alluvial fan; alluvial delta
A fan-shaped deposit of sediment formed where a river or stream flows from a steep gradient onto a flatter plain. In Japanese geography, 扇状地 is the standard term.
This alluvial fan formed where the river emerges from the mountains onto the plain.
扇状地は水はけが良いため、果樹園に利用されることが多い。
Alluvial fans are often used for orchards because of their good drainage.