Numerical Modeling of Storm Surge Forecast for the Venice Lagoon

An accurate sea level prediction for the Venice Lagoon is of great importance to the historical city maintenance. Here an operational forecasting system of the sea level for the Venice Lagoon, based on a finite element numerical model, is presented. The model solves the shallow water equations on two different finite element grids representing the whole Mediterranean Sea and the Venice Lagoon. The system has been operational for 7 years and runs at the Centre for sea level forecasting and flood warnings of the Venice Municipality (ICPSM). The hydrodynamic model provides a five-day forecast for the Mediterranean Sea and it is focused on the prediction of the surge near Venice. It has been refined during this period through several improvements such as spatially variable wind enhancement coefficients and a post-processing procedure. Results show that the system is capable of achieving forecasts comparable to the statistical models that are presently used by the Venice municipality as their flooding warning system. In particular, for forecasting periods of 24 hours and longer, the system out-performs the statistical models. For the application of the post processing routines, results near Venice are extracted and improved using neural networks. This method reduces by half the average error of the hydrodynamic model for the first day forecast (standard deviation of the differences of 4 cm) and maintains good performances also for longer forecasts.