Laserfiche WebLink
<br />depth 'lW is the distance in feet from the cuJ.vert invert at the outlet <br />to the water surface in the outlet channel. The relationship of HW to <br />the other terms in equation 3 is illustrated in figure 4. <br /> <br />e <br /> <br />1 <br />HW <br /> <br />J <br /> <br /> <br />~ <br /> <br /> <br />. <br />H <br />-r- <br /> <br />TW = ho <br />-L-: <br />'1 <br /> <br />= <br /> <br />LSo <br /> <br />,- <br /> <br />L <br /> <br />Figure 4 <br /> <br />If the tailwater elevation is below. the top of the cuJ.vert open- <br />ing at the outlet, figure 2B, 2C and 2D, ho is more difficuJ.t to deter- <br />mine. The discharge, size and shape of cuJ.vert, and the 'lW must be <br />considered. In these cases, ho is the greater of two values (1) 'lW <br /> <br />depth as defined above or (2) dc + D . The latter dimension is the dis- <br />2 <br />tance to the equivalent hydrauJ.ic grade line discussed previously. In <br />this fraction de is the critical depth, as read from Charts 15 through <br />20 and .D is the cuJ.vert!:leight. The value of de can never exceed D, <br />making the upper limit of this fraction equal to D. Where TW is the <br />greater of these two values, critical depth is submerged sufficiently <br />to make 'lW effective in increasing the headwater. The sketch in fig- <br />ure 5 shows the terms of equation 3 for this low tailwater condition. <br />Figure 5 is drawn similar to figure 2C, but a change in discharge can <br />change the water surface profile to that of figure 2B or 2D. <br /> <br />e <br /> <br />L <br /> <br /> <br />. <br /> <br />1 <br />HW <br />j <br /> <br /> <br />............... <br /> <br />LSo <br /> <br />Figure 5 <br /> <br />e <br /> <br />5-10 <br />