Turbidity or silt curtains should generally come within one foot of the lake or stream bed, but not touch it. Allowing a small space not only permits free movement of aquatic residents, but prevents situations where the curtain actually stirs up additional sediment through slight bouncing and shifting caused by water movement. In situations where a considerable amount of silt is collected, the accumulated load can actually trap the bottom of the curtain, preventing it from flexing and functioning properly. In circumstances where water levels rise, as in storm events or tidal fluctuations, a trapped curtain can actually pull the floats completely under and cause considerable damage to the entire setup.
If you’re working with a turbidity curtain in an area with fluctuating water levels, whether from stormwater or tidal movement, you’ll want to allow for this by designing your curtain to sit one foot from the bottom during an average low water event, using measurements like the low mean tide (LMT) or historic water levels during summer or periods of drought. Starting with this measurement, you’ll allow for high water fluctuations by adding slack to the depth of the curtain, which allows it to billow out in low water, but gradually straighten as the floats rise. This allows the curtain to provide maximum containment by responding effectively to changing conditions. If your situation appears to demand a different solution, speak with your supplier about possible alternative configurations and how the construction of your curtains will be modified.
