Open Channel Flume

[Sam1986sam]

I am a little bit confused about the utility of flume in concrete open channels. Let's assume that I have a concrete open channel with a steady flow inside, aren't we able to measure the flow by measuring the level inside the open channel !?

What I want to say is that we know exactly the dimensions of the open channel and we can measure the level by a level transmitter and therefore we can calculate the amount of volume passing through the open channel. Am I thinking wrong here !??

And here come my dumb question, why flumes are required for such an application !?

 

[LittleInch]

To give them their proper name they seem to be parshall flumes

https://en.wikipedia.org/wiki/Parshall_flume

They are measurement devices, carefully contoured and spaced and the physics worked out to give a good volumetric measurement.

Depth of water in a concrete channel tells you nothing about the velocity and hence volumetric flow.

with a very specific channel operating in controlled conditions you might over time be able to correlate depth with flow measured by some other means, but I don't believe you can get this from just a random depth in a random channel.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[akkamaan]

Flow is the AVERAGE velocity of a fluid through a specific cross-section area. Sure if you know the depth of water and the average width of the flume you know the cross section area. To measure the flow through that cross-section you can get AN IDEA by measuring the water velocity on the surface. The problem is that water velocity is slower the deeper down you get due to turbulence from internal and external friction. That's why fish always are staying down by the bottom of a river, to conserve energy where the flow is lower. If you get something down to the bottom of the flume that travels with the water flow (ie a turbine velocity meter) and measure its velocity you can calculate a BETTER IDEA of the flow rate in the flume. With 4-5 velocity measurements in the cross-section, you should be able to get enough data to calculate a pretty decent estimate of flow rate in the flume. The more non-symmetric the flume cross section is the harder it will be to design a good math algorithm for the calculation. Take a calculus class if you don't have it in your toolbox...
Here is an example of a flow probe for open channel velocity and flow measurements
Another example