Stream power can be an extremely useful index of fluvial sediment transport, channel pattern, river channel erosion and riparian habitat development. However, most previous studies of downstream changes in stream power have relied on field measurements at selected cross-sections, which are time consuming, and typically based on limited data, which cannot fully represent important spatial variations in stream power. We present here, therefore, a novel methodology we call CAFES (combined automated flood, elevation and stream power), to quantify downstream change in river flood power, based on integrating in a GIS framework Flood Estimation Handbook systems with the 5 m grid NEXTMap Britain digital elevation model derived from IFSAR (interferometric synthetic aperture radar). This provides a useful modelling platform to quantify at unprecedented resolution longitudinal distributions of flood discharge, elevation, floodplain slope and flood power at reach and basin scales. Values can be resolved to a 50 m grid. CAFES approaches have distinct advantages over current methodologies for reach-and basin-scale stream power assessments and therefore for the interpretation and prediction of fluvial processes. The methodology has significant international applicability for understanding basin-scale hydraulics, sediment transport, erosion and sedimentation processes and river basin management. 286 EARTH SURFACE PROCESSES AND LANDFORMS flood power at an unprecedented spatial resolution for both slope and discharge measurements. This is a significant improvement on earlier approaches (e.g. Lecce, 1997;Abernethy and Rutherfurd, 1998;Knighton, 1999). Many field studies, though useful, have necessarily relied on a limited number of crosssections, often from a single basin, given the time-consuming nature of field surveys. Also, even more recent studies have, at best, made use of finely resolved data in either slope (e.g. Reinfelds et al., 2004;Jain et al., 2006) or discharge, but not both, or have estimated flow at ungauged sites very simply, typically from an area-discharge relation (e.g. Fonstad, 2003). The CAFES methodology, however, integrates within a GIS framework several novel, high-resolution DEMs, digital land use and soil datasets and flood estimation systems to produce digital databases of flood discharge and slope relatively rapidly. These can then be co-registered and combined to generate Figure 3. Longitudinal flood discharge trends for rivers in western Britain in terms of distance downstream and catchment area for (a), (b) River