Applications of differential GPS in upland fluvial geomorphology

Recent technological developments in the application of the Global Positioning System (GPS) offer the prospect of rapidly mapping difficult terrain and quantifying temporal and spatial dynamics of erosion and sedimentation. While many developments in GPS have been considered from the viewpoint of geodesy, their versatility in geomorphological situations has had limited attention. In particular, the improved accuracy and reduced costs of some GPS systems makes them attractive for many mapping applications. Differential GPS allows the logging of position of a mobile receiver relative to a control station. In difficult terrain, such as uplands, the location and distribution of survey points by GPS is much more efficient than conventional survey techniques. However, it should be emphasised that GPS is not simply an alternative to existing techniques but has advantages and disadvantages which need to be evaluated. Three case studies in the uplands of Northern England demonstrate the trade-off between the advantage of speed and disadvantage of reduced accuracy afforded by GPS. The studies are concerned with the rapid mapping of flood extent based on ephemeral flow limit indicators; detailed mapping of alluvial fan surfaces and associated sediment sources; and the spatial distribution of colluvial sediment supply and downstream movement of bedload slugs. The extent to which approaches based on differential GPS, in combination with more traditional survey techniques, can provide information on sediment dynamics or validation of distributed models is evaluated.