Maintenance dredging

Gumm GJ (2001) Indiana harbor and canal maintenance dredging and disposal activities Project status report. Army Corps of Engineers, Chicago District... 

Table 7-1 Mean Annual Maintenance Dredging of Harbours Along the Coast of the Southern North Sea (Salomons Eysink, 1981)...

Much of the bottom of the Sound within the wave-affected zone is sandy. In some localities where the shore is bedrock, deposits of muddy sediment form up to the surf zone. This is possible because mud is trapped in mats of algae that mantle the bottom near the shore. Muddy material also accumulates in the dredged shipping channels of the harbors along the Connecticut shore at an average rate of 4 mm/yr, as computed from records of maintenance dredging (Bokuniewicz and Gordon, 1979). The surface area and volume of all of these deposits is small compared to the area and volume of the muddy sediment below the wave-affected zone. The rest of this article deals mostly with these deep mud deposits. 

Remediation techniques on contaminated sediments generally are much more limited than for most other solid waste materials, except for mine wastes. The widely diverse contamination sources in larger catchment areas usually produces a mixture of pollutants, which is more difficult to treat than an industrial waste. For most sediments from maintenance dredging, there are more arguments in favor of disposal rather than treatmenf. Mechanical separation of less strongly contaminated fractions. 

Nonavailability of rock material in sufficient quantities and at affordable costs. Avoiding sediment infiltration through rubble mound structures which may result in the shoaling of navigation channels and harbor basins, and thus in higher maintenance dredging costs. 

Also economists have their objections. They state that the costs of maintenance dredging would be so high that the canal could never be profitable and that the canal is not attractive enough for non-coastal ships, which are expected to constitute about 70% of the users of the canal. 

Channel maintenance (dredging and dredging reduction), lock and dam operation and maintenance, and jetty repair. 

Borrow Area Capital Dredging Maintenance dredging Plain suttion dredger Cutter suction dredger Trailing suction hopper dreclger... 

One of the most important conditions, having a significant impact on the feasibility of a land reclamation project, is the availabihty of sufficient suitable fill material within a reasonable haulage distance to the project location. In most cases special borrow areas are allocated for the supply of fill material, but fill may also have to be retrieved from capital or maintenance dredging. For instance in harbour projects, deepening of basins or approach channels are often combined with reclamation projects. 

In case no suitable quartz sands are available from a borrow area within a reasonable distance to the site, or from maintenance dredging or capital dredging, other fill materials may have to be used such as clay, carbonate sand or rock. These materials have a different mineralogy, particle size distribution, grain shape, etc. which results in different and/or unexpected fill mass properties. However, by adequately addressing the typical properties of these materials, it may be possible to construct a reclamation that meets the specifications. The possibilities and restrictions of the use of these materials for fill is described in Chapter 9. 

Johnston Island is approximately 7 percent natural the remaining 93 percent was created by dredging the surrounding coral reef to build a runway for military operations during World War II. A protective seawall surrounding the island requires periodic maintenance to keep most of the island (which is 7 feet above sea level) from being reclaimed by the sea. 

A slurry is a mixture of a liquid and solid particles. The term sludge typically refers to a highly concentrated slurry containing fine particulate material. Each year, vast tonnages of slurries are pumped. Slurries are often used to transport coal, phosphates and minerals. Dredging of sand and silt in the maintenance of waterways is another example of sohds handled in slurry form. In most slurries, the liquid phase is water. However, coal-oil and coal-methanol fuels are examples of slurries made up with liquids other than water. 

Maintenance of navigation channels includes the infrastructure such as jetties and breakwaters. Mobilization for dredging is a great expense, calling for the longest possible dredging cycle. Considerations include ... 

Both aspects, and their impact on the economical and environmental cost of entrance chaimels construction and dredging maintenance, should be taken into accoimt in the entrance chaimel and breakwater design. The application of present methodology can help to find the optimum design. 

Their construction and maintenance requires massive capital investment and a noticeable transformation of the landscape, particularly along the coastline with piers, docks and basins. For many ports, dredging is also a megaproject required to improve their accessibility to maritime shipping and maintain their operating conditions (siltation). 

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