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Dredging facts

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Dredging is performed to maintain navigation channels and harbors for shipping vessels. There are two main types of dredging: construction dredging removes previously undisturbed materials to create new channels, while maintenance dredging periodically removes accumulated sediment to maintain authorized depths. The Corps of Engineers is responsible for navigation channels, while port authorities oversee harbors. Dredged materials come from various areas like inlets, harbors, and inland waterways, and range from sand to silt and clay. Dredged materials are disposed of through ocean placement, beach nourishment, upland placement, open water placement, or within banks placement. Dredging provides environmental benefits such as wetland construction, landfill cover, and beach

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DREDGING Purpose: To establish and maintain navigation channels and harbors of sufficient size to accommodate shipping vessels. Types of Dredging: Construction - the removal of materials previously undisturbed to facilitate new navigation channels or water projects, e.g., locks and dams. Maintenance - The periodic and repetitive removal of accumulated sediment from navigation channels and harbors to maintain authorized depths and widths. Responsible Agencies: Corps of Engineers for navigation channels Port Authorities for harbors Major Areas of Dredging: 1 - Main approaches (approach channel in ocean); dredged material primarily sand.
2- Bar channels (sandbars at inlets); dredged material primarily coarse-grained sand. 3 - Entrance channels (to harbors); dredged material primarily sand to fine-grained silt and clay. 4- Berthing areas (harbors/ports); dredged material primarily silt and some sand. 5 - Inland waterways (intracoastal waterways and river channels); silt and sand. Types of Dredging Vessels: Snagboat - Used to break up logjams and to clear debris, sunken vessels, and dilapidated piers that may be hazardous to navigation. Mechanical - Dipper dredge and clamshell dredge - removes hard packed material or debris - cannot handle fine-grained sediment, such as silt or sand - places materials into barges for transport to disposal sites
Hydraulic - - cutterhead pipeline dredge - uses rotating cutter at end of arm to suck loose materials into pipeline for deposit at a disposal site - can work 24 hours a day - limited capability in rough weather - pipeline can be obstruction to navigation - operates primarily in shallow draft navigation channels
• - self-propelled hopper dredge - stores sediment within vessel for disposal later at approved site - works in deep water (primarily in harbors and ports) - cannot dredge continuously - can operate in rough water • dustpan dredge and sidecaster dredge
- used to remove loosely compacted coarse-grained material at rapid shoaling sites or where sediment is needed adjacent to a navigation channel. Types of Disposal Sites Ocean Placement - off-shore site approved by Environmental Protection Agency for disposal - hopper dredge or towed barge with material from inlets, bars, and main approaches - vessel opens hull and allows sediment to drift to bottom of ocean Beach Nourishment
- placement of material on or near a beach - usually to replenish an eroding beach - typically done with pipeline and hopper dredges Upland Placement - placement of material directly into a diked area, usually by pipeline dredge - generally the most economical method of dredging
Open Water Placement - placement of dredged materials in near-coastal or inland waters - may include contaminated materials placed in deep pits or bottom depressions - material is capped in a precisely engineered manner to ensure cap stays in place and isolates material from environment. Within Banks Placement
- generally occurs on river system - material is placed on banks or downstream of shoals along shoreline - material, usually coarse-grained sand can be used commercially Environmental Benefits of Dredging - Can be used for the following purposes: - wetland construction - borrow pit relcamation - landfill cover - construction aggregate - beach nourishment - wildlife habitat • Scientifically approved measures to isolate contaminated materials from environment Extracted From Dredging, US Army Corps of Engineers Pamphlet, Undated.

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Dredging facts

  • 1. DREDGING Purpose: To establish and maintain navigation channels and harbors of sufficient size to accommodate shipping vessels. Types of Dredging: Construction - the removal of materials previously undisturbed to facilitate new navigation channels or water projects, e.g., locks and dams. Maintenance - The periodic and repetitive removal of accumulated sediment from navigation channels and harbors to maintain authorized depths and widths. Responsible Agencies: Corps of Engineers for navigation channels Port Authorities for harbors Major Areas of Dredging: 1 - Main approaches (approach channel in ocean); dredged material primarily sand.
  • 2. 2- Bar channels (sandbars at inlets); dredged material primarily coarse-grained sand. 3 - Entrance channels (to harbors); dredged material primarily sand to fine-grained silt and clay. 4- Berthing areas (harbors/ports); dredged material primarily silt and some sand. 5 - Inland waterways (intracoastal waterways and river channels); silt and sand. Types of Dredging Vessels: Snagboat - Used to break up logjams and to clear debris, sunken vessels, and dilapidated piers that may be hazardous to navigation. Mechanical - Dipper dredge and clamshell dredge - removes hard packed material or debris - cannot handle fine-grained sediment, such as silt or sand - places materials into barges for transport to disposal sites
  • 3. Hydraulic - - cutterhead pipeline dredge - uses rotating cutter at end of arm to suck loose materials into pipeline for deposit at a disposal site - can work 24 hours a day - limited capability in rough weather - pipeline can be obstruction to navigation - operates primarily in shallow draft navigation channels
  • 4. • - self-propelled hopper dredge - stores sediment within vessel for disposal later at approved site - works in deep water (primarily in harbors and ports) - cannot dredge continuously - can operate in rough water • dustpan dredge and sidecaster dredge
  • 5. - used to remove loosely compacted coarse-grained material at rapid shoaling sites or where sediment is needed adjacent to a navigation channel. Types of Disposal Sites Ocean Placement - off-shore site approved by Environmental Protection Agency for disposal - hopper dredge or towed barge with material from inlets, bars, and main approaches - vessel opens hull and allows sediment to drift to bottom of ocean Beach Nourishment
  • 6. - placement of material on or near a beach - usually to replenish an eroding beach - typically done with pipeline and hopper dredges Upland Placement - placement of material directly into a diked area, usually by pipeline dredge - generally the most economical method of dredging
  • 7. Open Water Placement - placement of dredged materials in near-coastal or inland waters - may include contaminated materials placed in deep pits or bottom depressions - material is capped in a precisely engineered manner to ensure cap stays in place and isolates material from environment. Within Banks Placement
  • 8. - generally occurs on river system - material is placed on banks or downstream of shoals along shoreline - material, usually coarse-grained sand can be used commercially Environmental Benefits of Dredging - Can be used for the following purposes: - wetland construction - borrow pit relcamation - landfill cover - construction aggregate - beach nourishment - wildlife habitat • Scientifically approved measures to isolate contaminated materials from environment Extracted From Dredging, US Army Corps of Engineers Pamphlet, Undated.