Showing papers on "Dredging published in 2007"
TL;DR: In this article, the authors studied the effect of sand excavation in the Pearl River Delta (PRD) water system and found that >8.7 × 108 m3 of sand were excavated from 1986 to 2003 based on field surveys of excavating activities and the river hypsography, resulting in average downcutting depths of 0.59-1.73m, 0.34-4.43m, and 1.77-6.48m in the main channels of the West River, North River, and East River, respectively.
147 citations
TL;DR: This study investigated the possibility to strengthen the inference of dredging impact while simultaneously monitoring vessels and water turbidity in the northern Poyang Lake, China, where dredging was first introduced in 2001 and rapidly extended onwards and concluded that dredging caused the increase inWater turbidity.
134 citations
TL;DR: The extent to which cockle-dredging from 1998 to 2003 was selective with respect to non-target macrozoobenthic intertidal fauna is evaluated and four non- target species showed a significant decrease in abundance 1 year after dredging.
Abstract: Intertidal flats in the Dutch Wadden Sea are protected by national and international treaties. Still, mechanical dredging for edible cockles Cerastoderma edule was allowed in 74% of 1200 km(2) of interticlal flats. Cumulatively, between 1992 and 2001, 19% of the intertidal area was affected by mechanical cockle-dredging at least once. On the basis of a grid of 2650 stations sampled annually, we evaluate the extent to which cockle-dredging from 1998 to 2003 was selective with respect to non-target macrozoobenthic intertidal fauna. In all 4 years that comparisons could be made, to-be-dredged areas contained greater diversity of macrobenthic animals than areas that remained undredged. Targeted cockles were 2.5 times more abundant in areas that were to be dredged shortly, but other species also occurred in higher densities in these areas. Small amphipods and some bivalves occurred less in to-be-dredged areas than elsewhere. In terms of short-term responses to dredging, four non-target species showed a significant decrease in abundance 1 year after dredging. Only Tellina tenuis showed an increase a year after dredging.
69 citations
TL;DR: In this article, the potential impact of dredging on dissolved reactive P flux out of sediments and the equilibrium P concentration (EPCw) of post-dredge sediments were determined.
Abstract: Long-term phosphorus (P) loading to lakes has resulted in accumulation of P in sediments. Internal nutrient loading from sediments of shallow lakes such as Lake Okeechobee, Florida, has become a major concern in restoration programs. The objectives of this study were to determine (1) the potential impact of dredging on dissolved reactive P (DRP) flux out of sediments and (2) the equilibrium P concentration (EPCw) of post-dredge sediments. Intact sediment cores from one location representing P-laden mud sediments of the lake were obtained. Four simulated dredging treatments were implemented: control (no dredging-current conditions); top 30 cm; 45 cm; and 55 cm sediment removal. Phosphorus release/retention characteristics of sediments were determined at water-column DRP concentrations of 0, 0.016, 0.032, 0.064, and 0.128 mg/L. The water column in each core was replaced at approximately 60-day intervals, for a period of 1.2 years, with fresh lake water spiked with respective P concentrations. Signi...
67 citations
Journal Article•
TL;DR: In this paper, the authors compared the potential impacts of ditch dredging on water quality using a fluvarium (stream simulator) and found that the ditch bed material collected from drainage ditches prior to dredging was better able to remove NO3-N, NH4-N and soluble P from water than the ditch sediment collected from the bed of the ditch after dredging.
Abstract: Dredging of drainage ditches is necessary to ensure that agricultural fields are drained adequately. This study compared the potential impacts of dredging on water quality. Using a fluvarium (stream simulator), bed material collected from drainage ditches prior to dredging was better able to remove NO3-N, NH4-N, and soluble P from water than material collected from the bed of the ditches after dredging. Water column NH4-N concentrations were reduced to 0 mg L−1 (0 ppm) earlier in pre-dredged bed material. Nutrient uptake rates were greater for the ditch bed materials collected prior to dredging. Dredging decreased the specific surface area of ditch bed sediments and removed some of the biota responsible for nutrient uptake by the bed sediments in these ditches. Resource managers should perform maintenance tasks, including ditch dredging, when nutrient loads are expected to be low, thus minimizing the potential water quality impacts.
