Dredging

About: Dredging is a research topic. Over the lifetime, 3300 publications have been published within this topic receiving 28325 citations.

Lake restoration by sediment removal

Abstract: Fresh water lake sediment removal is usually undertaken to deepen a lake and increase its volume to enhance fish production, to remove nutrient rich sediment, to remove toxic or hazardous material, or to reduce the abundance of rooted aquatic plants. Review of more than 60 projects and five case histories reveals that the first three objectives are usually met through sediment removal. Dredging to control aquatic plants has not been well documented. Disadvantages of dredging include cost, temporary phosphorus release from sediment, increased phytoplankton productivity, noise, lake drawdown, temporary reduction in benthic fish food organisms, the potential for toxic material release to the overlying water and potential for environmental degradation at the dredged material disposal site. The technique is recommended for deepening and for long range reduction of phosphorus release from sediment. Sediment removal to control toxic materials is possible with minimal environmental impact when proper equipment is used, but it may more than double the cost. Lack of definitive information about rooted plant regrowth rates in dredged areas prohibits explicit recommendations on sediment removal to control plant growth.

Marine Habitats in One of the World’s Busiest Harbours

Abstract: Singapore’s limited marine territory of approximately 600 km 2 supports one of the world’s busiest harbours. Over 133,000 vessels (above 75 gross tonnes) called at the port in 2004. Thirty-five percent comprised regional ferries linking Singapore with various ports of Indonesia’s Riau province. Other vessels were mainly containers and tankers which facilitate movement of 1 billion gross tonnes of cargo through the port. To accommodate such intense shipping activity and provide safe navigation to the heavy vessel traffic, the port waters cover 82% of Singapore territorial waters. Most of the port provisions are located in the seas south of the main island, particularly the south-western sector (Figure 1). Wharf and berthing facilities dominate the southwestern coastline, which have been transformed by coastal reclamation. Fairways, anchorages and vessel manoeuvring areas intermesh between the fifty-odd smaller offshore islands scattered mostly in the southern waters. A spectrum of marine habitats typical of tropical regimes is found in this heavily utilized marine environment. Fringing and patch reefs are present among the southern islands together with seagrass meadows and mangrove stands, all varying in areal extent. A range of seashore types including rocky, sandy and muddy exists. The seafloor is now mostly dominated by mud bottoms as most of the sand deposits have been exhausted for reclamation while the continuous rain of suspended sediment adds more silt. Threats from shipping include vessel movement, grounding and accidental spillage of hazardous materials. Other activities such as land reclamation, seabed dredging and the dumping of dredged spoils contribute to increased suspended sediment, modification of hydrodynamic patterns and changed tidal speeds at different locations. High energy wash from increasing numbers and operating frequency of fast-going vessels such as high-speed passenger ferries scour exposed shores and reef flats. Large tracts of razed corals on reef flats provide evidence of grounding by flat-bottom barges, often connected with a nearby development activity. The spillage of 28,500 tonnes of heavy marine fuel oil into the sea

Benthic disturbance by fishing gear in the Irish Sea: a comparison of beam trawling and scallop dredging

Abstract: 1.?The distribution of effort for the most frequently used mobile demersal gears in the Irish Sea was examined and their potential to disturb different benthic communities calculated. Fishing effort data, expressed as the number of days fished, was collated for all fleets operating in the Irish Sea in 1994. For each gear, the percentage of the seabed swept by those parts of the gear that penetrate the seabed was calculated. 2.? For all gears, the majority of fishing effort was concentrated in the northern Irish Sea. Effort was concentrated in three main locations: on the muddy sediments between Northern Ireland and the Isle of Man (otter and Nephrops trawling); off the north Wales, Lancashire and Cumbrian coast (beam trawling); the area surrounding the Isle of Man (scallop dredging). 3.?In some areas, e.g. between Anglesey and the Isle of Man, the use of scallop dredges and beam trawls was coincident. A comparative experimental study revealed that scallop dredges caught much less by-catch than beam trawls. Multivariate analysis revealed that both gears modified the benthic community in a similar manner, causing a reduction in the abundance of most epifaunal species. 4.? Although beam trawling disturbed the greatest area of seabed in 1994, the majority of effort occurred on grounds which supported communities that are exposed to high levels of natural disturbance. Scallop dredging, Nephrops and otter trawling were concentrated in areas that either have long-lived or poorly studied communities. The latter highlights the need for more detailed knowledge of the distribution of sublittoral communities that are vulnerable to fishing disturbance. ©British Crown Copyright 1996.

Trace Metals as Tracers of Dredging Activity in Cleveland Bay - Field and Laboratory Studies

Abstract: This study has investigated in detail trace metal concentrations in Cleveland Bay in the central Great Barrier Reef and assessed the significant carrier phases of several metals during a simulated disturbance of sediments designed to investigate the effects of dredging. Organic, iron oxide and carbonate phases were shown to be important carrier phases for several trace metals. The application of an acid-leach technique to monitor labile or pollutant concentrations of copper, zinc, lead and nickel in sediments collected from coral reefs sampled before and after two dredging events in 1991 yielded useful information on the fate of dredged sediment. Trace metal contamination close inshore was attributed to port activities, sewage discharge and urbanization.