The gain would be the addition to the kingdom of a new and fertile province of the area of North Brabant, a saving of expenses on dikes, diminution of inundations, improvement of communication between the south and the north of the kingdom, protection of isles of the sea, &c. The costs were calculated as follows: (I) enclosing dike, sluices, and regulation of Zwolsche Diep, £1,760,000; (2) reclamation of four polders, £5,200,000; (3) defensive works, £400,000; (4) indemnity to fishermen, £180,000; total, £7,540,000.
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.