riverbed

英文解釋：

名詞 riverbed:

1. a channel occupied (or formerly occupied) by a river
   同義詞：river bottom

例句：

1. Sediment deposited by flowing water, as in a riverbed, flood plain, or delta.
   沖積層河床、洪水淹沒的平原或三角洲中的流水淤積所產生的沉積層
2. There are many pebbles on the riverbed.
   河床上有很多卵石。