Showing papers on "Dredging published in 1972"

Environmental aspects of dredging in estuaries

Abstract: Salt marsh estuarine environments along the Intracoastal Waterway of the southeastern Atlantic coast were studied to determine the environmental effects of dredging in these areas. The study dealt with the chemical response of salt marsh seidments to the deposition of dredge materials and with the water quality response to dredging and deposition of sediments in a salt marsh estuarine environment. After the initial destruction of the salt marsh plants due to spoil deposition, the rate of reequilibration of the marsh sediments to their original state (suitable for revegetation) is greatly dependent on the depth of the dredge spoil deposit. In natural and relatively unpolluted areas, dredging has no significant effects on water quality when either diked or undiked confinement techniques are used. In polluted areas in marine environments, water quality impairment caused by dredging activites do not necessarily bear any simple relation to the composition of the sediemtns to be dredged.

Predicting changes in the plan shape of beaches

Abstract: A mathematical model is described that is capable of predicting changes in the plan shape of a beach following the construction of sea defences or an alteration in the wave climate. The rate of change is calculated. The technique is illustrated by comparing model predictions with results from experiments carried out in a wave basin. The importance of the method in estimating coastal changes due to offshore dredging is mentioned, and the future development of the mathematical approach is outlined.

Arctic dredging and pipelaying

Abstract: Apparatus for arctic dredging and marine pipelaying during icefree and iced conditions is described. For dredging, a dredging facility is carried on a buoyant platform which is adapted for support on a cushion of air. The dredging facility includes a dredging head which is operable, when engaged with the bed of a body of water to be dredged, for removing material from the bed. A dredgings conductor tube is connectible between the dredging head and the platform for conducting dredged material from the head to the platform. The dredging equipment also includes means carried by the platform for forming a channel through a layer of ice below the platform for passage of the conductor tube through the ice when the dredging apparatus is operated during iced conditions. The pipelaying equipment includes a pipelaying facility carried by a buoyant platform, which is adapted for support on a cushion of air. The pipelaying equipment includes means carried by the platform operable for forming through an ice layer below the platform a channel through which pipe may be laid from the platform to the bed of the body of water across which the pipeline is to be laid. The portion of the pipeline which extends between the platform and the bed of the body of water is supported along at least a portion of its length adjacent the pipelaying platform. This support of the pipeline may be provided by a stinger assembly coupled to the platform with its upper end disposed within the area of air cushion support of the platform. The dredging apparatus and the pipelaying apparatus may be provided on a common buoyant platform adapted for support on a cushion of air. In such case, the dredging facility is located on the platform forward of the pipelaying facility so that, during pipelaying operations through ice, pipe is laid through the channel formed in the ice for the dredgings conductor tube.

Mesozoic rocks from the Labrador sea

Abstract: THE existence of Mesozoic rocks on the continental shelf of Greenland has been postulated by several authors1–4. During the summer of 1971 the US Naval Oceanographic Office conducted a reconnaissance survey in the southern Labrador Sea, which also included rock dredging on the south-western margin of the Greenland continental block. As well as containing deep glacially cut Canyons, the continental slope of south-west Greenland is swept by swift bottom currents and therefore has not prograded as extensively as most continental slopes throughout the world. It is therefore a better than usual structure for dredging operations. The results of any rock dredging operation in northern waters are, of course, immediately open to suspicion of ice-rafted contamination. McMillan5 summarizes the problem and concludes that most glacial erratics are derived locally. Indeed, we did collect a fine suite of glacial erratics. The data presented in Table 1 are, however, believed to represent in situ samples and their homogeneity lends support to this. In dredge 43 (Fig. 1), for example, the entire dredge haul (˜100 pounds) consisted of sandy limestone.

Research to Determine the Environmental Response to the Deposition of Spoil on Salt Marshes Using Diked and Undiked Techniques.

Abstract: : The research helps to determine the environmental response to the deposition to spoil on salt marshes using diked and undiked techniques. It considers the effects on water quality, motile and benthic biological communities and the marsh grass habitat. The emphasis of these studies has been on the identification of the processes responsible for observed effects and the assessment of ways of minimizing there. The ultimate goals in these studies has been to develop an approach to predicting environmental responses due to dredging activities. All of the studies described in this report were carried out in the salt marsh estuarine environment of the Southeastern Atlantic Coast. In every case studied, hydraulic pipeline dredging was the technique used. The disposal of the dredge material was carried out in confined or unconfined salt marsh areas.

