Showing papers on "Dredging published in 2005"

The effects of marine sand and gravel extraction on the macrobenthos at a commercial dredging site (results 6 years post-dredging)

Abstract: Boyd, S. E., Limpenny, D. S., Rees, H. L., and Cooper, K. M. 2005. The effects of marine sand and gravel extraction on the macrobenthos at a commercial dredging site (results 6 years post-dredging). e ICES Journal of Marine Science, 62: 145e162. Benthic recolonization was investigated at a site historically used for the extraction of marine sand and gravel. The main objective was to assess the effects of different levels of dredging intensity on the recolonization of benthic fauna and sediments. Preliminary observations from this study indicated that the fauna within an area of seabed exposed to high dredging intensities remained in a perturbed state some 4 years after the cessation of dredging. Thereafter, annual monitoring surveys of the benthos and sediments at the ‘‘treatment’’ and ‘‘reference’’ sites have followed the recolonization process. Results from univariate and multivariate data analyses show that distinct differences in the nature of assemblages at sites exposed to high and lower levels of dredging intensity persist at least 6 years after the cessation of dredging. This paper presents the physical and biological findings 6 years after dredging, together with a generic framework for evaluating postcessation recolonization studies.

Impacts of trawling and scallop dredging on benthic habitats and communities

Abstract: Impacts of trawling and scallop dredging on benthic habitats and communities , Impacts of trawling and scallop dredging on benthic habitats and communities , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Land Use Tourism Models in Spanish Coastal Areas. A Case Study of the Valencia Region

Abstract: YEPES, V. and MEDINA, J. R., 2005. Land Use Tourism Models in Spanish Coastal Areas. A Case Study of the Valencia Region. Journal of Coastal Research, SI 49 (Proceed ings of the 2 nd Meeting in Marine Sciences), 83 – 88 Valencia -– Spain, ISSN 0749-0208 The “sun and beach” tourist product is of major economic importance in Spain and particularly in the region of Valencia. Beaches are natural fragile resources that cont ribute greatly to a country’s economic productivity. In this paper, intensive and extensive tourism models are analyzed, concluding that from the economic as well as the environmental perspective, intensive tourism models are more efficient than extensive ones. The generalized erosion problem of the Valencia coastline is described and three fundamental causes are examined: damming, port breakwaters and urban development. “Beach sand” and “littoral space” are identified as critical natural resources limiting future economic development of the coastal areas. Restoration of the natural fluvial coarse sediment drift together with reservoir dredging and sediment bypassing in dams are considered essential for the sustainability of beaches. After restoring natural coastal sediments, it will be necessary to install sand bypasses in ports along the coast. Beach nourishment projects based on marine and fluvial deposits may contribute to solving local, specific erosion problems in the short -term.

Immediate impacts and recovery trajectories of macrofaunal communities following hydraulic clam dredging on Banquereau, eastern Canada

Abstract: A hydraulic clam dredging experiment, designed to mimic offshore commercial dredging practices, was carried out at a depth of approximately 70 m on a sandy seabed on Banquereau, on the Scotian Shelf, eastern Canada. The experiment was designed to study the separate and combined effects of dredging through three treatment boxes (Dredging Only, Dredging and Discarding, Discarding Only) and two spatially separated reference boxes. In all, 270 taxa were identified from grab samples. Of these, four bivalves are targeted in the commercial fishery (Arctica islandica, Cyrtodaria siliqua, Mactromeris polynyma, and Serripes groenlandicus) while 266 taxa were non-target species. Sample biomass was dominated by the propellerclam, C. siliqua, and the echinoderm, Echinarachnius parma, while the polychaete, Spiophanes bombyx, was the numerical dominant. The dredges captured 33 invertebrate and two fish taxa, although O80% of the catch biomass comprised propellerclams and echinoderms. Immediately after dredging, most macrofaunal species decreased in abundance, with the greatest declines inside dredge furrows (which covered 53e68% of the area inside the dredged boxes). Large numbers of propellerclams were excavated to the seabed surface, with a large proportion showing massive damage. There were few signs of discards on the sediment surface. Recovery trajectories of target and non-target species were followed for 2 years. Following initial declines in abundance and biomass of most taxa immediately after dredging, there were marked increases in abundance of polychaetes and amphipods after 1 year. Two years after dredging, abundances of opportunistic species were generally elevated by [100% relative to pre-dredging levels. Two years after dredging, average taxonomic distinctness had decreased (i.e. taxonomic relatedness between species had increased) due, in part, to increased numbers of species of certain polychaetes and amphipods, while communities had become numerically dominated (50e70%) by S. bombyx. It is concluded that the disturbed community was still in the colonizing phase 2 years after dredging. The mobile brittlestar, Ophiura sarsi, displayed increases in abundance ranging from 200% to 300% in the dredged and reference boxes over the 2-year post-dredging. A similar response of nontarget macrofauna in the reference boxes suggests, possibly, a coincident natural recruitment pulse. Dredging resulted in pronounced, sustained reductions in biomass (up to 67%) of the target bivalves with no signs of recovery after 2 years. Recruitment of target bivalves (O1-mm shell length) was very low throughout the experimental area during this interval.

