Showing papers on "Dredging published in 1997"

Wear of Rock Cutting Tools: Implications for the Site Investigation of Rock Dredging Projects

Abstract: This text deals with the dredging of rock by large cutter suction dredgers. The rock properties influencing the mechanical cutting of rock and the wear of cutting teeth are examined, and to verify the model of mechanical rock excavation developed, case studies of dredging projects were performed.

Optimal cost - effective sampling for monitoring and dredging of contaminated sediments

Abstract: We used spatial statistics to study variability within contaminated sediments of three zones in Lake Ketelmeer in the Netherlands. Attention focused on the copper (Cu) and benzo(A)pyrene (BAP) content of the contaminated layer, its thickness, and related clay and organic matter (OM) contents. Optimal sampling distances for monitoring aquatic pollutants and the thickness of the contaminated layer in the sediments were estimated taking spatial variability into account. These distances depend on water depth, sedimentation, erosion, shipping activities, and types of sediment. In 40% of the study area, the thickness of the contaminated layer can be surveyed at a grid spacing that is 18 times as wide as that needed in harbors, near shores, and shipping routes to achieve the same accuracy. A new optimizing and cost-effective method for accurate aquatic monitoring is suggested as a preliminary step to the removal of contaminants in the future.

Adjustments toward equilibrium of a large flood-tidal delta after a major dredging program, tauranga harbour, new zealand

Abstract: The Port of Tauranga is located within a tidal inlet estuarine lagoon system which has been dredged to improve navigation for shipping since 1968. In 1992 a major dredging program deepened the entrance navigation channel through the ebb-tidal delta from 10 to 14 m, and the inner harbor channels to -13 m. As a condition of the consent to dredge a detailed monitoring program was required which included annual hydrographic surveys over the flood and ebb-tidal delta as well as recording current meter records from morphodynamically sensitive locations to compare with records taken before the dredging. Results of the hydrographic surveys showed significant morphodynamic change of the flood-tidal delta had occurred essentially by the time the 6 month dredging program was completed. Comparison of the S4 current meter recordings showed current changes consistent with expectations of the EIA. Changes on the ebb-tidal delta were not expected but have occurred although not as rapidly, and seem to be ongoing.

Interaction of the colorado river project, texas, with longshore sediment transport

Abstract: In 1985, a weir jetty system was constructed at the mouth of the, Colorado River, Texas, and river discharge was diverted from this mouth in 1992. An evaluation of project impacts on longshore sediment transport was performed to determine the effectiveness of the project at preserving an open, navigable channel while preventing excessive erosion along adjacent beaches. This evaluation included both physical and numerical analysis of pre- and post-project conditions at the Colorado River mouth. Analysis of site data revealed that under the dredging and mechanical bypassing schedule followed during the first 8 years after jetty construction, the project resulted in significant trapping and sorting of sediment transported alongshore. Numerical modeling of the design maintenance dredging plan confirmed the plan to be sufficient for achieving project objectives. However, the entrance channel has continued to shoal considerably more rapidly than was anticipated during the project design.

Offshore sand sources for beach replenishment: Potential borrows on the continental shelf of the Eastern Gulf of Mexico

Abstract: Erosion of sandy beaches is a worldwide problem that elicits innovative geoengineer‐ing techniques to reduce adverse impacts of shoreline retreat. Beach replenishment has emerged as the “soft”; shore‐stabilization technique of choice for mitigating beach erosion. This method of shore protection involves the addition of sand to the littoral sediment budget for sacrificial purposes. Because inland sand sources are often uneconomical or impractical to use, and known nearshore sources are limited, finding adequate quantities of suitable sand on the inner continental shelf is often vital to beach replenishment projects. The technical studies of survey and materials analysis that identify and delineate usable sand sources are sometimes almost as expensive as small‐project dredging, pumping, and placing the sand on the beach as fill. Inadequate quantity or substandard quality of shelf sand, as well as often‐prohibitive overhead expenses, thus compel shoreline managers to seek suitable sand sources offshore. In t...

