![]() The equipment to be used, rating of pumps, and other considerations critically depend on it. While planning a dredging program, the location and depth from which the sediment is to be removed, the volume to be cleared, and grain size distribution of the sediment should be ascertained by sampling. Some coarse sediments may be used as construction material. If the material is dumped in the downstream river channel, it is carried away by the river flow. The sediment that is removed may be put in the river downstream of the dam or may be dumped in a depression away from the river. Ideally such sites should be near the reservoir to reduce the cost of transportation. ![]() Of course, there are problems in locating suitable sites to place the excavated material. Dredging may be resorted to when other methods of sediment management are not viable or successful.ĭredging is usually focussed on small areas in the reservoir, e.g., the intake structure, the regions that are being used for recreational purposes, due to cost considerations. However, with the increase in water demand and reduction in construction of new projects, it is expected that the number of incidents where dredging is taken up will increase. Generally, dredging is an expensive means of recovering the storage capacity unless the deposits removed can be used for beneficial purposes. Singh, in Developments in Water Science, 2003 12.8.2 Dredgingĭredging is the process of removing the sediment from a water body (reservoir or channel), transporting, and depositing it at another location far away. Additionally, release of nutrients from sediments may result in increased eutrophication and consumption of oxygen ( OSPAR, 2004, 2008a,b). Sediments can also settle out of suspension and can potentially smother bottom-dwelling organisms. Elevated suspended sediment levels can absorb and scatter or reduce light levels that are fundamentally important to the many photosynthetic benthic organisms including hard and soft corals, seagrasses, mangroves, macroalgae (including seaweeds), and algae. The sediment released into the water column can directly affect marine organisms such as corals, sponges, and shellfish and can cause membrane irritation and gill abrasion in fin fish ( OSPAR, 2004, 2008b). In most developed countries, there are strict controls on the disposal of potentially toxic dredged sediments which require treatment before disposal and/or placement in a secure landfill.ĭredging operations will almost always resuspend sediments and increase turbidity, but the level of resuspension and associated impacts depends on the physical and chemical characteristics of the sediment, as well as the site conditions, type of equipment, and dredging method. However, most of the material dredged in harbors, estuaries, and at sea is dumped at sea and only minor amounts of this dredged material are beneficially used. The sediment removed by dredging can be used for reclamation, or disposed on land. Maintenance dredging campaigns are undertaken at regular intervals (eg, annually), are typically of short duration (days to weeks), and generally remove sediments with a higher proportion of finer particles. Maintenance dredging keeps previously dredged areas at the required depth. There are two major types of dredging operations ( McCook et al., 2015): capital dredging is carried out to open up new developments such as marina or port basins or widen existing channels. Apte, in Marine Ecotoxicology, 2016 10.3.5 Dredgingĭredging involves the excavation or removal of sediment and/or rock from the seabed and is a routine part of port operations and of coastal and marine infrastructure developments. The chemical characteristics of this material have to be taken into consideration in any risk assessment of the consequences to the environment. The particle size characteristics of this material and the hydrodynamics of the site will determine how far it may drift before settling and this will influence the extent and severity of any physical impact outside the immediate dredging site. Most dredging activities, particularly hydraulic dredging, generate an overspill of fine solid material as a consequence of the dredging activity. Mining for ores is considered further within the section on industrial wastes. Types of material dredged can include sand, silt, clay, gravel, coral, rock, boulders, and peat. ![]() Dredging is also undertaken to win materials, for example, for reclamation or beach nourishment. These activities can generate large volumes of waste requiring disposal. Murray, in Encyclopedia of Ocean Sciences (Third Edition), 2009 Dredgingĭredging is undertaken for a variety of reasons including navigation, environmental remediation, flood control, and the emplacement of structures (e.g., foundations, pipelines, and tunnels).
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