Multiple floods impact on engineering structures in river flow

Abstract

Water flow in rivers during floods strongly impact transport system infrastructure - roads, bridges, dams, and etc. Frequency and intensity of flood events with high water levels and considerable discharges becomes more frequent and increases the loads on engineering structures in rivers and at the same time the possibility to be damaged. The stability of piers, abutments, guide banks and spur dikes in floods depends on the depth and dimensions of the scour hole at foundations. By preliminary computing scour development in time in multiple floods of different probability, frequency, sequence, and duration, we can estimate possible scour hole depth,width and volume values induced by expected floods. According to calculated scour we can take protection measures if necessary, and reduce the economical and environmental losses. During multiple floods the scour hole parameters near structures under clear-water conditions are summed up and increases from flood to flood, and each next flood can lead to failure. Contraction of the flow by bridge structures leads to considerable changes in flow pattern, local increase in velocities, and origin of turbulence, eddy and vortex structures. All those changes are the reason of local scour at the abutments, piers, guide banks, spur dikes. The differential equation of equilibrium for bed sediment movement in clear water was used, and a calculation method for the scour development at the abutment and guide banks during multiple floods was elaborated. According to the method proposed, the hydrograph was divided in time steps, and each step was divided into time intervals. Calculations were performed for each time step of the hydrograph, so that to estimate the influence of the flow unsteadiness during the flood, but in each time step, the flow was assumed to be steady