A comparison study between 10 Mediterranean lagoons has been carried out by means of the 3-D numerical model SHYFEM. The investigated basins are the Venice and Marano-Grado lagoons in the Northern Adriatic Sea, the Lesina and Varano lagoons in the Southern Adriatic Sea, the Taranto basin in the Ionian Sea, the Cabras Lagoon in Sardinia, the Ganzirri and Faro lagoons in Sicily, the Mar Menor in Spain, and the Nador Lagoon in Morocco. This study has been focused on hydrodynamics in terms of exchange rates, transport time scale, and mixing. Water exchange depends mainly on the inlet shape and tidal range, but also on the wind regimes in the case of multi-inlet lagoons. Water renewal time, which is mostly determined by the exchange rate, is a powerful concept that allows lagoons to be characterized with a time scale. In the case of the studied lagoons, the renewal time ranged from few days in the Marano-Grado Lagoon up to 1 year in the case of the Mar Menor. The analysis of the renewal time frequency distribution allows identifying subbasins. The numerical study proved to be a useful tool for the intercomparison and classification of the lagoons. These environments range from a leaky type to a choked type of lagoons and give a representative picture of the lagoons situated around the Mediterranean basin. Mixing efficiency turns out to be a function of the morphological complexity, but also of the forcings acting on the system.
Extreme sea levels at European coasts and their changes over the twentieth and twenty-first centuries are considered, including a method to analyze extreme sea levels and to assess their changes in a consistent way at different sites. The approach is based on using a combination of statistical tools and dynamical modelling as well as observational data and scenarios for potential future developments. The analysis is made for both time series of extreme sea levels and individually for the different components contributing to the extremes comprising (i) mean sea level changes, (ii) wind waves and storm surges and (iii), for relevant places, river flows. It is found that while regionally results vary in detail, some general inferences can be obtained. In particular it is found, that extreme sea levels show pronounced short-term and long-term variability partly associated with seasonal and nodal tidal cycles. Long-term trends are mostly associated with corresponding mean sea level changes while changes in wave and storm surge climate mostly contribute to inter-annual and decadal variability, but do not show substantial long-term trends. It is expected that this situation will continue for the upcoming decades and that long-term variability dominates over long-term
Abstract. This work is focused on the application of a modelling system to simulate 3-D interaction between the Curonian Lagoon and the Baltic Sea coastal waters and to reflect spatiotemporal dynamics of marine waters in the Curonian Lagoon. The model system is based on the finite element programme package SHYFEM which can be used to resolve the hydrodynamic equations in lagoons, coastal seas, estuaries and lakes. The results of a one year (2009) 3-D model simulation with real weather and hydrological forcing show that the saline water intrusions from the sea through Klaipėda Strait are gradually decreasing with distance from the sea and become negligible (average annual salinity about 0.5 ‰) at a distance of about 20 km to the south of Kiaulės Nugara island. Analyses of the simulation results also show this area to be highly heterogeneous according to the vertical salinity distribution. While in the deeper Klaipėda Strait (harbour waterway) differences in average salinity between near bottom and surface layers varies in the range 2-2.5 ‰, in the rest of the Curonian Lagoon it is less than 0.5 ‰. The exchange flow showed vertical structure, but was horizontally uniform with the presence of a two-directional flow that from time to time changes to either saline water one-directional flow to the Curonian Lagoon or fresh water one-directional flow to the sea. Two-directional flow duration decreases with a distance from sea entrance in Klaipėda Strait from around 180 days yr −1 close to the sea entrance to 50 days yr −1 just behind Kiaulės Nugara island. One-directional outflow duration is increasing with a distance from the sea entrance from 100 to 225 days yr −1 . One-directional inflow duration occurs in the range of 70-100 days yr −1 . The analysis of the ratio of buoyancy layer thickness to water depth (h b /H ) and the Wedderburn number identified the main importance of wind action on the flow structure. Strong winds from the North and NW determine a barotropic inflow which is mostly responsible for the salt water intrusion into the Curonian Lagoon. Absence of wind or cross-strait wind regimes allows the maintenance of a two-layer flow typical of estuarine dynamics.
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