Showing papers on "Dredging published in 2009"

Effects of dredging operations on sediment quality: contaminant mobilization in dredged sediments from the Port of Santos, SP, Brazil

Abstract: Background, aim, and scope Contaminated sediments are a worldwide problem, and mobilization of contaminants is one of the most critical issues in environmental risk assessment insofar as dredging projects are concerned. The investigation of how toxic compounds are mobilized during dredging operations in the channel of the Port of Santos, Brazil, was conducted in an attempt to assess changes in the bioavailability and toxicity of these contaminants.

Coastal, Estuarial and Harbour Engineers’ Reference Book

Abstract: Introduction. Part 1: The dynamic environment. The deep-water origins of the physical environment of coastal, estuarial and harbour regions. An introduction to nearly-horizontal flows. Element of the theory of turbulence. Diffusion, dispersion and sub-grid parametization. Elements of non-cohesive sediment transport. Elements of cohesive sediment deposition, consolidation and erosion. Three-dimensional hydrodynamic models. Quasi-three-dimensional modelling using mixed finite difference and spectral models. Two-dimensional nearly-horizontal flow models. One-dimensional nearly-horizontal flow models. Numerical modelling of short-period waves. Three-dimensional advection-diffusion models. Two-dimensional advection-diffusion models. One-dimensional transport-dispersion and water quality. Three-dimensional sediment-transport models. Two-dimensional models of sediment transport due to waves and currents. One-dimensional models of sediment-transport under the influence of currents. Physical short-period-wave models. Hydraulic-structure interaction. Part 2: The physical environment. Groynes, offshore breakwaters and artifical islands. Beach response modelling. Beach nourishment, offshore dredging and sand bypassing. Marinas. Physical and mathematical models in the optimisation of breakwater layout. Design of breakwaters and selected design wave height. Rock for maritime structures. Wave forces on structures. Wave loads on sea dikes. Coastal pollution and water quality. Hydromechanics of porous media in the maritime. Geotextiles in coastal and harbour engineering. Dredging and dredgers. Disposal of dredged material at sea. Field studies and the analysis of data. Coastal management. Construction of maritime works. Materials in the marine environment. Maintenance of coastal structures. Economic appraisal of coastal engineering works. Cohesive sediments. Hydraulic behaviour of fine sediment. Contamination in estuarine sendiments. Cohesive sediments in coastal engineering applications. Determining depth and navigability. Maintenance dredging. Estuarial problems. Barrages and barriers. Tendering, coastal management, site supervision and control. Arbitration. Index.

Contemporary ecological threats from historical pollution sources: impacts of large-scale resuspension of contaminated sediments on sessile invertebrate recruitment

Abstract: Summary 1. Historical contamination continues to pose a serious ecological threat to many ecosystems across the world. Marine sediments have long acted as sinks for contaminants from surrounding industry and urbanization, and sediment-bound contaminants are known to affect the ecology of sediment infauna. When sediments are disturbed, however, contaminants are resuspended and potentially released into the water-column and dispersed to other environments. The threat posed by the resuspension of contaminated sediments has been a focus of substantial research in the geochemical and ecotoxicology fields, yet to date there has been no ecological assessment of the impacts of a real-world resuspension event involving contaminated sediments. 2. We assessed the ecological threat posed by the resuspension of contaminated sediments by testing for impacts of a major dredging operation in an estuary with highly contaminated sediments. We sampled the recruitment of sessile invertebrates in this estuary and two external reference estuaries, before and during dredging. These invertebrates are filter-feeders that settle and live on hard substrata above the seafloor. Impacts of the dredging-related resuspension were tested using a Beyond BACI analysis. 3. Dredging activities resulted in the large-scale resuspension of contaminated sediments. Concurrently, the recruitment of the dominant filter-feeders (e.g. barnacles and polychaete worms) was virtually extinguished for 4 months, despite being abundant prior to dredging. This pattern contrasted with the recruitment of the same invertebrates in the reference estuaries, which showed little change over the same period. 4. Synthesis and applications. The severe decrease in the recruitment of sessile invertebrates within an estuary exposed to dredging and the deposition of contaminated sediments indicates that the resuspension of these sediments pose a real ecological threat to organisms in contact with the contaminated water-column. Containment measures (e.g. silt curtains) are, therefore, essential and further engineering innovations (e.g. dredging designs and operations) are necessary to reduce resuspension during the dredging and deposition of sediments. In addition, this study demonstrates that past pollution events can cause current ecological impacts that extend well beyond those habitats recognized as being contaminated.

