1,721,046 research outputs found
A comparison between fluid shear stress reduction by halophytic plants in Venice Lagoon, Italy and Rustico Bay, Canada - analyses of in situ measurements
No full textA series of in situ experiments on bed stability were carried out at three sites across Venice Lagoon using the benthic annular flume—Sea Carousel. Turbulence measurements were made at a range of flow speeds over different vegetated beds as well as ‘smooth’ muddy beds. The drag induced by the various bed types was estimated using flow deceleration. Bed shear stress was also estimated using three methods, and the results were compared with the bed shear stress as determined over a smooth bed in a laboratory equivalent of Sea Carousel—Lab Carousel. The stress was found to increase with increasing bed roughness and with the addition of vegetation in the form of the sea grasses Cymodocea nodosa and Zostera noltii. The stress was also found to be affected by the bending of the sea grass blades under flow velocities exceeding 0.4 m s?1, the sea grasses became flattened and the shear stress was found to decrease to produce skimming flow. It was concluded that the presence of sea grasses decreases erosion due to (1) stress reduction and (2) stabilization of the bed, thus reduction of the distribution of sea grass beds in Venice Lagoon will likely enhance bed erosion and hence habitat destruction. Stress was also reduced by an increase in levels of turbidity level in the water column
The Role of Ambiguity in the Evaluation of the Net Benefits of the MOSE System in the Venice Lagoon
No full textAn application of the Precautionary Principle under ambiguity: the impact of the MOSE system on harbour activity in the Venice Lagoon
No full textThe Role of Ambiguity in the Evaluation of the Net Benefits of the MOSE System in the Venice Lagoon
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SLIM: a numerical model to evaluate the factors controlling the evolution of intertidal mudflats in Venice Lagoon, Italy
No full textVenice Lagoon is suffering from a deficit in sediment supply, which results in the progressive destruction of salt marshes and tidal flats [Consorzio Venezia Nuova, 1996]. Nevertheless, some of the intertidal areas are accreting showing morphological changes, which are in contrast with the general trend within the Lagoon. The morphological evolution of Palude della Centrega, a well-preserved and vegetated intertidal area located in the northern part of the Lagoon, was investigated over a period of 3 years. The short-term accretion rate was measured to be 1.52 cm/year and was used to calibrate a three-element box model, Simulation of LIttoral Morphodynamics (SLIM) constructed to predict which of the accounted factors are more relevant to the evolution of the accreting intertidal mudflat.Sensitivity analyses using SLIM on Palude della Centrega suggest that the evolution of the flats is controlled by the balance between wave erosion during Bora events and tidal sedimentation during fine weather. This balance is strongly affected by (1) turbidity of the waters flooding the tidal flats, (2) sea grass density that suppresses wave action and tidal flow and (3) biostabilisation due to microphytobenthos, which enhances stability
Sea level rise and coastal flood protection in Cesenatico, Italy.
Full text linkWithin the THESEUS project (www.theseusproject.eu) detailed analysis of climate change scenarios, in terms of surge and wave climate changes, together with the related flooding scenarios are performed in the Emilia Romagna coastal area for assessing littoral risk and possible mitigation measures.
Following the indication of the IPPC, meteorological data from the A1B scenario, computed as a regional downscaling from a global climate model, are analyzed and used to force a finite element coastal model in the study area. As a chain from the global to the local scale marine variables, in terms of sea level variation, wave climate and statistics on extreme events are computed and provided for the implementation of detailed flooding models in the Cesenatico area.
Four simulations are carried out for the periods 1960-1990, 2010-2039, 2040-2069 and 2070-2100, from which useful engineering information are derived, such as the joint statistics of extreme wave height and surge, which are clearly positively correlated, and the lack of correlation between extreme significant wave height and wave steepness.
An overview of the site, including defense works and strategy is provided and discussed based on the climate scenarios and corresponding flooding maps.
Keywords
Meteorologica
A model of sand transport in Treporti channel: northern Venice lagoon
No full textThe origin of the sands in the Venice lagoon has been the subject of an extensive field survey in parallel with numerical modelling. Four transects along Treporti and Burano canals were conducted from which 33 bottom sediment samples were collected. These samples were analysed for grain size and sorting to examine any trends in the granulometry of these sediments that might shed light on transport paths. The modelling study consists of three parts: the sediment transport model sedtrans96 was used with a finite-element hydrodynamic model (Shyfem) and an empirical wave model (US Army Corps of Engineering) to simulate sand transport in the Treporti canal. A type of link box model was created where finite elements of the hydrodynamic model have been combined to macro-boxes on which the water and sediment flux over the sections, and a mass balance has been computed. Several grain size classes were simulated; the distributions before and after the simulation were examined. Idealised wind and tidal values were initially used to force 12 h simulations to test the sediment transport sensitivity. Finally, a full-year simulation (1987) has been carried out using measured tidal and wind data. Only a part of Venice lagoon was covered by the simulation: a major channel (Treporti) running from Lido inlet towards the northern lagoon. The total sand transport through all of the sections was computed for 1 year. Sediment mass balance was determined, and the resulting trends of erosion and deposition were computed. There were no trends in the median grain diameter and sorting of bottom samples from the Treporti canal; all sands were fine (120 ?m, one outlier of 300 ?m was removed). The absence of a trend in grain size suggests that there is no significant import of sand to the lagoon through the Lido inlet. The results from the simulations seem therefore to confirm the hypothesis of reworking of sand within the lagoon. The computed erosion is some centimeters per year diagnostic of channel scouring and enlargement with time. The Treporti canal is subject to strong current velocities of around 1 m/s, which hold fine sand in suspension and thus prevent sedimentation
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