117 research outputs found
Author Meets Critics Symposium. Alfredo Ferrarin, On Thinking and the I. Reply to my critics Clinton Tolley and Tobias Rosefeldt
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Venice as a paradigm of coastal flooding under multiple compound drivers
No full textFull comprehension of the dynamics of hazardous sea levels is indispensable for assessing and managing coastal flood risk, especially under a changing climate. The 12 November 2019 devastating flood in the historical city of Venice (Italy) stimulated new investigations of the coastal flooding problem from different perspectives and timescales. Here Venice is used as a paradigm for coastal flood risk, due to the complexity of its flood dynamics facing those of many other locations worldwide. Spectral decomposition was applied to the long-term 1872-2019 sea-level time series in order to investigate the relative importance of different drivers of coastal flooding and their temporal changes. Moreover, a multivariate analysis via copulas provided statistical models indispensable for correctly understanding and reproducing the interactions between the variables at play. While storm surges are the main drivers of the most extreme events, tides and long-term forcings associated with planetary atmospheric waves and seasonal to inter-annual oscillations are predominant in determining recurrent nuisance flooding. The non-stationary analysis revealed a positive trend in the intensity of the non-tidal contribution to extreme sea levels in the last three decades, which, along with relative sea-level rise, contributed to an increase in the frequency of floods in Venice
Tidal Prism Variation in Venice Lagoon and Inlet Response over the Last 70 Years
No full textThe Venice lagoon inlets have undergone extensive modification during the past, responding in their evolution to the changing physical forcings and human intervention. In order to quantify the adaptation to these forcings the northernmost inlet (Lido) has been studied in detail through numerical modeling and high-resolution bathymetry data collected during three consecutive years.Eleven sections have been chosen in these channels where the cross-sectional area has been determined. The discharges and with it the tidal prism through these sections have been computed through numerical simulations of an existing, calibrated hydrodynamic model (Shyfem). The obtained results have been compared to empirical relationships between the tidal prism and the cross-sectional area of tidal channels (O’Brien relation and Jarrett formula).The computations have been repeated with available data from bathymetry charts for the years 1990, 1970 and 1930 to detect any temporal variation of the cross-sectional areas of the channels and their tidal prism and to evaluate the stability of the Lido inlet. Results from all inlets indicate a relative stability of the tidal prism entering Venice Lagoon, though some changes were detected for the year 1970
Sedtrans05: An improved sediment-transport model for continental shelves and coastal waters with a new algorithm for cohesive sediments
No full textThe one-dimensional (vertical) sediment-transport model SEDTRANS96 has been upgraded to predict more accurately both cohesive and non-cohesive sediment transport. Sedtrans05 computes the bed shear stress for a given set of flow and seabed conditions using combined wave-current bottom boundary layer theory. Sediment transport (bedload and total load) is evaluated using one of five methods. The main modifications to the original version of the model are: (1) a reorganization of the code so that the computation routines can be easily accessed from different user interfaces, or may be called from other programs; (2) the addition of the Van Rijn method to the options for non-cohesive sediment transport; (3) the computation of density and viscosity of water from temperature and salinity inputs; and (4) the addition of a new cohesive sediment algorithm. This latter algorithm introduces variations of sediment properties with depth, represents the suspended sediment as a spectrum of settling velocities (i.e. size classes), includes the flocculation process, and models multiple erosion–deposition cycles. The new model matches slightly better the field measurements of non-cohesive sediment transport, than does the predictions by SEDTRANS96. The sand-transport calibration has been extended to high transport rates. The cohesive sediment algorithm reproduced well experimental data from annular flume experiments.<br/
Development and validation of a finite element morphological model for shallow water basins
No full textRecognising the importance of understanding sediment dynamics to evaluate the status of a coastal lagoon environment, this work has been focused on the investigation of the hydrodynamic and sediment transport processes occurring in such basins. In order to describe the lagoon system, a modelling approach combining hydrodynamics, waves and sediment dynamics has been developed. The framework of the numerical model consists of a finite element hydrodynamic model, a third generation finite element spectral wave model and a sediment transport and morphodynamic model for both cohesive and non-cohesive sediments. The model adopts the finite element technique for spatial integration, which has the advantage to describe more accurately complicated bathymetry and irregular boundaries for shallow water areas. The developed model has been applied to test cases and to a very shallow tidal lagoon, the Venice Lagoon, Italy. Numerical results show good agreement with water level, waves and turbidity measurements collected in several monitoring stations inside the Lagoon of Venice. Such a model represents an indispensable tool in analysing coastal problems and assessing morphological impacts of human interference.<br/
The contribution of a mesoscale cyclone and associated meteotsunami to the exceptional flood in Venice on November 12, 2019
No full textOn November 12, 2019, an exceptional flood event took place in Venice, second only to the one that occurred on November 4, 1966. The sea level reached a peak value of 1.89 m above the local datum determining the flooding of almost 90% of the pedestrian surface of the historical city. Several processes concurred to raise the water level in Venice and the northern Adriatic Sea on November 12, 2019. Among these, a fast-moving mesoscale cyclone travelled at about 12 m & BULL; s-1 in the northwestward direction over the northern Adriatic Sea, raising the sea levels at the shore in front of the Lagoon of Venice. High-resolution numerical simulations indicated that atmosphere-ocean resonance occurred on November 12, 2019, generating a meteotsunami-like wave that contributed significantly to the extreme sea level in Venice. The relative contributions of the wind and air pressure to the peak sea level were also estimated. Additional numerical experiments were performed to prove the occurrence of Proudman resonance and to determine a transfer function of such high-frequency sea-level perturbations for the Lagoon of Venice
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