Bed Load Transport in a Physical Scale Model of Two Merging Mountain Streams

Abstract

This chapter presents a methodology for physical scale modeling of bed load transport with a nonuniform grain size distribution. The approach includes the challenge of converting the natural sediment into model scale by avoiding or minimizing model effects. The chapter is based on the physical model of the flood protection project Meiringen at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) in Zurich. The model represents the confluence of two mountain torrents, which carry a lot of sediments during floods, exhibiting supercritical flow. The applied method uses Zarn’s approach (Zarn 1992) for the conversion of the grain size distribution from nature scale to model scale. It accounts for the size effects emerging from small grain size–related Reynolds numbers. The grains are scaled by shear velocity according to Froude’s law leading to a coarsening of the grain size distribution. This implies an adjustment of the sediment input via the model transport capacity and an adaptation of the model hydrograph, altogether resulting in a reasonable simulation of the bed load transport.