Showing papers on "Dredging published in 2011"

Sediment Flushing at the Nakdong River Estuary Barrage

Abstract: The Nakdong River Estuary Barrage (NREB) prevents salt-water intrusion but causes sedimentation problems in the Lower Nakdong River in South Korea. Its mitigation requires mechanical dredging to maintain the flood conveyance capacity during typhoons. This analysis focuses on the possibility of replacing mechanical dredging with sediment flushing through gate operations changes at NREB. The new approach first defines sediment flushing curves as a function of river stage and discharge. The feasibility of flushing is then assessed from the comparison of the flushing curves with the flow duration curves. The detailed analysis of long-term simulations using a quasi-steady numerical model provides detailed simulation results. The model applications from 1998 to 2003 incorporate tidal effects at 15-min intervals and also include major floods caused by typhoons Rusa in 2002 and Maemi in 2003. Accordingly, about 54% of the mean annual dredging volume could be eliminated by sediment flushing at NREB. The model also...

Assessing the recovery of functional diversity after sustained sediment screening at an aggregate dredging site in the North Sea

Abstract: The effects of dredging the seabed for aggregate on benthic functional diversity were assessed using a suite of suitable indices on a recovering macrofaunal assemblage. Recovery was assessed as the return of a dredged assemblage to a state found in neighbouring undisturbed (reference) sites. In situ sediment screening was permitted during dredging operations; a difference in the sedimentary profile of the seabed between dredged and undisturbed reference sites was also observed. At sites of relatively high and low dredging intensity the sediment appeared more homogenous than reference sites after the selective removal of the coarser component. Initial assessment of the macrofaunal assemblage using univariate analytical techniques suggested a recovery of functional diversity at the low dredging intensity site after two years (according to the Infaunal Trophic Index, Taxonomic Distinctness index and Rao’s Quadratic Entropy coefficient). However, multivariate analyses of the same data and of all indices except Taxonomic Distinctness indicated that assemblages at both high and low dredging intensity sites remained statistically indistinguishable from each other yet markedly different to the assemblage present in the reference area during the four-year study. The study concluded that recovery of functional diversity to a level found in a neighbouring undredged habitat had not occurred at either dredged site five years after the cessation of dredging. It is thought that the damage by dredging to functional diversity and to the capacity of the macrofaunal assemblage to recover is immediate and not so dependent on dredging intensity. The cumulative and wider ranging effects of sediment screening cannot be ignored or dismissed as a contributing factor to the similarities observed. The wider significance of these findings on the regulation of dredging activities is discussed.

The Four Major Rivers Restoration Project: Impacts on River Flows

Abstract: The ongoing Four Major Rivers Restoration Project will drastically change the river environment of South Korea. The objective of this study is to evaluate the impact of the Four Major Rivers Restoration Project on river flows using an unsteady flow simulation model. The computational model was applied to the stream reaches of the Han River and the Nakdong River. Historical floods were simulated for the changed river environment as well as for the current river condition to investigate the flood mitigation effect of the project. The simulation results show that once the project is completed, the flood water level of the entire reach of both rivers will fall because water level decline due to the channel dredging dominates water level rise due to the presence of weirs. This mitigation effect was particularly significant for the upstream region of the Nakdong River because of large-scale dredging. A steady flow simulation was carried out using normal flow discharges to investigate the effect of the project on flow characteristics during non-flood periods. For the Han River, the normal water level rises upstream of the weirs, whereas it falls downstream owing to the dominant dredging effect. However, in spite of heavy dredging, the water level decline in the case of the Nakdong River is very limited because the effect of dredging is overwhelmed by the high normal pool level of the weirs. The increase in flow travel time of the Nakdong River after the completion of the project will be more significant than that of the Han River.

