Dredging

About: Dredging is a research topic. Over the lifetime, 3300 publications have been published within this topic receiving 28325 citations.

In situ capping of contaminated sedi- ments: comparing the relative ef- fectiveness of sand versus clay min- eral-based sediment caps

Abstract: Ecological problems caused by sediment contamination occurring in deep water or wetland environments may be addressed through natural recovery, in-place containment or treatment, dredging and removal, or in some cases by in situ capping – which is defined as the placement of a subaqueous covering or cap of clean isolating material over an in-place deposit of contaminated sediment. While dredging and removal of contaminated sediments may be the most practical remedial method in many situations and sometimes necessary for navigational purposes, this remedial approach may not be the most environmentally protective and/or costeffective approach. In situ capping approaches are often considered to be more protective of faunal and floral communities inhabiting impacted ecosystems than dredging alternatives, or when converting an impacted area to a closed cell. According to current regulatory philosophy and recommendations, the three primary functions of an in situ sediment cap include (1) physical isolation of the contaminated sediment from the benthic environment; (2) stabilization of contaminated sediments, preventing re-suspension and transport to other areas or sites; and (3) reduction of the flux (transport) of dissolved contaminants into the overlying water column. To date, most in situ capping projects appear to involve the use of primarily granular (i.e., sandy) capping materials. Although such capping materials may adequately serve to meet stated cap functions at many sites, their relatively high permeability and low organic matter and clay content may limit their ability to reduce contaminant transport into the overlying water column. Furthermore, non-cohesive, granular materials can also be prone to erosional losses and redistribution, thus minimizing their effectiveness in isolating and stabilizing contaminated sediments. Finally, the thickness required to meet performance goals, many times on the order of several feet, can have a deleterious effect on channel hydraulics and waterway uses. As an alternative to granular sediment caps, a new in situ capping technology, AquaBlok™, has been developed for use in either deep water or wetland ecosystems. AquaBlok™ is a clay mineral-based capping material that offers several functional advantages over granular capping materials including lower permeability, higher resistance to erosive forces, and considerably higher attenuation capacity for many types of contaminants. The likely need for thinner AquaBlok™ caps at many sites would also minimize navigational constraints. In this paper, we compare the potential relative effectiveness of a typical granular sediment cap to that of a typical AquaBlok™ sediment cap, as each would be installed into “typical” impacted deep water or wetland ecosystems.

Ecological Aspects of Coastal Sediment Management in the Gulf of Mexico

Abstract: Reed, D.J.; Hijuelos, A.C., and Fearnley, S.M., 2012. Ecological aspects of coastal sediment management in the Gulf of Mexico. In: Khalil, S.M., Parson, L.E., and Waters, J.P. (eds.), Technical Framework for the Gulf Regional Sediment Management Master Plan (GRSMMP), Journal of Coastal Research, Special Issue No. 60, 51–65. Water and sediment resource planning is a vital facet of natural resource management. There have been many ecologically disruptive consequences from conventional resource management plans. In the northern Gulf of Mexico (GOM) nearby communities depend on water and sediment resources both ecologically as well as economically. The value of these resources is determined by habitat structure and ongoing sediment dynamics. This article explores how human activities have changed sediment dynamicsin relation to the ecology of the habitats present in the northern GOM. It further presents ideas to prevent future problems through sediment management plans that account for natural processes. The northern GOM contains several habitats that are affected by sediment/water resource management plans such as the shoreface (beaches and dunes), barrier islands, hardbottom (coral and oyster reefs), bays, marshes, and forested wetlands. Many common techniques for water/sediment resource management have been used in these areas such as dredging, hard structures (jetties, groins, seawalls, andbreakwaters),dams, diversions,levees,and coastaldevelopment. The implications of these different management techniques can lead to extensive changes in coastal habitats. Dredging causes disturbances to both borrow and placement sites and can change natural community structure at both sites. The installation of hard structures can cause severe changes in habitat structure that can lead to losses of species diversity. The impacts of river management structures (dams, levees, and diversions) alter the delivery of sediment needed by coastal habitats for growth and sustainability. Anthropogenic development in coastal regions prevents those areas from maturing naturally. Because of the importance of sediments to the ecology of the northern GOM coast and its vulnerability to natural and anthropogenic disturbances, several recommendations are made for holistic future sediment management plans.

