Sediments underwater

Combinations of VEAs, WRAs and SPs are used in controlling sedimentation in highly flowable slurry like concrete and in underwater concrete used... 

Can be used to remediate contaminants in soils, sludges, and underwater sediments to a maximum depth of 100 ft. 

Despite the low average consumption of pesticides, in the sporadic reports available, it could be seen that even the roadside dusts, rural and urban soils and the underwater sediments are contaminated. Many pesticides are degrading the Indian environment, even though faster dissipation and possible degradation of POPs chemicals like HCHs and DDTs were observed in Indian soils by the tropical climate of India (Pillai, 1986). Such a phenomenon of dissipation in the dry season was substantiated by Ramesh et al. (1991) in the river sediments (Fig. 9.2). Further, the relative flux of residues into the aquatic environment is smaller than the amount volatilized to the atmosphere in tropical countries like India (Tanabe et al., 1991). 

Keywords Coasts Shelf Continental slope Continental footstep Underwater canyons Deep-sea floor Bottom sediments... 

The Crimean shelf extends from Cape Khersones in the west to Cape Meganom in the east. It is widest off Cape Sarych (35-40 km) and narrowest off Cape Ayu Dag (5 km) [1,2]. This region is subjected to intensive wave action because it is exposed to all the southerly winds. The boundary of the underwater coastal slope is located at depths of 30-40 m. The near-shore zone is the area of alongshore sediment transport and smoothing of the bottom topography. Underwater and dried abrasive remnants are common the largest of them are confined to the capes composed of strong volcanic rocks [7,8]. 

The continental footstep of the Black Sea occupies an intermediate position between the continental slope and the floor of the central depression at depths from 1100-1200 to 1800-2000 m. Morphologically, it is represented by a slightly inclined plain that borders the base of the continental slope. It is a kind of accumulative tail formed owing to the merging of numerous alluvial fans near the mouths of underwater canyons and to the sedimentation matter supplied from the shelf and continental slope due to the sediment runoff and landslide processes. 

The Crimean region is characterized by alongshore variations in the sediments of the underwater slope. West of the Tarkhankut Peninsula up to Evpatoriya, biogenic coquina deposits dominate they cover the limestone bedrock. On the Crimean shelf, terrigenous sediments are also observed represented by boulders and pebbles in the near-shore zone, sands at depths down to 7-10 m, and fine sands and silty oozes at greater depths. Meanwhile, at depths of about 30 m, there exists a sandy-pebbly bar formed by extreme waves. 

The sediments of the Caucasian region are formed under the influence of the solid runoff of mountain rivers and due to the intensive development of the processes of abrasion and denudation. Waves and coastal currents significantly affect the distribution of the terrigenous-detrital matter over the underwater slope, concentrating largest particles of the matter of boulders, pebbles, and sands close to the coastline and on the beach. Beyond the zone of the wave action, fine-grained sands and silty oozes are accumulated. Often, bedrocks are exposed at abrasive surfaces of the underwater slope at depths down to 60 m. 

The sediments of the underwater coastal slope of the Bulgarian region from the shore to the depth of near 30 m consist of differently-grained sands, silts, and coquina bedrock exposures are abundant. 

Several more hours were necessary to establish the lack of significant man-caused radioactive contamination of seawater and bottom sediments accordingly, the monitoring program was re-oriented toward discovering initial indices of marine environment contamination. Underwater radiation monitoring complex PRM-K with 1-... 

External exposme dming underwater operations close to or immediately on sea bottom. (In such a case one has to do with an additional external exposure somce due to possible roiling of bottom sediments. Concentrations of re-suspended particles vary within a wide range depending on peculiarities of sea bottom structme and bottom sediment generation. One should also keep in mind that when concentrations of suspended particles exceed 10-20 mg/1, visibility could become very low to conduct any diving operations). 

Turbidity currents—Local, rapid-moving currents that result from water heavy with suspended sediment mixing with lighter, clearer water. Causes of turbidity currents are earthquakes or when too much sediment piles up on a steep underwater slope. They can move like avalanches. 

Sediment sampling of the seven stations using the CS equipment was carried out by running transects with the survey vessel parallel to, and as close as possible to, the marker buoys. The CS underwater seafloor sediment sampler was pulled at a speed of three knots and, when abreast of each buoy, the sediment collected was recorded as being from that station. The sediment wafers prepared aboard ship from the collected slurries were immediately analyzed by XRF for three elements (Mn, Fe, and Ti) and were stored for further land-based analyses of other elements. A comparison of the elemental content of the sediments collected from the seven stations by box coring and with the use of the CS equipment constituted the basis for ground-truth evaluation of the CS system. 

Ocean forces create a variety of features on secondary coasts. The constant erosion caused by waves pounding on the shore carves out sea cliffs and caves. Just off the coast, the same wave action sculpts natural arches or flat platforms. In places where the underwater slope of the seafloor is not steep, waves and tides can deposit sediment and build an area of loose particles called a beach. In the United States, about 30 percent of the coastlines have beaches. 

Offshore exploration has risks of sediment or underwater installation disturbance, but the overlying water column serves to minimize any visual impacts of these activities. 

In other parts of the world, a synthetic grass mat has been used to collect current-borne sediments enabling a protective mat of sand to accumulate. In Boa Vista, Cape Verde Islands the natural seabed is composed of water-worn pebbles of volcanic rock. These are easy to handle underwater and a layer of 100 mm pebbles overlain with some well-chosen boulders protects the site from marine and human interference. The insertion of a short tail of orange cord serves as buried marker. It is discrete, moving gently in the current, and to the casual intruder is much like other marine growth and debris. 

Many of the species living around thermal springs are involved in the precipitation of lime to form travertine. Filamentous species of Anabaena, Os-cillatoria and Spirulina are frequently found both floating in water (planktonic) or moving freely over the surface of underwater sediments (epipelic) and high concentrations of filaments appear bluish-green or black. 

Despite decades of research, surprisingly little is known about successful treatment of contaminated sediments. Presently, the most common approach to management of dredged sediment is generally limited to land (or aquatic) disposal. Confined aquatic disposal (CAD) involves underwater contaminated sediments capping with clean sediments or sand, geotextiles, liners, or even reactive barriers, either with or without lateral confinement. Sediments are deposited in natural or artificial depression, usually by means of a clamshell or a hydraulic pipeline. Capping may also shift... 

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