Showing papers on "Dredging published in 1999"

Ecological effects of dumping of dredged sediments; options for management

Abstract: Dredging and dumping of dredged sediments in estuarine and coastal waters may lead to increased turbidity and enhanced sediment deposition at dump sites This mainly affects primary production by phytoplankton, performance of visual predators (eg fish, birds), and growth and survival of benthic organisms This paper combines a compilation of literature information and results of additional experimental studies on the effect of enhanced concentrations of suspended matter (SPM) on growth of bivalve molluscs, and on survival of macro- and meiozoobenthos after dumping of dredged sediments Furthermore, it focuses on non-toxic dredged sediments only Release of nutrients from dredged sediments did, so far, hardly influence estuarine phytoplankton production Increased turbidity may affect dab as well as prey location by sandwich terns Enhanced SPM-concentrations are unfavourable for young herring and smelt Growth of filter-feeding bivalves may be impaired, especially at SPM-concentrations >250 mg/l Estuarine nematodes can survive burial by 10 cm of dumped dredged sediment provided that its physical characteristics are similar to those of the original sediment Sessile benthos organisms such as mussels and oysters can cope with sediment deposition of only 1–2 cm Other macrozoobenthos can survive sediment deposition of 20–30 cm Recovery of benthos at a dump site will occur if the interval between successive dumpings is sufficiently long Options for management of dumping of dredged sediments are described, relating to different locations of dump sites in estuarine and coastal waters, to different seasons, and to the actual use (area and frequency) of dump sites

Analysis of the relationship between sediment composition and benthic community structure in coastal deposits: Implications for marine aggregate dredging

Abstract: Seiderer, L. J. and Newell, R. C. 1999. Analysis of the relationship between sediment composition and benthic community structure in coastal deposits: Implications for marine aggregate dredging. – ICES Journal of Marine Science, 56: 757–765. The relationship between biological community structure and particle size composition is investigated in coastal deposits off the southeast of England. Sediments in the survey area fall into well-defined groups when analysed by multivariate techniques, indicating similarities and differences which could not be identified by mere inspection of the data. Biological resources also fall into relatively distinct groups, or communities, when analysed for species composition and population density, although similarity within the groups is lower than that obtained for the sediments. There is, however, little evidence of a close correspondence between the distribution of different sediment types and benthic communities in the survey area: comparison of the similarity matrices yields weighted Spearman rank correlation of less than 0.37. This suggests that factors other than sediment composition play a significant part in controlling biological community structure on the seabed. Still, there is evidence that some species such as the tube-dwelling worm Sabellaria spinulosa are associated mainly with sands and gravels whilst fine mobile silts and sands are characterized by ‘‘opportunistic’’ species such as the tube-worm Lagis koreni. The results suggest that although modification of sediment composition from mixed sands and gravels to silts would be expected to result in colonization by ‘‘opportunistic’’ species capable of survival in mobile deposits, restoration of sediment composition after cessation of dredging for marine aggregates is not, within broad limits, a prerequisite for establishment of biological communities which are comparable with those that occurred in the deposits prior to dredging. 1999 International Council for the Exploration of the Sea

Changes in Irish Sea Benthos: Possible Effects of 40 years of Dredging

Abstract: From 1946 to 1951 Dr N. S. Jones sampled the benthos around the south of the Isle of Man from over 200 sites. Multivariate methods have been used here to compare subsets of this historical data with recent data from the same locations: of these locations some have been subject to heavy scallop dredging over the intervening 40 plus years and some to little dredging. Clear changes were apparent regardless of scallop dredging intensity. Some of the changes in the heavily dredged areas were those expected to result from extreme physical disturbance—an increased polychaete mollusc ratio, loss of some fragile species, and an increase in the predominance of scavenger/predator species. However, changes in the lightly dredged areas also included the loss of a number of species including some potentially fragile tube-dwellers. Reasons for these changes were not apparent.

Impacts and efficiency of scallop dredging on different soft substrates

Abstract: Impacts of scallop dredges and their efficiency were examined experimentally in three areas with different soft substrates in Port Phillip Bay, southeastern Australia. Physical and biological chang...

