Bed topography and local scour in rivers with banks protected by groynes

Abstract

This paper provides some results of field investigations of bed topography and local scour at groynes in two bends of the Warta River. Concave banks of these bends are protected by impermeable groynes oriented upstream with almost constant spacing and geometric shape. Both bed topography in bends and local scour holes at the groyne heads were formed by channel flows equal to or smaller than the mean annual discharge. A two-dimensional (horizontal) numerical model of water and (bed-load) sediment motion for steady-state conditions was used to calculate the general bend scour. A new equation for a maximum scour depth prediction at groynes located along an outer bank of a bend is introduced. The maximum scour depth occurs inside the groyne field. This local scour is a function of a depth and depth-average flow velocity along the concave bank, spacing and location relative to the bend, and orientation to flow.