This report describes (1) the techniques developed to evaluate streambed scour at 41 bridges over tidal waterways in Alaska; (2) the results of these analyses; and (3) potential mitigating factors at high risk sites and recommendations for further analysis. Contraction and pier scour were evaluated at each bridge using variables computed from one-dimensional steady state step-backwater models. Abutment scour was not evaluated because all of the bridges in this study have abutments that are either founded in bedrock or armored by riprap or sheet piling. Hydraulic models were constructed from existing data and field data collected for this study. The degree of tidal influence at a bridge was quantified using water-stage data collected over one or more tidal cycles. Velocity data were collected during the falling tide at bridges that experienced flow reversals during tidal exchanges.
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