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Abstract
Worldwide, the overwhelming number of man-made barriers in fluvial systems has been identified as one of the major causes of the reported staggering average declines of migratory fish. Fish passages have been shown to help mitigate such problems. Close-to-nature types of fish passages, such as bottom ramps, bypass channels, and fish ramps can be used to minimize the impact of artificial steep drops (e.g., weirs) on the migration of aquatic fauna, especially in cases of low-head barriers. This study focuses on the characterization of the flow pattern in a bottom ramp. A 3-D numerical model based on the meshless smoothed particle hydrodynamics (SPH) method was successfully validated and then employed for the simulation of turbulent free-surface flow in a straight channel with complex geometry. The effects of bed roughness, channel slope, and flow rate were quantified in terms of flow depth, velocity fields, and area‒velocity ratios. During the study, several new tools were developed, leading to new functionalities in pre-processing, solver, and post-processing which increase the applicability of DualSPHysics in the field of eco-hydraulics.
Highlights
Migratory freshwater fish populations are in continuous decline [1], indicating the unsuccessful attainment of the good ecological status goal set by the European WaterFramework Directive
Following the methodology in [45], the present study focused on water surface elevations and horizontal velocity magnitudes in the vicinity of the fourth line of spheres (Figure 2)
The following aspects need to be taken into consideration: the different possible paths that different fish species and sizes can take during their migration along the fish pass, including the near-bottom region; the variety of flow directions, including the main region of longitudinal flow and areas of transverse flow; the frequency and size of resting areas; integration with natural upstream and downstream conditions, i.e., geometry resembling the natural conditions without abrupt transitions and with bed roughness and substrate elements similar to the ones at the actual site
Summary
This mainly results from the overwhelming number of existing barriers in freshwater systems that hamper the bi-directional movement of fish [2]. These vary from more technical types (e.g., vertical slot fishways) to close-to-nature types (e.g., bottom ramps and slopes, bypass channels, and fish ramps) [3]. Especially more technical ones with more uniform geometry, have been the subject of many studies. Guidelines on their design, operation, and applicability have been defined [4,5]
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