A framework for the integrated assessment and management of dredged materials in Italy: a case study based on the application of Local Sediment Quality Guidelines

Abstract: In order to assess sediment quality and to account for the great geochemical heterogeneity of Italian coasts, Local Sediment Quality Guidelines (LSQGs) have to be defined for specific portions of the coastline based on the approach developed by ICRAM–APAT (2007). This paper describes the application of LSQGs to the harbour of Fiumicino (Rome, Italy). The aims were to evaluate the quality of dredging sediments through an integrated chemical–ecotoxicological approach and to define suitable management options. Thirty-eight sediment cores, covering the planned dredging depth, were collected in the study area and sliced into 92 sediment samples. Chemical analyses, including inorganic and organic contaminants as well as microbiological parameters, were carried out for all the samples. A bioassay battery composed by the bacterium Vibrio fischeri, the sea urchin Paracentrotus lividus and the alga Dunaliella tertiolecta was applied on one third of the samples. LSQGs were derived from chemical and ecotoxicological data of the harbour area, and were integrated with those from the identified dumping site. The Baseline Chemical Level, corresponding to an absent or unlikely ecotoxicological hazard, and the Limit Chemical Level, corresponding to a probable ecotoxicological hazard, were the LSQGs derived for each chemical. A gradient of increasing contamination, moving inland due to urban and agricultural effluents, was observed. Ecotoxicological analyses, similar to microbiological ones, confirmed the poor sediment quality, with the exception of a sample located at the port entrance, where hydrodynamics flush sediment away from the site. Principal component analysis allowed a clear discrimination of three areas, each affected by a different contamination degree and influenced by many sources related to industrial, commercial and/or urban activities. Using LSQGs and the results of bioassays, it was possible to classify the sediment quality of the whole harbour area and to define the most suitable management options. It was found that Fiumicino harbour sediment was not suitable for either beach nourishment or for offshore dumping, with the exception of a negligible amount located at the port entrance. In turn, most sediment seemed to be suitable for disposal in a properly sealed confined disposal facility or for mechanical/chemical treatment. This case study provided useful insights for implementing the development of LSQGs for more realistic sediment management and will assist in promoting its application to harbour dredging at the local level.

BACI monitoring of effects of hydraulic dredging for cockles on intertidal benthic habitats of Dundalk Bay, Ireland

Abstract: Hydraulic dredging for bivalves, such as cockles (Cerastoderma edule), has the potential to cause significant impacts on marine intertidal benthos. Although this fishing activity is common in northern European Natura 2000 sites such impacts may be incompatible with conservation objectives for designated habitats and species within these sites. In 2009–2010 a spatially nested control-impact study was undertaken before (t0), 8–9 days after (t1) and 4 months (t2) following dredging and extraction of 108 tonnes of cockles from a standing stock of 2158 tonnes in Dundalk Bay. This study failed to detect significant effects on benthic sediments, or the overall community structure. However, a fishing effect on the target species C. edule in one sampling area and a short lived effect on the bivalve Angulus tenuis were identified. Significant spatial and temporal variability in abundance of species and taxonomic groups, unrelated to fishing effects, was observed. Previous studies on the effects of fisheries on marine intertidal benthos have reported variable results, related to study design and objectives and the physical characteristics of the study site. Site specific studies, relative to the intensity and frequency of proposed fishing activity, may be required to adequately inform managers whether such activities are compatible with specific conservation objectives for Natura 2000 sites.

Pollution and toxicity of sediment in potential dredging sites of the Marmara Sea, Turkey

Abstract: This study aims to assess the impact of the sediment in the potential dredging areas of the Marmara Sea. To that aim, sediments were analyzed for polycyclic aromatic hydrocarbons (PAHs), polychlori...