Response of Tidal Creek Fish Communities to Dredging and Coastal Development Pressures in a Shallow-Water Estuary

Abstract: To investigate the effects of dredging and associated development pressures (ie, shoreline armoring, developed land use) on fish, three sets of paired dredged and undredged tidal creeks were surveyed within Lynnhaven River, Virginia Fish species diversity, community abundance, biomass, and size structure were compared among creeks and related to watershed, shoreline, and physicochemical characteristics Mean fish community characteristics (eg, abundance) were similar among creeks; however, species-specific analysis revealed subtle differences Species biomass differed between dredged and undredged creeks, though species abundance was similar Turbidity highly influenced differences in species abundance among creeks, while organic matter, dissolved oxygen, turbidity, and shoreline hardening may be influencing biomass patterns The most recently dredged creek appeared to provide less suitable nursery habitat for some species than historically dredged creeks, suggesting initial adverse effects with eventual recovery Protective measures, such as preservation of marshes, dredge depth, and time-of-year restrictions, may be moderating development and dredging pressures

Longshore Sediment Movement and Supply along the U.S. Shoreline of Lake Erie

Abstract: To establish existing conditions for dredge material beneficial use projects and to help implement principles of Regional Sediment Management (RSM) into projects and studies, this paper is an assessment of sediment sources and sinks, physical processes, and longshore sediment transport along the west and south shore of Lake Erie. This summary compiles information from a widely scattered technical literature and synthesizes the results in preparation for development of a sediment budget. The U.S. shore of Lake Erie has 28 river or harbor mouths protected with jetties and structures, of which 16 are Federal navigation projects. Much of the sediment management since the mid-1800s has revolved around providing safe navigation, maintaining depth in navigation channels, and disposing of the dredged material. Sediment sources include material brought down the rivers (often fine-grained); industrial dumping and runoff from sewers, gravel, sand, and clay eroded from glacial till bluffs and clay banks; sed...

Effects of scallop dredging on temperate reef fauna

Abstract: Scallop dredging is considered to be one of the most destructive bottom fisheries, yet empirical field evidence to support this assertion, in particular for highly structured habitats, is limited. With this study, we investigated the effects of scallop dredging on the fauna of a temperate stony reef through a comparison of areas subject to different levels of fishing activity. Significant negative effects of scallop dredging were evident for 3 of the 9 species analyzed from video samples. Sessile emergent epifaunal species had significantly lower occurrences and abundances at fished sites compared to unfished sites, while commercial target species such as scallops and crabs were not significantly affected by fishing. Contrary to expectation, the pink sea fan Eunicella verrucosa, a species of local conservation concern, did not show a significant negative response with respect to abundance and average body size to the intensity of scallop dredging it had been subjected to. The absence of a clearly detectable fishing effect on this species may be related to its association with the topographically more complex areas of the reef in which the fishing efficiency of scallop dredges will be reduced. The evidence presented here demonstrates that not all species were equally affected by scallop dredging and that the complexity of stony reef habitats may provide some measure of protec- tion at low fishing intensities.

Turbidity and Other Effects Resulting from Trafalgar Sandbank Dredging and Palmar Beach Nourishment

Abstract: Beach-nourishment requirements on the southwestern Spanish coast have led to a significant increase in offshore dredging. Following a new research line, assessment of changes recorded in physicochemical and biological parameters due to dredging and dumping operations was performed at the Cape of Trafalgar and Palmar Beach during June and July 2008. Turbidity, salinity, pH, dissolved oxygen, temperature, and suspended-sediment data were collected at 10 stations. At the end of the study, a three-campaign monitoring program was implemented for 1 year to assess the possible effects on biological communities and sediment properties. The relevant results, such as the average extent of the sediment plume (<400 m) and its persistence in the environment (<10 min), are discussed in this paper. A precise correlation between turbidity and suspended sediments and the recovery time of ecological balance were also established. Furthermore, minimal and reversible effects caused by dredging and dumping operations in thi...

Shell strength and fishing damage to the smooth clam (Callista chione): simulating impacts caused by bivalve dredging

Abstract: The smooth clam Callista chione is exploited by a fleet of dredgers along the southwestern coast of Portugal and suffers from a high incidence of shell damage. The force required to break C. chione shells in relation to fishing impacts and dredge damage is quantified. Fishing trials and shell-strength measurements (compression and compaction experiments) were performed to determine whether shell damage was attributable to the direct impact of the dredge teeth or to sediment compaction. A three-dimensional model of C. chione was subjected to simulated force by the finite element method. Analyses of damage areas and breakage patterns revealed two groups of samples, one containing the samples from compression experiments and another with the samples from dredging and compaction experiments, suggesting that most shell damage was attributable to compaction within the sediment. Information is provided to help improve the design of bivalve dredges, by increasing both length and angle of the dredge teeth, which would reduce the compaction force and distribute it differentially within the sediment, forcing upward movement of the bivalves.

