Crossbar Block Ramps: Flow Regimes, Energy Dissipation, Friction Factors, and Drag Forces

摘要

Crossbar block ramps are a common solution for a naturelike channel. Current investigations deal with energy dissipation processes on block ramps, where large stones are arranged on the complete slope. Contrary, crossbar block ramps build several basins by arranging stones in a row transversal to the flow direction. Lower stones guarantee a minimum water level in each basin and allow for an overfall for small discharges and fish climb capabilities. With increasing discharges, the water also overflows the large stones and the basin flow regime changes over a waved flow regime into a channel flow regime. This paper deals with physical and numerical crossbar block ramp models. The physical model allows for the variation of discharges from 1 to 50 l/s; numerical simulations are run up to 200 1/s with varying slopes, crossbar heights, and distances. Water levels, velocities, and drag forces on single stones are measured. New approaches to relative energy dissipation and the friction factor to evaluate water depths for channel flow regimes are developed. Additionally, drag forces on single stones in various crossbars are measured and analyzed.