Experimental Hydraulic Investigation of Angled Fish Protection Systems—Comparison of Circular Bars and Cables

Heidi Böttcher,Markus Aufleger,Roman Gabl

doi:10.3390/w11051056

Abstract

The requirements for fish protection at hydro power plants have led to a significant decrease of the bar spacing at trash racks as well as the need of an inclined or angled design to improve the guidance effect (fish-friendly trash racks). The flexible fish fence (FFF) is a new developed fish protection and guidance system, created by horizontally arranged steel cables instead of bars. The presented study investigated experimentally the head loss coefficient of an angled horizontal trash rack with circular bars (CBTR) and the FFF with identical cross sections in a flume (scale 1:2). Nine configurations of different bar and cable spacing (blockage ratio) and rack angles were studied for CBTR and FFF considering six different stationary flow conditions. The results demonstrate that head loss coefficient is independent from the studied Bar–Reynolds number range and increases with increasing blockage ratio and angle. At an angle of 30 degrees, a direct comparison between the two different rack options was conducted to investigate the effect of cable vibrations. At the lowest blockage ratio, head loss for both options are in similar very low ranges, while the head loss coefficient of the FFF increases significantly compared to the CBTR with an increase of blockage. Further, the results indicate a moderate overestimation with the predicted head loss by common head loss equations developed for inclined vertical trash racks. Thus, an adaption of the design equation is proposed to improve the estimation of head loss on both rack options.

Highlights

Fish protection and downstream migration measures are considered essential in the design, construction or retrofitting and operation of hydro power plants
The results show that head loss at horizontal trash racks is comparably low and the hydraulic conditions at the bypass entrance are favourable from an ecological point of view [27]
The measured head loss coefficients were compared with literature equations and a regression model is fitted to the data to adapt Equation (6) to the studied rack options

Summary

Introduction

Fish protection and downstream migration measures are considered essential in the design, construction or retrofitting and operation of hydro power plants. Juveniles, tend to swim within the main current, they will pass the turbines without appropriate measures at the water intake [1]. Depending on site-specific conditions such as turbine type, total head, operation mode of the power plant or fish size, fish are injured, followed by a high risk of mortality [2]. Fish that refuse to enter the turbines remain in the reservoir area, sometimes for several days [3]. Particular trash racks with horizontal or vertical bars that are angled to the flow direction (angled trash racks) or inclined to the bottom (inclined trash racks), are one technical solution to prevent fish from turbine-passage and guide them to a bypass [4].

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Results

Discussion

Conclusion