Geomorphological Processes and Human Impacts in River Basins (Proceedings of the International Conference held at Solsona, Catalonia, Spain, May 2004). IAHS Publ. 299, 2005., 161-170.

1 Laboratoire d’Hydrographie et Géomorphologie fluviatile, University of Liège Dept. of Geography,
Allée du 6 Août, 2. 4000 Liège, Belgium

2 University of Lyon 2, Louis Lumière 5600, 5 Avenue Pierre Mendès-France, 69676 Bron cedex, France

Abstract This article deals with the application of lichenometry to the study of mountainous Mediterranean boulder-bed rivers, characterized by strong floods. Lichens present on blocks are a means of dating the reworking of this material, and therefore determining the maximal competence of floods. By associating the diameters of the blocks dated using lichenometry to the specific streampower of corresponding floods, several diameter/critical specific streampower relations for elements between 0.5 and 2.7 m were proposed. In this way several different relations were determined for the rivers studied, highlighting the uneven dissipation of energy due to the roughness of bed forms in these rivers.