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<br />I <br />1_ <br />/ ' <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />,I <br />I <br />I <br />I <br />I <br />I" <br />I <br /> <br />C. Reevaluate the Bridge Design <br /> <br />Reevaluate the bridge design on the basis of the for.going scour analysis. <br />REVISE THE DESIGN AS NECESSARY. This evaluation should consider: <br /> <br />o Is the wat.rway ar.a large .nough; i.... is the contraction scour too <br />1 arge? <br /> <br />o Are the pi.rs too clos. to each other or to the abutments: i.... do the <br />scour holes ov.rlap? Ar. there too many piers? <br /> <br />o Is there a n..d for reli.f bridg.s? Should they or the main bridge be <br />1 arger? <br /> <br />oAr. bridge abutments prop.rly aligned with the flow and located properly <br />in regard to the stream chann.l and flood plain? <br /> <br />o Is the bridge crossing of the stream and the floodplain in a d.sirable <br />location. If the location pres.nts problems: <br /> <br />- Can it b. changed? <br /> <br />- Can river training work. guidebanks or relief bridges s.rve to <br />provide for an acceptable flow pattern at the bridges? <br /> <br />o Is the hydraulic study adequate to provide the n.cessary information for <br />foundation design? <br /> <br />- Are flow patterns complex? <br /> <br />- Should a two dimensional water surface profile model be used for <br />analysis? <br /> <br />- Is the foundation design safe and cost-effective? <br /> <br />- Is a physical model study needed and warr.nt.d? <br /> <br />o Do local scour holes at piers and abutments ov.rlap? The top width of a <br />scour hole is about 2.75 times the depth of scour. If scour holes <br />overlap the local scour can b. d.eper. <br /> <br />43 <br />