SCALE-SPACE ANALYSIS OF STREAM-BED ROUGHNESS IN COARSE GRAVEL-BED STREAMS

This paper shows the usefulness of the scale-space filtering technique for the analysis of stream-bed roughness. In the first part of the pa per, the scale-space filtering technique originally developed for sign al analysis is adapted for the analysis of stream-bed microtopographic profiles. The modified technique provides a multiscale description of bed profiles, which allows the objective identification and measureme nt of individual roughness elements at all scales of observation. Thes e bed elements then are classified as either grain or form roughness e lements according to the roughness scales identified from a semivariog ram analysis of the bed profile. Roughness indices describing each rou gh,less scale are obtained by calculating the mean height and spacing of the grain and form roughness elements. Because they measure directl y the geometry of the bed, these indices provide a better description of stream-bed roughness than the traditional method based on a single grain index. in the second part of the paper, the technique is applied to the analysis of stream-bed roughness and resistance reflow of nine different gravel-bed stream reaches. The roughness indices calculated from this approach are used to obtain predicted values of resistance to pow which are in good agreement with the values observed in the fie ld. The quality of this prediction is compared to the one obtained fro m a traditional description of bed roughness based on a single grain-s ize index. The results indicate that the values of resistance to flow calculated using the traditional approach are significantly less accur ate than the values calculated using the new procedure which separates stream-bed roughness into a grain and a form component.