1,721,102 research outputs found
Sediment resuspension in the Lagoon of Venice: short-term observations of natural and anthropogenic processes
No full textTo monitor sediment resuspension in the Lagoon of Venice a small benthic lander was deployed next to the main shipping channel, used by cargo ships and oil tankers sailing to the port of Marghera. The site has a silty sand bed and the deployment lasted for about 16 hours, with water depths ranging between 1.1 to 2.0 m. During the first part of the experiment there were no wind waves but the ship traffic was consistent, generating waves with Hmax in the order of 0.23 m. Due to the presence of ship wakes resuspension reached peaks up to 30 mg l-1, but the suspended material settled very rapidly. The vessel traffic decreased during the night of the deployment, but a night breeze occurred, generating small amplitude waves with Hs=0.08 m. Suspended matter concentration during the flood tide averaged at about 30 mg l-1. At high water the suspended sediment concentration dropped to very low values, but as the tide turned, picking up speed, resuspension took place: constant concentrations of about 60 mg l-1 were observed for a period of about four hours. During this period short crested wind waves were present, therefore it is believed that the concomitant action of wave resuspension and wind driven currents was preventing sediment settling. Calculation of current only bed shear stresses confirmed that wind-induced current were able to resuspend sediment of the coarse silt-fine sand fraction. The correlation between wave orbital velocities and resuspension events indicates that vessel generated waves are able to resuspend the sandy fraction of the bed sediment, particularly where wave group are present, including diverging and transversal waves generated by the ship. Wind waves have comparable resuspension capacity, but the sediment fluxes generated under choppy seas are larger than under vessel waves, because of the additional importance of wind-driven currents
Coastal-Estuary Flux of Heavy Metals: The Use of Estuarine Salt Marshes as Recorder of Pollution in the Humber Estuary, UK.
No full textPreface (to: Sediment Transport in European Estuarine Environments: proceedings of the STRAEE Workshop)
No full textSediment transport in European estuarine environments - Proceedings of the STRAEE workshop - Preface
No full textHistorically, estuaries have been the focal point of extensive industrial activity for maritime nations. Similarly, it is well established that such marginal marine environments are particularly sensitive to both long- and short-term external factors. In particular, estuaries are subject to diverse anthropogenic influences, such as: maritime transport (port construction, navigational dredging and dumping, maritime traffic congestion), industrial development (both onshore and offshore), mineral and aggregate extraction, changes in hinterland agricultural practices, residential development and increased water- and sediment-based pollution. In future, these areas will be placed under enhanced environmental pressure.
All of the activities outlined will place this inherently unstable environment under excessive strain in terms of coastline evolution, intertidal saltmarsh development, and sediment contamination. In addition, superimposed upon these anthropogenic factors are the systems response to more globally-driven changes i.e. sea level rise. As the need for a coordinated and responsible approach to the effective management of these morphological systems becomes apparent, as seen by the development of national and international legislation for estuarine management plans, an improved understanding of the physical dynamics of these systems becomes imperative. Within this context, modern sediment processes require investigation whilst, at the same time, the development of the adjacent coastline should be established. Investigation of these data sets, representing different time-scales, will provide the essential scientific background to management decisions.
The research described in this Special Issue address these problems, through the application of a wide range of approaches (sedimentological, geological, physical and engineering-based); these, in turn, lead to an overall interdisciplinary investigation of estuaries. The research undertaken has involved the deployment of instrumentation at a number of differing localities within various estuaries, measuring processes using both established and newly-developed (state-of-the-art) techniques. Such measurements have been extended, within an historical and recent geological time-scale, to develop a conceptual understanding of the evolution of the estuarine systems. At the same time, interpretation of the interdisciplinary data sets has been placed within the context of coastal engineering and management
The Po Delta is restarting progradation: Geomorphological evolution based on a 47-years Earth Observation dataset
No full textFrom the 1950s, the Po delta, one of the largest anthropogenic world deltas, has been subjected to a fast degradation and shoreline retreat due a marked reduction of sediment supply, mainly controlled by human impacts/factors, including subsidence. Through the interpretation of satellite images, coupled with the analysis of the flow discharge, and of the annual frequency of marine storms, we show that recently (>2010) the Po River has resumed delta progradation, especially in its northern portion. This happens after decades of erosion, followed by alternating regrowth and degradation phases, indicating conditions of substantial stability (1970-2000). Today the delta shows aggradation of new mouth-bars at the main distributary mouth, a clear evidence of active constructive processes. The ongoing trend marks a countertendency compared to many deltas worldwide
Testing Green DRR Solutions by Dune Reconstruction at a Rapidly Eroding Coast in the Adriatic Sea
No full textIn the current scenario of climate change and increased sea-level the occurrence of high water level storms threatens
coastal landscapes that lye at a low elevation. Naturally coastal dunes provide the so-called first line of defence. At eroding
coastlines their reconstruction offers the opportunity to build dynamic coastal defences, in opposition to more static
approaches like sea-walls. In order to properly design a revegetated dune, modeling must be undertaken to identify the
optimal dune height and width able to withstand the effect of an exceptional storm. The primary role of the plants is to
modify the velocity profile above them: this implies to introduce in the model credible values of the drag coefficient that also
reflect the spatial distribution of the different plant species and the density of stems per unit area.
