Comprehensive Stream Stability Evaluation Methodology

The Federal Highway Administration (FHWA) provides guidance for stream stability and bridge scour evaluations in three FHWA Hydraulic Engineering Circulars (HECs): HEC-18 Evaluating Scour at Bridges (4th Edition); HEC-20 Stream Stability at Highway Structures (3rd Edition); and HEC-23 Bridge Scour and Stream Instability Countermeasures (2nd Edition). Together these three documents provide the guidance to State departments of transportation (DOTs) necessary for completing a comprehensive stream stability and scour evaluation for the design of new bridges and for evaluating and rehabilitating existing bridges. Experience has shown that the relationships among these three documents are not always readily apparent. This paper provides an overview of the most recent (2001) editions of these manuals and introduces a flow chart designed to integrate them into a comprehensive evaluation methodology. Techniques for stream stability analysis from HEC-20 and stream instability countermeasures from HEC-23 are highlighted. Although developed to assist bridge owners in their analyses of stream stability and scour issues, the information and procedures presented in these documents are useful and applicable to any type of channel stability or channel restoration project.