Field Investigation of Hydraulics and Fish Guidance Efficiency of a Horizontal Bar Rack-Bypass System

Mohammadreza Maddahi,Roland Hagenbüchli,Robert Michael Boes,Ricardo Mendez,Claudia Zaugg,Ismail Albayrak

doi:10.3390/w14050776

Mohammadreza Maddahi, Roland Hagenbüchli + Show 4 more

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https://doi.org/10.3390/w14050776

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Abstract

This paper investigates the hydraulics and fish guidance efficiency of a Horizontal Bar Rack-Bypass System (HBR-BS) installed at a hydropower plant with a design discharge of 33 m3/s. The HBR is placed at a horizontal rack angle of 38° to the flow direction with clear bar spacing of 20 mm. The BS has a vertical-axis flap gate with two openings. The HBR-BS complies with most literature design criteria. Velocity measurements were conducted using a moving-vessel Acoustic Doppler Current Profiler (ADCP). The fish monitoring study was conducted using a stow net, video, and ARIS sonar recordings. The fish monitoring calculations imply guidance efficiency of 84%, even for fish with total body lengths below 10 cm. Furthermore, the hydraulic results show that the flow field is favorable in terms of fish guidance due to a good alignment of the rack and the BS, corroborating the fish monitoring results. The results indicate that the HBR-BS functions not only as a physical barrier but also as a mechanical behavioral barrier for some small fish that are capable of physically passing the HBR. The present results are compared and discussed with the laboratory and field results from different studies in the literature.

Highlights

Hydropower plants (HPPs) have negative impacts on aquatic environments such as blocking fish migration and sediment movement, resulting in an impairment of biodiversity and river morphology [1,2]. Regarding the former, the main issues associated with hydropower plants (HPPs) are blocking or delaying up- and downstream fish migration, and fish injury or mortality when passing turbines, weirs, or spillways
The results show that Horizontal Bar Rack-Bypass System (HBR-BS) with sb = 20 mm have almost no protective effect for juvenile nase with an average total size of 72 mm, whereas the fish protection efficiency (FPE) exceeded 90% for spirlin and eel
The present study aims at filling a portion of the research gaps and contributing to a hydraulically optimal and biologically effective design of horizontal bars and narrow bar spacing (HBR)-BS

Summary

Introduction

Hydropower plants (HPPs) have negative impacts on aquatic environments such as blocking fish migration and sediment movement, resulting in an impairment of biodiversity and river morphology [1,2]. While upstream fish passage technologies are well developed and have been applied for decades, downstream fish passage poses challenges to scientists, engineers, local authorities, and HPP operators due to the current lack of design standards [3]. This has driven many research projects, resulting in technological developments such as fish-friendly turbines, physical fish protection barriers, mechanical and behavioral barriers, fish collection systems, and fish-friendly operations. Region-specific fish passage designs should be incorporated [6]

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