Impacts of maintenance channel dredging in a northern Adriatic coastal lagoon. I: Effects on sediment properties, contamination and toxicity

Abstract: Conservation and management of coastal lagoons envisage direct human intervention. To prevent siltation and to preserve the hydrodynamics features of the lagoon system, the inner channels undergo regular maintenance dredging. Sediment properties (RDP, organic matter, grain size), trace metals (Cd, Cu, Cr, Hg, Ni, and Pb), and toxicity vs. the amphipod Corophium insidiosum and the luminescent bacterium Vibrio fischeri, were analysed before and after dredging operations in a coastal lagoon (Pialassa Baiona, Italy). To detect the actual impacts, disturbed sites were contrasted with multiple controls in two distinct times, i.e. before and after disturbance, according to a sampling design based on Beyond BACI principles. The integrated methodology here adopted suggests that dredging operations carried out are not likely to pose dramatic effects on environmental quality of the lagoon.

Recovery rates of UK seabed habitats after cessation of aggregate extraction

Abstract: Marine aggregate extraction and benthic fishing are the 2 largest causes of physical disturbance to the UK seabed. Aggregate dredging is a damaging but highly spatially heterogeneous pressure with a footprint

Impacts of maintenance channel dredging in a northern Adriatic coastal lagoon. II: Effects on macrobenthic assemblages in channels and ponds

Abstract: Coastal lagoons are ephemeral habitats whose conservation requires human intervention, such as maintenance dredging of inner channels. Dredging can reduce the abundance of benthic species due to the removal of individuals with the sediment, modify sediment properties, and resuspend fine sediment, nutrients and pollutants, which can lead to eutrophication, hypoxic events and increasing toxicity. Both direct effects in the dredged channel and possible indirect effects in surrounding shallow areas could be expected. This study assesses the effects of the channel maintenance dredging, performed between October 2004 and August 2005, on the invertebrate assemblages both in channels and adjacent ponds in the northern Adriatic coastal lagoon of Pialassa Baiona. The lagoon is affected by eutrophication, chemical and thermal pollution from wastewater treatment and power plants. Three impacted sites were located in the dredged channel and three in the adjacent interconnected shallow water ponds, while three non-impacted sites were located in a channel and in a pond far from the dredged area. Replicate samples were collected from each site one time before and one time after the dredging operations. Despite the extent of the intervention, effects of the dredging on macrobenthic assemblages were detected only within the dredged channel, while in the surrounding ponds no clear and unequivocal effects were found. In particular the dredging could have promoted the increase of the abundance of the polychaete Streblospio shrubsolii in the southern and central parts of the dredged channel and the increase in abundance of the amphipod Corophium insidiosum in the northern side, compared to the controls. Instead, species diversity was reduced in the central and northern parts of the dredged channel. These effects on the macrobenthic invertebrate assemblages could be related to the observed changes of sediment characteristics, contamination and toxicity. Overall, direct effects on benthic assemblages in the dredged channels were more detectable than the possible secondary effects in the surrounding shallow ponds, where the higher spatial heterogeneity can mask any relevant effects.

Impact on biodiversity of scallop dredging in San Matías Gulf, northern Patagonia (Argentina)

Abstract: Between 1968 and 1994, Tehuelche scallop (Aequipecten tehuelchus) was fished in San Matias Gulf (Argentine Patagonia) using dredges. The catch was not sorted on board; epifaunal invertebrate bycatch and inorganic substrate removed by the dredges were landed together with scallops. Surveys were conducted in 1987 and 1997 on four fishing grounds following the same methodology to estimate the abundance of epifaunal components using catch and swept-area data. Univariate, distributional, and multivariate methods were used to analyze biodiversity and its change between surveys. There was no recorded dredging on two of the fishing grounds in the intervening period between the two surveys. Fishing effort in the order of 5,000 effective fishing hours occurred at each of the other two grounds, during that period. Multivariate analysis indicates that macrofaunal assemblages changed in each ground between 1987 and 1997, according to fishing intensity and time lapsed since last fishing action. Fishing grounds that were not dredged during the 10-year period showed no significant changes in species composition and dominance. The results support the hypothesis that dredging causes high levels of disturbance that affect the whole benthic ecosystem. Community “recovery” seems to be a non-stationary process that may not reverse the system to pre-harvest conditions, but lead instead to a sequence of new states with faunistic changes governed by colonization and slow rebuilding of habitat complexity.

