| Abstract from DBPedia | A point bar is a depositional feature made of alluvium that accumulates on the inside bend of streams and rivers below the slip-off slope. Point bars are found in abundance in mature or meandering streams. They are crescent-shaped and located on the inside of a stream bend, being very similar to, though often smaller than, towheads, or river islands. Point bars are composed of sediment that is well sorted and typically reflects the overall capacity of the stream. They also have a very gentle slope and an elevation very close to water level. Since they are low-lying, they are often overtaken by floods and can accumulate driftwood and other debris during times of high water levels. Due to their near flat topography and the fact that the water speed is slow in the shallows of the point bar they are popular rest stops for boaters and rafters. However, camping on a point bar can be dangerous as a flash flood that raises the stream level by as little as a few inches (centimetres) can overwhelm a campsite in moments. A point bar is an area of deposition whereas a cut bank is an area of erosion. Point bars are formed as the secondary flow of the stream sweeps and rolls sand, gravel and small stones laterally across the floor of the stream and up the shallow sloping floor of the point bar.ポイントバー（英語: point bar）もしくは突州（とっす）、寄州、蛇行州（だこうす）は、蛇行する河川において屈曲部の内側に形成されるの端に形成される砂州のことである。 曲流において、河床に沿った境界層におけるが岸と平行ではなく、流れの内側に向かって流れる。この流れにより、砕屑物が曲流の内側に導かれる。攻撃斜面で侵食された物質が滑走斜面に運搬・堆積することで、ポイントバーが形成される。 (Source: http://dbpedia.org/resource/Point_bar) |
