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<br />1. As flow passes through a channel constriction, most of the energy <br />losses occur as expansion losses downstream of the c:ontraction, <br /> <br />2. This loss of energy is reflec~:ed by a rise in the water surface and <br />energy line upstream of the constriction. The rise above the normal <br />water surfac:e is the bridge backwatel". Not all bridges cause <br />backwater, E~ven though they constrict the flow, <br /> <br />3. The effects of different alignment are illustrated as follows: <br /> <br /> <br />'rt--(OItStncttOlt flood leorels .t ... '"4 II ,IN' <br />~l.uel,. ~l. <br />'ost.constRCtfOlll Ie..' 4t A Is 1l191lCl" ttlan .,t C. ,."lch 1$ <br />1tI~ tlIoIJI lot I llcc.Iun of channel sloPl' dlllll I)..'ltqe <br />lNcboliur. <br />Olte as s'- _Iel protect A fl'tln ~ct...ce..- <br /> <br />( a ) <br /> <br /> <br />-----~-~[ ---------- <br /> <br />>:--'-."-,...:::~.._:-:-:' ..".,.:: <br /> <br />_____:~1_~__~ <br /> <br />( c ) <br /> <br /> <br />I <br />I <br /> <br /> <br />BACKWATER EFFECT ASSOClAlrED WITH llIREE TYP'ES <br />OF STREAM CROSSINGS: (A) A. SKEWE[t AUGNME~IT <br />ACROSS A FLOODPLAIN, (B) CONSTIlilCTlON OF <br />CHANNEL FLOW, AND (C) CONSTRIGT10N OF OVERBANlK fLOW <br /> <br />3.21 <br />