Applications of Computational Fluid Dynamics in The Design and Rehabilitation of Nonstandard Vertical Slot Fishways

Juan Bravo,Júlia Rossi,Daniela Sanagiotto

doi:10.3390/w11020199

Abstract

Vertical slot fishways are increasingly common structures for the passage of a wide variety of migratory fish and contribute to the maintenance of fish diversity in fragmented rivers. These structures are designed with several geometric arrangements and, consequently, flow patterns through them can be shaped to present suitable characteristics for the fish species. To aid in the design of vertical slot fishways, a three-dimensional numerical model was used to simulate the flow for different geometric configurations. An existing vertical slot fishway with nonstandard dimensions was initially modeled and validated. This geometry was used as a reference design. Modifications to the reference design, such as the insertion of cylinders, changes in the baffle shape and position of the vertical slots, as possible rehabilitation measures, were proposed and tested. In summary, five different designs were evaluated with several slopes, totaling 17 geometries. Hydraulic parameters, flow patterns, maximum velocities, velocity fields and turbulence kinetic energy in the pools were analyzed. The results indicate that the maximum velocity values were between 9% and 68% higher than those obtained by the theoretical equation. This indicates that maximum velocities can be underestimated for nonstandard vertical slot fishways if a simplified evaluation is conducted. The insertion of cylinders in the region close to the slot reduces the maximum velocity up to 8.2%. The positioning of the vertical slots on alternating sides increases the maximum values of turbulence kinetic energy and the regions subjected to higher values. However, this configuration provided greater energy dissipation and reduction of velocities by up to 27%. Thus, modifications in nonstandard vertical slot fishways can be useful in future design or rehabilitation of existing structures in order to provide velocities and turbulence more friendly for a higher number of fish species.

Highlights

The river fragmentation caused by the construction of physical barriers prevents the movement of fishes among other environmental impacts
This study aims to contribute to the design of new nonstandard vertical slot fishways (VSFs) and to improve existing nonstandard VSFs by changes in geometry that result in better flow patterns
Some hydraulic characteristics that can be useful to describe the flow in fishways were evaluated: the theoretical maximum velocityfor

Summary

Introduction

The river fragmentation caused by the construction of physical barriers prevents the movement of fishes among other environmental impacts. This effect may result in the disappearance of many species of ichthyofauna, mainly migratory, which move upstream during the reproduction phase [1,2]. To diminish this negative effect, fishways have been implemented for operation during the life of physical barriers. Fishways are structures or systems that allow for the movement of ichthyofauna between the downstream and upstream parts of a barrier, permitting the passage of migratory fish that move towards the headwaters of a river. Technical fishways include pool fishways, vertical slot fishways (VSFs), Denil fishways, eel ladders, fish locks and fish lifts [3].

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