の原因となるため、第二次世界大戦後の日本では河川改修が進んで直線化し、「元-川」「旧-川」といった場所に、蛇行を残すだけのことが多い。逆に自然を取り戻すために、一度直線化した河道をふたたび蛇行させる試みもある。 (Source: http://dbpedia.org/resource/Meander) |
