It refers to space during dam crest level; it is above maximum deposited beach face, storage bottom and normal water level as well as under maximum flood level.

某坝顶标高时，最高沉积滩面、库底、正常水位三者以上，最高洪水位以下的空间。

youdao

And just as each wave has a crest, it also has a trough. Sometimes your level of motivation will be like a rushing tsunami.

就像每个波浪有波峰，也有低谷，我们的干劲也是如此，会时高时低。

youdao

Revetments protect the space from dam crest to the line a certain distance, normally 2.5m, under the minimum water level of the dam upstream.

护坡覆盖的范围，上游由坝顶护至水库最低水位以下一定距离，一般在最低水位以下2.5米。

youdao

Obama had said his stimulus package would keep unemployment rate beneath that level, only to see it crest at 10% in October 2009.

FORBES: Move up http://i.forbesimg.com t Move down