River dredging, channel dynamics and bedload transport in an incised meandering river (the River Semois, Belgium)

Abstract: Dredging in the rivers of the Ardenne is generally carried out on a smaller scale to that described in the literature and is not conducted for commercial purposes. Extractions within the river channel are made in order to prevent flooding; hence the quantity of gravel extracted is limited. This study aims to evaluate the impact of dredging and the resilience of the riverbed in the Semois. This river is found in the south of the Ardenne region and is characterized by large incised meanders, a narrow floodplain, few pebble bars, numerous bedrock outcrops and a limited stock of sediment. The bed is particularly flat and shallow and the bankfull discharge (130 m3 s−1) is frequently attained (0.9 yr). Pebble tracers allowed the critical parameters (discharge, Shields criterion, and stream power), the diameter of mobilized sediment and the distance of sediment transport to be determined. A major dredging campaign resulted in the formation of a channel nearly 1 km long and 2 m deep which functioned as a sediment trap. Topographical cross-sections made before and after the dredging campaign and again 4 yr later allowed bedload discharge to be estimated (1.1 t km−1 yr−1). In order to examine the efficiency of the sediment trap, the sediment transport equations of Meyer-Peter and Muller, Schoklitsch, Bagnold and Martin were applied. With the exception of Bagnold's equation (1980), the observed transport values and those calculated theoretically are relatively close. Between October 1997 and June 2001, 5010 t were caught in the sediment trap. For the same period the equations calculate values between 6147 and 10 571 t. The overestimation from the theoretical calculations may result from a lack of sediment supply due to the characteristics of the basin and the frequency and magnitude of flood events during the study period. From the magnitude of the sediment transport rate, a return to the initial state of the riverbed (before dredging) may be expected after approximately 10 yr. Despite the scale of the dredging campaign for a river of this size, its results are limited in terms of flood prevention. Copyright © 2005 John Wiley & Sons, Ltd.

Introduction to the Treatment of Polluted Sediments

Abstract: This paper overviews the large variety of remediation options for polluted sediments that are currently available. These include physico-chemical and biological techniques that can be applied in situ or ex site.

Geomorphologic and physical characteristics of a human impacted estuary: Quequén Grande River Estuary, Argentina

