WASHINGTON, D.C. — The Federal Highway Administration (FHWA) announced publication of the revised and updated Hydraulic Engineering Circular 18, “Evaluating Scour at Bridges, Fifth Edition” and Hydraulic Engineering Circular 20, “Stream Stability at Highway Structures, Fourth Edition.” Also, the NHI Course No. 135046 "Stream Stability and Scour at Highway Bridges” has been revised to reflect the changes to HECs 18 and 20.
Notable changes and additions in this edition of HEC-18 include:
• expanded discussion on the policy and regulatory basis for the FHWA Scour Program;
• recommendations for applying a risk-based approach for determining scour and developing Plans of Action (POAs) for scour-critical bridges;
• expanded discussion on scour countermeasure design philosophies;
• a new chapter on soils, rock, and geotechnical considerations related to scour;
• a new section on contraction scour in cohesive materials;
• an updated abutment scour section, including alternative abutment design approaches;
• alternative procedures for estimating pier scour;
• a new approach for pier scour in coarse materials;
• new sections on pier scour in cohesive materials;
• a new section on pier scour in erodible rock;
• new guidance on pier scour with debris loading;
• revised guidance for vertical contraction scour (pressure flow) conditions;
• guidance for predicting scour at bottomless culverts;
• deletion of the "General Scour" term; and
• revised discussion on scour at tidal bridges (to reflect material covered in HEC-25 “Highways in the Coastal Environment,” Second Edition).
The HEC-20 document covers and provides information on:
• geomorphic and hydraulic factors that affect stream stability;
• a step-by-step analysis procedure for evaluation of stream stability problems;
• discussions on stream channel classification, stream reconnaissance techniques, and rapid assessment methods for channel stability;
• quantitative techniques for channel stability analysis, including degradation analysis; and
• introduction on channel restoration concepts.
Significant new material includes chapters on:
• sediment transport concepts;
• channel stability in gravel bed streams; and
• expanded coverage of channel restoration concepts.
The fifth edition of HEC-18 and fourth edition of HEC-20 are posted on the FHWA’s National Hydraulic Teams website and is available for downloading at:
• HEC-18: www.fhwa.dot.gov/engineering/hydraulics/pubs/hif12003.pdf
• HEC-20: www.fhwa.dot.gov/engineering/hydraulics/pubs/hif12004.pdf
The newly updated NHI Course 135046, "Stream Stability and Scour at Highway Bridges” has been restructured to reflect the enhancements to HEC-18 and HEC-20 (which are the primary reference documents. An overview of the information presented during this course includes:
• sixteen mandatory lessons with defined learning outcomes that teach the use of the procedural and technical approaches outlined in HEC-18 and HEC-20;
• eight optional lessons with clearly defined learning outcomes (three of which will be taught) that allows a presenter to customize a course based on their particular needs; and
• virtual tours and animations to help present the technical material as well as an Audience Response System to help gauge participant understanding.
A description of the course, information on scheduling, and information on how to obtain hard copies of HEC-18 and HEC-20 from the NHI store can be found at www.nhi.fhwa.dot.gov.