Long-term Dynamics of the Channel Network in a Glacial Floodplain, Val Roseg, Switzerland

Abstract

The fluvial system in the upper Val Roseg in the Swiss Alps is characterized by a complex glacial floodplain. To analyze the changes in floodplain morphology between 1947 and 1999, a period during which the two main glaciers lost 700 to 1600 m in length, ten sets of aerial images were rectified and channel network and active floodplain area were digitized into a Geographic Information System (GIS). Changes mainly included an increase in the active floodplain width in the upper part of the floodplain. In the 100- to 500-m wide floodplain, the average lateral shift of the main channel ranged from 2 to 10 m yr⁻¹. While the channel network was continuously renewed at a turnover rate of 25% per year, the overall structure of the Roseg floodplain remained relatively constant, despite rapid glacial retreat that increased the availability of glacial sediments potentially susceptible to fluvial transport. The sinuosity index averaged 1.15 ± 0.01 and the braiding index 4.6 ± 1.2. Only the connectivity index showed high variation (6.6 ± 5.0), about 34% of which may be attributed to variation in discharge.