Quantifying geomorphic and riparian land cover changes either side of a large flood event using airborne remote sensing: River Tay, Scotland

The potential of high resolution multi-spectral airborne remote sensing to detect and quantify changes in channel morphology and riparian land cover are illustrated. The River Tay is a partially embanked wandering gravel bed river, and Airborne Thematic Mapper data, which collect reflectance in the visible, near, mid and thermal infrared, were acquired in 1992 and 1994 either side of a 1:65 recurrence-interval flood event. Imagery was radiometrically, atmospherically and geometrically corrected in order to minimise atmospheric and geometric changes between the 1992 and 1994 scenes. A maximum likelihood classifier was then used on each image and change was quantitatively mapped using a classification comparison approach. Bathymetric mapping was undertaken by applying a Lyzenga algorithm to ATM bands 5, 6 and 8 to account for an exponential decrease in electromagnetic radiation penetration through the water column with depth. Despite the magnitude of the flood event, no major changes in channel position or form occurred but the change detection algorithms revealed subtle changes not observed in the field. Bar head accretion, bar tail formation and extension, bar dissection, localised bank erosion and the overriding of low level vegetated islands by gravel lobes were the main forms of change. On the floodplain, flood embankment failures resulted in fans of sands and gravels on agricultural land. More generally, the study reveals the potential for using airborne remote sensing to detect change in fluvial systems and as a mutually complementary tool to field survey. (C) 1999 Elsevier Science B.V. All rights reserved.