In the current state of engineering practice, there is a recognized lack of formulas for predicting the scour depth around hydraulic structures, such as bridge piers, abutments and barbs, in gravel-bed rivers. The majority of scour depth prediction formulas presently in use have been developed for sand-bed rivers and, as such, do not account for fundamental processes and characteristics that are unique in gravel-bed rivers. For instance, the inhomogeneity of gravel particles promotes particle interlocking armor development. At the same time, unique turbulent structures result from the interaction of the non-homogeneous material with the approach flow. Even after correcting their scour depth predictions using empirically derived coefficients to account for these processes, the traditional scour prediction formulas originating from sand-bed rivers still overpredict scour depths in gravel-bed rivers. Recent insights into gravel-bed river dynamics along with advances in sensing technologies, such as RFIDs and Ultrasonic Transducer Arrays, have improved understanding of these gravel-bed river processes and for the first time allow the development of a scour prediction formula that directly accounts for their effects.
The objectives of this research project are to: (1) investigate the effects of gravel interlocking and of turbulent structures, such as the horseshoe and wake vortices, generated in gravel-bed rivers on scour around hydraulic structures; and (2) develop a physically based formula for predicting scour depth around hydraulic structures in gravel-bed rivers that accounts for the sediment and flow conditions in the gravel-bed rivers.
The development of a scour prediction formula that has been developed specifically for gravel-bed rivers is of immediate importance and use to DOT and practicing engineers. Because of the lack of formulas for predicting the scour depth around hydraulic structures in gravel-bed rivers, DOT and practicing engineers resort to using formulas, which have been developed for sand-bed rivers and subsequently correcting their predictions with empirically derived coefficients. These formulas cannot fundamentally provide accurate predictions for the scour depth in gravel-bed rivers and even their corrected estimates are riddled with uncertainty.