Transport action - Unpansayo

The act of transporting materials by the force of flowing water, wind, glaciers, waves, etc. Wind transports materials against gravity, while flowing water transports materials according to gravity. Materials on steep slopes will be carried downhill in the direction of gravity even without flowing water, creating landforms such as talus.

Flowing water in a river carries gravel, sand, mud, and chemical substances dissolved in the water, depending on factors such as the flow velocity and the slope of the riverbed. There are three types of transport: tractive, floating, and solution. Traactive is the form of transporting sand and gravel near the riverbed, and there are three types: sliding, rolling, and pulsating. When the flow velocity increases, such as during a flood, a large amount of tractive material is carried, and the amount is proportional to the sixth power of the flow velocity. Suspended is the state in which fine sand, silt, clay, etc. are suspended and carried, which is why river water becomes muddy during floods. Solution transports materials dissolved in river water, and the amounts of tractive and floating materials are high during floods, but usually there is a lot of dissolved material, and the amount of dissolved material is the highest throughout the year.

[Masami Ichikawa and Akihiro Murata]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

流水や風、氷河、波などの力によって物質を運搬する作用。風は重力に抗して物質を運搬するが、流水は重力に従って物質を運搬する。急斜面上の物質は、流水が生じなくとも、重力の方向に斜面下方に物質を運び、崖錐(がいすい)などの地形をつくる。

　河川の流水は、流速や河床の勾配(こうばい)などの要因によって、礫(れき)、砂、泥や流水中に溶解した化学物質を運ぶ。その運搬形式には掃流、浮流および溶流がある。掃流は、河床付近の砂礫を運搬する形式で、これには「滑動」「転動」「躍動」の三つの型がある。洪水時のように流速が増大すると大量の掃流物質を運び、その量は流速の6乗に比例する。浮流は、細砂やシルト、粘土などを浮遊させて運搬する状態をいい、洪水状態になると河水が濁るのはこのためである。溶流は、河川水中に溶解した物質を運搬するもので、出水時には掃流、浮流物質の量が多いが、通常は溶流物質が多く、年間を通じても溶流物質量がもっとも多い。

［市川正巳・村田明広］

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