Abstract: Even though the Quequen Grande River Estuary has economic and strategic importance from an oceanographic point of view, it has been ignored until recently. Nevertheless, many anthropogenic modifications (i.e., dredging, jetty and harbour construction, etc.) have taken place in the last 100 years which, most of them, have resulted in significative economic expenses to the harbour and city authorities due to the lack of adequate prior studies. The purpose of this article is to provide a review of the present status of the geomorphology and main physical characteristics of the estuary and describe the effects of these man-made modifications upon the estuary. Data were gathered in several field cruises from 1994 to 2000 plus from continuous recording devices installed at or near the estuary directed to define the present geomorphologic and oceanographic conditions of the estuary and to establish a monitoring program. The ultimate goal is to provide some practical solutions in diminishing the maintenance of the harbour and to provide pollution-control devices. The estuary is classified as a microtidal, primary, coastal-plain system. It can be considered as a partly-mixed system 2 km from the mouth up to its head (15 km inland). Artificial dredging to accommodate the Quequen harbour in the last 2 km of the estuary has induced a highly stratified water column where the upper 2–3 m concentrates low salinity water and the lower layer is filled by water of the same or slightly higher salinity than the inner shelf waters. Due to the presence of a step at the head of the harbour, water circulation is very reduced and in some cases nonexistent, producing strong reductive and even anoxic conditions. The foot of the step is a sediment and organic matter trap that must be dredged periodically to insure adequate navigability.

Impacts of hydraulic dredging on a macrobenthic community of the Adriatic Sea, Italy

Abstract: Hydraulic dredging that targets the bivalve Chamelea gallina in the northern and central Adriatic Sea (Italy) has been taking place for over 30 years. Seventy-three commercial dredgers harvest the resource within the sandy coastal area of the Ancona Maritime District (central Adriatic Sea). Despite this chronic disturbance, studies aimed at investigating the impacts of the fishery on the macrobenthic community of the area have never been carried out. To remedy this, sampling was accomplished within an area of the District from which hydraulic dredging was banned, within the framework of a balanced beyond-BACI (before/after, control/impact) experimental design. Data regarding seven groups of species were analysed separately by means of permutational multivariate analysis of variance. No impacts attributable to hydraulic dredging were found upon consideration of the entire sampled macrobenthic community, the Polychaeta, the Crustacea, detritivores, and suspensivores. In contrast, a sustained press impact of...

Effects of dredging operations on soft bottom macrofauna in a harbor in the Patos Lagoon estuarine region of southern Brazil

Abstract: An evaluation was made of the effects of dredging on the soft bottom community in the channel of the Rio Grande harbor in the Patos Lagoon estuarine region of southern Brazil. During four seasonal cruises, samples were collected from nine biological stations, one of which was located outside the dredged area. Three macrobenthic samples were collected on each cruise from each station, using a 0.08 m2 van Veen grab. A cluster analysis was applied to group summer and autumn cruise stations before the dredging period, revealing larger numbers of species (35-36 spp.) and higher densities of organisms. The station located outside the dredging area was always included in this group, regardless of the sampling period or conditions of salinity. Another group comprised the winter and spring stations during the dredging period. This group was characterized by stations with the fewest species (20-18 spp.) and the lowest and most variable organism densities. The efficient strategies of resilience of the dominant estuarine species may minimize the effects of dredging on the biota through the rapid recolonization of the soft bottom of the harbor channel.

Assessing Sediment Loading from Agricultural Croplands in the Great Lakes Basin

Abstract: Soil erosion and sedimentation is one of the main environmental concerns in the Great Lakes Basin. Sediment dredging projects cost over $20 million in the Great Lakes each year. Sediment transport models are being developed to assist State and local resource agencies in reducing sediment and pollutants loading to navigation channels and Areas of Concerns (AOCs), and thus in reducing the costs for navigation maintenance and sediment remediation. To archive sediment reduction goals, it is important to identify areas with high sediment yield that can be of dredging concern. Controlling sediment loads also requires knowledge and quantitative assessment of soil erosion and the sediment transport process. An overall analysis on Great Lakes tributaries was conducted to assess and compare their relative loadings of sediments, state of conservation practices, and their potential for further reductions to sediment and contaminant loadings. GIS-Based erosion model and sediment delivery model were used to estimate the potential sediment loading from agricultural croplands with different practice scenarios in the Great Lakes Basin. Over 100 sub-watersheds based on U.S. Geological Survey's 8-digit watersheds were analyzed. Watersheds as potentially high contributors of sediment to the Great Lakes have been assessed. (The Journal of American Science. 2005;1(2):14-21).