Increased Bioavailability of Mercury in the Lagoons of Lomé, Togo: The Possible Role of Dredging

Abstract: Surface sediments of the lagoons of Lome, Togo, were analyzed for mercury, methylmercury, and trace elements. Concentrations were greater than typical for natural lagoon sediments, and with greater variability within the Eastern lagoon compared to the Western one. The Eastern lagoon is larger and has been dredged in the past, while the Western lagoon, which also receives major waste inputs, has not been dredged and shows less tidal flushing. Accordingly, one naturally believes that the Eastern lagoon is cleaner and probably safe to use due to its natural resources, including fishes to eat. Unexpectedly, we describe here that mercury methylation was greater in the Eastern lagoon, indicating increased bioavailability of mercury, as probably facilitated by past dredging that decreased solid-phase retention of inorganic mercury. Urbanization has historically been more developed in the southern part of the lagoons, which is still reflected in contamination levels of sediment despite dredging, probably because sources of contamination are still more important there today. Such urban contamination emphasizes the need to regulate waste discharges and possible airborne contamination in growing cities of developing countries, and implements environmental and public health monitoring, especially in relation to misbelieves systematically associated with the cleansing effect of dredging activity.

Quantifying Sediment Nitrogen Releases Associated with Estuarine Dredging

Abstract: Experimental studies of sediment pore water NH4 + chemistry, adsorbed NH4 + concentrations, sediment–water NH4 + exchange and N2–N flux were carried out to quantify the mass of labile N that can be released during large-scale dredging activities. Pore water NH4 + concentrations below 0.5-m sediment depth averaged 5 ± 2 mmol L−1 with average adsorbed NH4 + concentrations of 11 μmol g−1. Elevated NH4 + concentrations found in rapidly accreting dredge channels are partly a result of the rapid advective burial of both reactive organic matter and pore water. Elutriate tests, a dilution of sediment with site water, yielded adsorbed NH4 + concentrations very similar to those using the more typical KCl extraction. Intact deep sediment sections exposed to overlying water, used to simulate postdredging conditions, showed high initial fluxes of ammonium and no development of coupled nitrification–denitrification under the cold incubation conditions. Despite high concentrations and effluxes of NH4 + during dredging, the amount of NH4 + release during dredging was <0.5% of northern Chesapeake Bay sediment fluxes. The likelihood of large environmental effects of nitrogen release during the dredging of navigational channels in the Chesapeake Bay is low.

Review of the ecological effects of dredging in the cultivation and harvest of molluscan shellfish

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Gravel seeding – A suitable technique for restoring the seabed following marine aggregate dredging?

Abstract: Restoration of offshore marine habitats is a relatively new concept, with attempts in the European Union being largely instigated by requirements of various strategic directives. In this experiment, we investigate the practicality and effectiveness of gravel seeding, using a commercial aggregate dredging vessel, in order to recreate a gravel habitat. The experimental design consisted of a Treatment and Control site, both within an area of historic dredging characterised by an overburden of sand, and a gravel dominated Reference site. All sites were surveyed, using a combination of acoustic, camera and grab techniques, 2 months before, and then at 0, 12 and 22 months after the deposition of 4444 m 3 of gravel dominated sediments within the Treatment site. Although financial and practical constraints limited replication of the Treatment to one area, and so precluded strong statistical conclusions, our results suggested that the technique was both practically feasible, and successful in terms of returning the physical and biological attributes at the Treatment site to a state more representative of gravelly substrata in the wider, un-impacted environment.

