Controls on Pebbles’ Size and Shape in Streams of the Swiss Alps

Abstract

Although the size and shape of pebbles reflect the ensemble of sediment supply and transport processes along a stream, neither positive nor negative correlations have been found between the grain size of gravel bars, sediment flux, water discharge, and river flow strengths in Swiss streams. The relative frequency of 20°–30° hillslope angles per catchment is the only variable that positively correlates with the size of the largest clasts (D96 percentile). We relate these observations to the detachment-limited states of the Swiss streams where ongoing fluvial dissection steepens the bordering hillslopes, thereby promoting the supply of material through lithology-controlled failure.