58 citations
TL;DR: Comparisons suggest that the flocculent sediment transport model can be used to predict the concentration profiles of a plume of toxic compounds resulting from cutterhead dredge operation.
58 citations
TL;DR: In this article, the effect of dredging intensity on the physical and biological recovery times of the seabed following marine aggregate dredging was investigated, using a combination of acoustic, video and grab sampling techniques.
Abstract: The aim of this study was to investigate the effect of dredging intensity on the physical and biological recovery times of the seabed following marine aggregate dredging. Two areas of seabed, previously subject to, respectively, relatively high and lower levels of dredging intensity, were identified on the Hastings Shingle Bank. Two reference areas were also selected for comparative purposes. All four sites were monitored annually over the period 2001–2004, using a combination of acoustic, video and grab sampling techniques. Since the site was last dredged in 1996, this was intended to provide a sequence of data 5–8 years after cessation of dredging. However, an unexpected resumption of dredging within the high intensity site, during 2002 and 2003, allowed an additional assessment of the immediate effects and aftermath of renewed dredging at the seabed. The early stages of recovery could then be assessed after dredging ceased in 2003. Results from both dredged sites provide a useful insight into the early and latter stages of physical and biological recovery. A comparison of recent and historic dredge track features provided evidence of track erosion. However, tracks were still visible 8 years after the cessation of dredging. Within the high dredging intensity site, recolonisation was relatively rapid after the cessation of dredging in 2003. Rather than indicating a full recovery, we suggest that this initial ‘colonization community’ may enter a transition phase before eventually reaching equilibrium. This hypothesis is supported by results from the low intensity site, where biological recovery was judged to have taken 7 years. Further monitoring is needed in order to test this. An alternative explanation is that the rapid recovery may be explained by the settlement of large numbers of Sabellaria spinulosa. As the resumption of dredging within the high intensity site limited our assessment of longer-term recovery it is not yet possible to assume that a 7-year biological recovery period will be applicable to other, more intensively dredged areas at this or more distant locations.
56 citations
TL;DR: Sediment nutrients and sediment organic carbon were observed to associate with the finer fractions (silt and clay) of sediments and a shift in sedimentary carbon from inorganic carbon to organic carbon was observed with the onset of the dredging activities.
Abstract: This monitoring study encompassed a period prior to dredging, during dredging and post dredging between July 1999 to June 2000 in Ponggol estuary located along the northeastern coast of Singapore. Mean concentrations of sediment nutrients in mg x Kg(-1) (+/- standard error of means) prior to dredging, during dredging and post dredging were 9.75 +/- 4.24, 8.18 +/- 4.29 and 11.46 +/- 4.74 for ammonium, 0.08 +/- 0.05, 0.06 +/- 0.02 and 0.09 +/- 0.01 for nitrite, 0.04 +/- 0.04, 0.11 +/- 0.17 and 0.25 +/- 0.30 for nitrate, 4.83 +/- 3.48, 0.77 +/- 0.48 and 8.33 +/- 9.73 for phosphate respectively. Pre dredge, dredge and post dredge levels of total carbon (TC) were 18.5 +/- 3.7, 20.2 +/- 3.5 and 34.6 +/- 12.0, of total organic carbon (TOC) were 10.5 +/- 2.9, 19.5 +/- 3.6 and 34.6 +/- 12.0 and of total inorganic carbon (TIC) were 7.9 +/- 1.0, 0.7 +/- 0.4 and non detectable in the sediments, respectively. Both, sediment nutrients and carbon registered lower concentrations with onset of dredging, with the exception of nitrate and TOC. A shift in sedimentary carbon from inorganic carbon to organic carbon was also observed with the onset of the dredging activities when the organically enriched historically contaminated layer was exposed. Sediment granulometry showed that the sediments in the estuary were predominantly silt and clay prior to dredging, which changed to sand with onset of dredging. Silt load in the sediments was highest post-dredge. Sediment nutrients and sediment organic carbon were observed to associate with the finer fractions (silt and clay) of sediments. Finer fractions of sediments get resuspended during a dredging event and are dispersed spatially as the result of tides and water movements. Prior to this study, the potential for nutrient release and sediment granulometry due to dredging have been suggested, but there have been few studies of it, especially in the tropics. The baseline information gathered from this study could be used to work out effective management strategies to protect similar tropical ecosystems elsewhere, should there be no other alternative to dredging.
