Tricks of the Trade — Mini-Dredge Clears Silt Quickly from Boat Channel

The Mud Cat, a two-man-operated mini-dredge recently removed accumulated silt from a lagoon channel at Ventura Keys, Calif. in a test demonstration. Powered by a 175-hp diesel, the dredge operates through an auger assembly at the end of a boom lowered from the bow of the dredge barge. It dredges to a 10 -1/2 foot depth below the water surface. From the stern an 8-inch discharge pipe extended 3,445 feet to a disposal area.

Of this length, 800 feet was a floating line supported by attached flotation tubes. Another 700 feet was threaded by scuba divers through a 66-inch storm sewer. Another section went under Highway 101 through a 36-inch culvert on the way to the discharge end. The dredge was secured by anchor cables placed 250 feet apart and fastened to pilings on one side of the 100-foot-wide channel, and to screw anchors set in the ground on the opposite side of the waterway. At high tide the water is 10-1/2 feet deep.

Demonstration Test
In this initial operation, in a 400-foot channel section where as much as 4 feet of silt had piled up, the Mud Cat had an average pumping rate of 1,300 gallons/minute, or 82 cubic yards of silt per hour. Solids averaged 20 percent by dry weight.

In 26 hours of pumping, city officials calculated the dredge had removed over 2,000 cubic yards of silt. To reach a more distant spoil area, the dredge used a booster pump which increased its production to 100 cubic yards per hour.

The dredge barge is 30 feet long, has an 8-foot beam, and weighs about 8 tons. It can operate in as shallow a depth as 27 inches. The unit is transported over the highways on its own flat-bed launching trailer.

Reprinted from Contractors and Engineers