Boriss Gjunsburgs, Oskars Lauva, Romans Neilands

Equilibrium time of scour near structures in plain rivers

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Abstract

The equilibrium depth of scour is an important parameter for estimation of the foundation depth. The equilibrium depth of scour development under steady flow is depending on time and can be reached in equilibrium time. The aim of the study is to find the equilibrium time near elliptical guide banks at clear water and uniform river bed, which allows to predict the equilibrium depth of scour near structures in flow. The literature analysis shows that there are no methods or formulas to calculate equilibrium time of scour near elliptical guide banks. In formulas for equilibrium time calculation at piers or abutments the different parameters are not taken into consideration: contraction rate of the flow, Froude number, bed layering, sediment movement parameters, local flow modification, relative local and critical velocities ratio and relative depth. The differential equation of the bed sediment movement in clear water was used and method for computing equilibrium time of scour near elliptical guide banks was elaborated. New hydraulic threshold criterion is proposed for calculation of equilibrium time of scour. Computer modeling results were compared with equilibrium time of scour calculated by the presented method and they were in good agreement.

Keywords: local scour; equilibrium time; contraction rate of the flow.