Coastal and marine wetlands in Gulf St. Vincent, South Australia: understanding their loss and degradation

Abstract: Despite the vastness of South Australia's coastline, approximately 95% of the state's population of 1.4 million is on the Adelaide metropolitan coast of Gulf St. Vincent. The concentration of human activity around this shallow, sheltered gulf ecosystem has led to conflict and competition over the use of marine and coastal resources. The gulf supports extensive areas of ecologically significant subtidal and tidal coastal wetlands, comprising seagrass meadows, mangroves and saltmarshes, with nine wetlands having recognized national importance. The wetlands support economic activities such as commercial and recreational fishing, tourism and aquaculture, and to a lesser extent, mineral and petroleum exploration and shipping. These environments and activities are threatened by the effects of land-based urbanization, coastal development, stormwater runoff effluent and industrial discharges, and the resultant decline in water quality and food-chain contamination. Marine activities can also have adverse effects (i.e., dredging, sea-dumping, overfishing, fishing methods, oil spills, antifoulants, ballast water introductions), including the developing aquaculture industry. The continued loss and degradation of marine and coastal wetlands in the gulf is exacerbated by inadequate protection measures, lack of integrated management structures and policies, and conflict between competing user groups. Strong policies and integrated decision making based on sound information is required for the equitable and sustainable use of these wetlands. Gulf-level management of multiple-uses would limit the cumulative impacts of human use and coastal development. There is a particular need to protect areas with high conservation value and for future research and marine conservation to focus on the coastal nearshore ecosystem. High priorities are coastal and biodiversity inventories, understanding of ecological processes, linkages between coastal and offshore habitats, and coastal spatial mapping and information systems.

Ashtabula River, Ohio, Sedimentation Study, Report 4, Numerical Model

Abstract: : The Ashtabula River flows north into Lake Erie at the city of Ashtabula in northeast Ohio. The Federal navigation project in the lower Ashtabula River contains a breakwater protected harbor in Lake Erie and a navigable waterway extending about 3.2 km upstream to a point approximately 300 m downstream of the 24th Street Bridge. Sediments in the harbor and lower 600 m of the waterway are classified as suitable for open-lake disposal, whereas sediments upstream are classified as unsuitable for open-lake disposal. In the harbor and lower 600 m of the waterway, dredging operations are conducted as required to permit commercial navigation. Dredging operations in the remainder of the waterway were suspended in the 1970s, closing the channel to commercial navigation, in response to the increased cost of safe removal and disposal of sediments contaminated with heavy metals, chlorinated hydrocarbons, and polynuclear aromatic hydrocarbons. The waterway is heavily used for recreational navigation. Limited dredging operations were conducted in the reach upstream of the 5th Street Bridge in 1993 to maintain safe navigation conditions for recreational traffic. Numerical hydraulic and sedimentation models of the lower Ashtabula River were developed using the TABS-MD modeling system. The objective of the model study described herein was to estimate the potential magnitude and spatial distribution of scour that may occur during an extreme event, such as the 100-year return period flood, potentially causing exposure and dispersal of contaminants buried in the channel bed sediments. Other reports in this series describe field data collections and laboratory erosion experiments conducted in support of the model investigation. The model study revealed that a 100-year return period flood event coincident with Lake Erie stage held at the low-water datum has the potential to scour 80,000 cu m of bed sediments from the lower Ashtabula River producing scour depths generally less than 1 m.c

Remediation of contaminated sediments in oslo harbour, norway

Abstract: During the past 60-70 years, contaminated sediments from local rivers have been settling in the harbour basin of Oslo. This contamination, combined with that from other harbour activities, has developed into a serious pollution problem with both organic and inorganic contaminants. Since 1992 dredging activities have been restricted until the effect of dredging was determined and a safe disposal was found for the sediments. Because of this restriction, a conflict situation arose in terms of decreasing sailing depths, and dispersal of large quantities of contaminated sediments into the water column each day from ship traffic. A complete plan of action to remediate Oslo Harbour was started in 1994 and delivered to the State Pollution Control Authority (SFT) in August 1996. An evaluation of environmental risks connected to the remediation work has been carried out along with the determination of the requirements for the monitoring programme during and after the work. Preliminary evaluation of dredging techniques indicates that mechanic/hydraulic equipment will cause the least dispersion of sediment. Several options for treatment of the sediments have been evaluated. Study results point out that conditioning prior to disposal of the sediments in a confined disposal site in the harbour area, is the most cost effective solution. Seven disposal sites with a capacity of 0.5 mill. m 3 have been identified. Two of the sites are integrated with a subsea road tunnel crossing the harbour basin. The other disposal sites will serve as new dock area after closure.

