Turbidity curtains are deployed in situations where construction activities, whether on land or in water, lead to unavoidable silt and sediment movement. Since the stirred up sediment can cause direct and indirect injury to both human and wildlife populations as it moves and spreads, turbidity curtains are used to prevent the movement of silt and sediment outside the immediate construction area. Keep in mind that turbidity curtains are not intended to impede water flow, but rather trap the sediment itself and allow it to settle to the bottom. Fast or slow water movement, directional changes in tidal conditions, and changing depths all require different solutions to avoid excessive wear and tear on the curtain or other types of functional failure.
In most circumstances, turbidity curtains are installed approximately parallel to the water flow. That may seem counterintuitive, but curtains that are placed directly across channel flows are subject to intense loads and can generate even more turbidity. Cross channel placement is rarely used, except in the gentlest conditions, like calm lakes and small streams. These curtains may be constructed of impermeable materials, meaning that they do not permit water to flow through the curtain. Instead, the bottom of the curtain has a gap of about 1 foot from the bed of the lake. This setup reduces and delays water movement until silt has an opportunity to settle but still allows aquatic creatures to access and travel beyond the barrier. In situations where there’s moderate water flow, waves or tidal action, it’s necessary to use woven geotextile fabrics that permit water to flow through, while filtering out sediment. This not only reduces wear on the curtain itself, but simplifies the job of anchoring the barrier. To understand how barriers that are installed parallel to the water flow can trap silt, picture a series of Vs or even an array of long hexagonal lozenges that permit water to flow in, but filter it out as it moves through the fabric. In these conditions, a cross channel setup is still impractical, but series of smaller structures still allow the same volume of water to flow past while effectively trapping suspended sediment.
