If it were possible to develop a turbine that did not need such a water-head to operate, and that could sit in the riverbed, then a dam would be unnecessary.

如果有可能制造出一种涡轮无需水的落差来运转，并且可以放置在河床上，那么就不再需要大坝了。

youdao

The water closed over his head.

水没过他的头顶。

《牛津词典》

I bashed him on the head and dumped him in the water.

我猛揍他的头，然后把他扔到了水里。

《柯林斯英汉双解大词典》

Indeed, a calculation Dr Ip performed, based on the volume and composition of the urine he collected in the plastic buckets, and of the head-dunking water at the end of each day, suggested that only 6% of the urea excreted by the turtles was leaving them in the traditional manner, via urine.

ECONOMIST: Softshell turtles urinate through their mouths

But a low-head dam that delivered irrigation water also blocked fish movement.

CNN: Migrating fish get help in uphill battle

Justin Ferrari, a software engineer and water-polo coach, was shot in the head on May 24th while driving with his two children and his parents.

ECONOMIST: A startling rampage among the coffee shops