Problem 6 (10 points) in order to monitor the discharge of stormwater flow in a

Question

Problem 6 (10 points) in order to monitor the discharge of stormwater flow in a canal, a broad-crested weir is place in the flow to create a "choked" flow condition (ie, critical flow). The at the weir has a rectangular shape with width B 5(m). Please calculate the discharge when the water depths above the weir are 0.2,0.5 and 0.75 m, respectively cross-section of the channel water: 7-9 8 (KNhar") or 62.4 (lbt'). 8-931 un's) d 32.2 (fw) Formalas Hydraulic radius: Rp 2g (English unis-AR metric units) for a rectangular channe, and Ey ( 531/2 Lon -) Hydraulic jrmp: y2= 21 (Vit 4x91 Qu-A Fr.-for a rectangular channel R2/3S 1 /2 (English untst.:AR2/3,.. (merieuns) Fr= for arbitrary x-secnon: SAIT or a rectangular channe d E=y+1T 2gy for a rectangular chand 433, for abitrnany s section:ro a rectangidar chane L.49 R

Explanation / Answer

Given weir causes choked flow condition

i.e. E = minimum => Fr=1

Therefore V= (gy)

Q = AV = b*y*gy

= b* g* y^1.5

= 5*9.81*y^1.5

=15.66*y^1.5

Q0.2= 15.66*0.2^1.5 = 1.401 m3/s

Q0.5= 15.66*0.5^1.5 = 5.537 m3/s

Q0.75= 15.66*0.75^1.5 = 10.171 m3/s

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