DREDGE AND FILL
Aysun Koroglu
Coastal Sciences and Civil Engineering Department,
Istanbul Technical University, Istanbul, Turkey
Synonyms
Sediment disposal; Sediment excavation
Definition
Dredge-and-fill operations are conducted in coastal areas
mainly to re-nourish beaches, to restore wetland habitat,
to remove excessive amounts of bottom sediments from
waterways, and to construct lagoons and roads. Dredging
in estuaries is carried out to create new harbors, berths, and
waterways or to improve navigation. “Large estuaries,
such as Coos Bay, Oregon (U.S.), that function as deepwater ports for large freighters, tankers, and other ships
require the deepest channels and most frequent channel
maintenance” (Oberrecht, 2005).
Fill is an operation that is conducted mostly in coastal
regions using sand, rocks, gravel, shell, earth, and concrete as filling materials. Filling activities in estuaries,
lagoons, and coastal wetlands may include restoring and
modifying areas by deposition of sediments.
Characteristics
Dredgers are used to excavate bottom sediments from
estuarine water bodies that can then be dumped at appropriate locations. “Dredging is accomplished basically by
two mechanisms: (1) hydraulic dredging – removal of
loosely compacted materials by cutterheads, dustpans,
hoppers, hydraulic pipeline, plain suction, and sidecasters,
usually for maintenance dredging projects; and
(2) mechanical dredging – removal of loose or hard
compacted materials by clamshell, dipper, or ladder
dredges, either for maintenance or new-work projects”
(San Francisco Bay Conservation and Development Commission, 2001).
Dredge-and-fill operations may be deleterious or
beneficial to certain species of organisms in estuaries
and wetlands. Johnston (1981) noted that the ways to mitigate adverse effects of dredge-and-fill operations
should include careful pre- and post-construction
environmental studies. Dredge-and-fill activities are
regulated in the USA by municipal, state, and federal
government agencies.
Bibliography
Johnston, S. A., 1981. Estuarine dredge-and-fill activities: a review
of impacts. Environmental Management, 5, 427–440.
Oberrecht, K., 2005. Altering the estuary. In Estuaries Feature
Series Articles and Study Guide Questions. Charleston, Oregon: South Slough National Estuarine Research Reserve.
137–141.
San Francisco Bay Conservation and Development Commission,
2001. Long-Term Management Strategy for Bay Area Dredged
Material. Final Environmental Impact Statement/Environmental
Impact Report. San Francisco, California: Conservation and
Development Commission.
Cross-references
Dredging
DREDGING
Paul A. Work
School of Civil and Environmental Engineering, Georgia
Institute of Technology, Atlanta, GA, USA
Definition
Dredging is the process of excavating bottom sediments
from the estuarine floor for disposal at another location,
most frequently to increase the depth of a channel to facilitate navigation by floating vessels.
Introduction
Early navigators were in many cases limited by naturally
occurring depths in water bodies. As ships grew larger,
dredging became necessary to increase water depths to
allow safe passage. In some cases, dredging was used to
create navigable water where land previously existed, with
the Suez and Panama Canals serving as two prominent
examples from the nineteenth and twentieth centuries,
respectively. However, the digging of canals predates
recorded history.
Tidal inlets connect rivers and estuaries to adjacent seas
and are thus important for marine commerce. The natural
depth within an inlet is typically controlled by a balance
between tidal currents sweeping through, in alternating
directions, and waves and longshore currents pushing
sediment into the inlet. Dredging can effectively increase
the depth in the channel. But without any changes in the
tidal prism that defines the volume of flow through the inlet
per tidal cycle, the channel is then deeper than its equilibrium configuration and subject to shoaling (van de Kreeke,
1992). This implies that dredging to greater depths will
result in an increased need for maintenance dredging.
Dredging is also critical for maintenance of ship
berthing areas and turning basins. It is widely employed
for land reclamation purposes, habitat creation, sand
mining, and beach nourishment activities. Project scope
can range from maintenance of a small boat launching
area up to major land reclamation projects involving
many millions of cubic meters of sediment (e.g., Ports
of Los Angeles in the United States and Rotterdam in
the Netherlands; Palm Islands in Dubai). Bray and Cohen
(2010) provide other examples of projects around the
world.
