Pier Scour in Clear-Water Conditions With Non-Uniform Bed Materials

CHAPTER 1. INTRODUCTION

Hydraulics and scour hazards cause over half of the bridge failures in the United States and have been identified by State bridge authorities as one of the top issues in bridge design and maintenance.⁽¹⁾ Current pier scour design in the United States is mainly based on the Colorado State University (CSU) equation, which is described in Hydraulic Engineering Circular No. 18 (HEC-18).⁽²⁾ A recent evaluation of bridge scour research indicated a need to change the current method because substantial advances have been made in understanding pier scour processes.⁽³⁾ The evaluation compared several methods and considered which methods effectively included the variables now believed to determine pier scour characteristics.

The objective of this report is to describe a new method for estimating pier scour based on an understanding of the flow-structure-sediment interactions and to address the weaknesses in earlier methods. This research focuses on clear-water scour at singular piers in non-cohesive sediment mixtures. The approach was to review previous pier scour methods, formulate an improved model for scour formation, and evaluate the new model using laboratory and field data.