In situ capping of contaminated sedi- ments: comparing the relative ef- fectiveness of sand versus clay min- eral-based sediment caps

Abstract: Ecological problems caused by sediment contamination occurring in deep water or wetland environments may be addressed through natural recovery, in-place containment or treatment, dredging and removal, or in some cases by in situ capping – which is defined as the placement of a subaqueous covering or cap of clean isolating material over an in-place deposit of contaminated sediment. While dredging and removal of contaminated sediments may be the most practical remedial method in many situations and sometimes necessary for navigational purposes, this remedial approach may not be the most environmentally protective and/or costeffective approach. In situ capping approaches are often considered to be more protective of faunal and floral communities inhabiting impacted ecosystems than dredging alternatives, or when converting an impacted area to a closed cell. According to current regulatory philosophy and recommendations, the three primary functions of an in situ sediment cap include (1) physical isolation of the contaminated sediment from the benthic environment; (2) stabilization of contaminated sediments, preventing re-suspension and transport to other areas or sites; and (3) reduction of the flux (transport) of dissolved contaminants into the overlying water column. To date, most in situ capping projects appear to involve the use of primarily granular (i.e., sandy) capping materials. Although such capping materials may adequately serve to meet stated cap functions at many sites, their relatively high permeability and low organic matter and clay content may limit their ability to reduce contaminant transport into the overlying water column. Furthermore, non-cohesive, granular materials can also be prone to erosional losses and redistribution, thus minimizing their effectiveness in isolating and stabilizing contaminated sediments. Finally, the thickness required to meet performance goals, many times on the order of several feet, can have a deleterious effect on channel hydraulics and waterway uses. As an alternative to granular sediment caps, a new in situ capping technology, AquaBlok™, has been developed for use in either deep water or wetland ecosystems. AquaBlok™ is a clay mineral-based capping material that offers several functional advantages over granular capping materials including lower permeability, higher resistance to erosive forces, and considerably higher attenuation capacity for many types of contaminants. The likely need for thinner AquaBlok™ caps at many sites would also minimize navigational constraints. In this paper, we compare the potential relative effectiveness of a typical granular sediment cap to that of a typical AquaBlok™ sediment cap, as each would be installed into “typical” impacted deep water or wetland ecosystems.

Shoal-reduction strategies for entrance channels

Abstract: : Purpose: This Coast Engineering Technical Note (CETN) presents several methods for reducting sediment in navigation channels at coastal inlets and entrances. Background: From fiscal year (FY) 1995 through 1998, the US Army Corps of Engineers (USACE) dredged between 200 and 300 million m3/yr from Federal channels. Maintenance dredging accounted for an average of 89 percent of this volume, and new work and emergency dredging comprised the remainder. Total dredging expenditures increased from approximately $532 to $713 million in FY 1995 through FY 1998, with maintenance dredging accounting for 78 percent of the cost (see U.S. Army Corps of Engineers Navigation Data Center Long-Term Dredging web site at http://www.wrsc.usace.army.mil/ndc/ddhisbth.htm). A reduction in maintenance dredging can represent a significant cost and timesaving measure to the operation and maintenance of USACE waterways. The focus of this CETN is how sediment shoals into open-coast channels. The primary sediment-transport pathways can be referenced to the jetties stabilizing the inlet entrance. Sediment can move around the tip of a jetty, entering directly into the channel; around the tip of the jetty, on to the ebb shoal and into the portion of the channel that transverses the ebb shoal, through a jetty, over a jetty, and around the landward side (see green arrows in Figure 1). Pope (1997) gives a classification system of channel shoaling based on general considerations of geomorphology.