Sediment Characterization and Dynamics in Lake Pontchartrain, Louisiana

Abstract: FLOCKS, J.; KINDINGER, J.; MAROT, M., and CHARLES, C., 2009. Ssediment characterization and dynamics in Lake Pontchartrain, Louisiana. Journal of Coastal Research, SI(54), 113–126. West Palm Beach (Florida), ISSN 0749-0208. Lake Pontchartrain in southeastern Louisiana is the largest of several shallow estuaries that together cover over 15,000 km 2 . Wetlands, forests, and large urban areas surround the lake. Primary transport mechanisms of sediments to Lake Pontchartrain include urban runoff, major diversions of the Mississippi River, discharge from streams along the north and west shores, and tidal circulation. Sediments deposited in Lake Pontchartrain are subjected to resuspension and mixing by natural and human activities. Bioturbation and water turbulence throughout the lake are the major mixing agents, and mechanical shell dredging has reworked much of the lake bottom over the last century. Sediment characterization through direct sampling and geophysical surveys indicates that these processes continually rework the top meter of sediment. The lake receives discharge from roadways and industrial and agricultural sources. Contaminants from these sources accumulate in the lake sediments and are an important contributor to the degradation of the estuary. Decline in populations of various benthic organisms, such as shrimp and clams, has been documented in the lake. To characterize the health of this important estuary, the U.S. Geological Survey (USGS) conducted a comprehensive evaluation of the geology, geomorphology, coastal processes, and environmental condition of the Pontchartrain Basin from 1994 to 1997. This report presents an assessment of sediment distribution and quality using a multidisciplinary approach to characterize the influence of various physical and chemical parameters: nearsurface stratigraphy, major trace metal concentrations (Cu, Pb, Zn, and Ni), and short-lived radionuclides ( 210 Pb, 7 Be, and 137 Cs). The results are compared with water-circulation patterns to determine high-resolution sedimentation patterns in the lake. The data show a significant increase in trace metals in the top 1 m of lake sediments. Above this horizon, pollen analysis indicates a correlation with land clearing in the area, a proxy for increasing human development of the surrounding landscape and an increase in surface run-off. The data also show that the top meter of sediment undergoes frequent resuspension during high-energy circulation events and via circulation gyres in the lake. This regular turnover does not allow stratification of recently deposited sediments, restricting the sequestration of contaminated material that enters the lake.

Urban activity and mercury contamination in estuarine and marine sediments (Southern Brazil).

Abstract: The distribution of mercury in sediments of the Patos Lagoon estuary and nearby coastal marine deposits has been investigated for the period 1998-2008. Polluted urban soils and coastal reclamation fills are the principal sources of high mercury concentrations for shallow estuarine sediments. The shallow sediments that form near the urban area enter the navigation canal and are transported into the ocean. The mercury concentration in sediments of the navigation canal has considerably increased since 2004, due to intense reconstruction activity in the urban area. Periodic dredging of the canal strengthens the preconditions for coastal marine sediment contamination by mercury. However, this does not occur because the resuspended dredged sediments are significantly diluted by natural suspended particulate matter.

Relict sand dredging for beach nourishment in the central Tyrrhenian Sea (Italy): effects on benthic assemblages

