Applications of differential GPS in upland fluvial geomorphology

Recent technological developments in the application of the Global Position ing System (GPS) offer the prospect of rapidly mapping difficult terrain an d quantifying temporal and spatial dynamics of erosion and sedimentation. W hile many developments in GPS have been considered from the viewpoint of ge odesy, their versatility in geomorphological situations has had limited att ention. In particular, the improved accuracy and reduced costs of some GPS systems makes them attractive for many mapping applications. Differential G PS allows the logging of position of a mobile receiver relative to a contro l station. In difficult terrain, such as uplands, the location and distribu tion of survey points by GPS is much more efficient than conventional surve y techniques. However, it should be emphasised that GPS is not simply an al ternative to existing techniques but has advantages and disadvantages which need to be evaluated. Three case studies in the uplands of Northern Englan d demonstrate the trade-off between the advantage of speed and disadvantage of reduced accuracy afforded by GPS. The studies are concerned with the ra pid mapping of flood extent based on ephemeral flow limit indicators; detai led mapping of alluvial fan surfaces and associated sediment sources; and t he spatial distribution of colluvial sediment supply and downstream movemen t of bedload slugs. The extent to which approaches based on differential GP S, in combination with more traditional survey techniques, can provide info rmation on sediment dynamics or validation of distributed models is evaluat ed. (C) 1999 Elsevier Science B.V. All rights reserved.