Tweed River Sand Bypass: Concepts and Progress

Abstract: The objectives of the Tweed River Entrance Sand Bypassing Project on Australia's east coast are to establish and maintain a navigable entrance to the Tweed River and to enhance and maintain the southern Gold Coast beaches, with the objectives to be achieved in perpetuity. The joint project of the New South Wales and Queensland State Governments with the support of the Gold Coast City Council offers the opportunity to achieve this co-operatively in partnership. Agreements have been established. The environmental impact assessment of the first stage (initial dredging and nourishment) has been completed, and the first component of these works involving over 2.2Mm3 of sand was successfully completed in August 1996. Environmental impact assessment and design studies for the second stage (the permanent bypassing system) are in progress. The paper describes the overall project and its key features, the investigations and analyses undertaken to date, the identified impacts, the initial dredging and nourishment works, and the issues being investigated for the permanent system.

Dredging method and dredging apparatus

Abstract: A dredging method and a dredging apparatus which can efficiently suck large quantities of sand and gravels deposited on the bottom of dams, rivers, harbors, etc., convey them with as much saved energy as possible, and can prevent diffusion of turbid water. To achieve these objects, the apparatus includes a case laid down into the water in communication with the atmosphere. A suction pipe having a suction portion at the lower end thereof is connected to this case. The apparatus further includes a drain pump for draining water in the case and forming a level difference between the water level in the case and the external water level A container is removably disposed at an intermediate portion of the suction pipe. The sand and gravels are sucked from the suction pipe into the container by the siphon principle due to the level difference between the external water level and the water level in the container, and the container is cut off and the sand and gravels are taken out when the container is full.

Dredging and disposal within the limits of a national park

Abstract: In coastal areas under tidal influence, recurrent dredging is an important part of the maintenance work to secure the nautical situation and the functionality of the harbors. In the past, the orientation of dredging activities was purely economic but since the early 80's, environmental concerns have rapidly increased and these concerns often define the limiting or determining factors that cover all parts of such operations in the marine region. At present, the sometimes quite different interests of engineering and ecological groups are becoming more gentle. Besides the natural learning effect from the changes in general, economic conditions are also an important factor. This situation especially applies when maintenance dredging takes place within the limits of a national park where environmental concerns have the highest priority. The scope of the engineering investigations was the estimation of the environmental capacity as a function of hydrology, sedimentation and biology leading to a specific management for dredging and disposal areas.

Dredging and Management of Dredged Material

Abstract: This proceedings, Dredging and Management of Dredged Material, consists of papers presented at GeoLogan '97 Conference held in Logan, Utah, July 18, 1997. With dredging of ports and management of dredged material becoming a national issue, geotechnical engineers are increasingly involved with these matters. This publication discusses the latest environmentally sensitive dredging techniques, decontamination and reuse techniques for dredged sediments, and regulations on the dredging and management of dredge residues.

The Punaise: A Remotely Operated Submerged Dredging System

Abstract: The Punaise (Dutch for “thumbtack”) is a remotely operated, water-tight, submerged dredge pump system that can dredge sediments from the seafloor without impact to navigation or being affected by storms. The first Punaise was originally designed for silt removal and used in 1991 in The Netherlands. Since then, a second system has been constructed to remove sand for beach nourishment activities. PinPoint Dredging Company, a partnership of J.G. Nelis B.V., Ballast Nedam Dredging B.V. and Boskalis International B.V., operates the Punaise system and has most recently used it at beach nourishment project on the Dutch coast during the autumn of 1996. Though the Punaise has not yet operated in the U.S., PinPoint Dredging Company and the State of New York planned to demonstrate the Punaise technology for inlet bypassing, but a combination of procedural delays and limited geotechnical/geological information prevented implementation within the available environmental time frame. This paper was written with the intention of presenting a new dredging technology to the US and is funded by the USAE Waterways Experiment Station’s Dredging Operations and Environmental Research (DOER) Program. The Innovative Technologies Focus Area within DOER is tasked with identifying new and innovative dredging technologies for potential demonstration and monitoring to help USAE Districts conduct dredging more efficiently. This paper is not intended to be an endorsement for any particular technology or dredging company but merely to identify a technology with potential application in the US. Permission was granted by the Chief of Engineers to publish this paper. The paper was presented at the WEDA XVIII Conference in Charleston, South Carolina, June-July 1997, and was first published in the Proceedings of the conference. It received the “Most Outstanding Paper”award from the Dredging Contractors of America. The paper is reprinted here in a slightly revised form with permission. Terra et Aqua – Number 69 – December 1997 20 Gregory Williams is a Research Hydraulic Engineer in the Coastal and Hydraulics Laboratory at the US Army Engineer Waterways Experiment Station (WES) in Vicksburg, Mississippi. He has worked in the Dredging Research Program, Wetlands Research Program and the current Dredging Operations and Environmental Research Program. He received a BSc in Civil Engineering from North Carolina State University, an ME in Coastal Engineering from Old Dominion University, and is currently pursuing a PhD in Ocean Engineering at Texas A&M University. Kris Visser has a BSc in Civil Engineering and has worked for over 25 years with various Dutch dredging companies. From 1989 on, he has been General Manager of J.G. Nelis responsible for the development of the Punaise. In 1995, when the PinPoint Dredging Company was formed by Boskalis, Ballast Nedam Dredging and J.G. Nelis, he became the coordinator of all activities related to this dredge. Gregory L. Williams