Abstract: The aim of this study is to analyse the effects in space and time of relict sand-dredging activities on macrobenthic assemblages, in an area situated offshore Montalto di Castro (central Tyrrhenian Sea, Italy), and to analyse the recolonisation processes of macrobenthos in the dredged areas. The area in question is characterised by relict sand deposits (Holocenic paleo-beaches), used for beach nourishment along the Latium coast. The effects of sand extraction on benthic assemblages were investigated before, during and after three dredging operations. The sites analysed are located within the dredged areas (inside stations) and in neighbouring, not dredged, areas (outside stations). The results showed that the impact of sand extraction was confined to the dredged stations and to the areas in proximity to the dredged areas. During dredging activities, the structure of benthic assemblages within the impacted stations was characterised by low species richness and diversity. Both the direct removal of sediment and the re-suspension and consequent deposition of fine sediment affected benthic assemblages of the impacted stations. A few months after the dredgings, a recolonisation process was still observed at all the impacted stations. A gradual recolonisation process was observed at those stations affected by only one dredging, whereas a different recolonisation was observed at those stations affected by two dredgings over time. This study suggests that differences of re-colonisation processes of benthic assemblages are related to the intensity of dredging operations in terms of dredging frequency.

Cumulative effects of channel and ebb shoal dredging on inlet evolution in southwest florida, usa

Abstract: : This paper describes analysis and numerical modeling of tidal inlets in southwest Florida, where coverage of large temporal and spatial scales is necessary. A methodology is introduced for examining the response of complex inlet systems to dredging, including modeling of regional hydrodynamics, wave-current interaction, sediment transport, and application of the Inlet Reservoir Model. A case study for Longboat Pass, Florida, demonstrates this methodology. Longboat Pass is one of several tidal connections between the Gulf of Mexico and the Sarasota Bay system. The study covers evolution of Longboat Pass from 1880 to present. The analysis begins with natural conditions that existed before dredging or inlet modifications and investigates how inlet evolution is influenced by navigation improvements and mining of the ebb shoal for beach nourishment.

Whole Ecosystem Evidence of Eutrophication Enhancement by Wetland Dredging in a Shallow Tropical Lake

Abstract: The purpose of this research was to assess the effects of dredging performed in a marginal wetland colonized by aquatic macrophytes on eutrophication of the adjacent shallow tropical lake (Imboassica Lake, Brazil). The river mouth of the Imboassica River that drains into Imboassica Lake had been densely colonized by aquatic vegetation dominated by Typha domingensis (Pers.) when it was dredged. Total and dissolved nitrogen and phosphorus concentrations were measured monthly over 13 years at four stations in the Imboassica river-lake system. Dredging activities reduced phosphorus and nitrogen retention at the river mouth and subsequently increased these nutrient stocks in the lake waters. Nutrient retention by non-dredged wetland was estimated to be ca. 1,200 kg year−1 (87.3 g m−2 year−1) for nitrogen and 60 kg year−1 (4.5 g m−2 year−1) for phosphorus. Our whole-lake approach suggested that dredging might intensify rather than mitigate eutrophication in shallow tropical lakes when the removal of aquatic macrophytes is coupled to the persistence of anthropogenic nutrient inputs from the watershed.

Depth-utilization analysis for estimating economic activity supported by dredging

Abstract: The U.S. Army Corps of Engineers (USACE) has the federal mission of maintaining the national waterborne transportation

Nitrogen fate in drainage ditches of the coastal plain after dredging.

Abstract: Drainage ditches are a key conduit of nitrogen (N) from agricultural fields to surface water. The effect of ditch dredging, a common practice to improve drainage, on the fate of N in ditch effluent is not well understood. This study evaluated the effect of dredging on N transport in drainage ditches of the Delmarva Peninsula. Sediments from two ditches draining a single field were collected (0—5 cm) to represent conditions before and after dredging. Sediments were packed in 10-m-long recirculating flumes and subjected to a three-phase experiment to assess the sediment's role as a sink or source of ammonium (NH 4 ) and nitrate (NO 3 ). Under conditions of low initial NH 4 -N and NO 3 -N concentrations in flume water, sediment from the undredged ditch released 113 times more NO 3 -N to water than did sediment from the dredged ditch. When flume water was spiked with NH 4 -N and NO 3 -N to simulate increases in N concentrations from drainage and runoff from adjacent fields, NO 3 -N in flume water increased during 48 h compared with the initial spiked concentration, while NH 4 -N decreased. These simultaneous changes were attributed to nitrification, with 23% more NO 3 -N observed in flume water with undredged ditch sediment compared with dredged ditch sediment. Replacing the N-spiked water with deionized water resulted in two times more NO 3 -N released from the undredged ditch sediment than the dredged ditch sediment. These results suggest that ditch sediments could represent significant stores ofN and that dredging could greatly affect the ditch sediment's ability to temporarily assimilate N input from field drainage.

