Reconstitution de la dynamique du paysage alluvial de trois secteurs fonctionnels de la rivière allier (1946-2000), Massif central, France

Abstract

L’écocomplexe de la plaine d’inondation de la rivière Allier a été étudié dans trois secteurs fonctionnels présentant une dynamique géomorphologique contrastée : le secteur à méandres de Joze-Maringues où l’Allier est corseté par des enrochements et touché par les extractions de granulats, le secteur à méandres mobiles de la Réserve Naturelle du Val d’Allier et le secteur à bras multiples situé entre les villages de Villeneuve-sur-Allier et du Veurdre. L’étude se fonde sur six à huit missions de photographies aériennes prises entre 1946 et 2000 pour déceler la dynamique du paysage alluvial. L’occupation du sol, la largeur de la bande active et le taux d’érosion des berges ont été estimés par photo-interprétation et leur évolution spatiotemporelle a été mise en évidence par des traitements statistiques et cartographiques. Les résultats indiquent un accroissement des surfaces vouées à l’agriculture à partir des années 1950 et une progression du recouvrement de la végétation arborée en lien avec la modification des pratiques culturales et la rétroaction de la bande active. Dans les trois secteurs, le pourcentage de la végétation arborée est passé de 10 à 17 % en 50 ans. Depuis la seconde moitié du 20e siècle, la modification des pratiques agro-pastorales semble être un agent prépondérant pour expliquer la végétalisation progressive de la plaine alluviale de la rivière Allier. L’érosion des berges ne s’est pas atténuée durant cette période. Elle était plus active pendant la décennie 1970-1980 en raison des crues plus fréquentes et plus intenses.The landscape mosaics of the Allier river floodplain has been studied in three functional reaches with contrasted geomorphic activities : the Joze-Maringues meander reach where the river is constrained by embankments and affected by gravel mining, the shifting meander reach of the Val d’Allier Natural Reserve, and the anabranching reach between the village of Villeneuve-sur-Allier and Le Veurdre. This study is based on six to eight aerial photography, series taken between 1946 and 2000, to underline the dynamics of the alluvial landscape. Land cover types, active channel width and river bank erosion rate have been assessed from the photo interpretation, and their change in space and time has been statistically analysed and mapped. The results point to an increase of the cultivated areas from the 1950’s, and an extension of the tree-cover in relation with a change of agricultural practices and the decrease of the channel activity. In the three reaches, the percentage of the tree-cover has moved from 10 to 17% in 50 years. From the second half of the 20th century, the change in the agro-pastoral practices seems to be a major factor explaining the increase of the floodplain tree and bush cover. Bank erosion has not diminished during this period. It was more active in the 1970-1980 decade owing to more severe and frequent floods

Populus nigra L. establishment and fluvial landform construction: biogeomorphic dynamics within a channelized river

“…River Ain, France; Lassettre et al ., ), wandering (e.g. River Allier, France; Petit, ) or island braided rivers (e.g. River Tagliamento, Italy; Surian et al , ), the process of biostabilization is generally compensated by lateral erosions occurring on the opposite banks or vertical incision within the main channel.…”

Monitoring and reconstructing past biogeomorphic succession within fluvial corridors using stereophotogrammetry

“…Because of a diverse habitat mosaic it is suitable for the assessment of photogrammetric modelling of topographic change and of complex vegetation structures in their spatial distribution and their vertical organization. All four phases of the biogeomorphic succession are present, from the geomorphic phase (bare substrate) to the ecological (arboreous) phase dominated here by black poplar (Populus nigra L.) and white willow (Salix alba L.) (Petit, 2006). All four phases of the biogeomorphic succession are present, from the geomorphic phase (bare substrate) to the ecological (arboreous) phase dominated here by black poplar (Populus nigra L.) and white willow (Salix alba L.) (Petit, 2006).…”

“…Shields et al, 2000;Petit, 2006;Geerling et al, 2006, Corenblit et al, 2010. Many studies have characterized spatial changes in river landscapes and related vegetation succession dynamics based on historical aerial photographs (e.g.…”

“…Many studies have characterized spatial changes in river landscapes and related vegetation succession dynamics based on historical aerial photographs (e.g. Shields et al, 2000;Petit, 2006;Geerling et al, 2006, Corenblit et al, 2010. Until recently landscape and succession analyses were performed mainly in planimetric dimensions, that is, X and Y (Kadmon and Harari-Kremer, 1999;Miller et al, 2000).…”

Image Utilisation for the Study and Management of Riparian Vegetation: Overview and Applications

“…The nature of imagery employed by researchers relates directly to the latest technology available at the start of their study periods and the timeframe studied: satellite images since the 1970s, aerial photographs since the 1930s, oblique pictures since the nineteenth century (Charlton, 2000;Grams and Schmidt, 2002), or old maps mainly since the seventeenth or eighteenth century. Aerial photographs have been widely used to map landscape configuration changes, turn-over rates for geomorphic features, and the recovery process after flooding (Miller et al, 1995;Marston et al, 1995;Mendonca et al, 2001;Sloan et al, 2001;Freidman and Lee, 2002;Peinetti et al, 2002;Greco and Plant, 2003;Ferreira et al, 2005;Geerling et al, 2006;Petit, 2006;Gonzalez et al, 2010). The majority of studies using diachronic analysis are carried out on land cover or vegetation types.…”