Modelling of tidal and wind-induced currents and dispersion in the northern Adriatic

Abstract

      A three-dimensional nonlinear baroclinic model, developed at the Departments for Civil Engineering, University of Ljubljana, is described first. In the model, the "vertical" turbulent viscosity is computed by a one-equation turbulence model of Koutitas, while constant"horizontal" turbulent viscosity is utilized.

      Tidal circulation in the Gulf of Trieste is computed by the model. The M2 tidal constituent is used for boundary condition at the open boundary. To determine tidal circulation in the smaller Piran Bay and Koper Bay, the s.c. nested models are used, the results from the larger region being used as boundary conditions for smaller regions. Current measurements along the Slovenian coast, executed by members of the Water Management Institute in Ljubljana in 1984 to 1986, are used for verification, the agreement is relatively good. Both measurements and simulation show a cyclonic gyre in Koper Bay during falling tide and residual current of the order 3-6 cm/s was found in Koper Bay in the E to N direction. Measurements also show an indication of a weak residual E to NE current along the whole Slovenian coast towards Trieste, the order of magnitude being about 1 to 3 cm/s.

      Dispersion of pollutant from Rižana River into the Koper Bay is simulated further and compared qualitatively with measurements of dispersion of faecal pollution in the bay.

      Simulation of wind - induced circulation in the Northern Adriatic was performed with the same 3D model, where the trasnport and dispersion of the Po River water was also simulated. For Bura wind (NE) the simulated circulation shows a very good agreement with a satellite image, based on chlorophyll concentration (from Kuzmić). Bura and Sirocco (SE) winds are simulated under winter (no stratification) and summer conditions (temperature and salinity stratification). Both for NE and SE winds the simulation shows that a part of the polluted Po River water is transported towards Slovenian and Croatian coast.