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<br />CHAPTER 5 <br /> <br />EVALUATING THE VULNERABILITY OF EXISTING BRIDGES TO SCOUR <br /> <br />A. INTRODUCTION <br /> <br />Existing bridges over streams subject to scour should be <br />evaluated to determine their vulnerability to floods and whether <br />they are scour vulnerable. This assessment or evaluation should <br />be conducted by an interdisciplinary team of professional, <br />experienced engineers who can make the necessary engineering <br />judgments to decide: <br /> <br />o priorities for making bridge scour evaluations; <br /> <br />o the scope of the scour evaluations to be performed in <br />the office and in the field; <br /> <br />o whether or not a bridge is vulnerable to scour damage; <br />i.e. whether the bridge is a scour-critical bridge; <br /> <br />o which alternative scour countermeasures may serve to <br />make a bridge less vulnerable, <br /> <br />o which countermeasure is most suitable and cost- <br />effective for a given bridge; <br /> <br />o priorities for installing scour countermeasures; <br /> <br />o monitoring and inspection schedules for scour-critical <br />bridges; and <br /> <br />o interim procedures to protect the bridge and the public <br />until the bridge is repaired, replaced or until <br />suitable long-term countermeasures are in place. <br /> <br />The factors to be considered in a scour evaluation require a <br />broader scope of study and effort than those considered in a <br />bridge inspection. The major purpose of the bridge inspection is <br />to identify changed conditions which may reflect an existing or <br />potential problem. The scour evaluation is an engineering <br />assessment of the risk of what might possibly happen in the <br />future and what steps can be taken now to eliminate or minimize <br />the risk. <br /> <br />75 <br />