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Water 2017, 9(9), 637;

A Semi-Analytical Model for the Hydraulic Resistance Due to Macro-Roughnesses of Varying Shapes and Densities

Institut de Mécanique des Fluides de Toulouse (IMFT), Université de Toulouse, CNRS, INPT, UPS, 31400 Toulouse, France
Institut Nationale des Sciences Appliqués, 24 Bld de la Victoire, 67084 Strasbourg, France
Author to whom correspondence should be addressed.
Received: 21 June 2017 / Revised: 27 July 2017 / Accepted: 21 August 2017 / Published: 25 August 2017
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A friction model resulting from investigations into macro-roughness elements in fishways has been compared with a broad range of studies in the literature under very different bed configurations. In the context of flood modelling or aquatic habitats, the aim of the study is to show that the formulation is applicable to both emergent or submerged obstacles with either low or high obstacle concentrations. In the emergent case, the model takes into account free surface variations at large Froude numbers. In the submerged case, a vegetation model based on the double-averaging concept is used with a specific turbulence closure model. Calculation of the flow in the roughness elements gives the total hydraulic resistance uniquely as a function of the obstacles’ drag coefficient. The results show that the model is highly robust for all the rough beds tested. The averaged accuracy of the model is about 20% for the discharge calculation. In particular, we obtain the known values for the limiting cases of low confinement, as in the case of sandy beds. View Full-Text
Keywords: friction coefficient; double-averaging concept; rock-ramp; macro-roughness friction coefficient; double-averaging concept; rock-ramp; macro-roughness

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Cassan, L.; Roux, H.; Garambois, P.-A. A Semi-Analytical Model for the Hydraulic Resistance Due to Macro-Roughnesses of Varying Shapes and Densities. Water 2017, 9, 637.

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