A model of bridge pier scour during flood waves

ABSTRACT

The time-dependent bridge pier scour during flood waves is analysed. Scour experiments were conducted in a novel installation able to produce complex hydrographs with high precision. Experimental data were used to test scour formulas including a new mathematical model. Results confirm the reliability and superior performance of the proposed dimensionless, effective flow work based model under steady and unsteady hydraulic conditions. Analyses highlight the impact of different hydrographs on scour, demonstrating the strong control by the hydrograph shape of the temporal evolution of scour depth and scour rate, although final scour after a flood only depends on the total effective flow work exerted by the hydrograph on the sediment bed. Hysteresis between flow discharge and scour rate is reported and explained. Flow acceleration is shown to play a minor role in scouring. The proposed model is a promising alternative for computation of local scour under highly unsteady hydraulic conditions.

Keywords:

• Bridge scour
• flood waves
• local scour
• temporal scour
• unsteady hydraulics

Additional information

Funding

The presented results are part of the research project Fondecyt 1150997, entitled “Bridge pier scour under flood waves.” Financial support by Red Doctoral REDOC.CTA and by CRHIAM Fondap-Center 15130015 is greatly acknowledged. Academic exchange was possible through the financial support of the German academic exchange service DAAD, the Chilean research council CONICYT through grant PCCI12027, and the Erasmus Mundus project Elarch Grant Nr. 552129-EM-1-2014-1-IT-ERA MUNDUS-EMA21. This work was supported by Comisión Nacional de Investigación Científica y Tecnológica [grant number Fondecyt Nr. 1150997].