Winches Help Water District Position Floating Dredges

After using three generations of remote controlled, underwater dredges, the Orange County Water District (OCWD) was in need of a new dredge and positioning system that was both cost effective and efficient at removing the hardened crust layer (HCL) that forms in its water recharge basins and prevents water from percolating into Southern California’s major source of well-pumped water.

OCWD engineer Max Rasouli had the idea to use more off-the-shelf technology and get sensitive components out of the water. The district turned to Liquid Waste Technology, designer of the Pit Hog™ line of lagoon dredges, for a new floating dredge system that can be moved using winches.

The company custom built four remote-control dredges based on its Pit Hog Dredge Model BCV-4. They are designed to have a working depth of 20 ft. and weigh somewhere in the ballpark of 36,450 lbs.

“The new system is much easier to operate and maintain,” said Max Rasouli, Principal Engineer for OCWD. “Components for the new system aren’t as complicated as the underwater design so we don’t need the specialized technicians to be available all the time.”

The new shallow-water basin cleaning vehicle uses an OCWD patented roto-tiller type cutter head to break up the hard lakebed crust and captures the silt-sand slurry inside a chamber (hood) where the silt is hydraulically separated from the sand. The sand drops back to the lakebed, while the silt slurry is pumped to shore for dewatering.

To move the dredges around the basin, the system uses heavy-duty Thern Inc. power winches. The winch system took the place of the expensive rail system for the underwater basin cleaning vehicles and offered more flexibility for dredging.

The Thern Series 4HS Helical/Spur Gear Power Winches feature TEFC severe duty brake motors for precise control, enclosed gearing for added protection and flange style roller bearings for a longer life. They were also fitted with a custom clutch for added control during horizontal pulling.

Four to five winches are used by OCWD and positioned around the recharge basins. The winches position the dredge to any location in the basin (this can include irregular shaped basins). The dredge moves around the recharge basins via steel cables that are connected to winches. Movement for each winch is automatic and preprogrammed.

“We chose the Thern winches for this project because they gave us the option of using an advanced automation system in odd shaped ponds,” said DuWayne Richert of Liquid Waste Technology.

System Benefits

“The biggest benefit we got from the new system was its cost effectiveness. The capital cost of installing a rail system for an underwater basin cleaning vehicle just didn’t make sense from a budget standpoint,” Rasouli said. “We also don’t have to hire specialty O&M technicians with exclusive underwater equipment training to maintain the dredge and winch equipment.”

The new dredge system is used five days a week, full time. It is controlled by computers and software that automatically cleans the basins. According to Rasouli, maintenance is very minimal and easy to perform.