Author(s): Ralph Eikenberg; Patrik Andreasson; Jochen Aberle; David Aldven; Lo Persson

Linked Author(s): Ralph Eikenberg, Patrik Andreasson, Jochen Aberle

Keywords: Physical model; Unstructured block ramp; Fish migration; Ecohydraulics

Abstract: This paper describes the construction of a full-scale physical model of an existing block ramp from the in-situ survey to its operation in the laboratory. The laboratory experiments are part of a research project focusing on the identification and quantification of fish migration corridors on nature-like unstructured block ramps. An important aim of the research project is to link fish trajectories to bed topography and flow characteristics based on experiments with live fish in both the prototype and laboratory environment. An existing, and in terms of fish migration functional, block ramp in the Ilme river in Lower Saxony, Germany, was chosen as a best-practice example for the implementation of the project. For the in-situ survey, the block ramp was completely drained by setting up a temporal dam of gravel-filled big bags and a plastic foil to divert the water into an upstream side channel, while pumps installed in the backwater ensured an adequate environmental flow downstream of the drained ramp. Structure-from-motion (SfM) photogrammetry and terrestrial laser scanning (TLS) were used for the survey. After completion of the survey, the dam was dismantled, and the original situation in the river was restored. The collected data were postprocessed in several steps to create a digital twin of the ramp as a basis for the laboratory setup. For the model tests, a 4 m wide and 10 m long section along the main flow path on the ramp was chosen. The tests were performed in the Laxelerator, a unique etho-hydraulic facility at the hydraulic laboratory of Vattenfall Research & Development in Älvkarleby, Sweden. The Laxelerator is built as a race-track flume in which water quality, temperature and lightning are controlled and monitored, and the flow can be accelerated so that a flow capacity of up to ≃16 m³/s can be reached. It has two straight 25 m long test sections that are 4 m wide and 2 m deep, and one of these sections was used for the tests with the model-ramp. The 1:1 model was manufactured in Styrofoam using a CNC-technique and mounted with geometrical modifications of upstream and downstream ends to create appropriate flow conditions. Materials and construction of the model were chosen to provide a suitable environment for live fish tests but also to manage the harsh flow conditions and forces created by the flow and buoyancy of the Styrofoam. The laboratory is certified for research with live fish and ethical permit for the project was given for several to Sweden native fish species relevant for the German river. Preliminary results from the currently ongoing tests will be provided at the conference.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022838

Year: 2022