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Framework for Dredged Material Management
May 2004
4.4.2 Submerged Discharge
Submerged discharge is a control measure which may be considered to reduce
water-column impacts. The use of a submerged point of discharge reduces the area of
exposure in the water-column and the amount of material suspended in the water column
susceptible to dispersion. The use of submerged diffusers also reduces the exit velocities
for hydraulic placement, allowing more precise placement and reducing both
resuspension and spread of the discharged material. Considerations in evaluating
feasibility of a submerged discharge and/or use of a diffuser include water depth, bottom
topography, currents, type of dredge, and site capacity. Design specifications for
submerged diffusers are available, and the diffusers have been successfully used for
disposal operations (Neal, Henry, and Green 1978, Palermo 1994).
4.4.3 Lateral Containment
Lateral containment is a control measure which may be considered to reduce
benthic impacts. The use of subaqueous depressions or borrow pits or the construction of
subaqueous dikes can provide containment of material reaching the bottom during open-
water disposal, resulting in a reduced bottom area being affected by the placement. Such
techniques reduce the areal extent of a given disposal operation, thereby reducing both
physical benthic effects and the potential for release of contaminants. Considerations in
evaluating feasibility of lateral containment include type of dredge, water depth, bottom
topography, bottom sediment type, and site capacity.
Simply selecting a site amenable to lateral containment such as an existing bottom
depression or valley can be effective. Placement of material in constructed depressions
such as abandoned borrow pits has also been proposed. Submerged dikes or berms for
purposes of lateral containment have been constructed or proposed at several sites. Such a
proposal would not necessarily involve added expense to the project if the material used
for the berm comes from the same or another dredging project.
4.4.4 Thin-Layer Placement
The intentional spreading of hydraulically pumped dredged material over broad
areas to achieve overburdens less than 12 inches thick has been termed "thin-layer"
placement. The objective of thin-layer placement is to minimize impacts on benthic
fauna and to speed their recovery, particularly in estuarine environments. This strategy is
based upon knowledge that a portion of the benthos can migrate upward through the
dredged material overburden, usually present as a fluid mud layer. This concept has been
developed and demonstrated in Mississippi Sound by the Mobile District. Results of
monitoring studies indicated that recovery was enhanced in shallow, turbid Gulf coast
estuaries. A distinction should be made between thin-layer placement in open-water
applications and high-pressure spray disposal on marsh surfaces. Although sometimes
referred to as thin-layer placement, the latter case involves different equipment
requirements and generally is suitable for relatively small volumes of dredged material,
whereas open-water thin-layer placement uses conventional hydraulic equipment (with

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