Irrigation in the Pacific Northwest

Rectangular Contracted Weir

This calculator finds the water flow rate for a rectangular contracted weir. A rectangular contracted weir has a rectangular opening where the sides are straight up and down. A contracted weir means that the ditch leading up to the weir is wider than the weir opening itself.

The length is found by measuring the bottom width of the weir and the height is determined from measuring the water height above the bottom of the weir.

Learn more about the units used on this page.


Flow Rate:



* Note: 1 point = 1/100 ft.

The Equation

The Equation used to determine the flow rate of a Rectangular Contracted Weir is:


= Flow Rate in cfs.

= Bottom width of the weir in feet.

= Height of the upstream water above the weir crest in feet.





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