On January 16, we set up boards, this time videos show measuring flows over a weir and through an orifice!
Simple to set up weirs and orifices
Measuring Weir On Youtube: https://www.youtube.com/watch?v=-wOJrWIpPaM
Measuring Orifice On Youtube: https://www.youtube.com/watch?v=-wOJrWIpPaM
Last time, on January 16, we looked at how to set up weir and orifice boards in a dry diversion. This is more exciting – now we’re actually measuring flow over a weir and through an orifice!
Standing in front of the Wigno Weir, getting ready to “stick the weir” with an engineering ruler. The ruler has inches on one side and tenths and hundredths of a foot on the other side – which is how engineers and surveyors measure the world in English (non-metric) units.
Sticking the weir with the ruler face-on shows that the depth is 0.31′, the same as the depth in the upstream pool. The weir is 3.30′ wide and is suppressed or flat-sided – the water does not have to turn the corner while going over the weir.
With these measurements in hand, it’s a quick calculation using the suppressed weir equation:
to find 1.90 cfs.
Here is the same weir, before being set up with orifice boards. Flow is measured through a hole instead of over the top of the boards
The same engineering ruler is used, but this time measuring from the center of the hole, up to the top of the upstream water surface.
Actually, it’s easier to measurefrom the bottom of the hole and subtract off half the height of the hole. The hole is 1.00′ wide, 0.30′ high, and the water height is 0.25′.
This time, the flow is less, at 0.73 cfs, using the equation: WHY? I did not wait the 5 minutes it would take for the upstream head to stabilize. It was cold and about to get dark and the videographer was patient but getting cold. 🙂
A question I hear all the time is, “Hey, I got this letter from the ‘State Water Resources Control Board‘. What am I supposed to do about measuring my flow? How do I keep from getting in trouble?” The main number for the Water Board is (916) 341-5300 – and these folks have much more work to do than time to do it. Several calls may be required to reach a knowledgeable person who isn’t already talking to two telephone calls, or making three investigations in the field. Since the most calls I get are about enforcement letters, calls, or visits from the Board, it’s probably most useful to have the phone numbers and emails from Enforcement Program Staff. Here they are, from:
Enforcement Program Staff
Katherine Mrowka, Manager
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