Abstract
In this paper, flow resistance of debris bed having wide size distribution is studied.
Basic equation of flow resistance is deduced from assumption that shearing stress of bed is balanced with drag force of roughness elements, and numerical bed profiles are simulated assuming log-normal size-distribution of bed material and using random numbers generated by computer.
To clearify the relation between flow resistance and size-distribution, numerical experiments are made by use of the basic equation and numerical bed profiles. It becomes obvious from the numerical experiments that diameter corresponding to 70% of distribution curve, d70, is appricable as a representative diameter of bed debris, and relative roughness height, ks, is equal to 3d70 independently with standard deviation of the bed material size. As a result, new practical roughness formula is offered, and it shows good agreement with flume data.
