Would A Single Filter Fabric (Turbidity Curtain) Be Able To Handle Dredging Turbidity?

by Granite Environmental Tech Team
(Florida, USA)

A customer was looking for a silt barrier design for dredging work. His concern was if a single filter fabric would be able to handle the dredging turbidity. The customer also ask for more information about the microns they were looking at and EPA & the Department of Health requirements. Who would design the levee anchoring system was another question.

The project goal was to set up a floating silt or turbidity curtain across a concrete lined drainage channel so that the shoal materials upstream could be dredged out.

The project area was located in an intermittent stream that discharges into slack water and then into a large pond. The pond meanders into a small boat harbor and then discharged into a bay.

It was planned to set up the silt barrier in the slack water channel area that experienced some tidal action.

The work was planned during non-flow conditions but current could be a problem if the turbidity curtain would be left in when the stream flew. In case the weather caused the stream to flow the turbidity barrier would have to be temporarily removed through the contractor.

Our Granite Environmental Tech Team informed the customer that the turbidity curtains come complete and ready to work.

Normally contractors use either a ground anchor (auger type) or fence post set in concrete or reedbar, depending on the soil condition and loading. The type 2 turbidity screen has a 5/16 inch galvanized cable for load.

Our tech team suggested to install the barrier in a C- or U-shape by creating a scallop. Available standard silt barrier sections are 100 feet and 50 feet. In this project case 100 feet would be best suited and also reduces load due to greater surface area. The use of a filter fabric isn't recommended for this project. A filter fabric as any filter works as long as it isn't blocked. If it is blocked the permeable fabric will perform like a solid PVC skirt. 95 % of the supplied barriers are impermeable.