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Last modified
1/25/2010 6:45:23 PM
Creation date
10/5/2006 12:21:34 AM
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Template:
Floodplain Documents
County
Statewide
Basin
Statewide
Title
Interim Procedures for Evaluating Scour at Bridges
Date
9/1/1988
Prepared By
Federal Highway Administration
Floodplain - Doc Type
Educational/Technical/Reference Information
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<br />The problems associated with estimating scour and providing cost-effective and <br />safe designs need to be addressed further in research and development programs <br />of the FHWA and the States. The current equations and methods for estimating <br />scour at bridges are based mainly on laboratory research. Very little field <br />data has been collected to verify the applicability and accuracy of the various <br />design procedures for the range of soil conditions, stream flow conditions, and <br />bridge designs encountered throughout the United States. In particular, States <br />are encouraged to initiate HP&R studies for the purpose of obtaining field <br />measurements of scour and related hydraulic conditions at bridges for <br />evaluating and verifying or improving existing scour prediction methods. <br />Several States have already initiated HPIR studies to collect scour data at <br />existing bridges. A model cooperative agreement with the US Geological Survey <br />for purposes of conducting a scour study is included in Appendix A. <br /> <br />I <br /> <br />'I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br /> <br />, <br />" I <br />I <br /> <br />f'~ <br /> <br />experience floods on the order of magnitude of a 100 year flood or greater each <br />year. Because it is not economically feasible to construct all bridges to <br />resist all conceivable floods or to install scour counter-.easures at all <br />existing bridges to ensure absolute invulnerability from scour damage, some <br />risks of failure may have to be accepted from future floods. However, every <br />bridge over a scourable stream, whether existing or under design, should be <br />assessed as to its vulnerability to floods in order to detennine the prudent <br />measures to be taken. The added cost of making a bridge less vulnerable to <br />scour is small when compared to the total cost of a failure which can easily be <br />two or three times the cost of the bridge itself. Moreover, the need to ensure <br />public safety and to minimize the adverse effects stemming from bridge closures <br />requires our best efforts to improve the state-of-practice of designing and <br />maintaining bridge foundations to resist the effects of scour. <br /> <br />The interim procedures presented in this manual serve as guidance for <br />implementing the recommendations contained in the FHWA Technical Advisory <br />entitled, .Scour at Bridges." The recommendations have been developed to <br />summarize the essential elements which should be addressed in developing a <br />comprehensive scour evaluation progr... A key element of the progr.. will be <br />the identification of scour critical bridges which will be entered into the <br />National Bridge Inventory using the revised Recording and Coding Guide for the <br />Structure inventory and Appraisal of the Nation's Bridges (5). <br /> <br />E. IMPROVING THE STATE-oF-PRACTICE OF ESTIMATING SCOUR AT BRID6ES <br /> <br />2 <br />
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