Dredging equipment and the effects of dredging on the environment.
Dredging operations result in disturbing bottom sediments, and depositing a mixture of water and solids in a disposal area. Disposal of the material in open water can occur in different environments: (1) tidal estuary, (2) non-tidal estuary, (3) open bay, (4) nearshore areas up to the 30 m depth of water, (5) on the continental shelf up to 200 m depth of water, or (6) in deep ocean in water depth greater than 200 m. Disposal of material on land can occur in three ways: (1) unconfined disposal; (2) partly-confined disposal; and (3) confined disposal. There are two types of dredges: mechanical dredges and hydraulic dredges. Mechanical dredges can be classified into the grapple dredge, the dipper dredge, and the bucket-ladder dredge. The hydraulic dredges can be classified into the dustpan dredge, the hydraulic pipeline cutterhead dredge, and the self-propelled hopper dredge. Mechanical dredges pick up fine sediment and pollutants and return it to the immediate vicinity of the dredging site. Hydraulic dredges each have an environmental effect. Size, loads of solids, and horse power requirements are given in relation to their expected production.