An Economic Assessment of the Impacts of the MOSE Barriers on Venice Port Activities

Due to its hydro-geological features, the lagoon of Venice is especially vulnerable to climate change. In particular, it is strongly affected by gradual global warming that brings about the so-called ‘acqua alta’ (high water) phenomenon with greater frequency and intensity. In order to protect the city of Venice from the more and more frequent phenomenon of flooding, some protective measures have been adopted. Among them, the system of mobile barriers commonly known as MOSE: however, by separating the lagoon from the Adriatic Sea, it interferes with ship traffic and has negative impacts on port activities. Against this background, the aim of the present work is to provide an estimate of the direct costs of ship traffic interruption due to the functioning of the MOSE, i.e. the additional costs resulting from longer waiting time for ships passing through the Venice lagoon. The estimate uses inputs from the application of a specific hydrodynamic model and the elaboration of ship traffic data during the period 2000-2002. Results indicate that the additional costs would range between 347,943 and 1,288,067 €/year, depending on the hypothesis assumed.Climate Change, ‘Acqua Alta’, MOSE, Ship Traffic, Direct Costs

Hydrodynamic modeling in the channel network of Venice

A combined framework of hydrodynamic models is presented that describes the water dynamics in the channel network of the city of Venice. The application of these hydrodynamic models is part of a larger project carried out by UNESCO that has the aim of describing the water quality of the channels in Venice. An existing 2-dimensional finite element model simulates the hydrodynamic features in the Venice Lagoon. The simulated data is then used as the boundary condition for the 1-dimensional hydrodynamic model of the inner channels of Venice. Inside the channel system the water elevation and the current velocities are computed. The simulated variables are calibrated and compared with data from field measurements that UNESCO has carried out during the years 1990-92 and during 1998. It was possible to use a constant friction parameter for all the channels in the network. Simulated water elevation shows an excellent agreement with the measured data, and also current velocities are generally reproduced quite faithfully. Some low-energy channels show major errors in the reproduction of the velocity speed. It is believed that changing bathymetry (silting-up of the channels) could be a cause of this phenomenon. The hydrodynamic data will eventually be used in the second part of the project where the water quality of the channel network will be investigated. For this purpose the hydrodynamic parameters simulated will be used by the water quality model as a boundary and initial condition in order to simulate the biological and chemical variables and to describe the ecological dynamics

Changes in Venice Lagoon dynamics due to construction of mobile barriers

The MoSE project (construction of mobile barrier to safeguard the Lagoon of Venice) entails changes to the structure of the lagoon\u27s inlets. This could have consequences for the areas near the inlets and for the dynamics of the lagoon ecosystem as a whole. In order to predict the effects of the proposed alterations on the hydrodynamics of the lagoon, a well-tested hydrodynamic-dispersion model was applied. Simulations were carried out considering both idealised and realistic tide and wind scenarios. The results show that with the new structures the Lido sub-basin tends to increase its extension due the southward movement of the watershed, at the expense of the Chioggia sub-basin, whereas the Malamocco sub-basin changes its relative position, but not its extension. The residence time shows variations in agreement with this trend, decreasing in the southern part of the Lido sub-basin and increasing in the inner part of the Chioggia sub-basin. The variations in residence time and return fl ow factor indicate that they are caused by changes in both instantaneous current velocities and sea-lagoon interaction. In fact the new breakwaters in front of the Malamocco and Chioggia inlets modify the length and direction of the out fl ow jet (up to 1 ms− 1 ) and the patterns of the currents around the inlets and the nearby coast. The new arti fi cial island in the Lido inlet changes the current pattern and increases the current velocity on the southern side of the channel propagating this effect up to the Venice city. The risks and benefits individuated from our conclusion are that the Lido sub-basin can improve its renewal time, but the more intense current speeds can be a risk for the conservation of habitats and infrastructures. Finally the micro-circulation between the breakwater and the coast in Chioggia and Malamocco inlets can be a trap for pollutants or suspended sediment

Venice flooding and sea level: past evolution, present issues, and future projections (introduction to the special issue)

