Author(s): Caroline Selheim; Thorsten Husener

Linked Author(s): Caroline Selheim

Keywords: Hydraulics; Scale model; Form roughness; Inverse printing

Abstract: The Federal Waterways Engineering and Research Institute (BAW), specifically the section River Engineering, examines the quantification of water level decline as a result of the excavation of solid rock riverbeds in certain parts of Germanys waterway network to improve navigability. In order to predict the effect on the water level in the intervention area, a scale model in a 35m long and 2.5m wide flume is being operated in the laboratory of the BAW. The purpose of this model is to simulate the hydraulic behaviour of solid rock river bottom topography by using gravel chippings with a narrow grain size distribution. While the hydraulic roughness of rock formations is not only expressed by the surface roughness but also the form roughness, it is crucial to reproduce the actual river bed’s geometry in order to replicate the effect of bedrock excavation. Therefore, the model setup contains the representation of the river bed topography according to the digital terrain model at a scale of 1:20 in the constructed model. To shape the gravel chippings into the original riverbed terrain, an innovative approach to create accurate topography in scale models has been developed, called the 3D-InversePrinter. As the name suggests, the method allows the terrain to be “printed” by removing material instead of adding it. This is put into practice by using an industrial vacuum system with a corresponding 3D traverse measurement system, which allows a precise motion of the vacuum device to remove material, accurate to a millimetre. The topography preparation is monitored by using a laser scanner to compare original and manufactured digital terrain model in the flume. The hydraulic effects measured in the physical model and the natural flow conditions are compared by examining the velocity profiles. In the river site, special acoustic Doppler current profiler (ADCP) point measurements are used to generate a precise vertical velocity profile, while the physical model’s velocities are quantified by acoustic Doppler velocimeter (ADV). Comparing the velocity profiles, it can be shown that both the bed construction method and the chosen bed material are able to reproduce the hydraulic behaviour in the river flow with very high accuracy.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221439

Year: 2022