ADVANTAGES OF TRIANGULAR NOTCH OR WEIR OVER RECTANGULAR NOTCH OR WEIR A triangular notch or weir is preferred to a rectangular weir or notch due to following reasons The expression for discharge for a right-angled V-notch or weir is very simple. For measuring low discharge, a triangular notch gives more accurate results than rectangular weir or notch. In case of triangular notch, only one reading, i.e., (H) is required for the computation of discharge. Ventilation of a triangular notch is not necessary. Q10. Define velocity approach. How does the velocity of approach affect the discharge over aweir? (July 2014 , Jan 2015) Ans: It is the velocity of water which approaches just upstream of weir or notch. It is ‘ha’need affected by the nappe drawdown and correction to be applied based on velocity of head calculated with velocity of approach ‘Va’ Velocity of approach (Va) The total head over the weir will be the sum of static head (H) and velocity head (ha), V2  velocity head h is due to the Velocity of the liquid approaching the notch. a 2a a On similar lines, considering a strip of uniform thickness at a depth h below the ‘dh’ liquid surface. Discharge through the strip dq=area x velocity. dQ  Lxdhx Therefore Total discharge is given by 1 2 Q H       dq L H ha dh 0 0 3 3 2  2     L H ha ha 2   3 3 2   2    Q C ha L H  h 2 3   d a   Empirical Formula 3 3    Formula  1.84  0.1nH     Q L H ha ha 2 2  
ADVANTAGES OF TRIANGULAR NOTCH OR WEIR OVER RECTANGULAR NOTCH OR WEIR A triangular notch or weir is preferred to a rectangular weir or notch due to following reasons The expression for discharge for a right-angled V-notch or weir is very simple. For measuring low discharge, a triangular notch gives more accurate results than rectangular weir or notch. In case of triangular notch, only one reading, i.e., (H) is required for the computation of discharge. Ventilation of a triangular notch is not necessary. Q10. Define velocity approach. How does the velocity of approach affect the discharge over aweir? (July 2014 , Jan 2015) Ans: It is the velocity of water which approaches just upstream of weir or notch. It is affected by the nappe drawdown and correction ‘ha’need to be applied based on velocity of head calculated with velocity of approach ‘Va’ Velocity of approach (Va) The total head over the weir will be the sum of static head (H) and velocity head (ha), V2 velocity head h  a is due to the Velocity of the liquid approaching the notch. a 2a On similar lines, considering a strip of uniform thickness ‘dh’ at a depth h below the liquid surface. Discharge through the strip dq=area x velocity. dQ  Lxdhx Therefore Total discharge is given by 1 Q H 2  dq  L   H  ha  dh 0 0 3 3  L 2  H  ha 2  ha 2    3 3 Q  2 C  L  H  h 2  ha 2  3 d  a    Empirical Formula 3 3 Formula Q  1.84  L  0.1nH   H  ha  2  ha 2   
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