Preventing shoaling in ship berths

Many deep draft ship berths experience shoaling, gradually filling in with fine silt and clay sediments. Traditionally, the response has been to periodically dredge, an expensive and environmentally impacting process. SedCon Technologies, Inc. has developed the SedCon® Turbo System that prevents shoaling in a berth and eliminates the need for maintenance dredging.

Benefits include substantial savings in maintenance costs and increased revenues for the facility. After a system is installed, the berth will have full water depth at all times, increasing its availability for ship traffic and total cargo throughput.

Problems with dredging

Estuarine waters have a natural depth of five or six metres. At that depth, passing water currents are moving fast enough to prevent shoaling. When a berth is dredged, the increased water depth causes currents to slow down allowing sediment to fall out of suspension and accumulate.

Periodic maintenance dredging is a costly and inefficient way to deal with shoaling problems in berths. First, as shoaling proceeds, water depth decreases, eventually limiting the draft of visiting ships. Second, dredged material disposal areas are filling up and new ones are no longer being created. When a disposal area becomes
unavailable, dredging costs can rise, sometimes dramatically.

Third, permits for dredging are becoming difficult to obtain due to stricter environmental regulations. This consumes staff time and drives up costs. Finally,  maintenance dredging can significantly impact water quality, benthic and wetland habitats, degrading the environment.

System description

The SedCon® Turbo System consists of a series of submerged water pumps, called Turbo Units that are installed along the face of a ship berth. The Turbo Units are connected to a hydraulic power source via a system of header pipes, riser hoses and control valves. A computer controller, inline heater and heat exchanger complete the system.

The SedCon® Turbo System operates by boosting the speed of passing water currents just enough to prevent shoaling. The Turbo Units operate in sequence during ebb and flood tidal flows, beginning with the furthest-most up-current unit. During operation, an impeller draws water downward into the intake of the Turbo Unit and discharges it horizontally across the bottom of the berth as a powerful jet.

At the same time, the direction of discharge is slowly rotated through a 90-degree angle. Turbo Unit operation begins with the discharge pointed perpendicular to the face of the berth and ends with it pointed down-current. The jet discharge is designed to be strong enough to prevent sedimentation but not to cause erosion of the consolidated mud bottom. For this reason, the berth must be fully-dredged prior to system installation.

Russell Arnold, Vice President, SedCon Technologies, Inc., Carpinteria, CA, USA
Edition: Edition 37

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