Modeling steep-slope flow across staggered emergent cylinders: application to fish passes

Designing efficient rock-ramp fish passes with flows over a bottom with roughness on the same scale as the water depth requires a precise knowledge of hydrodynamics in order to avoid or limit characteristics unattractive for fish, particularly for small fish. This paper considered the numerical modeling of free-surface flow across a steep-sloped ramp covered with staggered surface emergent cylinders. Considering the importance of complex flow features for fish passage, computational fluid dynamics (CFD) was adopted because it is capable of predicting such features. Because of the longitudinal periodicity of the arrangement of the obstacles, cyclic boundary conditions made this fine simulation possible. Two computational meshes (coarse and fine) and two turbulence models [shear stress transport (SST) k-ω and Smagorinsky large-eddy simulation (LES)] were used. The SST k-ω coarse mesh model gives correct time-averaged values, the main flow unstationarities and is usable for rock-ramp fish pass design, but a fine model using LES turbulence closure can provide detailed flow characteristics in the wakes in order to provide possible rest zones, particularly for smaller fish

Flow and drag force around a free surface piercing cylinder for environmental applications

This paper investigates flows around a free surface piercing cylinder with Froude number F<0.5 and Reynolds number around Re = 50,000. The aim of this work is to gain a better understanding of the flow behaviour in environmental systems such as fishways. The advances are based upon experimental and numerical results. Several flow discharges and slopes are tested to obtain both subcritical and supercritical flows. The drag force exerted on the cylinder is measured with the help of a torque gauge while the velocity field is obtained using particle velocimetry. For the numerical part, two URANS turbulence models are tested, the k-w SST and the RNG k-e models using the OpenFOAM software suite for subcritical cases, and then compared with the corresponding experimental results. With fishways applications in mind, the changes in drag coefficient Cd versus Froude number and water depth are studied and experimental correlations proposed. We conclude that the most suitable URANS turbulence model for reproducing this kind of flow is the k-w SST model

A physically-based parsimonious hydrological model for flash floods in Mediterranean catchments

A spatially distributed hydrological model, dedicated to flood simulation, is developed on the basis of physical process representation (infiltration, overland flow, channel routing). Estimation of model parameters requires data concerning topography, soil properties, vegetation and land use. Four parameters are calibrated for the entire catchment using one flood event. Model sensitivity to individual parameters is assessed using Monte-Carlo simulations. Results of this sensitivity analysis with a criterion based on the Nash efficiency coefficient and the error of peak time and runoff are used to calibrate the model. This procedure is tested on the Gardon d'Anduze catchment, located in the Mediterranean zone of southern France. A first validation is conducted using three flood events with different hydrometeorological characteristics. This sensitivity analysis along with validation tests illustrates the predictive capability of the model and points out the possible improvements on the model's structure and parameterization for flash flood forecasting, especially in ungauged basins. Concerning the model structure, results show that water transfer through the subsurface zone also contributes to the hydrograph response to an extreme event, especially during the recession period. Maps of soil saturation emphasize the impact of rainfall and soil properties variability on these dynamics. Adding a subsurface flow component in the simulation also greatly impacts the spatial distribution of soil saturation and shows the importance of the drainage network. Measures of such distributed variables would help discriminating between different possible model structures

Session B5: 2D Modelling of Nature-Like Fish Passes

Abstract: The passability of nature-like fishpass depends on water depth, velocity and kinetic turbulent energy. To estimate these values the 2D Saint Venant code can be an interesting tool because it can simulate a large range of geometrical configuration and also take into account the deformation of the free surface. However the flow in a fish pass can reach the limit of the model assumptions as the hydrostatic pressure. As a consequence a series of experiments on down-scale are conducted to validate the numerical results. Velocity and turbulent fields are measured by Acoustic Doppler Velocimeter (ADV) for five combinations of discharge and slope. The comparison between experiments and model shows that the numerical results are relevant for a moderate Froude number which corresponds to fishpass application. Moreover, some crucial data related to passability are extracted from the computation as the maximum velocity location

Modelling nature-like fishway flow around unsubmerged obstacles using a 2D shallow water model

n the scope to create efficient nature like fish ramps using large-scale roughness elements, the present study is an audit of modelling such complex 3D free surface flows using an industrial 2D code solving shallow water equations. Validation procedure is based upon the comparison between numerous experimental measurements and numerical runs around large-scale roughness patterns disposed on the flume bottom in order to determine what 2D reliable numerical results can be expected. In this paper, we focused on cases of unsubmerged obstacles. The results demonstrate that 2D shallow water modelling using an industrial code such as TELEMAC-2D can be a convenient way for the hydraulic engineer to help design a nature-like fishway. This article emphasizes the limitations due to 2D depth integration of velocities and turbulence modelling and gives the domain of validity of the method

Modelling nature-like fishway flow around unsubmerged obstacles using a 2D shallow water model

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A physically-based parsimonious hydrological model for flash floods in Mediterranean catchments

International audienceA spatially distributed hydrological model, dedicated to flood simulation, is developed on the basis of physical process representation (infiltration, overland flow, channel routing). Estimation of model parameters requires data concerning topography, soil properties, vegetation and land use. Four parameters are calibrated for the entire catchment using one flood event. Model sensitivity to individual parameters is assessed using Monte-Carlo simulations. Results of this sensitivity analysis with a criterion based on the Nash efficiency coefficient and the error of peak time and runoff are used to calibrate the model. This procedure is tested on the Gardon d'Anduze catchment, located in the Mediterranean zone of southern France. A first validation is conducted using three flood events with different hydrometeorological characteristics. This sensitivity analysis along with validation tests illustrates the predictive capability of the model and points out the possible improvements on the model's structure and parameterization for flash flood forecasting, especially in ungauged basins. Concerning the model structure, results show that water transfer through the subsurface zone also contributes to the hydrograph response to an extreme event, especially during the recession period. Maps of soil saturation emphasize the impact of rainfall and soil properties variability on these dynamics. Adding a subsurface flow component in the simulation also greatly impacts the spatial distribution of soil saturation and shows the importance of the drainage network. Measures of such distributed variables would help discriminating between different possible model structures