Abstract: A suction dredge for mining solids from a water bottom, includes a floating barge, an elongated tubular suction line extending between the barge and the water bottom, a boom for raising and lowering the elongated tubular suction line, a valve in the elongated tubular suction line for allowing water to enter the elongated tubular suction line, a dredge pump for causing solids to be drawn upward from the water bottom, through the elongated tubular suction line, to the floating barge, the dredge pump having a cavitation level at which the vacuum level is so high that the dredge pump ceases to pump, and an automatic control device for controlling the degree of opening of the valve, the automatic control device allowing just enough water to mix with the solids such that the dredge pump is maintained substantially at but below the cavitation level, the automatic control device including a measuring device for measuring the vacuum level of the dredge pump, and causes the valve to open more as the vacuum level rises