The operations were usually terminated by the autumn floods. The river bed exposed by such methods was prospected and the pay-dirt when found taken out and washed, particular attention being paid to the surface of the bed-rock. Sometimes wing-dams were built out from the bank above and below the part of the river it was desired to work, and a third dam connecting their mid-stream ends was constructed parallel to the direction of the current. Sometimes, tunnels were made to drain permanently large reaches and deliver the water at a lower point.

This was usually done by building two dams from bank to bank, with their foundations on bedrock, the water being carried off in a wooden flume, starting above the head-dam and terminating below the foot-dam. In river mining, an entire river was frequently deflected from its course so as to lay bare a section of its bed. Gold dredging in now practised on the rivers of California, has is now superseded river mining.

To understand How Does a Gold Dredge Work, we may want to start by looking at California or Alaska.

Gold dredge parts diagram