54 citations
01 Jan 2007
TL;DR: In this article, the potential use of MODIS band 1 imagery in an optically sophisticated environment such as the Baltic Sea coastal waters for monitoring of total suspended matter in natural conditions and near dredging activities was investigated.
Abstract: KUTSER, T., METSAMAA, L., VAHTMAE, E. and APS, R., 2007. Operative monitoring of the extent of dredging plumes in coastal ecosystems using MODIS satellite imagery. Journal of Coastal Research, SI 50 (Proceedings of the 9th International Coastal Symposium), 180 – 184. Gold Coast, Australia, ISSN 0749.0208 MODIS band 1 imagery is the only satellite data with acceptable spatial resolution (250 m) and sufficient revisit times (up to 4 times a day) potentially available for monitoring dredging plumes. The aim of this study was to determine the potential use of MODIS band 1 imagery in an optically sophisticated environment such as the Baltic Sea coastal waters for monitoring of total suspended matter in natural conditions and near dredging activities. It was found that there is linear correlation between MODIS band 1 (620-670 nm) reflectance and the total suspended matter concentration measured from water samples. The regression algorithm was used to produce suspended matter concentration maps and monitor dredging activities. The results showed that in such shallow water environments as the Estonian Coast resuspension caused by strong wind may increase the suspended matter concentration to the levels similar to those occurring during dredging. Areas affected by wind resuspension are much larger than the areas affected by dredging plumes. Therefore, the natural variability of suspended matter concentration has to be taken into account when estimating environmental impact of dredging activities on local ecosystems.
47 citations
TL;DR: In this paper, the authors investigated whether there is any evidence of a large-scale cumulative impact on benthic macro-invertebrate communities as a result of the multiple sites of aggregate extraction located off Great Yarmouth in the southern North Sea.
38 citations
01 Jan 2007
TL;DR: The cumulative effect of fishing can lead to overfishing with a consequent decrease in the abundance of targeted species, the fisheries that depend on them and significant impacts on ecosystems as mentioned in this paper.
Abstract: The sustainable existence of particular fishing activities in a certain area depends on the maintenance of the stock of the target species in that area. The cumulative effect of fishing can lead to overfishing with a consequent decrease in the abundance of targeted species, the fisheries that depend on them and significant impacts on ecosystems. Ecosystem changes caused by fishing are mostly associated with mobile bottom gears, especially dredges, which impact the benthic habitat and associated assemblages of species. The magnitude of impacts from such fishing depends on factors such as the fishing frequency, towing speed, gear type, gear penetration into the sediment, time of year, local environmental conditions (such as water depth, tidal strength and currents), nature of the substratum and the structure of the benthic communities affected (de Groot 1984; Churchill 1989; Mayer et al. 1991). The environmental effects of shellfish dredging have received special attention throughout the world in recent decades (e.g., Caddy 1973; Conner and Simpson 1979; McLoughlin et al. 1991; Eleftheriou and Robertson 1992; Dare et al. 1993; Hall et al. 1993; Jennings and Kaiser 1998; HallSpencer and Moore 2000). These gears re-suspend and rework bottom sediments, move and bury boulders, reduce microtopography and may leave long-lasting grooves (e.g., Caddy 1973; Churchill 1989; Mayer et al. 1991). Sediment re-suspension by towed gears can alter the composition of sediments (usually to coarser grain sizes), reduce chemical exchanges in the water-sediment interface and increase water turbidity with deleterious effects on planktonic productivity (Hayes et al. 1984; LaSalle 1990; Coen 1995). Along with the target species, dredges also catch algae and other epifauna and infauna, many of which have no commercial value and are therefore discarded either alive or dead.
