Hindcast of a storm surge induced by local real wind fields in the Venice Lagoon

• Published in: Continental shelf research Vol. 17; no. 12; pp. 1513 - 1538
• Main Authors: Zecchetto, S., Umgiesser, G., Brocchini, M.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.10.1997
• ISSN: 0278-4343; 1873-6955
• DOI: 10.1016/S0278-4343(97)00023-X

This paper investigates the effects of the wind blowing over the Venice Lagoon on both water level and circulation patterns. This has been carried out using a finite element hydrodynamic model coupled, for the first time, with experimental wind stress fields obtained from measurement of the horizontal and vertical wind components. A spatially variable wind field is used to compute the wind stress directly from the velocity fluctuations. The hindcast concerns a case of strong northeasterly wind (Bora) which occurred from the 22nd to the 24th December 1994. Results are discussed both in terms of the spatial pattern of the storm surge levels and of the water exchanges with the open sea through the three lagoon inlets. There is an area of set-down in the north of the lagoon and of one of set-up in the south. At the centre of the lagoon, the effects of the storm surge are small. Results show that the set-down and set-up peaks occur in opposition of phase with the tide. In the south, this is related to the bottom friction term which enhances or reduces the magnitude of the storm surge elevation, whereas in the north the mechanisms of nonlinear interaction between tide and storm surge are less clear. Also, a positive surge difference is found between the western and the eastern lagoon, and between the water levels close to the inlets and the open sea, the latter triggering the sea-lagoon water exchanges. Analysis of the discharges through inlets and ideal transects (which divide the lagoon into three parts) shows that the spatial and temporal behaviors of the storm surge in the south and in the north of the lagoon are almost independent. During the entire period under study, the sea water inflow through the northern inlet was continuous and considerable compared with the outflow through the central and southern inlets. Interesting circulation patterns are found in the northern lagoon, whilst water dynamics in the southern lagoon are essentially driven by the outflow at the meridional inlet. Comparison of these results with the hindcast obtained using spatially constant wind stress fields shows the importance of the wind spatial gradients in determining the storm surge level patterns.