International Dredging Review

International Dredging Review

On April 27 Bob Phelps was waiting for rain to raise the water level in Lake Wildwood so he could start dredging. Phelps is general manager of the Lake Wildwood Association a lakeside community in Varna Illinois 30 miles northeast of Peoria. The area is entering its third year of drought.

|!|The lake is down to 30 inches below pool and the shallow area where we want to dredge is exposed|!| he said. The 218-acre lake drains 12 square miles of watershed mostly farmland requiring an average of 22000 cubic yards of maintenance dredging per year. The material collects in the upper end of the lake in a five- to six-foot layer.
Last year the association removed close to 30000 cubic yards of material in 825 hours of operation with a new eight-inch Moray swinging ladder dredge purchased from Dredging Supply Company. The dredge pumped a maximum distance of 2250 feet with a 30-foot elevation working 50 hours a week for 3 ½ months.

The Moray replaced a 1982 Mud Cat a 175 horsepower auger dredge that was not keeping up with the production needs on the lake. The association also wanted an alternative to the dredge’s traverse cable propulsion which interfered with boating and swimming on the lake.

The swinging ladder is a good alternative as it uses no cables. The dredge is stabilized by three spuds and the cutter is held into the material and through a 13- to 19-foot digging arc by powerful swinging and lifting cylinders. A 275 bhp Cat 3126B industrial diesel engine drives the eight-inch GIW ladder pump which can pass objects up to 3.5 inches in diameter.

The hydraulically-driven cutter is a 24-inch i.d. five-blade basket type with replaceable cast serrated edges. Cutter force is 2626 pounds with 20 horsepower nominal drive power.

|!|Rain will be a mixed blessing|!| said Phelps. It will raise the water level but will also bring in more sediment.

The Illinois agricultural industry sees an allowable tolerable loss of topsoil as .5 ton per acre which is 1/32 inch. The theory is that the soil mass grows by that much as a result of adding organic matter. However the sediment in Lake Wildwood is not topsoil.

|!|The sediment we’re fighting is not organic material|!| said Phelps. |!|It is material in the B and C horizons – sand gravel and clay — which has been cut from the sides of meandering drainage systems that feed into the lake. This tells us that the agricultural industry is doing a good job preventing erosion on productive land but not on the non-productive land which includes the drainage systems|!| he said.

The lake association has been pumping into a three-acre dewatering area divided into two cells then moving the dried material to other areas. Because of the increased productivity of the Moray dredge this area is no longer adequate and the association purchased another 55 acres for dewatering and storage of sediment which is expected to last another 10 years.

Dewatered material is hauled to permanent sites in common property areas of the development where it is placed in ravines and low-lying areas then shaped and graded into a usable configurations including adding tiles and other drainage structures. One such area was made into a storage area for boats and trailers and fees from this help offset the cost of development.

The Moray dredge is 42 feet 10 inches long with a transportation width of 12 feet and operating width – with hinged wing tanks extended – of 18 feet 6 inches. The mean operating draft is two feet nine inches; fuel capacity is 500 gallons and dry weight is approximately 35000 pounds.

The spuds are of eight-inch-diameter 24-foot-long tubular steel weighing approximately 800 pounds each. They are raised and lowered with a power up/power down system. The stern kicker spud can move the dredge forward from two to four feet.

Design improvements on this dredge are a larger lever room with ergonomic layout standard 18-inch manholes and hinged wing tanks.

“When running stability calculations on the dredge it performed best in all modes with the tanks out” said Robert Wetta CEO/Sales of Dredging Supply Company. “The reason the wing tanks swing in is to offer this dredge as a highly portable unit. When it arrives on site simply swing the tanks out launch and start dredging” he said.
The control system is a PLC capable of monitoring digital and analog inputs controlling digital and analog outputs performing automatic loop control displaying pertinent information and recording historical data.

The system protects against pump engagement and disengagement at high speed and locks out all hydraulic functions during startup and control activation. Alarms signal poor engine conditions and hydraulic and transmission problems. Alarmed conditions along with time and date are logged.

Electronic controls operate the prime mover throttle pump engagement and all hydraulic speeds and directions. Operating hours of all major dredge systems are recorded and displayed including engine dredge pump cutter swing winches spud winches and ladder winch.

The Lake Wildwood dredge has three operators: Chris Weide maintenance supervisor; Brad Jamour and Lee Spanbaurer.