Dredging Phases 4 phases excavation lifting transportation disposal
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Dredging Phases • 4 phases – – excavation lifting transportation disposal Guide 4: Machines, Methods and Mitigation; Chapter 2: Phases of a Dredging Project; Page 15 1
Dredging Phases • Excavation of the in-situ material by – cutter head – draghead – cutting edge of a bucket • Main environmental aspects – Increase of suspended sediments – Mixing of soil layers – Dilution (in case of hydraulic dredging) Guide 4: Machines, Methods and Mitigation; Chapter 2: Phases of a Dredging Project; Page 15 2
Dredging Phases • Raising the material – mechanically backhoe, dipper, bucket ladder dredger – hydraulically cutter suction, trailing suction hopper, disc bottom, auger and sweep dredgers • Main environmental aspects – – Release of suspended sediments Loose and mobile spill layers Density of material Overflow during loading of hopper or barges Guide 4: Machines, Methods and Mitigation; Chapter 2: Phases of a Dredging Project; Page 16 3
Dredging Phases • Horizontal transport by – – hydraulic pipeline hopper dredgers barges also: trucks or conveyor belts • Main environmental aspects – – safety dilution spillage noise and air pollution Guide 4: Machines, Methods and Mitigation; Chapter 2: Phases of a Dredging Project; Page 16 4
Dredging Phases • Placement or further treatment – – reclamation of a site beach nourishment wetland creation relocation on land, in a pit or at sea (underwater) • Main environmental aspects – – Occupation of space and surface Dispersion of the deposited material Noise and air pollution Groundwater quality Guide 4: Machines, Methods and Mitigation; Chapter 2: Phases of a Dredging Project; Page 17 5
Environmental Dredging • Often with normal equipment • Sometimes with adapted procedures • When required, with special tools • Always resulting in lower output, higher cost Guide 4: Machines, Methods and Mitigation Chapter 3: Dredging Equipment Page 19 6
Suction Dredger (SD) Guide 4: Machines, Methods and Mitigation Chapter 3: Dredging Equipment Page 19 7