Application of Long Distance Conveyance (LDC) of Dredged Sediments to Louisiana Coastal Restoration

Abstract: : Restoration of Louisiana's marshes and other coastal habitats will, in many cases, require dredged sediments to provide suitable substrate. Potential restoration sites are often at great distances from the sediment source. It will require special efforts, commonly referred to as long distance conveyance (LDC), to pump sediment to the sites. For the purposes of this report, LDC projects are defined as those Louisiana coastal restoration projects that involve hydraulic transport of slurry (mixture of sediment and water) through pipeline distances of 16 km (10 miles) or greater. Pumping slurry through a long pipeline is a mature technology for bulk transport that has been used efficiently in specific applications like coal and iron ore transport. At the workshop entitled "Long-Distance Pipeline Transport of Dredged Material to Restore Coastal Wetlands of Louisiana," the consensus of panelists and the audience (that consisted of national and international experts in the field of long-distance transport of dredged sediment and other materials by pipeline) was that there were no fundamental technological challenges to the delivery of sediment via LDC (Hales et al. 2003). The engineering challenges will be to optimize LDC design, operation, and maintenance to achieve respective strategic restoration goals in the most efficient, cost-effective, and environmentally acceptable manner possible. Technical literature was reviewed and interviews with personnel involved in LDC-related projects conducted to summarize state-of-practice LDC dredging project information. Dredging and transport methodologies in relation to LDC state-of- practice are presented, and potential environmental impacts of long distance pipeline transport across wetlands are discussed. Scientific and engineering uncertainties related to LDC optimization of dredged sediment for coastal restoration are identified.

Modelling Coastal Sediment Transport for Harbour Planning: Selected Case Studies

Abstract: During the planning phase of coastal development projects, it is often necessary to determine potential sedimentation and erosion rates. This is particularly relevant at harbours where dredged channels are proposed, and accurate dredging projections are crucial for economic feasibility analyses. In addition, new structures that interfere with the natural processes may have major impacts on the adjacent shoreline. In this chapter we consider a range of approaches for evaluating sediment transport for harbour planning studies (section 2), and present two detailed cases from Atlantic Canada. The sites described are representative of very different coastal environments. They include Saint John Harbour (section 3), a uniquely dynamic estuary on the Bay of Fundy with huge tides, a very large river outflow and significant sedimentation of silt and clay presenting various navigation and dredging challenges. The other site described is located on the sandy North coast of Prince Edward Island at Darnley Inlet, an exposed area where tides, storms and sea level rise are continuously reshaping the shoreline and navigation channels (section 4).

Fine sediments as a granular source for civil engineering

Abstract: Across the world, every year, several millions of tons of sediments are dredged in harbours. These sediments, which are sometimes polluted, represent an interesting granular resource for the civil engineering. For this study, fine sediments are chosen because of the difficulties to evacuate them after dredging, in comparison to sands, induced by their high water content, the presence of organic matters, their mechanical behaviour and, in some cases, the presence of pollutants. The paper shows the study carried out with fine sediments from harbours of the north of France. The authors propose recommendations to optimize the re-use of these sediments in considering technical, environmental and economical criteria. A re-use process has been studied in laboratory and tested on field site.

Electrokinetic remediation of dredged sediments from Le Havre Harbour

Abstract: Dredging is necessary for the development of the harbours and the maintenance of their activities. Dredging sediments, when polluted, present an effective and durable contamination risk of the ecos...

To preserve or to develop? East Bay dredging project, South Caicos, Turks and Caicos Islands

Abstract: The Turks and Caicos Islands are currently in the midst of an economic revolution from a marine-based provisional economy to a tourism economy. East Bay, South Caicos, is currently under construction with plans for a 160-unit condominium complex. Included in the project plan is removal of seagrass beds in front of the development to make a sandy beach for tourists. The aims of this study were to (i) describe the bathymetry and benthic habitat coverage of East Bay before dredging takes place and (ii) perform an economic valuation on the turtle grass beds that will be dredged using ecosystem valuation and emergy analysis techniques. The bathymetry survey revealed shallow waters (<1.5 m) until the reef drop off (∼650 m offshore). Benthic habitat exhibits zonation following the general progression: sand plain, algal plain, seagrass, coral rubble and seagrass, rock and turf algae, and reef flat. Ecosystem services valued the proposed dredging area at USD $28,807 per year, compared to emergy analysis, which valued the proposed dredging site at USD $32,060 per year. The baselines presented in the study may facilitate a quantitative assessment of dredging impacts on turtle grass once dredging is complete and an economical cost-benefit-analysis of the dredging project to see whether the economic gains outweigh the ecological costs of dredging in front of the East Bay development.