Dredging and disposing device

Abstract: PROBLEM TO BE SOLVED: To provide a dredging and disposing device by which precipitated mud on the water bottom of port, river, marsh, lake, etc., can be efficiently dredged and disposed in a dense condition with less water as far as possible. SOLUTION: A dredging and disposing device dredging mud precipitated on the water bottom and disposing it, is constituted of a dredger 40 installed on a dredging boat, a lifting and rotating device for the dredger 40 deg., and a pneumatic conveyor for the dredged material. The dredger 40 is constituted of a bucket 41 provided with a mud intake, a plurality of bar screens 45 arranged at the mud intake to prevent foreign materials, an excavating rotor 50 provided with a plurality of excavating blades arranged at the mud intake and a rotary driving means, a screw conveyor 46 scraping the mud collected in the bucket 41, and the rotary driving means for the screw conveyor. And the disposing device is provided with a delivery pipe connected to the mud delivery opening, a booster pump installed in the delivery pipes, a valve, and an ejector for compressed air.

The use of shear wave transmission as a non-destructive tool to assess soft soil stiffness in dredging applications

Abstract: Interest in the behaviour of naturally consolidated soils stems from the relevance of these materials to the dredging industry, and the environmental impact of dredging and the dumping of pollutants at sea above soft cohesive sediment beds. Since these soils are compositionally and behaviourally complex, there is a need to characterize their properties in a non-destructive manner. This paper presents the seismo-acoustic behaviour of a number of these soft soils as studied in the laboratory. It is shown that the changing behaviour of the sediment, as it consolidates, and as the soil structure develops, has a considerable influence on its stiffness characteristics. Shear modulus is determined using shear wave velocity and bulk density measurements which were found to range between zero and 160 kPa during the course of the experiments. Estimation of soil shear stiffness in this manner would be a parameter of interest to the dredging industry in defining navigable depth. In terms of environmental matters, such estimates of marine soil shear stiffness may be of use in quantifying the erodibility of the sea bed; this is of particular significance where sediments are contaminated by pollutants.

Development of a Portable Innovative Contaminated Sediment Dredge

Abstract: : The Cooperative Research and Development Agreement (CRDA) document was signed to undertake development of a portable innovative contaminated sediment dredge. Three major problems are associated with dredging of contaminated sediments: (1) The contaminated sediment are mostly fine and highly compacted, and specialized devices are needed for cutting and loosening them before transporting, (2) the dredged fine sediments are vertically resuspended and dispersed easily within the entire water column and adversely affect the aquatic plants and water quality, and (3) the sediments have a very low rate of deposition, and they may be transported over great distances from the point of origin even under a very weak current. Laboratory tests were conducted at WES in which different mixtures of clays, sand and water were pumped through a pipe, and pressure in the pipe was measured. The effectiveness of a positive displacement pump for pumping sediments with a very low water content was established, and the extent of the addition of clays and water for improving the relative ease of pumping was determined. The dredge was then used in a field trial for removing bottom sediments from a lake at WES. The new dredge removes sediments at near in situ water content with the use of a clamshell bucket. The sediments are placed in a hopper and are pumped by a positive displacement pump to the required disposal site.

The effect of dredging on light penetration in the Boro River, Okavango Delta, Botswana, from 1972 to 1975

Abstract: This paper presents data on the effects of dredging on light penetration along the lower 4.5 km of the Boro and Thamalakane Rivers, between 1972 and 1975. The short-term effects of dredging were a decrease in light penetration by 25 to 50% for a river distance of 12 km. This effect was evident up to 18 months after the dredging had ceased. This could be ascribed to wash-in of silt and clay colloids from unvegetated spoil heaps.

