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Influence of Inflow and Outflow Boundary Conditions on Flow Situation in Vertical Slot Fishways

Author(s): J. Klein; M. Oertel

Linked Author(s): Mario Oertel

Keywords: Fish passage; Vertical slot fishway; VSF

Abstract: Fishways are of importance for stabilization and regeneration of fish populations. Since most waterways and rivers are anthropogenic modified -- e. g., to make them navigable or to produce energy, etc. -- the effect on biology and morphology is not negligible. Some fish species are nearly extinct because they cannot reach their natural habitat to spawn or feed or the genetic diversity is lacking due to barriers that cannot be overcome. In the past decades a growing effort was made to decrease the ecological impact. Consequently, several fishways were built to provide migration corridors for various aquatic organisms. Since the 1980s different kinds of fishways have been biologically and hydraulically investigated. Numerous nature-like structures as well as technical structures were studied in physical, numerical, and prototype models. Vertical slot fishways can be categorized as technical fishways with a series of pools and a sloping bottom, where vertical openings in the cross walls provide a migration corridor. Hence, vertical slot fishways represent a technical bypass for dams and other lateral barriers. Even though vertical slot fishways are well studied, further hydraulic effects can be observed. In this context, the present paper investigates the hydraulics of vertical slot fishways and deals with the effect of downstream water levels on the hydraulic flow situation on vertical slot fishways. While most hydraulic models assume a quasi-uniform flow, it can be observed that varying water levels in geometrically equal pools are frequent. Herein, results of an experimental model are presented. Water levels in the pools and their dependence on inlet and outlet boundaries (water levels and discharge) are investigated. It can be shown that downstream water levels -- preset with an installed tailgate -- as well as upstream water levels (as a result of the inflow conditions) have an influence on the pools’water depths, while the influenced area, and consequently the number of affected pools, majorly depends on the specific discharge. A uniform distribution of total height difference at the fishway from one pool to the next could not be confirmed. Water level reduction and backwater effects result in continuously non-uniform flow situations on the structure.


Year: 2018

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