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<br />TABLE 3. Continued. <br /> <br />piers <br /> <br />1. pier foundations on floodplains should be designed to the <br />same elevation as the pier foundations in the stream <br />channel if there is a likelihood that the channel will <br />shift its location on the floodplain over the life of the <br />bridge. <br /> <br />2. Align piers with the direction of flood flows. Assess the <br />hydraulic advantages of round piers, particularly wtere <br />there are complex flow patterns during flood events. <br />3. Streamline pier shapes to decrease scour and minimize <br />potential for buildup of ice and debris, Use ice and <br />debris deflectors where appropriate. <br /> <br />4. Evaluate the hazards of ice and debris buildup when <br />considering use of multiple pile bents in stream channels. <br />Where ice and debris buildup is a problem, design the bent <br />as though it were a solid pier for purposes of estimating <br />scour. Consider use of other pier types where clogging of <br />the waterway area could be a major problem, <br /> <br />Abutments <br /> <br />1. Recognizing that abutment scour solutions lack definition, <br />it is recommended that riprap and/or guide banks be <br />seriously considered for abutment protection. Properly <br />designed, these two protective measures negate the need to <br />compute abutment scour. <br /> <br />2. Relief openings, guide banks (spur dikes), and river <br />training works should be used where needed to minimize the <br />effects of adverse flow conditions at abutments, <br /> <br />3. utilize riprap where needed to protect abutments. Design <br />riprap to resist the hydraulic forces associated with <br />design conditions using Hydraulic Engineering Circular No. <br />11, "Design of Riprap Revetment" (24). Chapter 7 provides <br />riprap design guidance. <br /> <br />4. Where ice build-up is likely to be a problem, set the toe <br />of spill-through slopes or vertical abutment walls some <br />distance from the edge of the channel bank to facilitate <br />passage of the ice. <br /> <br />5. Scour at spill-through abutments is about 50% of that of <br />vertical wall abutments, <br /> <br />29 <br />