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<br />III. GEOMETRY AND LOCA T'ION OF HIGI-IWA Y STf~EAM CROSSINGS <br /> <br />A. Problems at Bends, <br /> <br />~Eraoioa <br />~ &\ IUah ~ FIoi, <br />-- ~-: ...~:~~ ~" <br />----. .t.'i' ;:.. <br />,,~~~'7 PciIItBat <br />Ctaaia& OIl Slnipt CttlOliac __ Bendo - \?~.. Croainll at SIwp Bend - <br />Roach . ~ Risk l_ 10 Modaate Rdk liiab lllik <br /> <br />1. More hydraulic: problems occ:ur in bends because bemds are <br />naturally unstable. Problems include shifting thalwegs, <br />unanticipated flow direction and velocity. and nonunifoml velocity <br />distribution. I~! and debris problems are also greater in be,nds than <br />straight reaches, <br /> <br />2. When a crossing cannot be located in a straight reach, a crossing <br />at the inflection point between bends gene,rally reduces the risk of <br />instability. <br /> <br />3. Because of the, change of flow direction which results in centrifugal <br />forces, there is, a superelevation of the water surface in bends, A <br />simple equation to calculate superelevation is presented in HEC-20, <br />Section 3.2.4. <br /> <br />3,19 <br />