Flow pattern around the bridge piers with installed scour countermeasures

Bridges with elements interacting the flow, such as piers constructed in the main river channel or approach embankments blocking the overbanks, alter the flow conditions and initiate local and contraction scour in the bridge profile. Scour countermeasures are often placed around the bridge piers with goal to scour and associated risk of bridge failure. Effectiveness of scour countermeasures depend on its influence on the surrounding riverbed – in case that countermeasures obstruct significant area, flow can be concentrated and accelerated, inducing scour of the banks. Long-term effects of the scour countermeasures on the river morphology can lead to flow redistribution and lateral shifting of the river cross-section, altering the design conditions in the bridge vicinity. Aim of this work is to compare the flow environment at 4 distinctive bridge locations simulated in HEC-RAS model under characteristic hydraulic scenarios that induce scour. Results show that for all bridges current flow environment differs from the design state, so that additional intervention in the riverbed geometry doesn’t significantly change the flow conditions. Flow environment was simulated with sill placed on different distances downstream or excavation of the riverbed to reduce flow velocity. In all scenarios main flow remain concentrated similar to the current state, showing that countermeasures have to be substantial in order to be effective.

 

Acknowledgments

This work has been supported in part by Croatian Science Foundation under the project R3PEAT (UIP-2019-04-4046).