Slope-area relationships and sediment dynamics in two alpine streams

The paper focuses on the channel network of alpine basins, attempting to interpret channel reaches in terms of response to erosion and deposition processes. Two basins in the Dolomites (north-eastern Italy) were considered: the Rio Cordon (5 km(2)) and the upper Boite River (163 km(2)). The channel network was extracted from raster-type digital elevation models (DEM) using a slope-area threshold criterion. A contribution area index (CAI), which combines drainage area, A, and local slope, S (CAI = A(0.5)S), was used to identify channel heads. The channel network extracted from the DEM was then analysed to recognize cells showing a value of CAI lower than the threshold adopted for channel initiation. Contiguous cells with low values of CAI define channel reaches with low transport efficiency. Field surveys carried out for some selected cases showed a good agreement between prevailing sediment deposition predicted by the analysis of the channel network and observed channel morphological features. Sediment sources mapped in two study basins were also analysed in relation to the location of channels with high potential for sediment deposition: this made it possible to classify the potential role of different types of sediment sources with regard to basin sediment yield. Topographic characteristics of the channel network, expressed by CAI, were compared with a classification of channel morphology in the Rio Cordon. It was found that cells with low values of CAI frequently occur in the riffle-pool reaches, whereas the percentage significantly decreases in step-pool and bedrock channels. Copyright (C) 2003 John Wiley Sons, Ltd.