Figure 2-3. Upland, Nearshore, and Island CDFs

Framework for Dredged Material Management

May 2004

Figure 2-3. Upland, Nearshore, and Island CDFs

The two objectives inherent in design and operation of CDFs are to provide for

adequate storage capacity for meeting dredging requirements and to maximize efficiency

in retaining the solids. However, if contaminants are present, control of contaminant

releases may also be an objective. Basic guidance for design, operation, and management

of CDFs is found in Engineer Manuals (USACE 1983, 1987 and in preparation).

Hydraulic dredging adds several volumes of water for each volume of sediment

removed, and this excess water is normally discharged as effluent from the CDF during

the filling operation. The amount of water added depends on the design of the dredge,

physical characteristics of the sediment, and operational factors such as pumping

distance. When the dredged material is initially deposited in the CDF, it may occupy

several times its original volume. The settling process is a function of time, but the

sediment will eventually consolidate to its in situ volume or less if desiccation occurs.

Adequate volume must be provided during the dredging operation to contain the total

volume of sediment to be dredged, accounting for any volume changes during placement.

Some CDFs are filled by mechanically rehandling dredged material from barges

filled by mechanical dredges. Material placed in the CDF in this manner is at or near its

in situ water content. If such sites are constructed in water, the effluent volume may be

limited to the water displaced by the dredged material, and the settling behavior of the

material is not as important.

In most cases, CDFs must be used over a period of many years, storing material

dredged periodically over the design life. Long-term storage capacity of these CDFs is

therefore a major factor in design and management. Once water is drained from the CDF

following active disposal operations, natural drying forces begin to dewater the dredged

material, adding additional storage capacity. The gains in storage capacity are therefore

influenced by consolidation and drying processes and the techniques used to manage the

site both during and following active disposal operations. Additional discussion of

confined disposal processes is found in Chapter 5.