Inland waterways may provide problems. On canals and rivers, the transport distance between the dredging and disposal site may be long. On the right, a bucket dredger is shown removing alluvial silt, sand and gravel to restore depth on the Trent Navigation. Dredged material is transported by barge some 10km down river with a speed limit of 5knots. On all projects, the distance to the disposal site has a serious effect on production and hence cost. The Partnership studied the in-house operation and a range of alternatives, including contract dredging.

Cutter suction dredgers are often used in inland waterways. The dredger on the right is working to maintain the capacity of an irrigation canal on a Partnership project in Pakistan. Dredged material is pumped via a floating pipeline to land adjacent to the canal. Maintaining the carrying capacity of irrigation canals that are fed by rivers, with high sediment load, is an essential operation in arid countries.

Seen left is a deep suction dredger removing sediment from a hydroelectric dam reservoir high in the Ecuadorian Andes. Special dredging plant is used to remove sediments from water depths of up to 100m. Water jets around the suction intake fluidise bed materials. Dredged material is discharged downstream of the high dam by pumping it along a floating pipeline. The Partnership’s task was to assess the existing operation and propose methods of increasing the rate of production, either by modifying the existing dredger, or building new plant. Budget costs were also required.

The scene right may look like paddy fields in the Far East, but in fact shows settlement lagoons in the Norfolk Broads, UK. The Broads are extensively used for recreational activities. Under a dredging contract, arranged by the Partnership for the Broads Authority, water depth and quality was improved.
The dredged material was deposited in shallow lagoons, which were subsequently returned to high-grade agricultural land, following settlement and de-watering.