Modelling navigation in muddy areas through captive model tests

Abstract: Many access channels and harbours suffer from sedimentation and formation of mud layers. To keep navigation safe and economic, extensive maintenance dredging is needed. Until now, the required level of dredging has always been determined by making use of the physical characteristics of the mud layer, which does not necessarily result in efficient dredging. Ship behaviour also matters, and knowledge of ship manoeuvrability can help to redefine the level of dredging required. A mathematical model of manoeuvring for simulation purposes, based on a comprehensive series of captive model tests, is presented, along with a selection of results.

A review of the impacts of aquaculture and artificial waterways upon coastal ecosystems in the Gulf (Arabian/Persian) including a case study demonstrating how future management may resolve these impacts

Abstract: Preliminary calculations indicate that western Gulf intertidal mud and sand flat habitats such as those found in Kuwait may contribute some 30 percent of the gross marine productivity for this state, more than double that of any other intertidal biotope. Mud flats are dominated by a microbial mat system; recent application of the stable isotope ratio technique confirms a link between mat production and commercial fish and shrimp species. These findings demonstrate the importance of intertidal productivity so that dredging and coastal reclamation represent one of the most serious impacts on the Gulf environment. In addition, Gulf fish stocks are now fully exploited and many Gulf countries are placing further stress on coastal ecosystems through the development of aquaculture. Most of these countries now have coastal management plans with zoning of areas for conservation, recreation and development and future planning prioritization should ensure sustainability of marine biodiversity, fisheries, aq...

Silt curtains as a dredging project management practice

Abstract: INTRODUCTION: Environmental windows are imposed on many U.S. Army Corps of Engineers (USACE) dredging projects in both coastal and inland waterways. Over 83 protected or sensitive species that have been identified fall into at least 20 general categories of concern for potentially negative impacts from dredging and disposal operations. One of the most frequently cited reasons for establishing an environmental window is impacts from turbidity and suspended sediments (Reine, Dickerson, and Clarke 1998). Over the past 15 to 20 years there have also been increased concerns regarding the potential impacts that dredging of contaminated sediments may have on nearby environmental resources.

Offshore exploration for sand sources : General guidelines and procedural strategies along deltaic coasts

Abstract: Because of the large volumes of sand required for beach renourishment, dredging from offshore borrows is the preferred method of sediment supply. As easily accessible and previously known (obvious) deposits are exploited, apparent sand reserves are seen as a dwindling resource that becomes more precious over time. Because economically exploitable offshore sand sources are limited in many regions, renewed efforts are underway to locate additional offshore sand sources that can supply sand and mixed sediments (sand, silt, and clay) to barrier-island restoration efforts in Louisiana. Sediment volumes required for beach renourishment and marsh restoration are variously estimated on the basis of numerous assumptions to range in the extreme from 14 X 10 6 m 3 to 71 × 10 6 m 3 , respectively, for one complete restoration of the entire barrier island chains. Although estimates of required volumes are controversial, significant new borrow sites must be located on the continental shelf off Louisiana to restore the barrier islands. The search for new sand sources must be focused on logistical procedures that are economical and efficient in order to cover large areas of the shelf in a timely manner. Sand search protocols developed for US East Coast sedimentary environments are broadly applicable in a conceptual sense but need to be adapted to deltaic coastal frameworks in Louisiana. Procedures and protocols for the Delta Sand Search Model (DSSM) are thus based on bathymetric, geophysical, and geotechnical survey recommendations for the identification of targets that will be proven out by detailed studies and cultural resource investigations. Development of a DSSM has advantage because it is specifically adapted to coastal marine morphosedimentary units in different-aged lobes of the Mississippi Delta that have fine-grained (muddy) deposits interspersed by sandy deposits of paleodistributaries and interdistributaries.

