2-Dimensional Hydrodynamic Modeling - A Neglected Tool in the Instream Flow Incremental Methodology

Publication Date



applications, Atlantic salmon, channel, diversion, fish habitat, habitat, IFIM, incremental methodologies, instream flow, juvenile, models, physical habitat, resistance, Salmo salar, salmon, shear, Substrate

Journal or Book Title

Transactions of the American Fisheries Society


The instream flow incremental methodology (IFIM) needs to be improved to more reliably predict the effects of altering fish habitat. Two-dimensional (2-D) hydrodynamic modeling with moving boundaries by the finite element approach overcomes may limitations related to classical physical habitat simulation modeling (mostly 1-D). Some of its most important properties are: the spatial resolution of the model can be adapted to the scale of individual fish habitats and to the spatial variability of field data; the areas frequently uncovered because of flow regime are correctly taken into account through the drying-wetting capability; and the flow resistance variables are more accurate in 2-D because they can be specified as functions of the local substrate conditions or lateral shear stresses. This approach is illustrated by a study of the habitat of juvenile Atlantic salmon Salmo salar of the Moisie River (Quebec) where a water diversion has been planned. The results of simulations carried out at two sites (a braided reach and a deep, narrow channel) over a wide range of discharges are presented. Average model error was about 10% for velocity and 2% for discharges. A finite element integration procedure allowed habitat suitability indexes (HSI) to be combined with the results of the hydrodynamic model. In this manner, detailed maps of the spatial distribution of the HSI as well as a ''weighted usable area'' were obtained for each discharge simulated. Atlantic salmon habitat did not appear to be very sensitive to projected flow alterations. The improved accuracy and resolution in predicting the effects of altering physical habitat variables by 2-D models would permit a better understanding of the shortcomings related to biological aspects of IRM applications







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