In workings on a larger scale, where the supply of water is abundant, as in California, sluices were generally employed.
In larger plant the upper ends of the sluices are often cut in rock or lined with stone blocks, the grating stopping the larger stones being known as a " grizzly."
Sluices are often made double, and they are usually cleaned up - that is, the deposit rich in gold is removed from them - once a week.
The stream, laden with stones and gravel, passes into the sluices, where the gold is recovered in the manner already described.
Now, the dykes were cut and the sluices opened, and Amsterdam was covered by a wide inundation, against which the invader was powerless.