Sullage digging pumping vessel for ocean intertidal zone

Abstract: The utility model solves the technical problems that aiming at the defects in prior art, the utility model provides a special desilting dredging equipment which is used for excavation dredging, long-distance conveying and has high solid content, wide application range of conveying media and no backwater secondary pollution, in particular to a dredging pumping ship for ocean tidal zone. The dredging pumping ship comprises a propeller 8, a deck crane 10, power stations 10, 11 and 12, an operation chamber 5 and a living chamber 6 arranged on a deck upper platform 4; wherein, a ladder 7 which can be climbed up and down by crew is arranged between the platform 4 and the deck; a hydraulic excavator 1 and a vibration sieve 2 with a material hopper are sequentially arranged on the front end of the pumping ship body; the rear end of the vibration sieve 2 is connected with a slush pump 3; a sieving material sliding channel 16 is arranged on the lateral surface of the vibration sieve 2; the equipments are connected with a control chamber through cables and are controlled in centralized way by the operation chamber 5. The dredging pumping ship can adopt self-excavation channel method to adapt to variable water level of ocean tide; the solid content in conveyed material is high, the efficiency is high, the sedimentation time is short and the backwater secondary pollution is prevented.

Response of benthic invertebrate communities to the large-scale dredging of Muuga Port

Abstract: The dynamics of benthic invertebrate communities in Muuga Bay was described in connection with large-scale dredging activities. The spatial extent and duration of the effects were assessed by multivariate analysis and spatial modelling. In general, dredging had moderate effects on benthic invertebrates both in space and time. Still, dredging resulted in an elevated biomass of bivalves, namely that of Macoma balthica. These bivalves were more impacted on flat bottoms compared to steep slopes.

The impact of two newly built port terminals in the eastern Gulf of Finland on sedimentation processes and coastal zone dynamics

Abstract: The natural coastal zone in the Luga Bay and Bjorkezund Strait are characterized by a positive sediment balance. Recent sediment extraction and significant depth increase within the dredging areas in the vicinity of the newly built oil and coal port terminals in Ust-Luga and Primorsk disturb the dynamic equilibrium and sediment balance in the coastal zone. This activity leads to a change in sediment flows, with a high rate of accumulation in ship channels and an increase of coastal erosion.

Zooplankton community structure and inter-annual dynamics in two sand-pit lakes with different dredging impact.

Abstract: Zooplankton seasonal and inter-annual dynamics were investigated in two neighbouring sand-pit lakes with similar morphological features but different exploitation regime. We hypothesized that the dredging activities affected the zooplankton communities and the hydrochemical conditions of the studied lakes. Significant differences in zooplankton abundance were found. The analysis of similarity (ANOSIM) revealed that plankton communities were different between lakes and that the microcrustaceans largely contributed to the average dissimilarity. In particular, the lower densities of cladocerans and the presence of large-size species in the lake still under dredging during this study appeared to be related to the resuspension of sand in the water column. We report how the zooplankton communities evolved toward an higher taxonomical and functional diversity after conclusion of the dredging activities.

Restoration of an Eroded Estuarine Foreshore Using Cohesive Dredge Material, Orwell Estuary, UK

Abstract: Cohesive sediment recharge has considerable potential as a means of restoring estuarine shores on account of the large volumes of mud raised through maintenance dredging. However, few direct foreshore placements of muddy material have been undertaken to date. This paper evaluates a pioneering sediment recharge in the Orwell estuary (eastern UK), along a degraded mud-gravel foreshore backed by a seawall protecting agricultural land. Recharge was undertaken in December 1997 and involved placement of a retaining bank of potentially mobile gravel, which was filled with 22 x 10(3) m(3) muddy maintenance dredgings. Morphodynamic behaviour of the mud and gravel deposits over a 10 year period has been dominated by in situ dewatering and compaction of the mud, landward reworking of the enclosing gravel, and partial return of the mud to the wider estuarine system. Landward 'roll over' of the gravel has reduced the width of the newly created mudflat by around 60%, such that this is now only 15 to 25 m wide. However, top-up recharges of mud in 2000 and 2003 raised elevations to the extent that around 80% of the mud area has been colonized by a diverse community of saltmarsh halophytes. This study demonstrates the feasibility of direct placement of cohesive dredge material on low wave energy estuarine foreshores as a means of reducing damage to flood defence infrastructure and restoring degraded mud flat and saltmarsh habitats over a decadal timescale.

