Laserfiche WebLink
<br />. <br /> <br />. <br />, <br />l <br />t <br />t <br />~ <br />!- <br />t <br />f <br />. <br />l <br />. <br /> <br /> ~ <br />~ ~ <br />:t: - <br />- <br />z z <br />0 0 <br />l- I- <br /><l: <l: <br />> > <br />ILl Q_H,o/z ILl Q_hh <br />...J ...J <br />ILl ILl <br /> <br />t <br />~ <br />~ <br /> <br />. <br />t <br />t <br />t <br />~ <br />~ <br />~ <br />~ <br />. <br /> <br /> <br />FLOW RATE (Q) <br /> <br />WEIR <br /> <br />~ <br />. <br />~ <br />~ <br />~ <br />~ <br />~ <br /> <br />RECTANGULAR WEIR <br /> <br />Equation; <br /> <br />Q = CdL(HWr)3/2 <br /> <br />Q <br />Cd <br />L <br />HWr <br /> <br />= flow rate, ft3 Is (m3 Is) <br />= weir coefficient <br />= length of weir, ft (m) <br />= driving :tead above <br />weir crest, ft (m) <br /> <br />. <br />, <br /> <br />~ <br />. <br />. <br /> <br />t <br />~ <br />~ <br /> <br />t <br />~ <br />~ <br />r <br />. <br />t <br />r <br /> <br /> <br />FLOW RATE (Q) <br /> <br />ORIFICE <br /> <br />ORIFICE <br /> <br />Equation: Q = kah1/2 <br /> <br />Q = flow rate, ft3/s (m3/s) <br />k = coefficient <br />a = area of orifice,ft2 (m2) <br />h = driving head above <br />center of orifice, ft (m) <br /> <br />Figure I1I-IS--Performance curves <br />2nd equations for weirs and orifices. <br /> <br />a trial and error procedure to determine <br />the flow division between the overtop- <br />ping flow and the culvert flow, an overall <br />performance curve can' be developed. The <br />performance curve depicts the sum of the <br />flow through the culvert and the flow <br />across the roadway. <br /> <br />The overall performance curve can be <br />determined by performing the fOllowing <br />steps. <br /> <br />1. Select a range of flow rates and <br />determine the corresponding headwater <br />elevations for the culvert flow alone. <br /> <br />~ <br />~ <br />~ <br />, <br /> <br />These flow rates should fall above and <br />below the design discharge and cover the <br />entire flow range of interest. Both <br />inlet and outlet control headwaters should <br />be calculated. <br /> <br />2. Combine the inlet and outlet control <br />performance curves to define a single <br />performance curve for the cui vert. <br /> <br />3. When the culvert headwater ele- <br />vations exceed the roadway crest eleva- <br />tion, overtopping will begin. Calculate <br />the equivalent upstream water surface <br />depth above the roadway (crest of weir) <br /> <br />43 <br />