01 Nov 2007
TL;DR: In this article, the authors present guidance and best practices useful to evaluate dredged material from ongoing dredging projects or CDFs for beneficial uses (BUs), including habitat development, beach nourishment, aquaculture, parks and recreation, agriculture, forestry, and horticulture, Strip mine reclamation and solid waste management, 7) Shoreline stabilization and erosion control, 8) Construction and industrial use, 9) Material transfer, and 10) Multiple purpose.
Abstract: : The Corps of Engineers has the responsibility to maintain navigation of waterways across the United States. The Corps dredges more than 300 million cubic yards of sediment annually. Subsequently, methods to evaluate and determine environmentally and economically sound management alternatives are needed. Technological advances in equipment, treatment, and handling technologies continue to increase the options for beneficial uses (BUs). Ten categories of BU are: 1) Habitat development, 2) Beach nourishment, 3) Aquaculture, 4) Parks and recreation, 5) Agriculture, forestry, and horticulture, 6) Strip mine reclamation and solid waste management, 7) Shoreline stabilization and erosion control, 8) Construction and industrial use, 9) Material transfer, and 10) Multiple purpose. BUs of dredged material have a productive history resulting in over 2,000 man-made islands, more than 100 marshes, and nearly 1,000 habitat development projects. Corps islands provide vital habitat for rare, threatened, or endangered species. It is estimated that 1,000,000 birds nest on dredged material islands each year. BUs of existing dredged material in confined disposal facilities (CDF) should be considered along with all the alternatives available for CDF management. This report compiles current guidance and best practices useful to evaluate dredged material from ongoing dredging projects or CDFs for BUs.
TL;DR: Findings from the study demonstrated that the environmental dredging was an effective mechanism for removal of total phosphorus and heavy metals from South Lake, Nevertheless, the dredge was ineffective to remove total nitrogen from sediment.
Abstract: Environmental dredging is a primary remedial option for removal of the contaminated material from aquatic environment. Of primary concern in environmental dredging is the effectiveness of the intended sediment removal. A 5-year field monitoring study was conducted to assess the effectiveness of the environmental dredging in South Lake, China. The concentrations of total nitrogen (TN), total phosphors, and heavy metals (Zn, Pb, Cd, Cu, Cr, Ni, Hg, and As) before and after dredging in sediment were determined and compared. Multiple ecological risk indices were employed to assess the contamination of heavy metals before and after dredging. Our results showed that the total phosphorus levels reduced 42% after dredging. Similar changes for Hg, Zn, As Pb, Cd, Cu, Cr, and Ni were observed, with reduction percentages of 97.0, 93.1, 82.6, 63.9, 52.7, 50.1, 32.0, and 23.6, respectively, and the quality of sediment improved based on the criterion of Sediment Quality Guidelines by USEPA and contamination degree values (Cd) decreased significantly (paired t-test, p < 0.05). Unexpectedly, the TN increased 49% after dredging compared to before dredging. Findings from the study demonstrated that the environmental dredging was an effective mechanism for removal of total phosphorus and heavy metals from South Lake. Nevertheless, the dredging was ineffective to remove total nitrogen from sediment. We conclude that the reason for the observed increase in TN after dredging was likely ammonia release from the sediment impairing the dredging effectiveness.
TL;DR: The sediment-starved continental shelf off the central-west coast of Florida has traditionally supplied beach-quality sediments from ebb-tidal shoals and nearshore sand sheets, but as these supplies dwindle, sand searches increasingly look farther offshore for resources.
