Relocation of Dredged Material from Marano and Grado Lagoon: An Example of Sustainable Management

The high degree of dynamism of coastal and lagoon morphodynamic processes often implies the need for dredging operations to maintain the navigability of the main waterways towards harbours or sites which have important tourist or economical value. In particular, within sheltered and shallow lagoons this phenomenon is continuous and involves large volumes of material that requires to be properly managed. The dredged materials can provide sediments for environmental enhancement and they can be used, as an example, to create or improve habitats, mudflats and salt marshes. Numerical model can be a valuable tool to investigate the morphological evolution of the disposals, especially in the medium term, with the aim of verifying the sediment stability and the bed level changes. The present paper shows an example of sustainable management of cohesive materials dredged from two channels of the Marano and Grado lagoon. The non-linear interactions between tidal currents and locally generated wind waves are reproduced by means of a coupled spectral-hydrodynamic model associated with a transport equation to compute sediment load concentration. The comparison of the results confirms the validity of the adopted procedure.

Impact of Dredged Material Disposal on Heavy Metal Concentrations and Benthic Communities in Huangmao Island Marine Dumping Area near Pearl River Estuary

The Huangmao Island dumping area is adjacent to the Pearl River Estuary in the South China Sea. From its first dumping activity in 1986 to 2017, 6750 × 104 m3 dredged materials were dumped in this dumping area. Sediment pollution levels, ecological risk, and benthic communities in 2011–2017 were evaluated; the results showed that the concentrations of the heavy metals (HMs; except Hg) in surface sediments of the dumping area met the class I standard of marine sediment quality (GB 18668-2002). HMs in the surface sediments were relatively high in the northern and central areas but relatively low in the south of the dumping area. Speculation was that the spatial variation in HM concentrations might be caused by dumping activities. The Nemerow index implied that the contaminated area was mainly in the north of the dumping area (S1, S2, and S3), where the dumping amount was the largest. The potential ecological risk (Eir) indices of Zn, As, Cu, and Pb indicate that these metals posed a low risk to the ecosystem of the dumping area, whereas Cd and Hg posed a high risk at some stations. The geoaccumulation indices (Igeo) of Zn, As, Cu, and Pb specified no pollution or light pollution in the study area, whereas those of Cd and Hg in most years indicated mild contamination levels. Benthic organisms in the study area were arthropods, chordates, annelids, mollusks, echinoderms, nemertinean, coelenterate, and echiuran, among which arthropods were the most abundant. The abundance of taxa and density of benthic organisms had a little difference among the stations within the dumping area, but were significantly lower than those of the stations outside the dumping area. In addition, non-metric multidimensional scaling analysis confirmed that the observed patterns separated the stations within the dumping area from stations outside the dumping area. The evaluation results of the HMs revealed that the dumping area with a large dumping amount was more severely polluted. Dumping dredged materials seemed to have a negative impact on the benthic community in the dumping area.

The Impact of Waves and Tidal Currents on the Sediment Transport at the Sea Port

Dredged sediments in estuarine and coastal waters can cause sediment transport and water pollutant in marine environment since the sediments are diffused to waterbodies under the influence of wave and flow regimes. As a result, it increases turbidity and enhances sediment deposition at dump sites. In Vietnam, few authors have studied and assessed the environmental impact of dumping and dredged materials to the port areas. This paper combines a coupled spectral wind-wave, hydrodynamic, and sediment transport models in order to study the impact of tide and wave conditions to regional sediment transport patterns at Vung Ang port area in Vietnam. The results for the currents and waves were evaluated and validated using field data. Wind and wave data for the calculated domain are extracted from the WAVEWATCH-III (wave data) and NOAA global climate change models (wind data). The calibration and validation of the MIKE 21/3 showed a high conformity between the observed and simulated data based on the mean absolute error (MAE), the RMSE-observation standard deviation ratio (RSR) and the Percent bias (PBIAS). The MIKE 21/3 sediment transport simulation results showed that the highest suspended sediment concentrations were 2.5-3 g/m3 at the dredging position and the increased concentration along the transport route ranged from 1-1.5 g/m3. The simulation results showed the bed level change of the simulated domain. We found that the suspended sediment diffusion area decreased with the respective depth: Layer 1 (65.5 km2), Layer 2 (45.7 km2), and Layer 3 (37.4 km2). Therefore, the simulation results of the dredged materials activities were significantly affected by the wave and tidal regime on the sediment transport. Doi: 10.28991/cej-2021-03091749 Full Text: PDF

Analysis and Stabilization of Dredged Material Using Marble Dust for Its Potential Use in Sub-Grade

