Dispersion Plumes in Open Ocean Disposal Sites of Dredged Sediment

Management of estuarine systems under anthropogenic pressures related to port settlement and development requires thorough understanding about the long-term sediment dynamics in the area. In an era of growing shipping traffic and of ever larger ships; millions of tons of bottom sediments are dredged annually all over the world and the major question concerning dredging operations is not whether they should be done, because it is obvious that they are extremely important and necessary, but where the dredged sediments can be disposed of with the least possible ecological impact. The present study involves the evaluation of transport trends of dredged material from a turbid estuary disposed of in four different open ocean disposal sites using numerical model techniques, aiming to contribute to minimizing potential environmental impacts and maximizing efficiency of the dredging operation. The study is carried out in southern Brazil, investigating the fate of dredged material from the Port of Rio Grande, located inside the Patos Lagoon estuary. Simulations were carried with the TELEMAC-3D model coupled with the suspended sediment (SEDI-3D) module and incorporating results from the wave module (TOMAWAC) to evaluate the dispersion of the suspended sediment plume and its interaction with coastal currents. This modeling structure proved to be a valuable tool to study the hydrodynamics and sediment transport pathways in estuarine and coastal areas. Results indicate that the natural Patos Lagoon coastal plume was observed under the predominant ebb flows and NE winds, promoting fine sediment entrapment south of the mouth of the lagoon (in front of Cassino Beach). The dispersion plumes in the disposal sites responded to the wind intensity and direction and did not present any transport tendency towards Cassino Beach. Part of the dredged sediment disposed of in the proposed alternative sites located in deeper areas (Sites B and C) left the site and was transported parallel to the coast (SW–NE direction) according to the wind direction (NE–SW). The area where the disposal sites were located took around 4 days to recover from the dredging operation and reach the usual suspended sediment concentrations and the actual Port of Rio Grande Licensed Site for dredged material proved to be the best alternative among the investigated options

Analysis of Late Pleistocene megafauna and puparia from the Lent dredging site, province of Gelderland (the Netherlands)

More than 900 vertebrate bones, ranging from Late Pleistocene to Holocene in age, have been identified in a collection that was recovered by a single dredging operation for the construction of artificial lakes near Lent (Nijmegen, province of Gelderland, the Netherlands). The Late Pleistocene assemblage comprises mainly Weichselian glacial fauna such as mammoths, reindeer and bison. Some Eemian fauna is represented as well, e.g. straight-tusked elephant. The abundance of certain species over others suggests that preservation bias had a considerable impact on this assemblage, while its time-averaged nature resulted in overrepresentation of certain species. A case study is here conducted on a fragmentary skull of a subadult woolly mammoth bull with embedded blowfly puparia. Some of these puparia are fully developed, indicating prolonged exposure of the mammoth carcass.

Substantial Decrease in Contaminant Concentrations in the Sediments of the Venice (Italy) Canal Network in the Last Two Decades—Implications for Sediment Management

The Venice canal network requires periodic intervention to remove sediments that progressively accumulate. The most recent dredging operation was carried out in the second half of the 1990s and early 2000s. These sediments had accumulated over a period of more than 30 years and were highly contaminated with Cd, Cu, Hg, Pb, Zn and PAHs. Sediments deposited after the dredging work were investigated in 2005, 2009, 2014 and 2017 by analysing sediment cores collected from three sites in the canal network. Arsenic, heavy metal and PAH concentrations were observed to be much lower than past values, although Cu, Hg and PAH levels were still relatively high. The high Cu concentrations (mean 161 mg kg−1) are partly due to the widespread use of Cu-based antifouling paint. Current Italian regulations forbid the disposal of dredged sediments with these concentrations inside the lagoon, thereby increasing the cost of canal network maintenance.

EFFECT OF DREDGING ON HG DISTRIBUTION IN WATER AND SEDIMENTS IN THE MUCURIPE HARBOR, FORTALEZA, NE BRAZIL

Dredging and tailings disposal can mobilize mercury (Hg) accumulated in bottom sediments, increasing the exposure of the aquatic biota. In the Mucuripe Harbor, NE, Brazil, dredging is performed regularly, but the impact on Hg mobilization is unknown. This paper presents results from the monitoring of a dredging operation to characterize and quantify an eventual Hg mobilization. The results showed that remobilization is significant and is associated with suspended solids. Further deposition of the Hg-enriched, remobilized, suspended solids increased Hg concentrations by a factor of 1.2 and 2.0 in harbor and shelf sediments, respectively. Maximum concentrations in harbor and shelf sediments reached 79.9 ng.g-1 and 32.4 ng.g-1 (20 and 9 higher than the regional background, respectively). The progressive increase in Hg concentrations may result in higher exposure to the local biota.Keywords: metals, mobilization, contamination, coastal sediments.

Project Evaluation Review Technique Model to Dredging Operations in Niger Delta

This research applies Project Evaluation and Review Technique (PERT) model to estimate acceptable duration for execution of each activity having random variable of time and some probability distribution for sand dredging operation in Niger Delta. The study takes into account proper planning, scheduling, controlling and allotment of dredging activities time using a project network model PERT. The model evaluated how acceptable time and saving cost could be achieved in a scenario of activities having random time variables. Readily available data of activities time from 2014 – 2017 were used to analyze the time estimate for various activities at a selected dredge site Aleto-Eleme in Port Harcourt metropolis Rivers State-Nigeria. The PERT was applied for the data analysis, to construct the PERT scheme for the dredging operations. Finally, parametric control for project evaluation and review techniques of acceptable time for the dredging activities were determined.