The Experts’ Views of Horizontal Hydraulic Auger Dredging
Four Major Benefits of Horizontal Hydraulic Auger Dredges
By Jordan Webb, Design Engineer, SRS Crisafulli, Inc.
I attended the 42nd Texas A & M University dredging short course in January 2013. Despite the mountain of excellent information I gleaned from the course, I was disappointed that my dredging field wasn’t featured. Horizontal hydraulic auger dredging has been around for nearly 50 years, but remains the unknown stepchild of the dredging world. That may be changing as environmental dredging becomes more prominent. Horizontal hydraulic auger dredges are ideal for environmental projects for several reasons.
First, horizontal hydraulic auger dredges are small. I know everybody wants bigger, but small has advantages. One advantage is cost. Small horizontal hydraulic auger dredges are priced for as little as $200,000 for a new unit. Even the largest horizontal hydraulic auger dredges don’t break the $1,000,000 mark. Another advantage is transportability. Most horizontal hydraulic auger dredges can be carried on standard step-deck trailers. These units come fully assembled and are ready to begin dredging as soon as you put them in the water. A final advantage of small size is dredge productivity. Current dewatering and decontamination methods handle about 1000 gallons per minute with larger units handling about 2500 gallons per minute, numbers that match closely the productivity of horizontal hydraulic auger dredge pumps.
A second benefit is ease of use. Alternative cutter-suction dredges are complicated. To use a cutter-suction dredge the operator must worry about step angle, advance, moving into the cut, cutting the bank, Net Positive Suction Head Required (NPSHR) and vacuum, winch placement, cut angle and a host of other problems. Horizontal hydraulic auger dredges move forward; that’s it. Just point the dredge where you want to cut, lower the cutterhead, and move forward. This simple system can be taught to any employee/operator in less than half a day. The pump is mounted on a “ladder” eliminating worry about NPSHR. Dredge cuts are in broad lanes, which are easy to track even without a complicated sonar assembly.
A third benefit, and perhaps the most important, is turbidity. Cutter-suction dredges kick a cloud of dredged material into the water and then the operator hopes he can suck all that undesirable material into the mouth of the dredge pump. Unfortunately, cutter-suction dredges are never able to suck all that material up, and leave as much as much as 20% of all disturbed solids. In environmental cleanup projects that’s 20% of polluted material left in suspension, enough to get most job sites shut down. By contrast, horizontal hydraulic auger dredges push the dredged material into a shroud that directs the material into the pump’s suction mouth. The shrouding of material enables horizontal hydraulic auger dredges to suck up as much as 99% of dredged material, a highly desirable result.
The final reason to consider a horizontal hydraulic auger dredge for your project is closely related to the second reason. The cable traverse system of horizontal hydraulic auger dredges makes them easy to control remotely. Unmanned horizontal hydraulic auger dredges provide safety in jobs where you don’t want your people in the water. If the material is bad enough that it requires an environmental cleanup, you probably don’t want your people in the water. I know that when I’m operating a dredge I prefer to be sitting in a lawn chair sipping a cool drink, rather than on a dredge surrounded by 5 million gallons of toxic material.
This isn’t a comprehensive list of the reasons you might use a horizontal hydraulic auger dredge for environmental cleanup, but it covers many of the high points. No dredge is perfect. There are benefits and uses for every dredge type, but horizontal hydraulic auger dredges are ideally designed to handle most environmental dredging projects.