Bypassing of Dredged Littoral Muddy Sediments Using a Thin Layer Dispersal Technique

Abstract: Maintenance dredging of the navigation approach channel to Pine Harbour Marina is necessary to remove muddy sediment which accumulates as a result of depositional processes due to flocculation and the littoral "turbid fringe". Based upon analysis of the muddy sedimentation processes in the adjacent embayment a "thin layer" dredgings disposal method was instigated. This novel technique required a detailed monitoring program based upon a wide range of field measurements including turbidity and suspended sediment loads, detailed hydrographic surveys of the dredging disposal ground, high resolution side-scan sonar survey, SCUBA observations of sedimentation rods, and regular helicopter flights to obtain oblique air photo records. The results consistently demonstrated that thin layer disposal was achieved, and no mound of muddy deposits accumulated. Application of a 1-D numerical model of mud resuspension under storm waves realized suspended sediment concentrations similar to those measured in waters discharging from the adjacent catchment, and indicated that the erodibility of the bottom sediment in the disposal area was unlikely to change as a result of the disposal. It is thus most unlikely that muddy material would migrate from the disposal grounds to the adjacent beaches.

Remote-controlled submersible dredging vehicle

Abstract: The utility model relates to a remote-controlled submersible dredging vehicle-a mechanism device which is used for dredging the silt of rivers, or ditches or other water systems. The mechanism device is composed of a chassis, a power mechanism, an operating mechanism, a running mechanism, a control system and an auxiliary mechanism; the power mechanism, the operating mechanism, the running mechanism, the control system and the auxiliary mechanism are installed on the chassis. The remote-controlled submersible dredging vehicle walks by making use of crawler belts; the remote-controlled submersible dredging vehicle is provided with a lightening floating canister; a screw agitating and sucking device is fixed on a supporting frame. The sludge which is agitated up is conveyed to the inlet of a mud pump by a rotating screw reamer, and conveyed to a bank through a mud pump pipe. When the utility model dives to the bottom of a river to work, the action of walking, turning, mud mix, mud sucking, mud spouting, etc. of the remote-controlled submersible dredging vehicle can be remotely controlled. The utility model has the advantages of flexible operation, high dredging efficiency, etc.

Evaluation of an Inner Shelf Site Off Tauranga Harbour, New Zealand, for Disposal of Muddy-Sandy Dredged Sediments

Abstract: A planned extension of the Port of Tauranga requires capital dredging of material containing significant amounts of silt and clay. The existing disposal ground located about 4 km offshore in water depths of 15 to 25 m, is unsuitable as it was designed for slow migration of predominantly sandy materials onshore to nourish the adjacent beaches. Investigation for a new disposal site involved consideration of alternatives, but the "best practical option" selected was offshore of the existing ground in water depths of 28-33 m. Site research included side scan sonar imagery of the sea floor, sediment sampling by SCUBA diving, and deployment of a current meter for several weeks during the spring season to obtain background hydrodynamic data. Analysis of the data indicated that motion of medium to coarse sands occurs during periods of high swell conditions. Calculations of potential transport of discrete mud "clasts" suggest that small units (≤2 cm) may move under large waves (T s = 11 s, H s = 1.6 m), but larger mud "clasts" would be stable. It is expected that the existing high disposal mound immediately shoreward of the proposed new disposal ground would hinder onshore migration of muddy clasts.

Estimating Dredging Sediment Resuspension Sources.

Abstract: : The purpose of this technical note is to herein presents an approach for estimating the suspended-sediment source from cutterhead, hopper, and clamshell dredges. The approach involves modification of an existing method developed from limited field data. These estimates are needed to provide input to a numerical model called SSFATE (Suspended Sediment FATE) that is being developed under the Dredging Operations and Environmental Research (DOER) Program.

Minimizing dredging disposal via sediment management in New York Harbor

Abstract: The Port of New York/New Jersey is naturally shallow, and therefore dredging is required to maintain depths necessary for navigation. About six million cubic yards of material must be dredged annually to maintain navigation channels and berthing areas. Opportunities for disposal of dredged materials in the metropolitan region are limited. The existing ocean disposal site that has, until recently, received the majority of dredged materials is nearing capacity. Under the new, more stringent, guidance for ocean disposal, a large percentage of the dredged material is not considered acceptable for ocean disposal because of contamination. This paper explores nondredging alternatives to reduce the volume of materials to be dredged, thus reducing the disposal volume. These alternatives include short-term options (e.g., reprofiling operations, in which sediments from high spots in berths are dragged to depressions in lower spots) and long-term sedimentation minimization options (e.g., subsurface berms or air bubblers deployed around berths and interpier areas). These methods require an understanding of sedimentation/circulation patterns of the harbor as a whole and the local area in which the specific methodology may be employed.