Treatment and valorisation of stormwater sediments.

Abstract: The objective of this research is to show how sediment micro-pollution, including heavy metals, hydrocarbons and PAHs, can be reduced by means of a physical treatment based on screening and attrition. The study was carried out on five stormwater sediments, the developed pilot unit allows to isolate pollutants in the fine particles, hence a possible reuse of the coarse, unpolluted fractions. Geotechnical tests carried out on the treated sediments show that most of these fractions are likely to be reused as road embankments, capping layers or pipe embankments. The remediation of stormwater sediments is indeed possible and the development of a mobile unit is actually under study. As sediment treatment is a wide problem, largely exceeding stormwater, ATTRISED process could be used for the remediation of other sediments such as river dredging sediments or sediments from sewer networks.

Construction management method in dredging

Abstract: PROBLEM TO BE SOLVED: To provide a construction management method in dredging which enables construction with high dredging accuracy and facilitates operation of a back hoe by an operator when carrying out dredging construction by a back hoe dredger, thereby enabling efficient dredging construction. SOLUTION: In the construction management method in dredging, when dredging is carried out by the back hoe dredger, topographic data measured beforehand and a preset target dredging line are drawn on a monitor screen of display equipment in a back hoe operation room, the locus of the claw tip of the back hoe can be retain for a short time, and the boom, arm and bucket of the back hoe are displayed on the monitor screen of the display equipment in real time. COPYRIGHT: (C)2009,JPO&INPIT

Dredging system by grab dredger

Abstract: PROBLEM TO BE SOLVED: To provide a dredging system by a grab dredger which can accurately and efficiently perform a dredging operation by acquiring the actual state, at a water bottom, of a grab bucket which is displaced from a reference position or a reference orientation by the effect of a tidal current in the dredging operation for excavating the sea bottom in a predetermined water area by a grab bucket. SOLUTION: An accelerator sensor 30 and an angular velocity sensor 31 are provided to the grab bucket 5. A position signal 34 for the grab bucket 5 at the sea bottom 17 from the accelerator sensor 30 and a tilt signal 35 and an orientation signal 36 for the grab bucket 5 at the sea bottom 17 from the angular velocity sensor 31 are input into a data processing and calculating device 37 together with the reference data 38, and calculated to obtain the calculated data 55 on the actual position, tilted angle, and orientation of the grab bucket 5 at the sea bottom 17. Based on the calculated data 55, the grab bucket 5 is operated. COPYRIGHT: (C)2011,JPO&INPIT

Design of a dredging system to dredge sandy / muddy soil in navigation canals

Abstract: The main target of this research is to design an economically andenvironmentally feasible alternative system, to dredge sandy/muddy soil in navigable channels, by a fluidization system and a jet pump. A theoretical formula had been derived to predict jet pump performance under various working conditions using basic fluid mechanics equations. A special experimental test rig has been designed and built to study the effect of some parameters such as: area ratio, mass flow ratio, driving nozzle to mixing chamber distance, suction inlet configuration and speed of the jet pump upon operation. A set of experiments were conducted to check the validity of the theoretical formula to predict jet pump performance and to examine the various jet pump parts that achieve the best performance. The best values for design parameters have been obtained from the experimental work. Moreover, the study has proved that the new dredging system is more economically feasible and more cost-effective as compared with other traditional dredging methods, when applied under the same operating conditions. Also, this work includes a brief comparison between the dredging cost per cubic meter in the current study and in other dredging operations undertaken by the Suez Canal Authority.

Remotely operated submerged dredging system

Abstract: A remotely operated underwater dredging system that can excavate many hundreds of feet below the surface of a water body. By placing dredge pump at the bottom of the water body, the vacuum to lift water and dredged material to the pump is minimized. In addition, the mechanical advantage of the cutterhead can be greatly enhanced by mounting it directly to a submerged dredging chassis close to the pump.