Effects of bed slope on the flow field of vertical slot fishways

Abstract

Vertical slot fishways (VSFs) are the most efficient and least selective typology of technical fish passage, due to their ability to remain effective even when significant upstream and/or downstream water level fluctuations occur. Fishway construction costs can be reduced by increasing its bed slope, but this affects the flow field inside the pools, with higher head drops between the basins, as well as turbulence levels and flow velocities, which may affect fish passage. In light of this, a VSF was investigated by 3D numerical simulations to identify the possible effects of the bed slope (using values from 1.67% to 10%) on the flow field and subsequent implications for fish passage. A particular focus was devoted to cyprinind species, but the results can be extended to other species of similar swimming abilities and, therefore, be applicable to multispecies rivers. Flow velocity and turbulence values such as turbulent kinetic energy and Reynolds stresses were analysed from a fish passage perspective in relation to threshold values derived from previous studies. Pool areas where turbulence values are compatible with fish ability and behaviour were quantified. Maps of the location of fish-friendly zones in the VSF pools were produced and can constitute a reference for practical applications in fishway design. The flow field generated with bed slopes lower than 6.67% is more compatible with fish swimming capabilities, because it exhibits a predominantly 2D behaviour and more suitable hydraulic conditions, whereas at higher slopes, turbulence levels in the pools increase.

Assessment of Retrofitted Ramped Weirs to Improve Passage of Potamodromous Fish

“…Thus, to assess the effects of hydrodynamics on the fish behavior, numerical modelling (the 3D CFD model FLOW-3D ® ) was used in this study to characterize influential hydrodynamic variables, such as velocity magnitude, TKE, and water depths, present in each configuration tested, in order to identify areas of high velocity and turbulence gradients that might have affected the fish movements. Over the last few years, 3D CFD models have proved to be a practical and robust tool to characterize hydrodynamics on several hydraulic structures, being widely used for the assessment of fish passages (e.g., studies on functioning over a wide range of discharges, prediction of suitable conditions for fish), optimization of designs, and evaluation of different retrofitting solutions [52][53][54][58][59][60][61][62][63][64]. However, given that uncertainty in CFD modelling for environmental fluid mechanics in complex flow fields, like the flow field in the vicinity of a macro-scale roughness (e.g., wake region), can arise from a very wide range of sources, care should be taken when performing a numerical model study [65].…”

Designs for T Shape Fishways

“…k=0.0144ui 2 (9) ε=k 0.5 /(0.5hi) (10) In Equations (9) -(10), ui and hi are the velocity and the depth of the inlet, respectively. The hex-shaped grid was used in the entire model, and the time step was set as 0.002 s.…”

“…Three types of technical fishways are commonly used in engineering: (1) Denil fishways [3], [4], [5] (2) pool and weir fishways [6], [7], [8] ( 3) vertical slot fishways [9], [10], [11] The Denil fishway is impressionable to fluctuating water levels and is prone to clogging up with silt and debris, so it needs to operate at higher water levels than other types of fishways. The pool and weir fishway is inadaptable to large water level fluctuations, and does not allow fish passing across the entire cross section.…”

Considerations for Multi-Species Fish Passage in California: A Literature Review

“…Extensive modifications created the Ice Harbor Fishway design ( Figure 6) with a partial-depth side slot to improve overflows that resulted in greatly improved Shad passage and some improvement to salmon passage (Monk et al 1989;Petersen et al 2003). Although challenging to design fishways for multiple species, recent research provides optimism that knowledge, experimental and field studies, computational tools (e.g., computational fluid dynamics [CFD] software), and data-based swimming performance curves for many species are better now than 10 or 30 years ago (Katopodis and Williams 2012;Silva et al 2012;Katopodis Ecohydraulics Ltd. 2013;Marriner et al 2016;Amaral et al 2018;Quaranta et al 2019).…”