Author(s): B. Gjunsburgs; O. Lauva; K. Kokina

Linked Author(s): Boriss Gjunsburgs

Keywords: Unsteady flow; Multiple floods; River bed layering; Scour

Abstract: The depth of scour depends on unsteady flow (floods of different probability, duration, frequency, sequence) river bed stratification (with different grain size, thickness and sequence of the layers) and the types and the size of hydraulic structures. The mutual impact of unsteady flow and bed stratification on the depth of scour at guide banks was studied. Differential equation of equilibrium for bed sediment movement in clear-water conditions was used and the model for calculation depth of scour hole evaluation on time at unsteady flow conditions and bed layering has been developed. The scour development in flume was studied within one 7-hour step time interval and within two 7-hour step time search. The condition FrR = Frf were fulfilled, where FrR = Froude number for low-land river, Frf = Froude number in flume. Flow modification- local velocity V|, relative local Vlt/V, and relative critical Vot/Vo velocities, relative velocity pVot/Vlt changes, unsteady flow, grain size, thickness and sequence of the layers of the bed impact on scour at elliptical guide banks. The model was validated through experimental results and computer program was elaborated. The method allows to make computer modeling of various scenarios of time-dependent scour at unsteady flow during the flood and river bed layering with different grain size, thickness and sequences. The flood forecasting and geology data can be used to calculate the depth of the scour by the method proposed and to make an advance estimation of the safety of an engineering structure during a possible flood events.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p1147-cd

Year: 2023