Dredging & Sediment Control

Dredged spoil, channel sediment and lagoon or settlement-pond silt dewatered in filter bags: filled by pump or excavator, drained in batches on a prepared pad, and lifted out once drained.

Dredging contractors, canal, marina and harbour operators, treatment works with settlement ponds, and environmental remediation firms. The buyer is normally a site or project engineer who has a dredge volume, a solids figure and a limited area on the bank to lay bags out.

Get the water out of the sediment where it is dredged, so the spoil is dry enough to lift, haul and dispose of, and the water can be returned or discharged under the site's own permit.

Bags are laid out empty on a prepared pad, sometimes lined, and filled by pump from the dredge or by excavator from the bank. They drain on the pad for days or weeks, then are lifted out by plant and taken to a drying or disposal area. Bags are worked in batches: one group fills while another drains. Where the fill point has to be kept clear, bags can be filled in a frame and lifted out of it.

Dewatering performance controls the job, and it depends on sediment that varies along the dredge, so a fabric that suits one stretch may blind on the next. Grit and shell fragments abrade the fabric as they are pumped in and again when the drained bag is dragged. The water that leaves the bag is not clean water: anything dissolved in the sediment leaves with it, so on contaminated dredgings the water has to be handled as the site's permit and waste classification require. The fill weight is unknown until the bag is full of water, so the pad, the frame and the lifting plan have to assume a heavy, wet, variable load. Bags that stand outside for weeks to months need UV-stabilised fabric.

Start from the solids content and the particle size range, not from a bag size. Coarse sand and gravel drain quickly and suit a tighter fabric; silt and clay drain slowly and usually mean more bags at a smaller size, because the area available to drain on is the limiting factor and not the bag. Where the water returns to the channel or goes to treatment, agree the condition it has to meet before the bags are ordered, because that sets how fine the fabric can be. A trial bag filled with the actual dredgings is the normal way to confirm drainage and retention before an order.

This page covers filter and dewatering bags for dredged spoil and for channel, lagoon and settlement-pond sediment. It does not design the dredge, the drainage pad or the discharge route, does not set discharge or consent limits, and does not replace the site's own permit, waste classification and water-quality duties. Drainage, retention and drained weight are confirmed per project against the customer's own material.