Framework for Dredged Material Management
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.