The impact of dredging on macrobenthic invertebrates in a tributary of the Warri River, Niger delta

Abstract: The macrobenthic invertebrates of a canal, created from a tributary of the Warri River in the mangrove swamp of the Niger Delta, Nigeria, were studied before and after dredging. In the canal dredging resulted in at least a 93% decrease in the benthic population while the Margalef's diversity index reduced from 3.8 to 1.4. Of the 15 species identified during the pre-dredging studies, only Nereis operta and Baetis sp. were recovered after dredging. The site 500m downstream of the canal was also slightly impacted, showing a 31% decrease in population. We conclude that the drastic reduction of benthic species is due to the direct destruction of benthic species, larvae and habitat, as well as settling turbidity plumes, reduction of sediment nutrients, physical disturbance and, physiological and toxic stress. To conserve biodiversity it is recommended that mitigation measures should be put in place by stakeholders involved in dredging and that long-term monitoring of dredged canals is carried out to ensure that...

Effects of harvesting methods on sustainability of a bay scallop fishery: dredging uproots seagrass and displaces recruits

Abstract: Fishing is widely recognized to have profound effects on estuarine and marine ecosystems (Hammer and Jansson, 1993; Dayton et al, 1995) Intense commercial and recreational harvest of valuable species can result in population collapses of target and nontarget species (Botsford et al, 1997; Pauly et al, 1998; Collie et al 2000; Jackson et al, 2001) Fishing gear, such as trawls and dredges, that are dragged over the seafloor inflict damage to the benthic habitat (Dayton et al, 1995; Engel and Kvitek, 1995; Jennings and Kaiser, 1998; Watling and Norse, 1998) As the growing human population, over-capitalization, and increasing government subsidies of fishing place increasing pressures on marine resources (Myers, 1997), a clear understanding of the mechanisms by which fishing affects coastal systems is required to craft sustainable fisheries management

Trace Elements in Sediments of an Aging Reservoir in Rural Mississippi: Potential for Mobilization Following Dredging

Abstract: Since 1948, the United States Department of Agriculture has assisted construction of over 10,000 flood control dams, many of which are reaching the end of their design life. Rehabilitation by dredging, or decommissioning by dam removal both have the potential to mobilize contaminants currently sequestered in the sediments. Plans to rehabilitate a small aging reservoir in a rural area of northern Mississippi led to a study characterizing the chemical composition of the reservoir sediments, and the potential for mobilizing contaminants if aerated. Sediment analyses included bulk and trace elements, and a suite of agrichemicals. Trace element concentrations are highly correlated with clay and Fe concentrations, with no elevated levels indicative of anthropogenic inputs. Batch leaching studies under reducing conditions simulating in situ conditions, and under mildly oxidizing conditions simulating disturbed sediments indicate that aeration should lead to a decrease in the aqueous concentration of trace metals currently found in sediment pore water. Decreased aqueous concentrations under oxidizing conditions are probably caused by precipitation of iron as amorphous oxides that scavenge released metals. Based on these results, dredging is a viable rehabilitation strategy for reservoir rehabilitation.

Water Quality Aspects of Dredged Sediment Management

Abstract: About 500 million yd3 of sediment are dredged annually to maintain navigation depth in the United States' approximately 25,000 miles of navigable waterways. Sediments in some of these waterways are contaminated with potential pollutants (e.g., heavy metals, organics including pesticides, PCBs, and nutrients) from municipal, industrial, and agricultural sources. As a result of this contamination, concern exists about the potential water quality impacts that could be caused by the dredging and disposal of these sediments. In the 1970s, the U.S. Congress authorized the U.S. Army Corps of Engineers to conduct a $30 million, five-year Dredged Material Research Program (DMRP) to evaluate, with laboratory and field studies, the potential water quality impacts associated with dredged sediment management and to develop protocols for evaluating sediments for their potential to cause adverse impacts on disposal. Those studies showed that open water disposal of dredged sediment would not be expected to be adverse to water quality, aquatic organisms, or other beneficial uses of waterbodies. However, on land, so-called “confined” disposal of dredged sediments could lead to water quality impacts to surface and groundwaters because of the release of heavy metals and some other pollutants. The DMRP studies and subsequent studies also reaffirmed that the concentration of contaminants in sediments does not predict the potential for contaminant release from sediments during or after disposal. More recent attempts to develop numeric, cooccurrence-based sediment quality criteria are also technically unsupportable and unreliable for screening, evaluation, or regulatory purposes. Keywords: contaminated sediment; dredging; sediment; water quality; U.S. waterways; sediment criteria

