engleski

Morphodynamic impact of scour countermeasures on riverbed topography

Local scour at bridges is natural phenomenon that occurs when structure is placed in riverbed in a way that effects flow pattern. Riverbed can be protected from scour by implementation of scour countermeasures on riverbed section that is expected to be eroded. Scour countermeasures most commonly placed in the vicinity of bridge piers or abutments. Placement of scour countermeasures must be evaluated using numerical models in order to investigate their influence on flow pattern. Inadequately placed scour countermeasures can have adverse effect on morphodynamic development of riverbed, initiating scour hole development further away from the bridge, thus causing bank undermining and flow displacement. In cases where riprap is used as scour countermeasure it can be of large proportions and have significant influence on the flow, sediment transport and consequently riverbed erosion. This paper investigates morphological development of Sava River reach at the bridge that has 3 groups of piers located in the riverbed around which riprap scour countermeasures were placed. Flow is accelerated through constricted bridge openings, inducing erosional and depositional patterns that are evident in bridge profile and on downstream reach. In addition to scour countermeasures, weir has been constructed immediately upstream of the bridge profile. Flow overtopping the weir creates hydraulic jump in the bridge profile behind the weir, in which energy is dissipated and riverbed is further deepened. For analysed river reach coupled hydrodynamic/sediment transport model is established in order to describe flow patterns and estimate morphodynamic development of the riverbed. Three different scenarios are evaluated under three characteristic flow events and variables that indicate further riverbed development are compared. It is shown that riverbed hasn’t reach equilibrium state at this point and further erosion and riverbed evolution can be expected on this river reach. This insight highlights the need for plan of action on scour-susceptible bridges.

Bridge scour, local scour, sediment transport, morphodynamic development, Sava River

nije evidentirano