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<br />BRIDGE SCOUR AND STREAM INSTABILITY <br />COUNTERMEASURES <br /> <br />Experience, Selection and Design Guidance <br /> <br />1.0 INTRODUCTION <br /> <br />Bridge scour and stream instability problems have always threatened the safety of our <br />nation's highways. Countermeasures for these problems are defined as measures <br />incorporated into a highway-stream crossing system to monitor, control, inhibit,' change, <br />delay, or minimize stream instability and bridge scour problems. An action plan for <br />monitoring structures during and/or after flood events can also be considered a <br />countermeasure. <br /> <br />Countermeasures include river stabilizing works over a reach of the river up- and <br />downstream of the crossing. Countermeasures may be installed at the time of highway <br />construction or be retrofitted to resolve stability problems as they develop at existing <br />crossings. <br /> <br />While considerable research has been dedicated to design of countermeasures for scour <br />and stream instability, many countermeasures have evolved through a trial and error <br />process. In addition, some countermeasures have been applied successfully in one locale, <br />state or region, but have failed when installations were attempted under different geomorphic <br />or hydraulic conditions. In many cases, a countermeasure that has been used with success <br />in one state or region is virtually unknown to highway design and maintenance personnel in <br />another state or region. Thus, there is a significant need for information transfer regarding <br />stream instability and bridge scour countermeasure design, installation, and maintenance. <br /> <br />l <br /> <br />This document represents an initial step toward sharing countermeasure experience, <br />selection, and design guidelines among Federal, State, and local highway agency personnel. <br />This information may facilitate the selection and design of countermeasures as State <br />highway agencies (SHAs) develop Plans of Action for bridges identified as scour critical. <br /> <br />2.0 PURPOSE AND SOURCES <br /> <br />The purpose of this document is to identify bridge scour and stream instability counter- <br />measures that have been implemented by various SHAs to protect bridges in the United <br />States. The approach was to supplement information gathered from the SHAs with <br />guidelines reported, primarily, in Federal Highway Administration (FHWA) publications, and <br />to develop a matrix which summarizes countermeasure application and use throughout the <br />United States. In addition, design guidelines are provided for several countermeasures <br />which have been applied successfully on a state or regional basis, but for which only limited <br />design references are available. <br /> <br />1 <br />