Cyclic Sedimentation in Agua Hedionda Lagoon, Sourthern California

Abstract: Agua Hedionda Lagoon is near Carlsbad, CA, and is near the middle of the Oceanside littoral sedimentation cell. Since its initial dredging in 1954, the lagoon has become a coastal sediment trap that must be dredged almost yearly. The purpose herein is to show the rate of sediment deposition in the lagoon from 1955 to 1961.

Coastal sand management system

Abstract: Interruption of sand transport is the most persistent worldwide coastal problem. Wave action produces sand transport which is not a problem in some areas but in others results in coastal erosion, obstruction of harbor entrances, and permanent loss of sand. Conflict between saving sand and bypassing it is caused by a lack of methods to manage this valuable resource. Separate elements of control have been used with varying degrees of success; now it is proposed to incorporate subsystems into an integrated system for management of the littoral transport. A coastal sand management system is to be evaluated using three principal subsystems: (1) a mobile jet pump for use with a crater sink and fluidization accessories; (2) interlocking inertial modules which simulate structural materials because of high intergrain stresses; and, (3) the tactical deployment of phase dependent roughness elements to direct (or reverse) the net transport of sand. A coherent sand management system promises to make a start toward true control of littoral sand transport. In addition, there is the prospect of eventually establishing the first self maintaining harbors. It is attractive to consider systems which would be operative within reasonable cost, which may be entirely submerged, and which are capable of operating without regard to surface seakeeping problems. Some aspects of the system indicate possible use of the mobile jet pump as a means for estimating longshore transport in the field, use in archaeology, and as a dredging and maintenance tool for small nations whose investment capital could not support massive dredging operations.

Hydrodynamic analysis of sludge dumped in coastal waters

Abstract: Due to increased environmental pressures, there is a rapidly growing tendency to shift from traditional land disposal of dredged material to offshore or ocean disposal. The quantities of such materials are quite large, resulting in a very serious disposal problem. For example, maintenance dredging alone produces approximately six million cubic yards of material annually in Charleston Harbor. Existing techniques are reasonably adequate to describe the transport and settling characteristics of coarse, sandy dredge materials discharged from barges or hopper dredges at sea. However, such approaches need to be modified to describe the transport of fine-grained clay and silt materials. This material constitutes a significant portion of the dredged material resulting from both new harbor and channel construction and maintenance dredging along the coast of the Carolinas and Georgia. These fine-grained materials are subject to many additional physical forces as well as chemical phenomena, e.g., flocculation, salinity and temperature variations, etc. A hydrodynamic model for fine-grained dredged material has been developed which considers many of these forces. It is also applicable for describing the transport mechanisms associated with barge disposal of wastewater sludges from municipal and industrial sources. The results of the model indicate what discharge strategies are necessary for placing the sludge at a desired location or depth with a predetermined concentration.

Ocean mining operations

Abstract: The ever increasing size of bulk carriers of deeper draft requires dredging at ever increasing depths and distances from the coast. This article compares various methods of dredging, especially bucket dredging and suction dredging. In deep areas suction dredging is usually the preferred method. It is shown how a centrifugal pump system has about twice the economy of a venturi system. The article then discusses the application of dredging plants to offshore mining, considering the area to be mined and the type of mineral to be removed. An overlaying horizontal layer of granular material, it is concluded, can best be removed using a trailing hopper dredger. To penetrate the bottom to greater depths suction dredgers provide the best method. A cuttersuction unit is best for gradual excavation over a certain height and width.

San francisco bar dredge material disposal

Abstract: Studies were conducted on San Francisco Bar in June 1971 and February 1972 to monitor dredge material disposal. The purpose of the study was to determine the effects of dredging and material disposal on the physical and biological environment and to develop dredging procedures and disposal sites to mitigate possible adverse effects.. This paper presents the results of the material dispersion portion of the study including bottom deposition, current measurements and aerial photography. The biological studies and water quality monitoring are not presented.

Hydraulic and Sediment Transport Studies in Relation to River Sediment Control and Solid Waste Pollution and Economic Use of the By-Products

Abstract: The distribution of sediments and conditions of transport were studied in the Kentucky, Big Sandy and Ohio Rivers. The sand and coal were in transport at different flow velocities for the rivers and the deposition of these sediments was a direct function of the flow conditions at a particular locality. The flow conditions of transport of the sediments were studied in flumes as were the hydraulic conditions in model dredge holes to determine the feasibility of trapping sediment. The conditions of scour and fill were also established and compared with known conditions in a dredge hole in the Ohio River. Flow records from gaging stations were analyzed to determine the periods of sediment transport. The results indicate that solid waste pollutants can be trapped in dredge holes in certain conditions of flow. The principal source of the coal appears to be natural erosion.