Discharge over a broad-crested weir


Today we are going to demonstrate the operation of the broad-crested weir.

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We turn on the pump on the demonstration flume.

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We set the bottom slope at 1%.

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We check the level.

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The width L of the flume is 6 in or 152.4 milimeters.

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We set the point gage at zero at the weir crest

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We move the point gage upstream for a distance of at least four times the estimated head above the weir.

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We measure the operating head H above the weir.

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With L and H, we can calculate the theoretical discharge over the weir.

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Q = 3.087 L H 3/2 [cfs]

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Q = 1.704 L H 3/2 [m3/s]

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In an actual case, the discharge may vary from approximately 80 to 130% of this value.