Repeat terrestrial laser scanner survey of pebble cluster creation and formation in response to flow change

Water flow level in river channels is moderated by the interaction with the roughness of the surface over which it flows. The interaction is highly complex and remains poorly understood despite its economic and social importance in flood level forecasting. Much of the hydraulic resistance has been attributed to grain roughness, often with no account of microscale bedforms (pebble clusters). Gravel-bed rivers exhibit many micro-scale sedimentological forms and structures including particle clusters and these dynamic units respond to changes in the flow regime, being created, growing, or being destroyed. The aim of this project is to document the evolution of the type distribution of micro-scale sedimentological bedforms from an unsorted bed following complete disruption of the surface as a result of bank protection works. Laser scan survey data are utilised and roughness elements classified based on the statistical properties of particle cluster arrangement and organisation. A Riegl LMS Z210 field laser scanner collected random field data along a 80m reach of Kingsdale Beck, North Yorkshire on three occasions following geomorphologically effective flow events. A moving window approach was used to compute the local standard deviation of the elevation data. The resultant surface of standard deviations were interrogated to determine the values corresponding to known micro-topographic roughness elements and these statistics were used to compute a surface displaying all elements within the river for each flow. The results indicate that micro-topographic roughness elements rapidly developed and changed with each flow supporting previous research which suggests that they are important in regulating flow resistanc