Author(s): Anton Burman; Anders Andersson; Gunnar Hellstrom; Qiancheng Xie

Linked Author(s): Anton Burman, Anders Andersson, Gunnar Hellström, Qiancheng Xie

Keywords: Numerical Modelling; ADCP; Field Measurements; Pressure Loggers; Ecohydraulics

Abstract: In the near future, the operating conditions of hydropower plants in the Nordics are expected to change, in order complement expansion of intermittent power production such as solar- and wind-power. This in turn might increase the amount and frequency of short-term flow regulations events, so called hydropeaking. In recent years, hydropower’s effect on local ecosystems has drawn much attention. Especially hydropeaking has been shown to affect the ecosystems and induce morphological changes in the reach downstream hydropower plants. In order to assess the potential impact of a change in operating conditions, different numerical models can be used to examine the downstream reach when subject to potential future operating conditions. In-flow parameters, such as depth and velocity, can be predicted by using numerical approximations of the Navier-Stokes equations in either one-, two- or three-dimensions. These modeling approaches have different advantages and disadvantages. In this work the uncertainties that arise naturally from field measurements and numerical modelling, and how it might affect in-flow parameters, specifically variables frequently used in ecohydraulics, with special emphasis on 2D models was investigated. The flow in a regulated reach was here modelled with the open-source hydrodynamics solver Delft-3D. A stretch of the river Umeälven in northern Sweden was modelled based on bathymetry measurements from a multibeam sonar. The model was calibrated with measured water levels and validated with ADCP velocity measurements. The results show that the model is significantly dependent on the calibrated roughness. Additionally, it is shown that 2D models might be insufficient for some ecohydraulical applications. Lastly, a discussion on the merits of one-, two and three-dimensional models is presented.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221796

Year: 2022