Abstract: Beach nourishment requires large volumes of sand from offshore and new sources are constantly sought for development. The sediment-starved continental shelf off the central-west coast of Florida has traditionally supplied beach-quality sediments from ebb-tidal shoals and nearshore sand sheets, but as these supplies dwindle, sand searches increasingly look farther offshore for resources. Widely spaced sediment ridges, interspersed by karstified limestone seafloor (hard grounds), offer potential as sand resources that can be exploited by dredging to renourish eroded beaches for shore protection. The sand ridges, late Holocene in age, are generally shoreface detached, sediment starved, and clustered in “ridge fields.” Six sediment ridge fields identified along 285 km of coast (Anclote, Sand Key, Sarasota, Manasota, Captiva, and Collier) contain about 1.4 billion cubic meters of sediments that are potentially available for dredging. Evaluation of these sediment sources, within the purview of the USMi...
TL;DR: In this paper, the authors focus on the physical changes through the analysis of historical survey data and the use of hydrodynamic modelling and evaluate whether dredging has influenced the estuary morphology or hydrodynamics and thus impacted on the ecological habitat.
Abstract: The Tamar Estuary, S.W. England, is a commercial and military port and the site of a major naval dockyard. Parts of the estuary require regular maintenance dredging and some capital dredging has been undertaken. The estuary is also assigned Special Area of Conservation (SAC) status under the European Habitats Directive and is an important site for migrating wildfowl and wading birds. As part of an assessment undertaken for a consortium of the port operators and regulatory authorities, we have analysed the ecological, physical, chemical and socio-economic impacts of dredging on the Tamar Estuary ecosystem. This paper focuses on the physical changes through the analysis of historical survey data and the use of hydrodynamic modelling. The objective was to evaluate whether dredging has influenced the estuary morphology or hydrodynamic regime and thus impacted on the ecological habitat. Bathymetric survey data collected between 1895 and 1968 were compared with multi-beam echo sounder data obtained in 2001. The paper survey records were digitised, geo-referenced and adjusted to the modern datum and units. The accuracy and limitations of this approach are discussed. Both sets of data were contoured and analysed using a GIS package. Comparisons between 1895 and 2001 hydraulics were made using a 1-D hydrodynamic and sediment transport model set up for the bathymetry at those times but ‘driven’ using a single, common, year-long data set for tides and river flows. The results suggest that although the deep channel in the region that is mainly south of the Tamar road bridge, is on average 0.5 m deeper in 2001 than it was in 1895, this has had a negligible effect on the area of intertidal mud and, thus, on habitat available for wading birds, and minimal impact on the large-scale hydrodynamics of the estuary.
TL;DR: In this article, the authors investigated the processes and time-scales of pits refilling at two extraction sites over 6 years following cessation of dredging, focusing on the evolution of a single pit at a gravel extraction site and the development of a group of three pits located at a sand extraction site.
Abstract: The growing demand for marine mineral resources introduces anthropogenic impacts in the coastal zone, among others also through aggregate dredging. Pits created by anchor hopper dredging may affect local sediment budgets, local hydrodynamics and biological habitats. In this study we investigate the processes and time-scales of pits refilling at two extraction sites over 6 years following cessation of dredging. We focused on the evolution of a single pit at a gravel extraction site and the development of a group of three pits located at a sand extraction site. In the case of the gravel pit, a series of six sonograph and two multibeam surveys were evaluated. We observed a spatial expansion of the edge of the pit, decreasing availability of screened sand in the neighbourhood of the pit (a possible source of refilling), and a slowing down of the refilling process with time. At the sandy pit site a series of seven sonographs and two multibeam surveys were available. We observed a smoothing of the edges and larger mean refilling rates than in the gravel pit case. We conclude that the most effective method for monitoring of pit evolution is to make measurements every six months by simultaneously deploying sidescan sonar and multibeam devices.
