Evaluating bulk velocities and dispersion effect in a steep gravel-bed channel by detecting tracer clouds

Abstract

The measurement of flow velocity in steep mountainous channels is extremely difficult due to the shallow flow environment. One promising method is capturing the path of tracers and establishing the relation between bulk velocity and tracer transport processes. In this study, two types of dye and salt tracers were utilized for bulk velocity measurement in a steep gravel-bed rectangular channel by analyzing color and electrical conductivity signals. Characteristics velocities gained from the electrical conductivity approach are close to the true values and those from the color space approach need to be corrected. The HSV space signals are more effective to indicate those characteristic boundaries of the dye solution. By analyzing the tracer residence time, longitudinal dispersion characteristics are essentially associated with turbulence negatively and flow resistance linearly and affect the velocity estimation. This study provides new insights to estimate bulk velocity and turbulence induced dispersion in gravel-bed streams.