fluvial sand

例句：

1. 1. The riverbed is covered in fluvial sand, making it difficult to walk on.
   河床上覆盖着河流沙，使得行走变得困难。
2. 2.The construction crew used fluvial sand to build the foundation of the new bridge.
   施工队使用河流沙来建造新桥的基础。
3. 3.The floodwater carried away a large amount of fluvial sand, leaving behind only the hardiest plants.
   洪水带走了大量河流沙，只留下了最坚韧的植物。