Measurement and analysis of alluvial bed roughness

Techniques for measurement and analysis of the physical roughness of alluvial beds are introduced and evaluated. Precise digital elevation models (DEMs) of bed surfaces are developed using laser-scanning technology. Hydraulic roughness is represented by the standard deviation of local bed surface heights. which can be measured by physical profiling, analysis of DEMs or by a simple sand-spreading technique. Results from grain size analyses are compared with these different surface roughness determination techniques. At low relative depths the blocking of flow area by roughness elements is shown to be related to the standard deviation of local bed surface heights. A directional standard deviation is suggested for beds with structural polarization and an inclination index is introduced to identify bed imbrication.