Numerical tests of the effectiveness of dune reconstruction and revegetation as a Disaster Risk Reduction (DRR) measure
were undertaken on the Bellocchiocoastline, south of Porto Garibaldi, in the northern Adriatic sea coast of Emilia-Romagna.
The work was developed as a part of the EU FP7-RISC-KIT project, which elected the site as the pilot case study after
selection of a number of highly exposed hotspots (Armaroli and Duo, 2017). A detailed digital elevation model was
producedmerginga topographic Lidarfor the emerged area, a nearshore bathymetric Lidar up to -4.5 m water depth and a
multibeam bathymetric survey for the offshore up to – 10 m. The storm selected to test the efficiency of the natured-based
DRR occurred on 5-6 of February 2015, with a maximum offshore significant wave height of 4.66 m and a peak of 1.2 m of
water level above MSL. These conditions approximately correspond to a return period of 50 years. The two-dimensional
domain extends 3000 m alongshore and 3600 m cross-shore. The resolution of the ranges from 18m alongshore and 21m
cross-shore at the offshore open boundary at (10 depth) to 1m cross-shore and 8m alongshore in the area where the dune
is located. The reconstructed dune was built mimicking the current dune but enlarging it and increasing its crest, according
to literature knowledge of comparable dune systems in the region. The vegetation was introduced according to spatial
distribution of local species assuming either the current stem density or doubling it. Two indicators were chosen to assess
performance, respectively the Maximum Water Volume (MWV) and the sediment volume variation (SVV).
The results outline a reduction of inundation with the reconstructed dune (Fig. 1a), which is still breached and overtopped
at some points. If the vegetation is reconstructed on the dune there is considerable decrease of inundation (Fig. 1b).
Minimum changes are observed between normal and high density of vegetation for the reduction of MWV (Fig. 1c). The
high-density vegetation set-up provides instead the most efficient solution for SVV reduction. Further tests will be
undertaken at a number of European sites in the context of the EU H2020-ANYWHERE Project, encompassing also
different vegetation taxonomy and distribution
Morphodynamic evolution of a microtidal barrier, the role of overwash: Bevano, Northern Adriatic Sea
No full textThis study discusses the morphological changes of the Bevano "microtidal barrier" and the washover dynamics and evolution in response to several storm surges recorded during one year between September 2008 and September 2009. This barrier corresponds to the old Bevano river spit (characterised by a northward migration) which was abandoned after the relocation of the river mouth some 600 m to the south of the previous inlet position. The first overwash event was recorded in this barrier just after one of the highest surges recorded in the last 100 years (01 December 2008) with a high a surge level of 0.97 m, combined with an offshore significant wave height of 1.45 m (measured at Cesenatico). Seven separate washover fans were identified together with severe damages to fences and dune vegetation. The washover fans had different dimensions, the most important one being around 18 m wide, and generating a ∼ 9 m landward migration of the back-barrier limit. The study area was therefore subjected to a series of storm-surges during the study period with surge values fluctuating between 0.6 m and 0.8 m. The overwash processes and particularly the exceptional surge of 01 December 2008 was the instigator of initial morphological changes which then facilitated successive morphological changes caused by the subsequent storm surges and, as a result, generating the complete change of the morphologic configuration of the microtidal setting
Progetto sperimentale di iniezione d’acqua in unità geologiche profonde per il controllo della subsidenza costiera: il caso di studio di Lido Adriano (Ravenna)
No full textStabilizzazione di arenili in erosione tramite sistemi di drenaggio della battigia: casi studio in Italia
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