CHAPTER 7 - WEIRS

14. Velocity of Approach Corrections

If the traditional standard weirs need correction for excessive velocity of approach, then their limits, as expressed in the previous sections, have been exceeded. Velocity cannot be effectively corrected by adjusting head alone as done with older procedures. Recognizing this limitation is probably the reason for the development of the Kindsvater equations and methods, which account for velocity of approach caused by allowing partial contraction. Thus, Kindsvater methods will directly recalibrate most rectangular and triangular weirs with excess approach velocity. Correcting a Cipoletti weir reading is more difficult, and (1/4)h1 must be added to the crest length to approximate a rectangular overflow opening. Then, the Kindsvater-Carter relationship is used to calculate discharge for both the fully contracted discharge case and the partially contracted case, causing the excess velocity of approach to determine the correction discharge ratio to apply to the Cipoletti table or equation value for discharge.