ALLUVIAL CHANNEL GEOMETRY - THEORY AND APPLICATIONS

The downstream hydraulic geometry of alluvial channels, in terms of ba nk-full width, average flow depth, mean flow velocity, and friction sl ope, is examined from a three-dimensional stability analysis of noncoh esive particles under two-dimensional flows. Four governing equations (flow rate, resistance to flow, secondary flow, and particle mobility) are solved to analytically define the downstream hydraulic geometry o f noncohesive alluvial channels as a function of water discharge, sedi ment size, Shields number, and streamline deviation angle. The exponen ts of hydraulic geometry relationships change with relative submergenc e. Four exponent diagrams illustrate the good agreement with several e mpirical regime equations found in the literature. The analytical form ulations were tested with a comprehensive data set consisting of 835 f ield channels and 45 laboratory channels. The data set covers a wide r ange of flow conditions from meandering to braided, sand-bed and grave l-bed rivers with flow depths and channel widths varying by four order s of magnitude. Figures illustrate the results of the three-part analy sis consisting of calibration, verification, and validation of the pro posed hydraulic geometry equations. Field and laboratory observations are in very good agreement with the calculations of flow depth, channe l width, mean flow velocity, and friction slope.