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

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 Design Guidelines are:
• NCHRP Report 544 - Environmentally Sensitive Channel and Bank Protection Measures
• NCHRP Report 568 - Riprap Design Criteria, Specifications, and Quality Control
• NCHRP Report 587 - Countermeasures to Protect Bridge Abutments from Scour
• NCHRP Report 593 - Countermeasures to Protect Bridge Piers from Scour
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