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Hydraulic dredging: Maintaining waterway health

Supplier: KSB Australia
26 May, 2011

KSB / GIW slurry pumps are renowned for their high efficiency, favorable suction characteristics that remain consistent with use, robust construction, superior materials and reliability.

These qualities have helped KSB / GIW acquire loyal customers from all over the world, and their slurry pumps are used by dredging operations in various locations around the globe.

KSB / GIW is currently building pumps for a new trailing suction hopper dredge being built to operate in the Atlantic Ocean near the mouth of the Loire estuary in France. KSB / GIW was awarded the contract thanks to its ability to supply pump sets capable of handling slurries with a sand concentration of 40 percent while achieving an efficiency of 80 percent.

What is hydraulic dredging?
Hydraulic dredging is the process of using a pump — submersible or inboard — to remove material from the sea floor or a riverbed, and then depositing that material in a different location. In some dredging operations, the material may be deposited on the riverbank or outside the shipping channel. In other cases, the material is stored on the dredging ship, also known as a Trailing Suction Hopper Dredge (TSHD), and transported to another location to be deposited.

The dredging process can be used to reclaim land, add land to shorelines, nourish beaches and build islands. In Dubai and Singapore, this technique has been used to create entirely new land masses. The dredged material can also be repurposed for construction applications, such as aggregate.

A TSHD generally suspends its submersible pump on a ladder or drag arm that holds the pump in the water during dredging. Material on the bed of the sea, river or lake is agitated by either jetted water or a cutter, and then the submersible pump brings the material into the hopper.

When the hopper is full, the drag arm is hoisted onto the deck and the dredge sails to the point of discharge. Jet water pumps turn the material in the hopper into slurry, and then the main inboard pumps discharge the slurry, either through a nozzle using a technique called "rainbowing" or through a floating pipeline. 

Dredges operating in shallow waters (30 to 35 meters or 100 feet) dredge directly with inboard pumps without using submersible pumps.

Dredging and waterway health
Rivers that discharge into the ocean tend to build up silt at the river delta. This buildup can block shipping channels, reduce water flow in the river and even cause flooding upstream. Dredging is especially important in Europe, where river transport is a critical factor in commerce. Many industries rely on river transport to move their materials and products. If waterways become impassable, then products and services are affected.

For European waterways that exit into the Atlantic Ocean, dredging presents some unique problems that are not present in other locations. This portion of the Atlantic is very cold, and rough seas are common. It can be difficult to guide a large dredging ship along a specific path when the seas are over 5 meters.

GIW pumps to be used in the Loire River Delta
KSB / GIW has been tasked with developing pumps to be installed in a trailing suction hopper dredge that will operate in the Atlantic Ocean near the mouth of the Loire River. The ship is designed to operate in Atlantic Ocean waves that could be up to seven meters high. The capacity of the hoppers is around 2,000 cubic meters of sand and gravel. An articulated suction pipe helps the dredge pump to pick up slurry from a depth of up to 45 meters. The main dredge pumps will be powered by a 6000-horsepower motor located in the hull of the dredge.

How GIW equipment improves dredging operations:
KSB / GIW pumps are constructed of materials that are specially designed to withstand abrasion from the sand, silt and rocks that they pump at high volumes and densities. KSB / GIW's proprietary material, WD29G, is acknowledged in the dredging world as the best material for withstanding impact loads from occasional rocks that may pass through the pump. It can also effectively withstand the constant abrasion from coarse slurry. KSB / GIW materials provide far superior wear life for liners, casings and impellers than competitors' materials.

This long wear life is crucial for dredging operators, who are generally paid based on the volume of material that they remove or transport. The less downtime that is required, the faster the company completes its contract — and the higher its profit. If a pump breaks down, it can take several days to identify the problem, get parts, fix the pump and get it back into service.

Jonathan Samuel, KSB / GIW’s regional manager for Global Dredge, notes that the performance of KSB / GIW pumps can also benefit a company’s bottom line. "If your pumps are more efficient, less energy is required to run them, and therefore fuel costs are reduced. Since fuel costs are one of the largest expenses of dredging operations, the fuel savings that KSB / GIW’s high efficiency pumps can provide is extremely significant."

For further information on KSB/GIW Slurry pumps, please contact KSB Australia Pty Ltd.