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[en] The use of a suction field aided by a jet system in a dredging process is one of the recent hydraulic methods in underwater dredging. The jet parameters have a great influence on the dredging efficiency. Jet induced impact energy that is required to initiate the bed motion and sediment pulsation is considered. Parametric sensitivity of various factors on dredging performance was carried out in an experimental set-up. Effects of changing the number of jets, jet geometry, suspension concentration, horizontal and vertical distances between jets and suction inlet on the dredging efficiency and the geometry of the excavation hole have been investigated. The results showed that several of these parameters have variable and significant effects on the dredging efficiency as well as the resulting geometry of the excavation. (author)
[en] Highlights: • The most important factor determining mortality in buried Crepidula fornicata was the thickness of the sediment layer. • The invasive non-native slipper limpet C. fornicata died when buried under ≥6 cm of sediment. • Duration, shell size or whether the species occurred in stacks or as individuals was not significant. • C. fornicata was able to emerge from shallow, 2 cm burial after 7 days. • C. fornicata was not found at a dredge spoils disposal site. - Abstract: The American slipper limpet Crepidula fornicata is an invasive, non-native species (INNS) abundant along the European coast. Its further distribution may be facilitated by activities such as dredging and spoil disposal, and the aim of this study was to assess whether C. fornicata is able to survive sediment burial. The slipper limpet was found attached to hard substratum in intertidal areas, but it was absent at a nearby subtidal dredge spoil site. In laboratory experiments 22% of C. fornicata emerged when buried under a 2 cm sediment-layer; only half of them survived. When buried under ≥6 cm none re-surfaced or survived. The results provided evidence that C. fornicata is poorly adapted to adjust its vertical position in sediment and is killed by sudden burial underneath 2 to 6 cm of sediment. The combined laboratory experiments and field surveys suggested that C. fornicata has limited scope to survive the dredge spoil disposal process.
[en] Radiotracers may be used to validate models of bed load transport with a range of applications in coastal engineering including: optimisation of the alignment of dredging channels and the location of dredge spoil grounds; the development of ports and harbours and the fate and behaviour of contaminants associated with particulates. The Port of Songkhla lies at the entrance to Songkhla Lake, a brackish tidal lake covering 1040 km2. Sedimentation of the dredged shipping channel at the Port of Songkhla in the Gulf of Thailand, poses a significant economic problem affecting Thai shipping. Large tidal flows pass through the 380 m wide channel to the Gulf of Thailand but long-shore transport supplies sand which is deposited in the channel. Engineering structures such as breakwaters and jetties result in severe coastal erosion problems along the coastline, but in contrast the beach south of the port experiences rapid accretion. To assist in addressing this problem a numerical model of the port entrance was developed and validated using radiotracer studies of actual sand transport in the area under an IAEA/RCA funded project involving Australia and Thailand. The principal aim of the investigation was to validate the model prediction of the bedload transport in the vicinity of the Port of Songkhla using tracer techniques so the model could be used to evaluate engineering options for port redesign
[en] In this study, the erosion properties of four sediments related to the Canaveral Ocean Dredged Material Disposal Site have been determined as a function of density, consolidation, and shear stress by means of a high shear stress sediment erosion flume at Sandia National Laboratories. Additional analysis was completed for each sediment to determine mineralogy, particle size, and organic content. This was done to support numerical modeling efforts, aid in effective management, and minimize environmental impact. The motivation for this work is based on concerns of dredged material transporting beyond the designated site and estimates of site capacity
[en] Highlights: • Proposals are set out to improve the monitoring of dumping sites. • Comparison of the efficiency of sampling strategies used to monitor a dumping site. • Study of the influence of sediment sampling replicates on confidence of results. • Sediment replicates to be sampled are linked to the environmental context. • The number of replicates is dependent on the prevailing environmental conditions. - Abstract: Dredged sediments have different physical and chemical characteristics compared with the sediments in place, which generates multiple effects on the environment. In this study, we show that the sampling strategy used to monitor the effects of dredge spoil deposition on the surrounding environment can lead to different interpretations. It appears that sediment sample replicates may or may not be necessary, depending on the studied area, the prevailing environmental forcings before sediment sampling and the combination of these two factors. The proposed modus operandi allows us to optimize both the confidence on the obtained results and the cost of the sediment studies (sampling and laboratory analyses). The results are based on the sediment fine fraction, which is considered as a key environmental component due, for example, to its strong association with the structure of benthic faunal communities as well as its role in the build-up of pollutants.
[en] Both interstitial water and plant tissue associated with the DC-A substrate exhibited low metal concentrations. Also in agreement with the previous study, plant performance in the DC-A substrate was found to be comparable to plant performance in the dredge spoil and topsoil substrates. This was extremely important because it indicated that the drill cuttings themselves served as an excellent substrate for wetland plant growth, but that the processing and stabilization techniques and drilling fluid formulations required further refinement
[en] This discussion highlights the impact of treating disposed material as barge loads, instead of as single particles. The specific objectives of this discussion are: to present the effect of initial plume dynamics on water column exposure time; and to qualitatively show the effect of horizontal diffusion of particulates in a water column and bed exposure to particulates. A model for instantaneous release of dredged material from a hopper dredge is adapted to illustrate these effects
[en] The guidelines for dredged material adopted by the Oslo Commission in June 1991 impose stricter obligations on its member states regarding the management of dredged material in the marine environment. It can be assumed that the basic ideas of these guidelines will become the model for inland waterways as well. For an environmentally acceptable management of dredging operations and the collection of evidence against polluters, ecotoxicological investigations on the behaviour of contaminants in waters are required in addition to chemical analyses. The practical application of these guidelines is hampered by the fact that no standardized biotests for sediments exist in Germany to date. The paper describes situations in which standardized biotest methods of aquatic ecotoxicology can already be used. A concept for the biological assessment of sediments is still lacking. It is necessary to define quality objectives for the evaluation of chemical and ecotoxicological data with a view to ecologically acceptable management of dredged material. (orig.)
[de]Die von der Oslo-Kommission im Juni 1991 beschlossenen Baggergut-Richtlinien legen den Vertragsstaaten verschaerfte Pflichten fuer die Unterbringung von Baggergut im Kuestenbereich auf. Es ist abzusehen, dass die Grundgedanken dieser Richtlinien auch fuer den Binnenbereich Modellcharakter bekommen. Fuer eine umweltvertraegliche Handhabung der Baggerungen und als Beweismittel gegenueber Einleitern von Schadstoffen sind ergaenzend zu den chemischen Analysen gewaessertoxikologische Untersuchungen erforderlich. Die Anwendung dieser Richtlinien wird dadurch erschwert, dass es in Deutschland noch keine standardisierten Sedimentbiotestverfahren gibt. Fuer welche Fragestellungen bereits heute Methoden der aquatischen Oekotoxikologie eingesetzt werden koennen, wird beschrieben. Ferner fehlt ein biologisches Bewertungskonzept fuer Gewaessersedimente. Kriterien fuer eine Einschaetzung der chemischen und oekotoxikologischen Daten hinsichtlich einer oekologisch vertretbaren Unterbringung des Baggergutes sind zu erarbeiten. (orig.)