Laserfiche WebLink
<br />. <br />~ <br />~ <br />~ <br />~ <br />~' <br /> <br />, <br />, <br /> <br />The barrel velocity is calculated as <br />follows: <br /> Q <br />V = (2) <br /> A <br /> <br />. <br /> <br />. <br />.. <br />.. <br />, <br />~ <br /> <br />. <br />.. <br />.. <br />, <br />, <br />.. <br />.. <br />, <br /> <br />V is the average velocity in <br />the culvert barrel, ft/s (m/s) <br /> <br />Q is the flow rate, ft3/s (m3/s) <br /> <br />. <br /> <br />A is the full cross sectional <br />area of the flow, ft2 (m2) <br /> <br />, <br />.. <br />.. <br />" <br /> <br />t <br />~ <br />~ <br />t <br /> <br />The velocity head is: <br /> <br />V2 <br /> <br />H = <br />v <br /> <br />(3) <br /> <br />2g <br /> <br />.. <br />, <br />t <br />, <br />~ <br />~ <br />~ <br />~ <br />~ <br />, <br />. <br />.. <br />. <br />. <br />.. <br />~ <br />. <br />.. <br />.. <br /> <br />g is the acceleration due to <br />gravity, 32,2 ft/s/s (9,8 <br />m/s/s) <br /> <br />The entrance loss is a function of <br />the velocity head in the barrel, and can <br />be expressed as a coefficient times the <br />velocity head. <br /> <br />H.... (;;-) <br /> <br />(4a) <br /> <br />t <br />~ <br />t <br /> <br />Values of k. based on various inlet <br />configurations are given in table 12, <br />appendix D, <br /> <br />. <br /> <br />The friction loss in the barrel is <br />also a function of the velocity head. Based <br />on the Manning equation, the friction <br />loss is: <br /> <br />~ <br />, <br />~ <br />t <br /> <br />~ <br />.. <br />. <br />. <br />. <br />i <br />, <br />~ <br />, <br /> <br />~ <br />. <br />~ <br />.. <br />'~ , <br /> <br />[ 29 n2 L ] <br />Rl,33 <br /> <br />V2 <br /> <br />Hr= <br /> <br />(4b) <br /> <br />2g <br /> <br />n is the Manning roughness coeffi- <br />cient (table 4) <br /> <br />L is the length of the culvert <br />barrel, ft (m) <br /> <br />R is the hydraulic radius of the <br />full culvert barrel = A/p, ft (m) <br /> <br />A is the cross-sectional area of <br />the barrel, ft2 (m2) <br /> <br />p is the perimeter of the barrel, <br />ft (m) <br /> <br />V is the velocity in the barrel, <br />ft/s (m/s) <br /> <br />The exit loss is a function of the <br />change in velocity at the outlet of the <br />culvert barrel. For a sudden expansion <br />such as an end wall, the exit loss is: <br /> <br />rV2 <br />Ho = 1.0 r;; - <br /> <br />~(] <br /> <br />(4c) <br /> <br />V d is the channel velocity down- <br />stream of the culvert, ft/s (m/s) <br /> <br />Equation (4c) may overestimate exit losses, <br />and a multiplier of less than 1.0 can be <br />used. (40) The downstream velocity is <br />usually neglected, in which case the <br />exit loss is equal to the full flow velo- <br />city head in the barrel, as shown in <br />equation (4d). <br /> <br />V2 <br /> <br />H = H = <br />o v <br /> <br />(4d) <br /> <br />2g <br /> <br />Bend losses, junction losses, gra te <br />losses and other losses are discussed in <br />chapter VI. These other losses are added <br />to the total losses using equation (I). <br /> <br />Inserting the above relationships for <br />entrance loss, friction loss, and exit loss <br />(equation 4d) into equation (I), the <br />following equation for loss is obtained: <br /> <br />H = ~ + k. + --~~--~~-~] -~~- (S) <br />[ Rl,33 2g <br /> <br />3S <br />