Turbidity Barriers: Controlling Turbidity on Dredge Sites

Turbidity BarrierThe primary purpose of turbidity barriers is to provide sediment containment during construction activities either adjacent to or within a water body. Choosing the right barriers will require several considerations in selecting the proper barrier type along with installation to serve the application.

Primary application considerations are water conditions such as flow velocity, waves and tides combined with climatic and site conditions such as wind, storm frequency, project duration, types of silts and governmental regulations or contractual requirements pertaining to sediment release. Three primary types of turbidity curtains are produced with the flotation diameter, section connectors, ballast chain, skirt fabric, skirt depth and section length the main factors considered in turbidity curtain selection. TYPE I curtain should be used in protected areas where there is no current and area is sheltered. Type II curtain should be used with small to moderate currents (2 knots or3.5ft / second) with limited wind and wave action. Type III should be used in areas with stronger currents (up to 3knots or 5.ft/second) where tidal action may be present and subject to wind and wave conditions. More detailed product information is available at www.abasco.com.

 This image is a standard turbidity curtain set up with floating boom and filter skirt.  Custom curtains can be manufactured to reach depths of 100 ft.+

Design considerations can be impacted by contractual or application issues but generally you should not place a turbidity barrier across a fast moving body of water; turbidity barrier should remain one foot off bottom at low mean tide; turbidity barriers should be properly secured to either posts, concrete blocks or anchor systems to insure proper perimeter and or migration from work site; either permeable or impermeable fabric selected for application and duration of the project. Basic fabric selections include thickness, strength and UV resistance and skirt permeability if required (a typical 6% monofilament offers a 70 US std. sieve/18 gpm/ft2 flow rate). Basic tensile load considerations include the use and number of top cables; section connectors utilized; ballast chain weight/diameter and fabric webbing to secure special applications. Section lengths and anchor points are further considerations based upon turbidity barrier selected for application. TYPE II and TYPE III turbidity barriers should have engineered anchoring plans to calculate loads, anchor type and placement with analytical software the best option.

Turbidity barriers can be used for dredging zones and for general turbidity control on shorelines where construction is taking place.

A complete review of these considerations will support the proper selection of correct turbidity barrier which will also need to be properly secured during installation and maintained by the on-site supervisor.

For more information on applying custom sized turbidity curtains to your dredging project contact Chuck LaBounty at [email protected]

Contributing Blogger: Chuck LaBounty, VP & General Manager at ABASCO LLC, www.abasco.com

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