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extensive study done ir 1978 (2) indicated local scour at bridge piers to be a problem about equal to abutment scour problems. A number of case historiEs on the causes and consequences of scour at major bridges are presented in Transportation Research Number 950(3), D. OBJECTIVES OF A ERIDGE SCOUR EVALUATION PROGRAM The need to minimize fcture flood damage to the nation's bridges requires that additional attention be devoted to developing and implementing improved ~rocedures for designing and inspecting bridges for scour. (SEe National Bridge Inspection standards, 23 CFR 650 Subpart C.) A~proximately 86 percent of the 577,000 bridges in the National Bridge Inventory are built over waterways. Statistically, we can expect thousands of these bridges to experience f~oods on the order of magnitude of a 100 year flood or greater Each year. Because it is not economically feasible to construct all bridges to resist all conceivable floods or to instal~ scour countermeasures at all existing bridges to ensure absolute invulnerability from scour damage, some risks of failure ~ay have to be accepted from future floods, However, every bridge ever a stream, whether existing or under design, should be assessed as to its vulnerability to floods in order to determine the prudent measures to be taken. The added cost of making a bridge less vulnerable to scour is small when compared to the total cost of a failure which ca~ easily be two or three times the cost of the bridge itself. Moreover, the need to ensure public safety and to minimize the adverse effects resulting from bridge closures requires our best efforts to improve the state-of-practice for designing and maintaining bridge foundations to resist the effects of scour, The procedures presentE,d in this manual serve as guidance for implementing the recommendations contained in the FHli';', Technical Advisory entitled, "Scour at Bridges," The recommendations have been developed to summc,rize the essential elements which should be addressed in developing a comprehensive scour evalcation program. A key element of the program will be the identification of scour-critical bridges which will be entered into the National Bridge Inventory using the revised Recording and Coding Guide for the Structure inventory and Appraisal of the Nation's Bridges (4) . E. IMPROVING THE STJ.TE-OF-PRACTICE OF ESTIMATING SCOUR AT BRIDGES The problems associated with estimating scour and providing cost- effective and safe des~gns need to be addressed further in research and development programs of the FHWA and the states. In 2