Channel Flow Calculations Distance Learning Math Index Websites for Those Who Need Help Homepage Flow Calculations  Rectangle Weirs:         Contracted:                 Flow, Q = 3.33 (L  -  0.2H) H1.5             Suppressed:                 Flow, Q = 3.33 L(H1.5)                  Q = Flow, cubic feet per second                  L = Length of crest, feet                  H = Upstream head, feet  Cipoletti Weirs:                 Flow, Q = 3.367 L(H1.5)                  Q = Flow, cubic feet per second                  L = Length of crest, feet                  H = Upstream head, feet  V-Notch Weirs:         90' V-notch:                 Flow, Q = 2.50 H2.50             60' V-notch:                 Flow, Q = 1.443 H2.50             45' V-notch:                 Flow, Q = 1.035 H2.50             30' V-notch:                 Flow, Q = 0.685 H2.45              Q = Flow, cubic feet/second             H = Upstream head, feet     Example: The upstream head for a 90* V-notch weir is 3 inches.  The flow in cubic feet per second is: Convert head to feet: Determine flow rate: This can then be converted to other units of measure i.e. Million gallons per day or gallons per minute    Example: Calculation of Flow Rate: The flow can be calculated in cubic feet per second (cfs) using the following equation:                 Flow, Q = 4 (W)(Ha)1.52W0.026                 Q = flow cfs                  W = Width of the throat, ft                  Ha = Upstream head, ft    Example: The upstream head (Ha) in a 2.5 ft. throat flume is 9 inches.  There is no submergence to be corrected for.  What is the flow rate in cubic feet/second?                 Q = 4 (W) (Ha) 1.52W0.026            First convert the head to feet     This flow can then be converted to million gallons per day or gallons per minute.  Flow Calculations