Kelvin waves in Lake Geneva

Abstract

The passage of Kelvin waves in Lake Geneva after strong wind events was experimentally investigated in 1987 and 2002 using thermistor chains, current meters and Acoustic Doppler Current Profilers (ADCP) probing the whole water column, including the bottom boundary layer. Characteristics of these internal waves such as period, amplitude, exponential decay with distance from the shore and damping were determined. A significant increase of shear was observed in the thermocline region during the passage of a Kelvin wave crest. The passage of a Kelvin wave crest also led to a well-mixed bottom boundary layer characterized by a logarithmic velocity profile, complying with the so-called “law of the wall” up to an average height of 11m. A bottom drag coefficient of 2.5×10−3 was determined from our measurements. We estimated that ~70% of the Kelvin wave energy is dissipated in the bottom boundary layer. This study shows that the passage of Kelvin waves energizes the thermocline and near bed region and that this process is of fundamental importance in the dynamics of the nearshore region of mid-latitude large lakes.