Environmental Engineering Reference
In-Depth Information
Confined channel
Perched channel
FIGURE 3.18
Conined and perched channels.
Channel design depths are often maintained by dredging. In the United States today, approxi-
mately 250,000 yd
3
of sediments are removed from navigation channels annually. In many river
systems, maintenance dredging is a nearly constant activity so that natural recovery is prevented
and the benthos is continuously disturbed. Therefore, consideration of the dredging process and
dredging impacts is an essential component of river management.
The process of maintenance dredging consists of the following stages:
•
Excavation (loosening or dislodging) and removal of the loosened material to the dredge vessel
•
Transportation of the material
•
Placement or disposal of the material
The basic types of dredges include mechanical clamshell or backhoe dredges (Figure 3.19)
that essentially have a large excavation bucket that is dropped or lowered to scoop the sediments.
FIGURE 3.19
Backhoe dredge. (Courtesy of the U.S. Army Engineer Research and Development Center,
Vicksburg, MS.)
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