The tidal bore, is an enomene of abrupt elevation of the water of a river or an estuary caused by the wave of the rising tide during high tides. This phenomenon occurs in the mouth and the lower course of some rivers when their current is thwarted by the flow of the rising tide. The most spectacular tidal bore can be seen at the mouths of the Qiantang (China), the Severn (England) and the Amazon (in Brazil). Physically, the tidal bore corresponds to the propagation of a projection along the course of a river or a canal.
The Tidal Bore allows surfers to engage in the distance-on-the-wave competition. The Tidal Bore advances at a speed of 10 to 20 km / h (the less there is, the more it slows down), the wave can reach 1.36 meters in height but is not constant. As the bottom changes, the succession of waves moves across the width of the Dordogne (commune of Saint pardon) and widens, flattens, bulges, surges, bubbles, disappears, resurfaces, it is constantly changing.