sluice

Other heavy construction equipment including excavators and sluice and slurry pumps were brought in, as well as technical experts and "several hundred tons of gravel and earth", the US Army said.

Yet after back-to-back atmospheric rivers walloped California in less than a week, it wouldn’t take much for water, mud and boulders to sluice down fragile hillsides, experts warned.

Fish and Wildlife Service, which otherwise protects the birds — the Corps in 2015 unleashed a concerted kill program on the cormorants to control predation on baby salmon sluicing downriver to the sea.

Postgraduate researcher David Vandercruyssen said: "High tides can be limited to existing levels simply by closing sluices and turbines and existing low tide levels can be maintained by pumping."

As the tide ebbs the water is released through a sluice, which pushes a water wheel, which turns the grinding stones.