Numerical modeling of water flow conditions with spatial distribution of boulders in main channel

Abstract

The article presents a study on the influence of spatial distribution of boulders placed in the main channel on parameters of flow conditions. Restoration guidelines recommend boulders structures but engineering solutions must be individually adapted to local situation. The depth-averaged 2D numerical model of unsteady, free-surface flow in open channels was used to calculate spatial distribution of velocity magnitude, slope of water surface level and water depth. The impact of individual boulder on the flow conditions in river channels increases through the group arrangement. Model of the Wisłoka River section was changed by implementation of boulders in various configurations: a group of three or four placed in triangles or rhomboids, openwork deflectors, groups located by the banks, groups located alternately to form a curvilinear thalweg. The effect of boulders structure on velocity spatial distribution along the channel was calculated for discharge Q 10-day = 15 m3 s−1Impact of single boulder structures on flow velocity is visible up to 20–30 m and increases for multiple single boulders structures up to 30–60 m. In addition, stability of individual boulder for discharge Q 1% and influence the flood hazard were tested.