When a river mouth has a flat, converging shape and when the tidal range exceeds 6 to 9 m, the river may experience a tidal bore (Photo). A tidal bore is basically a series of waves propagating upstream as the tidal flow turns to rising. Hubert Chanson observed the tidal bore of the Dordogne river (France) on 27 September 2000. The bore propagates first in the Gironde before separating and continuing both in the Garonne and in the Dordogne. At St Pardon, the tidal bore of the Dordogne river was an undular bore and the photograph shows the arriving bore with kayaks and surfers riding the bore undulations. This photographs was published in CHANSON (2004, p. 183). It was further shown as Earth Science Picture of the Day on 19 Dec. 2001. It is also used to illustrate two websites on tidal bores
