Je was op zoek naar: riverbed (Engels - Japans)

this is a riverbed.
ここは坑道排水の貯水池だ

to the bottom of a muddy riverbed
川の底面に潜り

this restaurant is located on the riverbed.
このレストランは川床にあります。

drifting in on the currents, settling on the riverbeds, and kicked up by the wild thrashing of the crocodiles.
流れを漂い川底に沈み... ワニがかき回します