Dredged Material Isolation on the Abyssal Seafloor: A Feasibility Study

Abstract: : This report is the result of an examination of the feasibility of isolating contaminated dredged material on the abyssal seafloor. The focus is on the technical and environmental factors that constrain the considerations of feasibility. The sources of the materials are assumed to be in U.S. coastal waters. A thorough conceptual design of a dredging to abyssal deposition system is analyzed with regard to each subsystem and to the entire operational concept. These subsystems include: (1) a low leakage dredge, (2) equipment for material handling and loading into geosynthetic fabric containers (GFCs), (3) the barge for transport and navigation, and (4) the subsystem for releasing the GFCs to sink to the abyssal seafloor isolation site. Particular consideration is given to the exclusion of dredged material from the ocean's productive zone in the upper 1000 m; this exclusion requires highly stable, reliable navigation and seakeeping by the barge transporter and control of the configuration of GFCs within it. New theoretical models and previous empirical results are used to predict GFC motion through the water column and response to impact on the abyssal seafloor, including the case of potential release of contaminated, turbid water at impact. A geochemical model of the temporal and spatial evolution of the post-deposition geochemistry of the water column, the GFC contents and the sediments below is developed and analyzed; the results show that release of metals into the ocean waters would be insignificant. A model of the biological impacts of the introduction of dredged material in the abyssal environment is used to infer that: (1) biological diversity in the vicinity of the deposition site will be diminished, (2) biomass will be increased by dominance of a few fast growing, opportunistic benthic species, and (3) concentrations of trace elements and organic contaminant

Dredging of main pier foundations for the Northumberland Strait bridge project

Abstract: The Northumberland Strait Bridge recently named the Confederation Bridge, is 12.9 km in length and crosses the Northumberland Strait between Prince Edward Island and New Brunswick. The 44 main bridge pier foundations are supported on circular and oval-shaped ring footings set on prepared bedrock foundations. Foundation preparation involved the removal by dredging of up to 15 m of overburden and weak rock in water depths of 14-40 m. A trial dredging program was carried out at three main piers to determine which bedrock materials could be dredged and to develop criteria for use in establishing dredging elevations at the remaining main pier locations. Results of the trial-dredging program were used to develop and compare methods of predicting the dredgeability of bedrock using the intact rock strength and rock mass properties. The trial dredging program was also used to develop procedures to verify that the dredged surface met both geotechnical and cleanup criteria. (A)

Modelling of the Morphodynamics of a Sill in the Scheldt Estuary (The Netherlands)

Abstract: Dredging activities over the years have strongly affected the morphology of the Scheldt Estuary (The Netherlands) with the result that important ecological habitats have reduced in size. A new dredging program, necessary for further deepening of the shipping channel, is initiated. Authorities are in search of alternative ways of dredging and dumping to minimise their negative side effects. As these dredging activities mainly take place on the sills (shallow parts of the shipping channel), a research program to study the behaviour of sills is initiated. Besides an extensive measurement campaign, a numerical model (DELFT2D-MOR) is used to study the hydro- and morphodynamics around a specific sill. Preliminary modelling results show good similarities with results from the measurement campaign.

Dredging control device of cargo oil tank

Abstract: PROBLEM TO BE SOLVED: To provide a dredging control device of a cargo oil tank in which the dredging work is automatic and efficient, and a sensor is of simple constitution. SOLUTION: A dredging control device is provided with a main bell mouth 2 connected to a suction tube 3 having a main valve 4, a sub bell mouth 5 connected to a suction pipe 6 which is installed in a recess 9 of a cargo oil tank 1 and has a dredging valve 7, an upper dredging starting point sensor B to detect the cargo oil level which is the dredging preparation starting point, a lower dredging starting sensor A which is installed lower than the sensor B and detects the cargo oil level which is the dredging starting point, and a control part which receives the signal from the sensor A, B and transmits the signal to control the operation of a pump 8 connected to opening/closing and suction pipes 3, 6 of the main valve 4 and the dredging valve 7. The control part gradually closes the main valve 4, and opens the valve 7 through the detection of the cargo oil level by the upper dredging starting point sensor B, and starts the pump through the detection of the cargo oil level by the lower dredging starting point sensor A, sucks the dredged oil by the sub bell mouth 5, and the dredging and suction operation is intermittently repeated several times.