United States Department of Transportation
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Edition:4th
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Abstract:This document is the fourth edition of HEC-18. It presents the state of knowledge and practice for the design, evaluation and inspection of bridges for scour. There are two companion documents, HEC-20 entitled "Stream Stability at Highway Structures," and HEC-23 entitled "Bridge Scour and Stream Instability Countermeasures." These three documents contain updated material from previous editions and the publication, "Interim Procedures for Evaluating Scour at Bridges," issued in September 1988 as part of the FHWA Technical Advisory T 5140.20, "Scour at Bridges." T5140.20 has since been superseded by T 5140.23, "Evaluating Scour at Bridges" dated October 28, 1991. This fourth edition of HEC-18 contains revisions obtained from further scour-related developments and the use of the 1995 edition by the highway community. The major changes in this fourth edition of HEC-18 are: change in nomenclature to using General Scour to include both contraction scour and other general scour components, changing the order of Chapters 2 and 3 so that the policy chapter entitled "Designing Bridges to Resist Scour" comes before the chapter entitled "Basic Concepts and Definitions of Scour;" and separating Chapter 4 into separate chapters dealing with each of the major scour components. In addition, a new K4, to account for coarse bed material in the pier scour equation, improved methods to compute scour for complex pier configurations, example problems, and additional information on computer programs for modeling tidal hydraulics are given. There is no change in the recommendations regarding abutment scour. In addition to minor editorial revisions, the following substantive changes have been made in this revised edition of HEC-18: revised definition of grain roughness ks, (p. xii); changed guidance on determining the magnitude of the 500-year flood (p. 2.9). Note 3 definition of K3 factor corrected (p. 6.5); revised guidance on minimum value of K4 factor (p. 6.6); revised definition of grain roughness ks (p. 6.13); and corrected multiplier for kinematic viscosity in Appendix A (Table A.7).
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Content Notes:Project Manager: Mr. Jorge E. Pagán-Ortiz Technical Assistants: Larry Arneson, J. Sterling Jones, Joseph Krolak, Jorge E. Pagán-Ortiz, Philip Thompson, FHWA; A. Firenzi, P.F. Lagasse, Johnny L. Morris, Arlo Waddoups, L.W. Zevenbergen, Ayres Associates
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