Influence of benthic boundary layer dynamics on wind-induced currents in the Ebro delta inner shelf -: art. no. 3054

[1] Measurements taken by two instrumented tripods deployed on the Ebro delta inner shelf at 8.5- and 12.5-m depth were used to characterize low-frequency currents under the action of a moderate eastern storm. Results show that inner shelf currents respond very rapidly to wind action with along-shelf currents dominating over the across-shelf ones. Mean along-shelf velocities of 0.35 and 0.24 m s(-1) at the inner and outer position, respectively, were recorded during the event, and they were highly correlated with the along-shelf wind stress. The measured current profiles were used to derive wind drag coefficients, assuming a balance between the along-shelf components of the wind and current bottom stresses. Since under eastern wind events, wave action in the Ebro inner shelf is significantly enhanced, wave-current interaction processes controlling the current bottom stress and sediment mobilization can affect the current structure. During the event, depth-averaged concentrations in the lower meter of the water column larger than 1 g L 1 were recorded that were also accompanied by the generation of vertical concentration gradients larger than 1 g L-1 m(-1). When the bottom drag coefficient was obtained from velocity profiles without considering the presence of these gradients, the required wind drag coefficients to fulfil the along-shelf balance were much higher than the ones derived from wind data, and they vary across the inner shelf. However, when bottom drag coefficients are obtained including stratification effects, the wind drag coefficients fulfilling the along-shelf balance were of the same order of magnitude as the ones derived from wind data and without any difference at both locations.