If S is the length of the crest, H is the height of water source of a weir whose length is L and discharge is Q m3/sec, the velocity of approach Vd is

• A. <span class="root">2<i>gH</i></span>
• B. <img src="/_files/images/civil-engineering/hydraulics/152-7.141-1.png">
• C. <img src="/_files/images/civil-engineering/hydraulics/152-7.141-2.png">
• D. <img src="/_files/images/civil-engineering/hydraulics/152-7.141-3.png">
• E. none of these.