What Are the Best Practices for Silt Curtain Installation?

Published on 30 Sep ‘24

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 the best practices for silt curtain installation to ensure a successful setup and prevent failures.

OPTIMAL SILT CURTAIN INSTALLATION

Silt curtain position

To ensure proper performance, the silt curtain should be positioned at least 50 meters away from any discharge or reclamation site. This distance helps prevent the curtain from becoming submerged due to rising seabed levels. Additionally, placing the curtain further away helps reduce the forces exerted on it in case of strong discharges. It also allows for a larger settlement area and increases the volume of water contained within the curtain.

This setup helps slow the water flow underneath the curtain, reducing the risk of sediment escaping. However, note that water should always be allowed to flow underneath the curtain. A minimum gap of 0.5 meter should exist between the weighted, lower end of the skirt and the bottom at Lowest Astronomical Tide (LAT). This prevents the skirt from being covered by silts, which may cause submersion of the flotation as the tide rises. It also prevents re-suspension of particles on the other side of the curtain that might be caused by the weighted lower end of the skirt hitting the seabed in waves.

Silt curtain depth

In tidal or windy conditions, it is rarely practical to extend a silt curtain deeper than 3-4 meters, even in deep water. Silt curtains are less effective in exposed areas because water stays turbid longer, delaying settlement. In these cases, focus on the wave and tidal forces on the curtain, rather than the depth of the seabed.

Installing silt curtains too deep can place heavy loads on the curtain and mooring system, leading to failure or dragging. This can cause bigger environmental problems or project delays, increasing costs.

Silt curtain length

When determining the length of a silt curtain, add at least 10% to straight line measurements from the site or drawings. It is nearly impossible to install a marine barrier in a straight line due to waves and tides, which naturally cause slight curves.

These curves can increase the required length by 10-20%. Adding extra length makes installation easier, ensures accurate coverage and reduces strain on the curtain, helping to prevent failure.

Anchoring section

Anchoring is a very important consideration. If done incorrectly, it can reduce effectiveness of the entire structure. A typical anchor setup contains either Danforth or concrete anchors.

Anchor selection depends on the type of curtain, wave and tidal conditions, water depth and project duration. Danforth anchors are best for calm, soft seabeds, while heavy gravity anchors are ideal offshore. Anchor spacing should be advised by the manufacturer or engineer based on the site conditions.

It is always better to over-anchor a silt curtain than under-anchor. Incorrect anchoring causes over half of all silt curtain failures we see and can result in unrepairable damage to the silt curtain. A small additional cost for extra anchoring at the start can make a significant difference in the lifespan of the silt curtain. This can dramatically reduce potential downtime and future costs.

Key components include:

Crown buoy & pickup line: Used to locate and release the anchor. For Danforth anchors, a rope is used to free it from the seabed. For concrete anchors, a sling rated for the anchor’s weight is used for retrieval. The slings should always be checked prior to lifting an anchor that has been installed in the water, to ensure there is no damage or degradation.

Mooring chain and rope: A 2-3 meter mooring chain is placed after the anchor to protect the rope and provide slack for wave movement. The rope should be 2-3 times the water depth at high tide (HAT) for proper angle and pull. In rough conditions, we recommend using a chain instead of rope.

Anchor buoy: Acts as a shock absorber for waves and currents, ensuring a horizontal pull on the curtain to reduce stress on the anchor line.

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.

Design and layout of anchoring systems is one of the most critical (and often overlooked) components that influence marine barriers performance. Ecocoast uses proprietary software Marineforce to design and customize each anchoring system for the project environmental conditions and barrier type.

We can carry out the complete installation, repositioning, relocation, removal or provide supervision for marine barriers. Get in touch to know more!

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