Defining an unusual littoral regime to optimize dredging at east london

Abstract: Maintenance dredging at the Port of East London is a major annual expense. The aims of this investigation were to obtain relevant information on the sedimentary processes and to apply this information to reduce or optimize various facets of the required maintenance dredging. Information gleaned on various components of the sediment transport regime led to a holistic understanding of the sediment budget for the littoral sub cell at the port. The sedimentary regime is very interesting with a complex pattern of sediment movement around the harbour. In turn, this information could be applied practically in terms of: more efficient sandtraps, a new dump-site closer to the port, a spur which successfully protected the dolos armour units, and proposed extensions to the breakwater which potentially could significantly reduce maintenance dredging. Most of these applications have already led to significant savings on maintenance dredging costs for the port .

Use of the Sediment Quality Triad to Assess Metal Contamination in Freshwater Superficial Sediments from the Le An River, China

Abstract: By integrating data on the chemistry, toxicity and benthic community structure, the sediment quality triad was used to evaluate the current situation of superficial sediments from the Le An River. This river has been strongly polluted with large amounts of copper, lead and zinc in waste water discharging from riparian mining and smelting activities. The response of the benthic environment was illustrated by ratio-to-reference (RTR) scale in corresponding triaxial graph. From upstream to downstream, the response intensity of three components showed sectional characteristics. The upstream area was relatively clean due to less disturbance. Within the middle stream area, extreme toxicity and serious deterioration of the benthic community structure could be mainly ascribed to strong acidity in drainage and high concentrations of multiple metals in superficial sediments, especially copper. Because of the river self-purification capability, pollution gradually declined and the sediment quality began to recover downstream. The situation was closely associated to the distribution of major pollution sources, therefore, source control and dredging operation on contaminated sediments in the middle stream area are required urgently.

Cartographic ally controlled water channel dredging method detects position of dredger during dredging operation for updating vector map of dredged water channel

Abstract: The dredging method uses a floating dredger, with the water scanned to provide a depth profile which is correlated with map data for providing a vector map, the position and alignment of the dredger and the device for removing material from the water bed detected during the dredging operation, e.g. via a global positioning satellite system, to allow the vector map to be updated.

Maintenance Dredging Required after Port Extensions at Walvis Bay

Abstract: Walvis Bay, the major port of Namibia, is earmarked for extensions. The extension of the entrance channel and the port can increase the maintenance dredging cost considerably, and if not correctly planned could impact negatively on the nearby Walvis Lagoon. An improved layout for the extended port is recommended taking into account the sediment transport regime. The future maintenance dredging rate for the extended port is determined to be 720 000 m3/year compared with the 200 000 m3/year for the existing commercial and fishing harbours. The future general cargo quays could be located so as to minimise the influx of sediment into the Walvis Lagoon. It is shown that the water exchange to the lagoon will not be significantly affected.

Exposing the U.S. coastal zone

Abstract: Overdevelopment of shores and wetlands, dwindling sites on land for the disposal of human-generated waste, contamination of estuaries and nearshore sediments, the disruption of coastal-water ecosystems by dredging, and the specter of rising sea level due to anthropogenically induced global warming are but a few of the pressures humans are exerting on coastal environments around the world. In the United States, a lot is riding on the response of its coastal environments to these pressures. The majority of the U.S. population resides in the coastal states, where the country's largest cities and most popular recreation areas are located. If the United States is to sustain the health and beauty of its coastal environments, then they must be managed, not only on the federal scale, but also on the state and local scales. One of the most fundamental types of data required to conduct this management will be detailed elevation data. On land, topography dictates the flow of water and the maximum extent of flooding. Offshore, bathymetry is a major control on shallow-water ocean currents and the dissemination of sediments eroded from the continent.

