Standard size mini-ex’s can reach from 12 to 20 feet along the ground. Bigger excavators can reach from 20 to 30 feet along the ground with 25 feet being the average distance. Long reach excavators usually reach from 30 to 60 feet out. The 60 feet reach is the standard size long reach excavator. Specialized long reach excavators (not typically available) can reach 70 to over 100 feet.
Long-reach excavators are primary used in dredging applications and cleaning out detention ponds. Long reaches have the same cab and tracks as a standard excavator but are fitted with an extra long boom or arm. The bucket size is smaller to off-set the weight of the material further from the machine. Long reach excavators are efficient and precise at removing material both above and under water. They can work from the shoreline or mounted on a barge.
Mechanical and hydraulic dredging are the two main types of dredging methods. Mechanical dredging is the removal of sediment with the use of a bucket, usually with an excavator. Draglines and clamshells are the other types of mechanical dredging methods. Hydraulic dredging involves a barge with a pump that vacuums sediment from beneath the water’s surface and pumps it through a pipeline to a different location. Both are effective in certain applications.
A dredge alone usually is limited to about 2000 feet of pumping distance. However, there are many factors that can limit or increase this distance. Dredges along with booster pumps can essentially pump an indefinite distance but in most cases it becomes unfeasible economically.
A marsh buggy or amphibious excavator is an excavator mounted on a set of specialized tracks designed to allow it to travel over land, mud, swamps, and even open water. River Sand has customized multiple sized amphibious excavators to dredge within lakes, ponds, and rivers.
All dredges are not made the same. Gold dredges have a very specific purpose and do not pump sediment past the surface of the water. Small 4” and 6” dredges may be suitable for sludge but not for silt within a pond or lake. Small dredges cannot pass debris through the pump easily and don’t have enough horsepower to pump sand long distances. Larger 8”, 10”, 12”, and 14” dredge pumps may be too large for small ponds or lakes but suitable for reservoirs. Large dredges can be difficult to mobilize and may pump too much water. Dredges for sand are designed with pumps for highly abrasive materials. Auger dredges work best in fine silt and sludge. Walking dredges are best when cables cannot be anchored nearby. Before you purchase or rent a dredge be sure to select the dredge designed for your application. Before you select a contractor, be sure they know what type of dredge is suitable and not just the only one they have or can afford. You may end up with a project that is not completed properly.
Determine the characteristics of the sediment that you need to pump including the distance and vertical head. Select a pump based on its pump curve that can perform sufficiently for the project. Select an engine that has the power requirements for the pump. Determine the weight required for the pump and engine. Build the barge capable to float and balance the weight of the engine and pump. Most portable barge sections are built in 4’, 6’, 8’, 10’, or 12’ widths for transport. Attach a ladder and cutterhead capable of desired dredging depths and pump capability.
A small dredge starts about $125,000. A typical dredge cost between $500,000 and $1,000,000. Larger portable dredges cost $1,000,000 to $10,000,000.
Ellicot and Liquid Waste Technologies (LWT), DSC, Geoform International are some of the US portable dredge manufacturers. River Sand, Inc. has dredges made by these companies and manufactures custom dredges as well.
Dredging is highly variable in cost. Cost involved for dredging projects are typically as follows:
Costs to operate the dredge include wear parts, labor, fuel, and maintenance. Dredges are unique in that break-downs and maintenance usually have to occur on the water so adequate support personnel and equipment must be available. All of these factors is why dredging cost range from a $3 to $300 per cubic yard. Dredging is often limited by other factors such as dewatering or disposal, so costs can be affected by the entire process as well.
