Salt wedge

Japanese: 塩水くさび - えんすいくさび（英語表記）salt wedge

Seawater infiltrates the estuaries of rivers where the riverbed is lower than sea level. The saltwater has a wedge-like shape that becomes thinner the further upstream it is, and this wedge-shaped saltwater is called a saltwater wedge. Typical saltwater wedges are found in rivers on the Sea of Japan side, where the tides are small. River water flowing over the saltwater wedge tries to push out the seawater due to friction, so the shallower the saltwater wedge is and the greater the river flow, the shorter it becomes. There is an upstream flow in the bottom layer, and bottom sediments tend to be carried and accumulated at the tip of the saltwater wedge.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

川底の高さが海水面より低い河川の河口部では，海水が浸入する。塩水の形状は上流ほど薄いくさび型をしており，このくさび型をした塩水を塩水くさびと呼ぶ。典型的な塩水くさびは，潮汐の小さな日本海側の河川に見られる。塩水くさびの上を流れる河川水は摩擦力により海水を押し出そうとするので，塩水くさびは浅くて河川流量が多いほど短くなる。底層には上流に向かう流れがあり，底質は塩水くさびの先端部に運ばれ，集積される傾向がある。

出典　株式会社平凡社世界大百科事典第２版について　情報

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