WWRC 95-14
Channel Metamorphosis, Floodplain Disturbance, and Vegetation Development: Ain River, France
Abstract
The purpose of this paper is to describe and explain channel metamorphosis of the Ain River in east-central France and the
effects of this metamorphosis on floodplain disturbance and vegetation development. The Ain River is a 195 km long stream
originating in the Jura Mountains which flows into the Rhone River between Lyon, France, and Geneva, Switzerland. The lower
40 km of the Ain River, beyond the mountain front, are situated in a valley of outwash deposits where the floodplain is 0.2 to
1.2 km wide. A complex mosaic of floodplain landscape units has developed. Maps dating back to 1766 and six sets of aerial
photographs dated between 1945 and 1991 were used to document changes in channel pattern. Aerial photos and field surveys
were used to compile maps of landscape units based on dominant vegetation life-forms, species, and substrate. Six maps dated
between 1945 and 1991 were digitized in ARC/INFO and an overlay was generated to determine the changes in landscape units
as related to channel disturbance. Change from a braided to a single-thread meandering channel probably took place in the period
1930-1950. The process of river entrenchment has occurred throughout the Holocene but has accelerated in the present century
due to shortening of the river course, construction of lateral embankments, and vegetation encroachment following reservoir
construction and cessation of wood-cutting and grazing. The increase in horizontal channel stability coupled with channel
entrenchment have decreased floodplain disturbance and lowered the water table by approximately one meter. Pioneer and
disturbance-dependent landscape units have experienced a more terrestrial-like succession to an alluvial forest. Abandoned
channels have also been replaced by alluvial forests. On poorly drained soils, shrub-swamp communities of willow and
hydrophytic herbaceous plants have been replaced by mixed forests of ash, alder, black poplar, and oak. On well drained alluvial
soils, ash and oak dominated hardwood forests have declined in favor of mesophytic stands of black poplar. All types of
vegetation, but particularly dry grasslands-shrublands, have been cleared for mines, campgrounds, agriculture, and other types
of development. Using several measures, landscape diversity decreased between 1945 and 1991.
Water Resources Publications List
Water Resources Data System Library |
Water Resources Data System Homepage