01 Jan 2007
TL;DR: In this article, a numerical coastline evolution model (LTC) is developed to support coastal zone planning and management in relation to erosion problems, which is used in the evaluation of the relative importance of each of the identified causes of coastal erosion at a medium term horizon.
Abstract: SILVA, R., COELHO, C., VELOSO-GOMES, F. AND TAVEIRA-PINTO, F., 2007. Dynamic numerical simulation of medium term coastal evolution of the West Coast of Portugal. Journal of Coastal Research, SI 50 (Proceedings of the 9th International Coastal Symposium), 263 – 267. Gold Coast, Australia, ISSN 0749.0208 Coastal erosion is a common problem within Europe. The main causes of this phenomenon are the generalised sea-level rise, the coastal interventions (defence and harbour structures), which cause serious perturbations in the littoral drift system, the littoral occupation and the river sediment supply reduction caused by dams, dredging and fluvial regularisation. Numerical models are helpful tools in future planning and management of coastal policies, by allowing the projection and analysis of different scenarios of medium term coastal evolution. A numerical coastline evolution model (LTC – Long Term Configuration) is being developed to support coastal zone planning and management in relation to erosion problems. The model simulates the dynamic variability of sandy beaches, where the alongshore sediment transport is controlled by waves, currents, wind, water level, sediments’ sources and sinks and sediments’ properties. The model also simulates different coastal interventions (groins and breakwaters, longitudinal revetments, artificial nourishments, river sediments supply). It may be applied to extensive coastal areas up to one hundred years time scale. In this paper, LTC will be used in the evaluation of the relative importance of each of the identified causes of coastal erosion at the Northwest Portuguese coast at a medium term horizon. Special attention will be given to the discussion of common coastal defence interventions influence in the littoral drift system and impact in what concerns erosion.
Book Chapter•
01 Jan 2007
TL;DR: In this paper, the authors present a review of different beach restoration projects conducted since 1992 till toda y at the northern coast of Cadiz (Chipiona and Rota counties) by analyzing the diffe rent coastal engineering and coastal management considerations used in their design.
Abstract: The main purpose of this paper is to present a crit ical review of different beach restoration projects conducted since 1992 till toda y at the northern coast of Cadiz (Chipiona and Rota counties) by analyzing the diffe rent coastal engineering and coastal management considerations used in their design. In particular, four different cases of beach nourishment projects are analyzed, having eac h one specific and interesting points to be stressed : a) Regla beach nourishment project ; b) Rota beach nourishment project; c) Punta Candor dune restoration project ; and d) L a Ballena nourishment project.
Journal Article•
TL;DR: In this article, the authors evaluated the potential of associated bed material changes to impact water column concentrations of atrazine, metolachlor, and glyphosate, and found that the bed sediments remaining after dredging, which had coarser texture and lower organic matter, may contribute to overall higher water herbicide levels in the short term by removing significantly less glyphosate from contaminated water and contributing marginally higher sustained levels of herbicide to uncontaminated water.
Abstract: In artificially drained agricultural areas, dredging of drainage ditches is often necessary to ensure adequate field drainage. Stream-simulator (fluvarium) experiments were performed to evaluate the potential of associated bed material changes to impact water column concentrations of atrazine, metolachlor, and glyphosate. In the first experiments, water having high herbicide concentrations flowed across bed sediment collected from a ditch immediately before or after dredging. Afterward, water having initially zero herbicide concentrations flowed across these sediments. Results indicate that the bed sediments remaining after dredging, which had coarser texture and lower organic matter, may contribute to overall higher water herbicide levels in the short term by removing significantly less glyphosate from contaminated water and contributing marginally higher sustained levels of herbicide to uncontaminated water, applicable where sediments exhibit similar dredging characteristic effects. In this case, dredging when herbicide levels are expected to be lowest can help minimize increased transport of some herbicides.
