The National Academies

NCHRP 24-48 [Anticipated]

Develop a Formula for Determining Scour Depth around Structures in Gravel-bed Rivers

  Project Data
Source: Washington
Funds: $600,000
Staff Responsibility: Waseem Dekelbab
Fiscal Year: 2018

This project has been tentatively selected and a project statement (request for proposals) is expected in July 2017. The project statement will be available on this world wide web site. The problem statement below will be the starting point for a panel of experts to develop the project statement.

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.

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