AMPLITUDE OF INCISED QUATERNARY MEANDERS AND RIVER-BASINS AREA IN NORTH-EASTERN FRANCE - PALEOGEOGRAPHIC IMPLICATIONS

A new definition of incised meanders is proposed in order to correlate their size with stream-morphogenic potential. Measurements of meander amplitude were undertaken on 211 Quaternary incised meanders from the climatic, lithologic and morphostructurally homogeneous area of north -eastern France. 1/25000 topographic maps of the Seine, Marne, Aisne, Yonne, Meuse, Moselle and Saone rivers were used in the study (fig. 2) . Only meanders in which meander amplitude (A) is at least equal to or greater than half a meander wavelength (L) are considered (fig. 1). R esults were related to the river-basins areas (S) (fig. 4 and 5). Resu lts suggest that meander amplitude (A) and wavelength (L) tend to incr ease with the square root of river-basin area (fig. 4 and 5), but stru cture hasn't so much influence on amplitude than on wavelength (fig. 6 and 7). For the greater part (88%) meanders of small amplitude (small er than 2500 m amplitude) square-rootS <A <1.8 square-rootS (fig. 4). For 86% meanders of large amplitude (larger than 3000 m amplitude) amp litude is larger than 1.8 square-rootS (fig. 4). The largest amplitude meanders demonstrate severe change in Quaternary river-basins, possib ly due to river capture. So, the largest amplitudes of incised meander s on the Meuse between Pagny and Dun are related to Moselle upper Toul and Meuse river-basin (fig. 8). Then, meanders amplitude becomes smal ler than 2.2 square-rootS and larger than 2 square-rootS. In order to balance river-basins hydrologic heterogeneity, amplitude were related to present day discharges (M). For 88% meanders, 0.25 square-rootM <A <0.6 square-rootM or 0.5 square-rootM/pi <A <square-rootM/pi (fig. 9 a nd 11). The amplitudes of incised meanders on the former Aire-Bar vall ey (fig. 12) are also overlarge, and are related to a larger former ba sin (fig. 10). Meanders of large amplitude correspond with the mean an nual discharge of a former basin which may have included not only the Aire river but also the upper Aisne, Ornain, Saulx and Marne rivers (f ig. 12). The present-day drainage network (fig. 16) suggests three suc cessive captures of the Aire (fig. 13), the Aisne-Ornain-Saulx (fig. 1 4) and the Marne (fig. 15), each of which are discussed.