Bed forms and bend‐arc spacings of some coarse‐bedload channels in Upland Britain

Abstract Seventy‐eight riffle to riffle and 80 bend spacings along eleven coarse‐bedload, low sinuosity stream channels in upland Britain have been surveyed. Frequency distributions of these spacings are notably right‐skewed. The most common repeating distances between riffles and bend inflections are between 4 and 6 channel widths although spacings up to 20 widths are also present. Riffle and pool locations around bends at different stages of planform development indicate that change is largely through increased sinuosity between two consecutive riffles of an original straight reach. Observed straight segments exhibit alternating riffles and pools evenly spaced at 4‐6 widths, and most bends have similarly spaced riffles at their inflections in plan, with the intermediate pool at their apex. However angular deflections between axial lines joining inflections indicate existing sequences of bends did not develop from a single straight reach. Bends which are significantly longer than 4‐6 widths are of low sinuosity and represent variability in naturally irregular planforms rather than arcs in advanced stages of meander growth. Adjusted bed topography around such long bends takes two forms. Either a single riffle‐pool cycle is present with one or both bed forms being longer than average, or a 4‐6 widths spacing is maintained by more than one riffle‐pool sequence. Locally, the cross‐section characteristics of riffles and pools are also influenced by planform location.