gravel beds

Where 50-kilogram king salmon once fought their way up waterfalls to lay their eggs in gravel beds, there now are only concrete walls holding back still water and deep beds of muddy deposits.

50公斤重的大马哈鱼王曾经奋力爬上瀑布，把卵产在砾石床上，现在只有混凝土墙挡住静止的水和深深的泥床。

Removing the mud, uncovering gravel beds where fish spawn, and finding suitable salmon types to rebuild the population is a daunting task.

清除淤泥，发现鱼类产卵的砾石层，找到合适的鲑鱼种类来重建种群是一项艰巨的任务。

The ancient gravel beds in the suburbs of Nanjng is one of the important types of rock of the Cenozoic era.

南京附近的古砾石层是组成该区新生代地层重要岩石类型之一。