The effect of wind on the residual current velocities in the inlets of Venice Lagoon

The residual flow in the inlets of Venice lagoon subject to Bora and Sirocco winds has been studied.Current velocities have been monitored since 2001 using Acoustic Doppler Current Profilers (ADCP)installed on the beds of the inlets that connect the lagoon to the Adriatic Sea; these inlets are Lido,Malamocco and Chioggia. Wind velocity data have also been continuously measured at an oceanographicplatform 14.8km offshore from the lagoon; these data were subsequently decomposed into PrincipalComponents, which are associated with Bora and Sirocco wind directions. Analyses show that the inflowin Lido inlet is strongly related to the Bora wind. The outflow in Chioggia inlet occurs during Bora eventsbut shows a slightly weaker correlation with the wind speed, while Malamocco inlet shows little or noinfluence of Bora winds on flow patterns. A net residual inflow through Lido and Malamocco inlet wasfound, while outflow prevails in Chioggia inlet. During Bora events, the average residual inflow increasedthree-fold in Lido inlet, whereas the outflow in Chioggia inlet doubled. The current velocities in Lido andChioggia inlets are best described by an exponential function of wind velocity with exponents of 0.1187 and 0.0924, respectively. The response to Sirocco events was evident mainly in Chioggiainlet. Specifically, there was a slow down of the outflow in linear proportion to wind speed. In excess of10 m/s a complete current reversal was observed. Lido and Malamocco inlets showed little or noresponse to Sirocco winds, except during rare cases when wind speeds exceeded 15 m/s.