Venice is an iconic place and a paradigm of huge historical and cultural values at risk. The frequency of the flooding of the city centre has dramatically increased in recent decades, and this threat is expected to continue to grow – and even accelerate – through this century. This special issue is a collection of three review articles addressing different and complementary aspects of the hazards causing the floods of Venice, namely (1) the relative sea level rise, (2) the occurrence of extreme water heights, and (3) the prediction of extreme water heights and floods. It emerges that the effect of compound events poses critical challenges to the forecast of floods, particularly from the perspective of effectively operating the new mobile barriers (Modulo Sperimentale Elettromeccanico – MoSE) in Venice and that the relative sea level rise is the key factor determining the future growth of the flood hazard, so that the present defence strategy is likely to become inadequate within this century under a high-emission scenario. Two strands of research are needed in the future. First, there is a need to better understand and reduce the uncertainty of the future evolution of the relative sea level and its extremes at Venice. However, this uncertainty might not be substantially reduced in the near future, reflecting the uncertain anthropogenic emissions and structural model features. Hence, complementary adaptive planning strategies appropriate for conditions of uncertainty should be explored and developed in the future

A flexible <i>z</i>-layers approach for the accurate representation of free surface flows in a coastal ocean model (SHYFEM v. 7_5_71)

We propose a discrete multilayer shallow water model based on z-layers, which, thanks to the insertion and removal of surface layers, can deal with an arbitrarily large tidal oscillation independently of the vertical resolution. The algorithm is based on a classical two-step procedure used in numerical simulations with moving boundaries (grid movement followed by a grid topology change, that is, the insertion/removal of surface layers), which avoids the appearance of surface layers with very small or negative thickness. With ad hoc treatment of advection terms at nonconformal edges that may appear owing to insertion/removal operations, mass conservation and the compatibility of the tracer equation with the continuity equation are preserved at a discrete level. This algorithm called z-surface-adaptive, can be reduced, as a particular case when all layers are moving, to the z-star coordinate. With idealized and realistic numerical experiments, we compare the z-surface-adaptive against z-star and we show that it can be used to simulate coastal flows effectively.</p

Development of a novel tool to predict different water quality scenarios within a Marine Protected Area (MPA) in the Maltese Islands : the 2D SHYFEM-BFM model

Effective operational marine conservation and management is thwarted by a lack of financial and human resources. A coupled 2D hydrodynamic (SHYFEM) and ecological (BFM) model was developed in the current study as a Decision Support System (DSS) to spearhead good governance of a Marine Protected Area (MPA) in Dwejra (Maltese Islands) in the Central Mediterranean. Two scenarios were considered – one with the current levels of nutrient runoff from land and one in which such levels are increased as a result of a greater human activity within the area. Although the developed numerical modeling platform needs to be refined and to be run for a longer time -frame, its output suggests that it is a promising tool to assist in the operational management of an MPA.peer-reviewe

Modeling the inter-annual variability of salinity in the lagoon of Venice in relation to the water framework directive typologies

The Water Framework Directive (2000/60/EC) requires member states to classify and enhance the ecological quality of water bodies in accordance with their type. To estimate the effect on type of the natural variability of lagoons, we applied a two-dimensional hydrodynamic model to the lagoon of Venice. The model calculated the mean annual spatial distributions of two variables: salinity and residence time. The standard deviation of salinity was also included, in order to estimate the variation of salinity values around the mean, which is associated with the instability of the mean salinity value. A highly detailed numerical grid was calibrated and high-frequency tributary discharge data were used. The simulations, under realistic forcing conditions, are based on the years 2003 and 2005. The former was characterized by low precipitation, around 30% less than the typical value. A comparison of model results and measurements shows the high reliability of the model in reproducing the spatial distribution and temporal evolution of salinity. We found strong inter-annual variation in salinity, standard deviation of salinity and residence time. The effect on the typing process is that the most representative types shift from one category to another. On the basis of the spatial patterns of the variables and their superposition, we identi fi ed types that described the bulk of the lagoon. This numerical tool offers support for lagoon management on various levels, in terms of both WFD requirements and other applications, by: (1) providing unbiased and objective zoning indications for the basin; (2) evaluating the response of water quality elements; (3) establishing the reference status of a water body; and (4) establishing a hierarchical division of a lagoon that can be used to select an appropriate number of sampling stations for monitoring