Environmental History, Environmental Management and the Public Record: Will the Records Be There When You Need Them?

Abstract: Developing solutions to current environmental crises depends on understanding through the historical record how the planet attained its current state. Since first European settlement in 1788 parts of the Sydney estuary (Port Jackson. Middle Harbour, Lane Cove River and the Parramatta River) have been substantially modified by dredging and foreshore reclamation, activities with significant environmental implications. Dredging in particular took place over a period of more than 140 years, removing as much as 100M tonnes of material from the estuary and redistributing it in reclamation sites or offshore. Investigation of the history of dredging in the estuary reveals major gaps in the records, with even basic information on gross annual expenditure and quantities not available through periods of major dredging works. This article examines the availability of the ‘public record’ relating to this single government activity in the light of archival theory on the appraisal and retention of records. The dredging ...

Dam sediment washing system

Abstract: PROBLEM TO BE SOLVED: To move sediment back to rivers without polluting the rivers. SOLUTION: This is a dam sediment washing system which washes sediment deposited on the bed of a dam reservoir by dredging and returning the sediment. Therefore, the system comprises a mud and sand separation means 1 separating the sediment deposited into sand content and slurry containing organic component, a slurry separating means 18 separating the slurry separated by the means 1 into the mud content containing organic components and water content to be discharged to rivers, and a deposition area 16 for sand separated by the mud and sand separation means 1 located in a river channel area downstream of the dam, which is discharged downstream with a water flow created when the river water level rises.

Effects of Nearshore Sand Disposal on Subtidal and Intertidal Organisms at New Plymouth, New Zealand

Abstract: The Port of Taranaki (west coast North Island, New Zealand) has an annualised dredging requirement of approximately 180,000m{3}, primarily composed of volcanic sands. Historically, this material has been deposited offshore in 16-22m water depth, considered to be beyond the zone of predominant littoral transport A cumulative effect of this dredging procedure has been down-stream erosion of inter-tidal sand deposits along the foreshore of the city of New Plymouth. A nearshore disposal site has been proposed to ameliorate this condition. The results of biological monitoring of subtidal and intertidal reefs to assess the effects of an experimental sand disposal trial are reported. The trial disposal involved placing 47,000m{3} of sand in 6-10m water, down-drift from the port entrance. The rocky subtidal in the path of the spoil was dominated by large brown seaweeds, gastropods and echinoderms, whereas the intertidal fauna and flora included mainly gastropods. Preliminary data suggest little effect of sand disposal on either subtidal or intertidal organisms, though monitoring confirms that sand has been eroded from the nearshore deposition site. We relate the absence of effects to the short residence times of sand on the reef. The trial disposal emulates natural events on this wave-dominated coast, and there is little evidence of negative effects on the fauna to date.

Bucket submersible mud pump dredge boat

Abstract: The utility model relates to a bucket wheel submersible mud pump dredge boat, belonging to the technical field of digging and dredging. The utility model comprises a hull, a positioning device, a power device, a control mechanism, a boat moving mechanism, a digging device, a mud sucking and discharging mechanism, etc. The utility model is characterized in that the digging device adopts a bucket wheel form. The periphery of the bucket wheel is provided with buckets which are distributed uniformly and are provided with no bottom. The submersible mud pump is used for sucking and discharging the mud, and the suction inlet of the submersible mud pump is installed in the mouth of the bucket wheel to receive the cut mud, and the mud is conveyed to a piling place by a mud conveying pipe. The utility model has the advantages of big cutting force, high efficiency, transportation for a long distance, simple structure, small dimension for the boat, low cost, etc. the utility model is widely used for desilting and dredging a river network region, a lake, a wharf, and a bridge brake in a countryside in China.

Engineering Techniques for Polluted Sediment Dredging of Lakes: Caohai of Lake Dianchi

Abstract: The characteristics of engineering for environmental protection dredging, main contents for preparation of program for environmental protection dredging, selection of equipment for environmental protection dredging, and disposal and dewatering program for polluted sediment were elaborated. The engineering techniques for dredging of polluted sediment of lakes based on engineering for polluted sediment dredging and disposal of Caohai of Lake Dianchi were introduced.