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<br />L.ESSON 1 <br />INTI~ODUCTIONI <br /> <br />I. HOST WELCOME <br /> <br />II. INTRODUCTION OF INSTRUCTORS <br /> <br />III. MAGNITUDE OF STREAM INSTABILllY AND SCOUR PROBLEM <br /> <br />A. There are about 575,413 highway bridges in the nation's ~Iational <br />Bridge Inventory - 84% (483,158) are over streams or rivers. <br /> <br />8, Stream instability, long-term stream aggradation or degr~ldation, <br />contraction scour, local scour, and latl~ral scour olr erosion caUls,e 60% <br />of the bridge failures in the U.S, <br /> <br />C, Nationally, the annual cost for scour-related bridge failures is about $30 <br />million and flood damage repair costs fOI' Federal-aiel highways are about <br />$50 million, <br /> <br />1,1 <br />