Improvements to a Coastal Management Plan in Sicily (Italy): New Approaches to borrow sediment management

Abstract: LANZA, S. and RANDAZZO, G., 2011. Improvements to Coastal Management Plan in Sicily (Italy): New Approaches to Borrow Sediment Management. Journal of Coastal Research, SI 64 (Proceedings of the 11th International Coastal Symposium), 1357 – 1361. Szczecin, Poland, ISSN 0749-0208 Sicily is a Mediterranean island-region, whose economy is based especially on tourism and also connected with beaches. Unfortunately, in the last fifty years about 2.5 km 2 of beach were lost due to erosion, causing damages worth approximately 5 billion Euros. At the moment about 300 km of the 1600 km of coast present erosion problems, 1/3 of which is threatening the economic and important historical assets as well as Sicilian cultural heritage. The Sicilian region decided to solve the issue, avoiding passive protection systems only used for urgent action, but instead adopting a Coastal Management Plan (CMP) aimed essentially at the use of soft protection systems, e.g. beach replenishment. In order to put into practice this type of intervention, thanks to a synergic collaboration with the CMP, a Borrow Deposits Plan (BDP) was drawn up, identifying three possible sources of materials: fluvial material, harbour dredging and submerged deposits. The detected deposits can be estimated in about 5 million m 3 of fluvial deposits useful for the pebbly beaches of the north-eastern sectors, while the ones coming from harbour dredging, about 3 million m 3 , can be used only for local intervention. Submerged deposits located along the north-western coast of the island have a strategic importance. They are situated at a depth of 100 m and are about 120 million m 3 , with excellent granulometric (fine and medium sands) and compositional features (quartz > 50%). It is clear that in order to better exploit the resources and above all reduce costs, it will be necessary to correctly manage the intervention, that will have to be carried out with the appropriate timing.

Short and mid‐long term effects of cockle‐dredging on non‐target macrobenthic species: a before‐after‐control‐impact experiment on a tidal mudflat in the Oosterschelde (The Netherlands)

Abstract: To study the possible environmental impact of hydraulic cockle-dredging on macrobenthic communities and the environment, a fishing experiment was executed on a tidal mudflat in the Oosterschelde (SW Netherlands) according to a BACI (before-after-control-impact) design. Following the characterization of the initial situation, a part of the mudflat was commercially fished, after which dredged and undredged areas were compared on the basis of macrofauna descriptors and sediment constitution approximately 2 months (short term) and 1 year (mid-long term) after fishing. Whereas a clear reduction of the larger Cerastoderma edule cockles (>23 mm) in the fished areas was found, no effect of dredging on total macrofauna densities or median grain size was observed. No negative effect of fishing on total macrofauna biomass was found; in contrast, an increase of the biomass of the non-target species almost compensated for the loss in weight due to the extraction of the larger cockles. No significant effect of dredging on species diversity, richness or evenness was found in the short or mid-long term, these descriptors tending to have increased rather than decreased in the dredged plots after 1 year. The selective fishing for larger cockles reduced the average cockle size, but 1 year after fishing the average size had returned to the initial values in the dredged area. However, compared to the control area, the average size might still be reduced, as the size of the cockles in the control area also increased during the year. Local environmental conditions, with their specific macrobenthic communities, seem to be crucial for the type of effects and the impact of dredging. It is therefore of eminent importance to follow a research design with pre-defined environmental conditions, rather than a comparison of different areas that are open or closed to fisheries. The present study based on a BACI approach indicates that mechanical cockle fisheries had no overall negative impact in our study area.

