How to install silt curtains?

Published on 07 Jun ‘17

How to install silt curtains?

Every silt curtain installation is unique. Therefore, the installation tips below are general recommendations only. Actual conditions might vary, depending on many factors. Each installation should be planned according to the site conditions and silt curtain model. Check out the tips below on how to install silt curtains.

Optimal Silt Curtain Installation

Silt curtains should be located parallel to the flow of moving water. They should not be placed across the main flow of a significant body of moving water.

When sizing the length of the floating curtain, allow an additional 10-20% variance in the straight-line measurements. This will allow for measuring errors, make installation easier, and reduce stress from potential wave action during high winds.

An attempt should be made to avoid an excessive number of joints in the curtain. A minimum continuous span of 15 meters between joints is a good ‘rule of thumb’. For stability, a maximum span of 30 meters between anchor or stake locations is also a good rule to follow.

Skirt and water flow

When you install silt curtains, ensure there is a minimum 0.5 meter gap between the weighted lower end of the skirt and the bottom at Low Altitude Tide (LAT). This gap allows water to flow under the curtain, which:

• Reduces forces on curtains and anchors.
• Lowers the risk of curtain failures.

In exposed waters with strong tides, the curtain depth should be much less than the water depth to minimize forces on the curtain. The water should flow under the curtain, as it will not flow through it.

Sedimentation

Silt curtains act as a containment barrier, allowing sedimentation inside the containment area. The settlement time varies in different conditions. In calm waters, silt settles in 24-48 hours. However, in rough waters, this time increases considerably.

In rough waters, the objective of the silt curtain is to reduce the spread area as full containment is not possible. The silts should settle from the upper 2-3 meters of the water column, drastically reducing the spread area.

Anchoring section

Anchoring is a very important consideration. If done incorrectly, it can reduce effectiveness of the entire structure. Silt curtains are typically attached to floats weighed down to the sea floor and anchored in place. Anchors use a painter-line system to ensure current or wave force on the anchoring is displaced by the tripping line, limiting the force on the curtain.

For installation, the anchors should be placed to form a right-angle triangle at High Altitude Tide (HAT). Therefore, take the water depth at HAT and the rope length at each location to determine the anchor placement distance from the silt curtain. Adjustments will need to be made on-site during the installation. It is also recommended to monitor the silt curtains and anchoring for 24 hours following installation to ensure adequate functioning.

Typical anchor setup:

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Influence of Tidal Flows

For every doubling of tidal flow, the force on the curtain is multiplied by a factor of 4. The difference between currents of 1 knot and 2 knots increases force by 4 times, significantly loading the curtain. Minimize this load where possible.

In offshore environments, wave forces running perpendicular to a curtain section add additional loading, equal to the tidal loading. Wave forces are very difficult to accurately predict. So, a conservative design calls for as short a curtain as practically possible.

Additional Installation Tips

• Install silt curtains at least 50 meters from the toe of any reclamation works to reduce risk of damage and allow adequate settlement.
• Keep the curtain’s skirt base clear of any rock breakwater and out of shallow water where significant breaking waves may be present.

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Ecocoast can carry out the complete installation or provide installation supervision if required. We can also provide you with silt curtain installation manuals for step-by-step instructions. Get in touch with us.

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