204
DREDGE AND FILL
Aysun Koroglu
Coastal Sciences and Civil Engineering Department,
Istanbul Technical University, Istanbul, Turkey
Synonyms
Sediment disposal; Sediment excavation
Definition
Dredge-and-fill operations are conducted in coastal areas
mainly to re-nourish beaches, to restore wetland habitat,
to remove excessive amounts of bottom sediments from
waterways, and to construct lagoons and roads. Dredging
in estuaries is carried out to create new harbors, berths, and
waterways or to improve navigation. “Large estuaries,
such as Coos Bay, Oregon (U.S.), that function as deepwater ports for large freighters, tankers, and other ships
require the deepest channels and most frequent channel
maintenance” (Oberrecht, 2005).
Fill is an operation that is conducted mostly in coastal
regions using sand, rocks, gravel, shell, earth, and concrete as filling materials. Filling activities in estuaries,
lagoons, and coastal wetlands may include restoring and
modifying areas by deposition of sediments.
Characteristics
Dredgers are used to excavate bottom sediments from
estuarine water bodies that can then be dumped at appropriate locations. “Dredging is accomplished basically by
two mechanisms: (1) hydraulic dredging – removal of
loosely compacted materials by cutterheads, dustpans,
hoppers, hydraulic pipeline, plain suction, and sidecasters,
usually for maintenance dredging projects; and
(2) mechanical dredging – removal of loose or hard
compacted materials by clamshell, dipper, or ladder
dredges, either for maintenance or new-work projects”
(San Francisco Bay Conservation and Development Commission, 2001).
Dredge-and-fill operations may be deleterious or
beneficial to certain species of organisms in estuaries
and wetlands. Johnston (1981) noted that the ways to mitigate adverse effects of dredge-and-fill operations
should include careful pre- and post-construction
environmental studies. Dredge-and-fill activities are
regulated in the USA by municipal, state, and federal
government agencies.
Bibliography
Johnston, S. A., 1981. Estuarine dredge-and-fill activities: a review
of impacts. Environmental Management, 5, 427–440.
Oberrecht, K., 2005. Altering the estuary. In Estuaries Feature
Series Articles and Study Guide Questions. Charleston, Oregon: South Slough National Estuarine Research Reserve.
137–141.
San Francisco Bay Conservation and Development Commission,
2001. Long-Term Management Strategy for Bay Area Dredged
Material. Final Environmental Impact Statement/Environmental
Impact Report. San Francisco, California: Conservation and
Development Commission.
Cross-references
Dredging
DREDGING
Paul A. Work
School of Civil and Environmental Engineering, Georgia
Institute of Technology, Atlanta, GA, USA
Definition
Dredging is the process of excavating bottom sediments
from the estuarine floor for disposal at another location,
most frequently to increase the depth of a channel to facilitate navigation by floating vessels.
Introduction
Early navigators were in many cases limited by naturally
occurring depths in water bodies. As ships grew larger,
dredging became necessary to increase water depths to
allow safe passage. In some cases, dredging was used to
create navigable water where land previously existed, with
the Suez and Panama Canals serving as two prominent
examples from the nineteenth and twentieth centuries,
respectively. However, the digging of canals predates
recorded history.
Tidal inlets connect rivers and estuaries to adjacent seas
and are thus important for marine commerce. The natural
depth within an inlet is typically controlled by a balance
between tidal currents sweeping through, in alternating
directions, and waves and longshore currents pushing
sediment into the inlet. Dredging can effectively increase
the depth in the channel. But without any changes in the
tidal prism that defines the volume of flow through the inlet
per tidal cycle, the channel is then deeper than its equilibrium configuration and subject to shoaling (van de Kreeke,
1992). This implies that dredging to greater depths will
result in an increased need for maintenance dredging.
Dredging is also critical for maintenance of ship
berthing areas and turning basins. It is widely employed
for land reclamation purposes, habitat creation, sand
mining, and beach nourishment activities. Project scope
can range from maintenance of a small boat launching
area up to major land reclamation projects involving
many millions of cubic meters of sediment (e.g., Ports
of Los Angeles in the United States and Rotterdam in
the Netherlands; Palm Islands in Dubai). Bray and Cohen
(2010) provide other examples of projects around the
world.
204
DREDGE AND FILL