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<br />Pier shaoe--Because of the di~ersity of pier shapes, a classification of the <br /> <br />shapes has been developed (Brice and Blodgett, 1978, fig. 39). In some cases, <br /> <br />piers classified as pile bents are constructed as several rectangular or round <br /> <br />columns in a bent. The classification is based on the pier configuration as <br /> <br />exposed the the streamflow. <br /> <br />Abutment type--Bridge abutments are classified as spillthrough or vertical. A <br /> <br />spillthrough abutment has a fill-slope on its streamward side (Brice and <br /> <br />Blodgett, 1978, fig. 40). A~ertical (full height) abutment usually has <br /> <br />wingwalls but no fill-slope 01 its streamward side. <br /> <br />Geomorphic Factors <br /> <br />Channel slope--Channel slopes may be determined form topographic maps, but <br /> <br />surveyed stream profiles may also be available. Channel slope is based on the <br /> <br />difference in streambed elevation between two points and the horizontal <br /> <br />distance as measured along the stream centerline. Slopes determined during <br /> <br />low flow may not be accurate if local (section) control conditions such as <br /> <br />pools and riffles are present. <br /> <br />Bed material--At some sites, bed material samples may have been collected and <br /> <br />the particle size distribution analyzed. The median grain size (D50) is used <br /> <br />as an expression of the predo~inant size of the bed material when estimating <br /> <br />Manning's roughness coefficient. <br /> <br />7 <br />