spawning zones. A hydrodynamic model based on the Reynolds-averaged Navier-Stokes equations was set up and used for the calculation of flow parameters in the spawning reach during autumn 2011. For discharges that were exceeded 10% of the time, the water depths in the spawning zone ranged between 0.1 and 0.7 m and the mean column velocities between 0.1 and 1.0 m/s. A comparison with published preference ranges for the two species reveals that in particular the flow velocities for brown trout were sometimes remarkably lower. More detailed hydrological information is necessary to increase
confidence and comparability between different data sets. It was not possible to satisfyingly explain the observed extent of the spawning zone only based on water depth, mean flow velocity and substrate as independent flow parameters for median flow conditions. Spawning habitat suitability formulations should take into account the interrelations between these variables and include the bed shear stress and more integrated hydraulic parameters.