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<br />. <br /> <br />. <br /> <br />. <br /> <br />"flared" cross sections were created to account for the expansion <br />and contraction losses caused by the structure's encroachment into <br />the effective flow area. HEC-2 was initialized with standard <br />contraction and expansion coefficients of 0.30, and 0.50 <br />respectively to enable the program to calculate losses due to <br />channel transitions from cross section to cross section. <br /> <br />Manning's N values were estimated from photographs taken in June of <br />1991. All channel and left and right over-banks were estimated to <br />have an N value of 0.050 due to homogeneous vegetative growth in <br />all of these locations. <br /> <br />2. Bridaes <br /> <br />The special bridge method HEC-2 option was used in order to compute <br />both pressure and weir flows through and over all three bridge <br />structures. The basis of the special bridge method is the Yarnell <br />energy equation for class A low flow, the orifice equation for <br />pressure flow and the weir equation for weir flow. These methods <br />compute the change in water surface elevation through a bridge <br />under each type of flow regime. The Yarnell equation contains a <br />pier shape coefficient. For the trestle and highway bridge a pier <br />shape coefficient of 1. 05 was selected (round piers). For the <br />County Road 21 bridge a pier shape coefficient of 1.25 was used. <br />The total loss coefficient, "K" for the trestle and highway bridge <br />was estimated at 1.56 and 1.60 for the county bridge. The <br />coefficient of discharge for all bridge structures was estimated at <br />2.6. The total loss coefficient and the coefficient of discharge <br />were estimated due to the lack of calibrated datal. <br /> <br />lHEC-2 Programmers Manual, page IV-22. <br /> <br />Paoli Flood study <br />September 29, 1991 <br /> <br />Hydraulic Analysis Report <br /> <br />-4- <br />