Contemporary channel changes in the Eygues basin, southern French Prealps: the relationship of subbasin variability to watershed characteristics F. Lie ´bault a,b, * , P. Cle ´ment a,b , H. Pie ´gay a,b , C.F. Rogers b,c , G.M. Kondolf d , N. Landon b a Laboratoire Rhodanien de Ge ´omorphologie, Universite ´ Lumie `re Lyon 2, 5 avenue Pierre Mende `s-France, 69 676 Bron cedex, France b Laboratoire Environnement-Ville-Socie ´te ´, UMR5600-CNRS, 18 rue Chevreul, 69 362 Lyon cedex 07, France c CRENAM, UMR5600-CNRS, Universite ´ de Saint-Etienne, 6 rue Basses-des-Rives, 42 023 Saint-Etienne, France d Department of Landscape Architecture and Environmental Planning, University of California, 202 Wurster Hall, Berkeley, CA 94720-2000, USA Received 24 September 1999; received in revised form 10 July 2000; accepted 14 October 2001 Abstract The southern French Prealps are sub-Mediterranean mountains in which forest cover has increased since the end of the 19th century. Forest development, linked with agricultural decline and planned reafforestation, has induced a decrease of bedload supply from hillslopes. In response to this evolution, several channel changes are observed in mountain streams: channel narrowing, channel degradation and pavement development. The intensity of these adjustments differs from one stream to another. Twenty catchments (10– 100 km 2 ) located in the Eygues River basin (1150 km 2 ), a tributary of the Rho ˆne River, are studied to highlight the subbasin variability of channel changes and to give causal interpretations. We conducted field surveys and analyzed aerial photographs to characterize present channel morphology and contemporary channel changes and GIS was used to quantify morphometry, relief, land use and geology of the watersheds. Multivariate statistical analysis determined relations between channel changes and watershed characteristics. The potential bedload supply of these mountain streams is controlled largely by watershed morphometry and land use. The most active tributaries of the Eygues River are characterized mainly by high drainage density and poor vegetation cover linked to agricultural land use. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Channel change; Channel narrowing; Watershed control; Land use; Southern French Prealps; GIS; Coinertia analysis 1. Introduction Historical channel change in response to environ- mental and human controls is a major focus of recent research on river dynamics in mountainous watersheds (Castaldini and Piacente, 1995; Madej, 1995; Billi and Rinaldi, 1997; Garcia-Ruiz et al., 1997; Gaillot and 0169-555X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0169-555X(01)00189-1 * Corresponding author. Laboratoire Rhodanien de Ge ´omorpho- logie, Universite ´ Lumie `re Lyon 2, 5 avenue Pierre Mende `s-France, 69 676 Bron cedex, France. E-mail address: frederic.liebault@free.fr (F. Lie ´bault). www.elsevier.com/locate/geomorph Geomorphology 45 (2002) 53 – 66