Dispersion Plumes in Open Ocean Disposal Sites of Dredged Sediment

Abstract

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

Detecting turbid plumes from satellite remote sensing: State-of-art thresholds and the novel PLUMES algorithm

“…It is connected to the south Atlantic Ocean through a narrow inlet with less than 700 m width. This single inlet shelters the navigation channel of one of the most important commercial ports of southern Brazil, the Port of Rio Grande (Fernandes et al, 2021).…”

Analysis of the calibration and validation of hydrodynamic simulations with TELEMAC-3D model of the Patos Lagoon

“…The surface of the computational mesh is dynamically forced with results from the global model European Center for Medium-Range Weather Forecast with contribution of wind speed, air temperature and atmospheric pressure from the reanalysis ensemble (at the surface) with interval with a temporal resolution of 6 h and spatial resolution of 0. 75°, European Centre for Medium-Range Weather Forecasts interim reanalysis used in works such as those of (Marques, 2010); (Fernandes et al, 2021).…”

Assoreamento nas baías de Antonina e de Paranaguá – PR: análise integrada das áreas fontes de sedimentação e obras de dragagem

“…As alterações antrópicas desenvolvidas em estuários tais como atividades de dragagens, retificação de canais, ocupações de zonas intermarés e de manguezais, tendem a aumentar a taxa de sedimentação, favorecendo o assoreamento (Bianchini et al, 2019;Angulo et al, 2020;Fernandes et al, 2021;Wang et al, 2021). Pesquisas relacionadas (Monge-Ganuzas et al, 2013;Williams et al, 2014;Traini et al, 2015;Van Maren et al, 2015;Elliott et al, 2019) afirmam que essas atividades antrópicas podem: diminuir a área de atuação da maré (alteração da dinâmica do prisma de maré), o que modifica as velocidades de enchente ou as de vazante e faz com que o sedimento seja transportado em diferentes taxas (Dijkstra et al, 2019); e alterar a circulação estuarina (Lana e Soares, 1994;Nichols, 2018).…”