Numerical wave propagation for the triangular P1DGP1_{DG}-P2P2 finite element pair

Inertia-gravity mode and Rossby mode dispersion properties are examined for discretisations of the linearized rotating shallow-water equations using the $P1_{DG}$-$P2$ finite element pair on arbitrary triangulations in planar geometry. A discrete Helmholtz decomposition of the functions in the velocity space based on potentials taken from the pressure space is used to provide a complete description of the numerical wave propagation for the discretised equations. In the $f$-plane case, this decomposition is used to obtain decoupled equations for the geostrophic modes, the inertia-gravity modes, and the inertial oscillations. As has been noticed previously, the geostrophic modes are steady. The Helmholtz decomposition is used to show that the resulting inertia-gravity wave equation is third-order accurate in space. In general the \pdgp finite element pair is second-order accurate, so this leads to very accurate wave propagation. It is further shown that the only spurious modes supported by this discretisation are spurious inertial oscillations which have frequency $f$, and which do not propagate. The Helmholtz decomposition also allows a simple derivation of the quasi-geostrophic limit of the discretised $P1_{DG}$-$P2$ equations in the $\beta$-plane case, resulting in a Rossby wave equation which is also third-order accurate.Comment: Revised version prior to final journal submissio

Evaluating meteorological climate model inputs to improve coastal hydrodynamic studies

Abstract. This work compares meteorological results from different regional climate model (RCM) implementations in the Mediterranean area, with a focus on the northern Adriatic Sea. The need to use these datasets as atmospheric forcings (wind and atmospheric pressure fields) for coastal hydrodynamic models to assess future changes in the coastal hydrodynamics, is the basis of the presented analysis. It would allow the assessment of uncertainties due to atmospheric forcings in providing coastal current, surge and wave climate changes from future implementations of hydrodynamic models. Two regional climate models, with different spatial resolutions, downscaled from two different global climate models (whose atmospheric components are, respectively, ECHAM4 and ECHAM5), were considered. In particular, the RCM delivered wind and atmospheric pressure fields were compared with measurements at four stations along the Italian Adriatic coast. The analyses were conducted using a past control period, 1960–1990, and the A1B IPCC future scenario (2070–2100). The chosen scenario corresponds to a world of very rapid economic and demographic growth that peaks in mid-century, with a rapid introduction of new efficient technologies, which balance fossil and non-fossil resources (IPCC, 2007). Consideration is given to the accuracy of each model at reproducing the basic statistics and the trends. The role of models' spatial resolution in reproducing global and local scale meteorological processes is also discussed. The Adriatic Sea climate is affected by the orography that produces a strengthening of north-eastern katabatic winds like bora. Therefore, spatial model resolution, both for orography and for a better resolution of coastline (Cavaleri et al., 2010), is one of the important factors in providing more realistic wind forcings for future hydrodynamic models implementations. However, also the characteristics in RCM setup and parameterization can explain differences between the datasets. The analysis from an ensemble of model implementation would provide more robust indications on climatic wind and atmospheric pressure variations. The scenario-control comparison shows a general increase in the mean atmospheric pressure values while a decrease in mean wind speed and in extreme wind events is seen, particularly for the datasets with higher spatial resolution

Hydraulic zonation of the lagoons of Marano and Grado, Italy. A modelling approach

The hydraulic regime-based zonation scheme of the Lagoons of Marano and Grado (Italy) has been derived by means of numerical models. A finite element modelling system has been used to describe the water circulation taking in account different forces such as tide, wind and rivers. The model has been validated by comparing the simulation results against measured water levels, salinity and water temperature data collected in several stations inside the lagoons. The analysis of water circulation, salinity and spatial distribution of passive tracers released at the inlets, led to a physically-based division of the lagoons system into six subbasins. The derived classification scheme is of crucial value for understanding the renewal capacity and pollutants distribution patterns in the lagoon