Dredging effects on eelgrass (Zostera marina) distribution in a New England small boat harbor

Abstract: : While speculation on effects of dredging on seagrass beds is plentiful, actual empirical data documenting these effects are not. In this study, acoustic-based seagrass mapping techniques were used to generate detailed maps of seagrass distribution before and after dredging operations. Eelgrass (Zostera marina) within Scituate Harbor, MA, was monitored during mid-summer in 2001, 2003, and 2004; navigation maintenance dredging of the harbor was performed during fall 2002. Similar surveys were also performed during the same timeframe at an undredged harbor near Wood Island, ME. Two types of potential impacts were examined. Direct impacts involved physical removal of vegetation along with the dredged sediments. Indirect impacts in adjacent undredged areas may occur as a result of increased turbidity and/or siltation associated with dredging activities. Using hydroacoustic techniques, the authors were able to easily map and quantify direct impacts to eelgrass resources. Assessment of indirect impacts, however, was more complex. In the first post-dredging survey, a substantial reduction in coverage occurred in adjoining undredged areas, suggesting possible indirect impacts. This was followed by a modest recovery between the first and second post-dredging years. However, monitoring of other undredged sites within the region showed natural year-to-year variations in eelgrass coverage to be almost as large as those occurring at the dredged site. Results emphasize the need for long-term data to discern any potential effects of dredging on seagrass dynamics as opposed to a host of other factors contributing to high variability in measured parameters.

17. Ecological effects of pump-scoop dredging for cockles on the intertidal benthic community

Abstract: Awareness of the ecosystem effects of fishing activities on the marine environment means that there is a vital need to assess the direct and indirect effects of those activities that may have negative effects on target and non-target species. The Edible Cockle Cerastoderma edule is the target of an artisanal and commercial fishery that occurs in estuarine and intertidal habitats across northern Europe. Poole Harbour has opened up its cockle beds to pump-scoop dredging over the last few years. This study investigated the effect of pump-scoop dredging on the intertidal sedimentary environment and the macro-infaunal community. The results demonstrated that the dredging did not have an effect on the size distribution of sediment particles. After the fishery opened, no immediate impact of cockle dredging on the infaunal community was observed. Within 3 months, however, a reduction in species richness and abundance of the benthic community was noted. This may be indicative of a chronic rather than acute impact. However, further investigations are required to assess whether this was directly related to pump-scoop dredging. The findings of this study are discussed in relation to possible impacts on the ecosystem as a whole.

Using a sand wave model for optimal monitoring of navigation depth

Abstract: In the Euro Channel to Rotterdam Harbor, sand waves reduce the navigable depth to an unacceptable level. To avoid the risk of grounding, the navigation depth is monitored and sand waves that reduce the navigation depth unacceptably are dredged. After the dredging, the sand waves slowly regain their original height. To reduce the high costs of surveying and dredging, the North Sea Service of the Department of Transport, PublicWorks andWater Management, is implementing a Decision Support System to reduce the required amount of surveys and provide optimal information on the necessity to dredge. Currently, the system predicts the growth of sand waves using a linear trend. The trend is determined from observations using a Kalman-filter including geo-statistical components to incorporate spatial dependencies. This works well for sand waves that are close to their maximum height. After dredging however, the sand wave height is far from its equilibrium and the growth rate is much higher, making the linear prediction worthless. Here we show that replacing the linear trend with a landau equation improves the predictions of the regeneration. Comparison shows that the landau equation predicts the crest evolution better than the linear equation for both undisturbed sand waves and dredged sand waves, with an root mean square error that is 25% less.

Multi-purpose vessel and method for recovering, storing and/or offloading material in a dredging operation

Abstract: A method of building a levee or an island is disclosed. The method includes dredging material from a surface of a body of water with a dredge assembly mounted to a hull and supporting a hopper with the hull. The hopper is adapted to receive the material. The hopper includes a floor with a portion of the floor moveable to permit movement of the material in the hopper, and depositing at a desired location dredge material from the dredge using a transfer conveyor.