Turbidity Barriers 101 – Understanding The Basics

 In Turbidity Barriers

Turbidity barriers, commonly referred to as turbidity or silt curtains, are used to contain the excess suspended sediment created by construction in or around a body of water. Barriers are typically deployed to protect ecologically sensitive habitats as well as seagrass meadows, corals, mangrove forests and shellfish beds. Environmental regulations at the state or national level can also dictate the use of turbidity barriers.

When it comes to manmade turbidity, one of the biggest culprits is dredging. The amount of solid sediment stirred up during this type of construction can have a significant negative impact on water quality and aquatic life. The resulting turbidity can block light to aquatic plants and smother aquatic organisms as well as carry contaminants and pathogens. If not contained, the sediment can spread to other areas, causing further contamination and disrupting the aquatic ecosystem.

The Purpose of Turbidity Barriers

Turbidity barriers are often used during dredging as well as pile driving, remediation, and shoreline restoration. These barriers are basically floating curtains that are set up in strategic positions around the area which is being dredged to effectively contain the suspended sediment. The top of the barrier is a float that sits on the surface of the water. Attached to the float is a skirt material that hangs down into the water. The length of the skirt will vary depending on the water’s depth. The barrier is secured by anchoring it to the bottom or attaching it to an existing structure.  

The Clean Water Act and the NPDES (National Pollution Discharge Elimination System) require that federal and state agencies enforce laws to regulate point of source pollution. Turbidity barriers are a cost-effective solution to protecting the environment and remaining compliant throughout your project.

Types of Turbidity Barriers

Type 1 Floating Turbidity Barrier

This type of barrier is considered light-duty and is appropriate for use in calm waters with no waves or tides and little or no flow. Small ponds, lakes, canals, and waterways with light wind or current are typically where the Type 1 barrier would be used.

Type 2 Floating Turbidity Barrier

This type of barrier is considered medium-duty and is appropriate for moving water applications such as rivers, harbors, protected ports with some wind or current. The Type 2 barrier is an effective solution for most applications regulated by Clean Water Act, NPDES and any state (DOT) and local regulations.

Type 3 Floating Turbidity Barrier

This type of barrier is considered heavy-duty and is appropriate for tidal water applications. It is constructed to withstand substantial wind, current, and tidal forces in some ports applications, shoreline and offshore. Type 3 barriers are usually customized to the specific conditions of the project.

DOT Floating Turbidity Barrier

All three types of turbidity barriers can be built to meet or exceed most state DOT requirements and regulations.

Economy Floating Turbidity Barrier

Economy turbidity barriers are manufactured from a lesser quality fabric and hardware and in most cases will not be as effective or retain its integrity for the duration of the project.

Custom Turbidity Barriers

Each marine construction project is unique. In addition to type 1,2 & 3 barriers, there are a variety of custom and specialty barriers that effectively contain suspended sediment, protect the aquatic ecosystem and keep your project in compliance.

Floating Baffle/Bedload Baffle System

Baffle systems are flow control devices used to prevent the migration of silt and turbidity from predefined structures. By increasing retention time and decreasing the amount of TSS (Total Suspended Solids), These systems increase water quality, keeping the project in compliance with regulations.

Deep Water Turbidity Curtains

Many standard turbidity barriers are designed for depths of ten meters or less. Deep water curtains are custom designed to effectively withstand the conditions of depths beyond ten meters.

Moon Pool Curtains

A moon pool, sometimes referred to as a wet dock, is an underwater opening in a marine platform or drilling vessel. The custom barriers used for moon pools are often designed in collaboration with the contractor. Hung from the marine platforms, moon pool curtains are configured to completely enclose a dredge site creating a containment cell.

Dredge Barge Silt Curtain

This type of barrier is designed to specifically contain sediment and solids displaced by barge dredging operations. The system mounts to the barge and can move with it. A dredge barge slit curtain can accommodate hydraulic or mechanical clamshell dredging while effectively protecting the surrounding areas.

Fish Excursion Barrier

This type of barrier is used In order to keep a project running and in compliance during the spawning or migration of fish. It goes from the water’s surface to the bottom and is constructed of a mesh-like material that allows water to flow but keeps all sizes of fish protected and away from the work area.

Jellyfish Barriers  

Jellyfish barriers are typically used in resort or water sports areas. As the name implies, these barriers are used in areas where stinging jellyfish are prevalent to protect swimmers.

Effectiveness

In addition to the type of turbidity barrier, there is a range of parameters that impact the effectiveness of a barrier. These include the construction and deployment of the barrier, both of which are impacted by the aquatic environment in which it is deployed.

silt curtain dredging

Anchoring and Moorings

Anchoring and moorings are vital to the effectiveness of turbidity barriers, especially in a situation where tides or waves cause vertical movement. Different types of anchors can be used to secure the barrier. It should never be directly attached to pilings driven in the bottom. The mooring system plays an important part in closing off the site to minimize the amount of material dispersed.

Hydrodynamic Loads

It is critical to thoroughly understand the hydrodynamic loads associated with the intended location. These loads are the result of combined water flow and waves. They will directly apply force to the structure and moorings of the barrier. Estimated hydrodynamic loads, as well as the level of redundancy, need to be considered when designing the barrier to maximize its effectiveness.

Deployment

Configuration is a major factor in the effectiveness of turbidity barriers. There are four primary configurations: maze, open, closed onshore and closed offshore. A variety of factors go into determining the best configuration. These include hydrodynamic conditions, the application of the barrier, and other external operational factors such as marine traffic and potential access.

floating turbidity barrier

Typical silt curtain deployment configurations

Source: HR Wallingford – http://eprints.hrwallingford.co.uk

The maze (configuration A) is seldom recommended as the flow will carry suspended sediment through the open corridor. However, in a situation where there is heavy marine traffic, it may be the only solution. Provided the water depth is sufficient along the shore to accommodate this traffic, the open semi-circle (configuration B) is preferred rather than the maze. Potential leaks and uncontrolled exchanges must be assessed and minimized with this configuration. The closed onshore (configuration C) is the most effective when discharging from land. For offshore tidal situations where currents reverse, the closed offshore elliptical (configuration D) is recommended.

Turbidity Barrier Professionals

It is always best to work with an environmental protection product expert to ensure that you choose the right turbidity barriers and marine accessories for your specific project.

IWT Cargo-Guard has been at the forefront in the evolution of turbidity barriers and silt curtains.   We are a design innovator of durable turbidity barriers and silt curtains that can withstand even the harshest jobsite conditions.

Founded with the purpose of developing products to protect our environment, IWT Cargo-Guard’s mission is to assist our clients in winning business by providing the most cost-effective products necessary for your project. By quickly analyzing the products and services required for the project, we become an extension of your estimating department.

We carry all types of turbidity barriers as well as containment booms, marine accessories and more. Contact us and our team will work with you to ensure you have exactly what you need to keep your project in compliance and on track.  

 

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