Wood accumulation at bridges: Laboratory experiments on the effect of pier shape

The accumulation and blockage of wood at bridges is a relevant problem in flood hazard man-agement. Blockage may cause a strong reduction in the flow rate through the contracted opening and therefore a strong increase in upstream water levels, which may lead to flooding of nearby urbanized areas. Further-more, the wood jam formation at bridge pier may increase the pier scour. Physical scale model tests on bridge clogging were conducted in the hydraulic laboratory of the University of Florence with the aim to identify the more critical pier shapes for wood accumulation. We reproduced five different pier shapes, three classes of wood size using wooden cylindrical dowels with no roots and no branches, one wood transport regime (con-gested transport), and two different flow scenarios. A dimensionless index quantifying the capability to block the transport of wood was defined and calculated for the various geometrical configurations employed.