Patent•
29 Aug 2007
TL;DR: In this paper, a river bottom mud dredging dewatering process technology is described, which includes the following steps: dredging river bed, separating mud and sand, separating sand and water, de-watering and sterilizing.
Abstract: The invention discloses a river bottom mud dredging dewatering process technology that includes the following steps: dredging river bed, separating mud and sand, separating sand and water, dewatering and sterilizing. The processed water could reach the discharging standard, and could be recycled. It supplies a entire, low cost and high value method to treat river course.
TL;DR: In this paper, the stability of sand spit is studied with different criteria and the results confirm that the mouth is a near permanent zone of deposition, and a dredging scheme has to be designed without affecting the spit stability.
01 Jan 2007
TL;DR: In this paper, the authors propose a novel approach to deal with the problem of plagiarism in online learning, e.g., this paper...,.. ].
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Patent•
26 Apr 2007
TL;DR: In this paper, a closed grab bucket axially supported at a distal end of an arm of a backhoe shovel is used to carry out horizontal excavation in a dredging support system.
Abstract: PROBLEM TO BE SOLVED: To provide a dredging support system for dredging a subaqueous bottom in a dredging objective zone easily by a constant thickness with a high accuracy by using a closed grab bucket. SOLUTION: In the dredging support system, the closed grab bucket 5 axially supported at a distal end of an arm 4 of a backhoe shovel 1, has a structure that can carry out horizontal excavation. Then, calculation is made based on detection data of a plurality of sensors 19, 20, 21, an RTK-GPS receiver 24, etc., of inclination data of the grab bucket 5 with respect to a vertical shaft, plane directional data indicative of a plane directional location of the grab bucket 5 and a maximum opening region at the plane directional location, and height directional data indicative of a height directional corresponding to a cutting edge location of a pair of shells 7, 7, and the calculated data are displayed on a monitor of an operating chamber 2a in rear time. Further, a plane directional region already dredged and desired depth data indicative of a dredging depth location set beforehand in the dredging objective zone are displayed. COPYRIGHT: (C)2009,JPO&INPIT
TL;DR: Sediment dredging can effectively lower the contents of nutrient, heavy metals and persistent organic pollutants in sediment, but resuspensiou of sedi- ment during dredging will induce the release of pollutants from sediment to the water column.
Abstract: The effectiveness of sediment dredging is still strongly debated up to now,and the environmental effects resulting from sediment dredging may be not ideal as the people have expected.Sediment dredging can effectively lower the contents of nutrient,heavy metals and persistent organic pollutants in sediment,but resuspensiou of sedi- ment during dredging will induce the release of pollutants from sediment to the water column.In addition,the inter- face processes will exert great influence on the dredging effect.There are successes and lessons for the control of eutrophication,different effects appear for the control of the release of nutrients in different lakes.Sediments dred- ging has dverse effcets on benthos,e.g.decreases of taxa numbers,abundance and biomass.Moreover,there could be a change of community composition and a fall in the diversity.Extracellular enzymes activities could be depressed significantly.As a result,sediment dredging has profound impact on the hydrolytic activities of sedi- ments.It is a long term for the recovery of benthos and enzymes activities.The effectiveness of sediment dredging on water pollution control is usually time-limited.The methods of dredging,the depth of dredging,as well as the season when dredging is carried out should be concerned in dredging program implementation.
TL;DR: A kinetic model using a mass balance approach incorporating dredgehead particle generation, particle settling, biphasic desorption, flux from the sediment bed, and evaporation to air has been developed for plug-flow stream hydraulics.
Abstract: Sediment particles can be displaced from the bed to the water column by both natural processes and human activities. Navigational and environmental dredging operations are known to generate particularly high concentrations of suspended sediment and have a significant environmental impact. Once contaminated particles are resuspended a fraction of particle-sorbed chemical is dissolved and equilibrium models are typically used to estimate chemical release. A kinetic model using a mass balance approach incorporating dredgehead particle generation, particle settling, biphasic desorption, flux from the sediment bed, and evaporation to air has been developed for plug-flow stream hydraulics. A key model output for steady-state dredging is concentration in water vs. distance downstream. Typical results for mechanical and hydraulic dredges operating at two sites, the Fox River and Indiana Harbor Canal, will be presented. The kinetic model shows lower concentrations than the equilibrium model in all cases. The most ...
