Circulation of rules reservoir induced by atmospheric forcing

Résumé

This thesis investigates the influence of the surrounding local topographical features on the free surface oscillation of a small reservoir in complex terrain. The study shows the existence of high frequency components (<10min) in the atmospheric forcing that can create resonant excitation of the free surface. The water free surface response to the atmospheric forcing is studied in detail with a two-dimensional, depth-averaged, hydrodynamic numerical model developed from the linearized shallow water equations. The high frequency atmospheric forcing variation (barometric pressure and wind shear stress) and the free surface response are presented from field measurements of a small reservoir located in complex terrain (Rules Reservoir, Granada). At certain times, harmonics in the measured atmospheric forcing were observed, ranging between periods of 200-700 seconds. Surface seiches are generated when the harmonic forcing matches the reservoir eigenmodes, even for low wind speeds. The spatial variation of the atmospheric forcing over the reservoir water surface is enhanced from simulations in a boundary layer wind tunnel. The surrounding topographical features are modeled at a scale of 1:3000 for a single wind direction, providing a high resolution map of the mean wind speed and directionality variation and the surface pressure distribution. The measurements from the field study and the wind tunnel simulation are merged together to provide a high resolution map of the spatial and temporal variability of the atmospheric forcing which are included as loading conditions in a numerical model, simulating the free surface response. The model describes the formation of the free surface oscillations observed during the field campaign.