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

Chapter 7

COUNTERMEASURE DESIGN GUIDELINES

7.1 INTRODUCTION

In Volume 2, 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 in the matrix (Table 2.1). There are, however, references in Chapters 8 and 10 to publications that contain at least a sketch or photograph of a particular countermeasure, and in many cases contain more detailed design guidelines.

Countermeasure design guidelines formerly presented in HEC-20 (Lagasse et al. 2001a) (spurs, guide banks, drop structures) and in HEC-18 (Richardson and Davis 2001) (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.

A number of DOTs 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 DOTs (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 in Volume 2 are:

• NCHRP Report 544 - Environmentally Sensitive Channel and Bank Protection Measures (McCullah and Gray 2005)
• NCHRP Report 568 - Riprap Design Criteria, Recommended Specifications, and Quality Control (Lagasse et al. 2006)
• NCHRP Report 587 - Countermeasures to Protect Bridge Abutments from Scour (Barkdoll et al. 2007)
• NCHRP Report 593 - Countermeasures to Protect Bridge Piers from Scour (Lagasse et al. 2007)

7.2 DESIGN GUIDELINES

The following specifications, procedures, or design guidelines are included in Volume 2. The application of the countermeasure and the contributing source(s) of information are also indicated below.

7.2.1 Countermeasures for Stream Instability

Design Guideline 1

• Bendway Weirs/Stream Barbs
  • Source(s): Colorado Department of Transportation
    Washington State Department of Transportation
    Tennessee Department of Transportation
    Soil Conservation Service (now Natural Resources Conservation Service)
    U.S. Army Corps of Engineers
  • Application: Bankline protection and flow alignment in meandering channel bends

Design Guideline 2

• Spurs
  • Source(s): HEC-20 Stream Stability at Highway Structures (Second Edition) NCHRP Report 568
  • Application: Bankline stabilization and flow alignment

Design Guideline 3

• Check Dams/Drop Structures
  • Source(s): HEC-20 Stream Stability at Highway Structures (Second Edition) HEC-14 Hydraulic Design of Energy Dissipators for Culverts and Channels
  • Application: Correcting or preventing channel degradation

7.2.2 Countermeasures for Streambank and Roadway Embankment Protection

Design Guideline 4

• Riprap Revetment
  • Source(s): NCHRP Report 568
  • Application: Bankline/abutment protection and riprap component of many other countermeasures

Design Guideline 5

• Riprap Design for Embankment Overtopping
  • Source(s): NCHRP Report 568
  • Application: Protection for roadway approach embankments and flow control countermeasures

Design Guideline 6

• Wire Enclosed Riprap Mattress
  • Source(s): New Mexico State Highway and Transportation Department
  • Application: Revetment for banklines, guide banks, and sloping abutments

Design Guideline 7

• Soil Cement
  • Source(s): Portland Cement Association
    Pima County Arizona
    Maricopa County Arizona
  • Application: Revetment for banklines and sloping abutments, drop structures, and bed armor

Design Guideline 8

• Articulating Concrete Block Systems for Bank Revetment or Bed Armor
  • Source(s): Harris County Flood Control District (2001)
    Federal Highway Administration
    Maine Department of Transportation
    Minnesota Department of Transportation
  • Application 1: Bankline revetment and bed armor

Design Guideline 9

• Grout-Filled Mattresses for Bank Revetment or Bed Armor
  • Source(s): Federal Highway Administration
  • Application 1: Bankline revetment and bed armor

Design Guideline 10

• Gabion Mattresses for Bank Revetment or Bed Armor
  • Source(s): Federal Highway Administration
  • Application 1: Bankline revetment and bed armor

7.2.3 Countermeasures for Bridge Pier Protection

Design Guideline 8

• Articulating Concrete Block Systems at Bridge Piers
  • Source(s): NCHRP Report 593
  • Application 2: Pier scour protection

Design Guideline 9

• Grout-Filled Mattresses at Bridge Piers
  • Source(s): NCHRP Report 593
  • Application 2: Pier scour protection

Design Guideline 10

• Gabion Mattresses at Bridge Piers
  • Source(s): NCHRP Report 593
  • Application 2: Pier Scour Protection

Design Guideline 11

• Rock Riprap at Bridge Piers
  • Source(s): HEC-18 Scour at Bridges (Third Edition)
    NCHRP Report 593
    NCHRP Report 568
  • Application: Pier scour protection

Design Guideline 12

• Partially Grouted Riprap at Bridge Piers
  • Source(s): NCHRP Report 593
  • Application: Pier Scour Protection

7.2.4 Countermeasures for Abutment Protection

Design Guideline 13

• Grout/Cement Filled Bags
  • Source(s): Maryland State Highway Administration
    Maine Department of Transportation
  • Application: Protection of undermined areas at piers and abutments, and bed armor

Design Guideline 14

• Rock Riprap at Bridge Abutments
  • Source(s): NCHRP Report 568
    NCHRP Report 587
  • Application: Abutment scour protection

Design Guideline 15

• Guide Banks
  • Source(s): HEC-20 Stream Stability at Highway Structures (Second Edition)
    NCHRP Report 568
  • Application: Abutment scour protection

7.2.5 Filter Design

Design Guideline 16

• Filter Design
  • Source(s): NCHRP Report 568
    NCHRP Report 593
  • Application: Filter for revetment or countermeasure armor

7.2.6 Special Applications

Design Guideline 17

• Riprap Design for Wave Attack
  • Source(s): HEC-25 (1st and 2nd Editions)
  • Application: Protection for coastal roadway embankments

Design Guideline 18

• Riprap Protection for Bottomless Culverts
  • Source(s): FHWA Reports FHWA-RD-02-078 and FHWA-HRT-07-026
  • Application: Scour protection at bottomless culverts

Design Guideline 19

• Concrete Armor Units/Toskanes and A-Jacks^®
  • Source(s): Testing at Colorado State University
  • Application: Pier scour protection