This research paper deals about the experimental study on the stabilization of dredged material for its potential use in sub-grade. Large amounts of sediments are dredged from rivers and lakes as a result of environmental dredging in India. These dredged materials have poor geotechnical properties and are treated as wastes, On the other hand, there is a huge demand of sub-grade materials due to the increasing number of highway construction projects, so therefore it forms the significant topic for research. The stabilization of dredged material by marble dust is considered as an environmentally friendly option and economical because both marble dust and dredged material are waste products. Marble dust is formed by the cutting and polishing of marble stone. Marble dust contains high amount of calcium, silica, alumina which aids in the stabilization of the dredged material. Thus, the use of DM as sub-grade material may be considered as an environmentally friendly and economical option. Keywords: Dredged material, stabilization, environmental dredging, Subgrade etc

Inverse Infiltration Modeling of Dike Covers Made of Dredged Material Using PEST and AMALGAM

A variety of studies recently proved the applicability of different dried, fine-grained dredged materials as replacement material for erosion-resistant sea dike covers. In Rostock, Germany, a large-scale field experiment was conducted, in which different dredged materials were tested with regard to installation technology, stability, turf development, infiltration, and erosion resistance. The infiltration experiments to study the development of a seepage line in the dike body showed unexpected measurement results. Due to the high complexity of the problem, standard geo-hydraulic models proved to be unable to analyze these results. Therefore, different methods of inverse infiltration modeling were applied, such as the parameter estimation tool (PEST) and the AMALGAM algorithm. In the paper, the two approaches are compared and discussed. A sensitivity analysis proved the presumption of a non-linear model behavior for the infiltration problem and the Eigenvalue ratio indicates that the dike infiltration is an ill-posed problem. Although this complicates the inverse modeling (e.g., termination in local minima), parameter sets close to an optimum were found with both the PEST and the AMALGAM algorithms. Together with the field measurement data, this information supports the rating of the effective material properties of the applied dredged materials used as dike cover material.

Use of concrete formulations based on dredging sand in the fabrication of tetrapods for protection of harbour dykes

Port structures (quays and dykes) need an enormous consumption of materials, in particular concrete and its components, as well as sand, hence the need to develop alternative solutions using port dredging sand, estimated at thousands of tonnes through its use in the concrete that forms the blocks of the quay walls. After having demonstrated in a previous work the possibility of using the dredged sand from the port of Agadir in concrete formulations, the present work consists in showing the possibility of using the dredged sand from the port of Agadir in concrete formulations that can be used in the construction of concrete tetrapods from a concrete formulation based on dredged sand, more precisely 50% of the sand entering in the formulation is dredged sand extracted from the port of Agadir. The eventual use of dredged sand in the concrete of the tetrapods will lead to enormous gains in the quantities of sand and thus to a lower consumption of construction materials, and will also play a more important role in the preservation of the marine environment by avoiding the trapping of the dredged materials.

Incorporating Color Change Propensity into Dredged Material Management to Increase Beneficial Use Opportunities

Dredged materials provide a number of beneficial use opportunities, including beach nourishment, habitat creation and restoration, and other activities. In situ sediment color is important for determining aesthetic and habitat suitability, for beach nourishment, and for other projects. However, dredged materials must meet locally established color compatibility requirements (for example, material cannot be too dark). Often, potential sediment sources are close to meeting specified color thresholds, and previous observations suggest that sediments lighten over time. In response to these observations, this study quantified sediment color change potential in a dredged m aterial management context. Results indicate that dredged material sediment color responded to changes in secondary color components, sediment mixing, and photolytic bleaching improving the sediment color for beneficial use application. Findings allowed for development of a conceptual color change capacity framework and supported development of tools for resource managers to incorporate color change dynamic into planning and operations activities.The following report provides a framework for determining the color change capacity of dredged materials using (1) a comprehensive laboratory approach and (2) a semiquantitative index based on source material and placement location conditions. These tools allow practitioners to incorporate dredged-material color change into resource management decisions, thus increasing beneficial use opportunities.

Zoning Marine Disposal to Minimize Environmental Impacts for Dredged Material Management: A Case Study in Hai Phong Port Area, Vietnam

The fast growth of Hai Phong ports in the two last decades requires not only their upgrading facilities but also expanding port area and dredging their shipping channels (existing and new ones) that generate a huge amount of unreused dredged materials. While all existing dumping sites in sea waters and onland get over capacity, looking for new dumping sites in sea waters is an urgent need. This study is to zone coastal waters of Hai Phong for suitable dumping sites meeting sustainable coastal management. Multi-criteria overlay analysis on GIS platform was employed with criteria of natural conditions, environment and socio-economics for zoning coastal waters of Hai Phong. These criteria were detailed into eight sub-criteria and then developed to eight GIS weighted thematic sub-layers of bottom depth, litho-hydrodynamics, ecosystems, distribution of benthos, distance to residential areas and tourist sites, distance to aquaculture area, distance to ecosystems and distance to conservation areas. Analysis results show the highly suitable zones for dredged material dumping in South, South West Hai Phong at depth below 15m to the deeper areas. Disposals of dredged materials in the zones would minimize impacts on the environment, ecology and socio-economics in surrounding waters and coastal areas.