Bridge Scour and Stream Instability Countermeasures: Experience, Selection, and Design Guidance-Third Edition Volume 2

Abstract

In this volume design guidelines are provided for a variety of stream instability and bridge scour countermeasures. Most of these countermeasures have been applied successfully on a state or regional basis, but, in several cases, only limited design references are available in published handbooks, manuals, or reports. No attempt has been made to include in this document design guidelines for all the countermeasures listed or referenced in Volume 1. Countermeasure design guidelines formerly presented in HEC-20 (spurs, guide banks, drop structures) and in HEC-18 (riprap at abutments and piers) are now consolidated in this document. Since many bridge scour and stream instability countermeasures require riprap revetment as an integral component of the countermeasure, riprap revetment design guidance is summarized in Design Guideline 4. An appropriate granular or geotextile filter is essential for any countermeasure requiring a protective armor layer (e.g., riprap, articulating concrete blocks, etc.). Filter design guidance is provided in Design Guideline 16. Design Guideline 8 – Articulating Concrete Block Systems, Design Guideline 9 – Grout-Filled Mattresses, and Design Guideline 10 – Gabion Mattresses each contain two countermeasure applications: (1) bankline revetment or bed armor, and (2) pier scour protection. Consequently, these three design guidelines appear in Section 2, but are referenced in Section 3 with a page citation to the pier protection application. A number of highway agencies provided specifications, procedures, or design guidelines for bridge scour and stream instability countermeasures that have been used successfully locally, but for which only limited design guidance is available outside the agency. Several of these are presented as design guidelines for the consideration of and possible adaptation to the needs of other highway agencies (see for example, Design Guideline 6, Wire Enclosed Riprap Mattress, and Design Guideline 13, Grout/Cement Filled Bags). These specifications, procedures, or guidelines have not been evaluated, tested, or endorsed by the authors of this document or by the FHWA. They are presented here in the interests of information transfer on countermeasures that may have application in another state or region. Since publication of the Second Edition of HEC-23 in 2001, both the Transportation Research Board through the NCHRP Program and FHWA have sponsored a number of research projects to improve the state of practice in bridge scour and stream instability countermeasure technology and provide definitive guidance to bridge owners in countermeasure design. Among the projects that represent advances in countermeasure technology that have been incorporated into the Desi