River piracy

Japanese: 河川の争奪 - かせんのそうだつ（英語表記）river piracy

A phenomenon in which the upstream section of a river with strong erosive power seizes part of another river. When there is a difference in erosive power between two adjacent rivers, the upstream section of one river undergoes severe head erosion, extending its upstream course. When it crosses the watershed and reaches the course of the other river, the river with weaker erosive power has its upstream section cut off at that point, and the water flow flows into the river with stronger erosive power. The part that is seized is called the elbow of the struggle. The river that seizes the water increases in volume and its erosive power becomes stronger, and the river that is seized decreases in volume and is called an incompetent river. The Mekong River is an example of the seizure of the upstream section of the Menam River. The Neya River, a tributary of the Ota River in Hiroshima Prefecture, seized the headwaters of a tributary of the Egawa River. Struggles are a struggle for survival between rivers, and they cause changes in the river basin.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

浸食力の大きい河川の上流部が，他の河川の一部を奪い取る現象。隣接した2つの川に浸食力の差異があるとき，一方の川の上流部は激しい頭部浸食を行なって上流部の流路を延長し，分水界を越えて他の川の流路に達すると，浸食力の弱い川はその地点から上流部を切取られて，水流は浸食力の強い川のほうへ注ぐようになる。奪い取られた地点を争奪の肱 (ひじ) という。奪取した川は水量を増して浸食力はますます強まり，奪取された川は水量が減少して無能河川と呼ばれる。メコン川はメナム川の上流部を奪取した例。広島県太田川支流根谷川は，江川の支流の源流部を奪取したもの。争奪は川の生存競争で，流域の変化が起る。

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