TL;DR: The bottom sediments of the turbidity maximum area of the Scheldt estuary were mapped in 1999 using echo sounding, sidescan sonar and grain-size analyses of bottom sediment as mentioned in this paper.
Abstract: The bottom sediments of the turbidity maximum area of the Scheldt estuary were mapped in 1999 using echo sounding, sidescan sonar and grain-size analyses of bottom sediments Four sediment types, sand, muddy sand, sandy mud and mud were recognised Mud, with very little sand, occurs mainly in the access channels to the sluices giving access to the harbour docks of Antwerp The sediments of the main channel have a sandier texture One might conclude that the total mud stock in the middle estuary has increased, both between 1964–1986 and 1986–1999, but on the contrary the mud supply from the river, the mud stock in the river channel and the mud supply to the lower estuary have all decreased The increase in the mud stock in the area as a whole was completely at the expense of mud deposition in the access channels to the sluice gates giving access to the harbour of Antwerp The mud stock in the river channel decreased over the years because of a decreasing mud supply from the river The mud stock in the rive
Patent•
29 Mar 2007
TL;DR: The in situ conditioning by remedial dredging method for maintenance of navigable depths in air-locks, outer ports, sea lanes and rivers, comprises ventilation of silt/mud present at bed of the water bodies by contacting with atmospheric oxygen using dredging/desilting procedure or by supplying oxygen-containing water into the bed sites.
Abstract: The in situ conditioning by remedial dredging method for maintenance of navigable depths in air-locks, outer ports, sea lanes and rivers, comprises ventilation of silt/mud present at bed of the water bodies by contacting with atmospheric oxygen using dredging/desilting procedure or by supplying oxygen-containing water into the bed sites. The fluid mud formations and deposited bacterial cultures are activated for the improvement of the fluidity by enhancement of the aerobic conditions. The activation serves for the production of microbial slime through bacteria. The in situ conditioning by remedial dredging method for maintenance of navigable depths in air-locks, outer ports, sea lanes and rivers, comprises ventilation of silt/mud present at bed of the water bodies by contacting with atmospheric oxygen using dredging/desilting procedure or by supplying oxygen-containing water into the bed sites. The fluid mud formations and deposited bacterial cultures are activated for the improvement of the fluidity by enhancement of the aerobic conditions, and for the production of microbial slime through bacteria. The sedimentation of the slime is minimal due to its very less specific density than that of the surrounding water and slip property that is the nautical locomotivity of the slime remains high.
TL;DR: In this paper, the authors studied seasonally psychrophilic, mesophilic and denitrifying bacterial abundances in the water column and surface sediment layer (0-5 cm) in the post dredging pit Kuźnica II and natural areas of Puck Bay.
Abstract: Abstract In this study psychrophilic, mesophilic and denitrifying bacterial abundances were studied seasonally (summer, autumn, winter and spring) in the water column and surface sediment layer (0-5 cm) in the post dredging pit Kuźnica II and natural areas of Puck Bay. The research was conducted between VI 2001 and III 2003. In the pit area an increase in mesophilic bacteria and a decrease in denitrifying bacteria numbers were observed, when compared to the natural areas. In the case of the mesophilic bacteria, the increase was visible in the near-bottom waters and surficial sediments during the period of well developed vegetation - in summer and autumn. In the case of denitrifying bacteria, the decrease of number concerned the sediments. Numbers of psychrophilic bacteria in both the natural and dredged areas did not differ significantly over the course of the study. These results suggest that deep dredging can cause the self-purification potential of the ecosystem to be diminished and induce strong bacteriological pollution.
Dissertation•
01 Jan 2007