Response of river nile dredging on water levels

Abstract: River transport is one of the main activities that affect the national economy; however, it is affected by the available water depths on the River. The water depths of the River Nile depend upon the morphological characteristics of the River and the water flow release. The River Nile flow varies seasonally during the same year. Safe navigation along the river is considered an important task for different low water levels scenarios. Therefore, it was decided to dredge many locations along the River Nile to achieve the required water depth in the low flow season. However, the dredging in some cases may have some negative impacts on river water levels. The purpose of this paper is to study the impact of dredging on River Nile water levels. The considered study reaches are extending from Old Aswan Dam to Delta barrages. Actual water levels and discharges were considered to monitor the changes of water levels. More detailed study was applied on the reach from Esna to Naga Hammadi using mathematical model to study the water level changes along the reach. Actual cross sections before and after dredging were considered. Study results, conclusions, and recommendation were illustrated at the end of the study.

Framework of the approximate cost estimating model for river dredging construction

Abstract: Recently, construction on the Four River Restoration Project began in South Korea. The project includes the maintenance of river embankments, the development of river areas, and river dredging. Accordingly, considerable attention is being paid to the necessary budget and estimation of construction costs. However, only a few studies have been carried out for the cost estimation of construction projects for river development or maintenance. In particular, approximate construction cost estimations for river dredging have not been studied. The lack of sufficient studies on estimating the approximate construction cost of river dredging has caused some doubt about the validity of the project’s estimated construction cost. This study proposes a framework of an approximate cost estimating model for river dredging construction. For this purpose, the construction operation process, type of river section, and the combination of equipment employed for river dredging were analyzed from the historical data of river dredging projects conducted in South Korea. The appropriateness of the analysis was examined through interviews with experts in the field. The framework of the approximate cost estimating model for river dredging construction proposed in this study provides a basis from which to develop a more accurate construction cost estimation of river dredging at the planning stage.

Environment-friendly dredger dredging reamer

Abstract: The invention relates to an environment-friendly dredger dredging reamer, belonging to the field of dredging technology The environment-friendly dredger dredging reamer comprises a reamer and a non-proliferation cover, and is characterized in that the non-proliferation cover consists of a fixed cover and a movable cover, wherein, the fixed cover is connected with the movable cover by a shaft, and the movable cover is connected with a hydraulic cylinder and is controlled to be opened by a hydraulic structure mode The dredging reamer saves the time used for clearing out sundries, improves theutilization rate of dredging time of a dredger, and reduces the dredging cost The proposal has the advantages of being convenient for dredging construction, reducing working strength of constructionpersonnel, improving the construction efficiency of environment-friendly dredging, etc The invention has good promotional value

Valorisation des sédiments de dragage de barrages algériens: Cas du barrage de Cheurfas

Abstract: In environmental geotechnics, the valorization of dredging sediments and their use in embankments is a way increasingly prospected by researchers these last years. This paper treats exploitation of dredging sediments of the dam Cheurfas (Algeria) and their valorization in road embankments. Physico-chemical, mineralogical and mechanical analyses were studied to determine their level of influence on the mechanical behaviour. These analyses showed that a treatment by sand, lime and cement proved to be necessary. Various formulations were elaborate in this direction and a synthesis of the mechanical characteristics was elaborate in accordance with the standards and the classification of materials used in road embankments.

Addressing an Optimal Schedule for Inlet Bypassing

Abstract: St. Augustine Inlet is located on the NE coast of Florida, connecting the Atlantic Ocean to the Tolomato and Matanzas rivers. The inlet is unique because it was relocated in the 1940s, resulting in considerable perturbations to the adjacent coastal system, especially the downdrift (southern) shoreline. The relatively low, permeable, and short north jetty has allowed sediment to move around, through, and over the jetty, resulting in deposits on the interior lagoon/bay and on the ebb shoal system. Since 2001, dredging has occurred on the ebb shoal and bypassed to the downdrift side of the inlet on St. Augustine Beach. At present, dredging and bypassing have occurred on an irregular schedule, although questions remain about what a reasonable schedule would be to prevent excessive problems on both the updrift and downdrift beaches. This article presents an evaluation of a potential approach for use in addressing the dredging and bypassing schedules to assess how various intervals of dredging/bypassin...