Figure 1. Schematic representation of silt curtain acting to force a turbid plume downward to the top of the fluid mud layer

ERDC TN-DOER-N7

August 2000

Limited data suggest that in-air or submerged discharges normal to the water surface have lower

near-surface turbidity than horizontal discharges or discharges at some angle (Schubel et al. 1978;

Neal, Henry, and Greene 1978). Discharge deflector plates help reduce near-surface turbidity for a

horizontal discharge (Schubel et al. 1978; Neal, Henry, and Greene 1978). An inward circulation

set up near the water surface helps to contain the near-surface turbid zone to the proximity of the

discharge point. Discharge into air significantly increases near-surface turbidity generation (Neal,

Henry, and Greene 1978).

Silt curtains can be used in some cases to reduce the visible surface turbidity and confine it to the

immediate vicinity of the discharge (JBF 1978). Silt curtains can be used, in cases where currents

are less than 0.3 m/sec (1 fps), to force the turbid layer downward to the top of the fluid-mud

underflow layer as shown in Figure 1.

Figure 1. Schematic representation of silt curtain acting to force a turbid plume downward to the top of the

fluid mud layer (Saucier et al. 1978)

Submerged diffusers can also reduce turbidity at the surface as well as reduce overall entrainment

of ambient water, and deliver material close to the bed. By reducing the entrainment of ambient

water during descent to the near-bed layers, diffusers can be used to maximize fluid mud

concentrations in these layers (Neal et al. 1978). Diffusers can also reduce stripping of material

from the pipeline jet into the water column. Even a relatively simple vertical diffuser can help to

reduce turbidity generation during descent through the water column to a very low level (Thevenot

et al. 1992).