STUDY ON DOUBLE-AVERAGED VELOCITY PROFILE FOR ROUGH BEDS AND LOW-FLOW CONDITIONS

Velocity profile have important functions in open-channel flow. In low and rough-bed stream conditions, which is a condition where relative submergence is h/D84 < 4 (h is mean flow depth and D84 is representative grain size), the flow is strongly influenced by bed irregularity that causes heterogeneity of flow velocity. The distribution of velocity has been known to deviate logarithmically especially in areas near the stream bed. This study was aimed at testing a simple approach to estimate the velocity profile based on the double-averaging method. Two types of distributions (linear and logarithmic) were assumed to govern the velocity profile in the rough-bed and low flow stream conditions. The input parameters for the velocity distribution equations were obtained from general hydraulic characteristics information from field measurement, calculated by using the flow resistance equation known as the variable-power equation (VPE). From the results, the problems in the parameterization of double-averaged velocity profile estimation were highlighted.