How do I estimate the height of water in an open channel?

[Lonelywish]

Currently I am designing a open flow channel flowing through a screen which is installed at an angle of 70 degrees in the open channel. I have my discharge rate, and the width of the channel. Is there any possible ways that I can estimate the height/depth of the water without knowing the velocity?

 

[bimr]

Most users install an ultrasonic type level transmitter for this application. When the height of the water gets too high, then a signal is sent to the screen to clean itself.

 

[aspearin1]

Is the question really about calculating depth based on flow or depth based on water flowing over the top of a screen of known dimension positioned at 70 degrees? If you know your screen dimension, you know the useful cross-sectional area. Otherwise, I would say, "No, you need to know velocity, differential pressure or some other measurement to cover that 2nd unkown."

Aaron A. Spearin
ASQ CSSBB

http://www.Engineering6ss.com

"The only constant in life is change." -Bruce Lee

 

[Lonelywish]

yes i do know the screen dimension except the height of the screen. But the design is intended to screen water with depth less than the height of the screen and therefore I don't have the height of the water which is my unknown. I tried the approach of giving it a variable H to calculate but I don't seem to get any results from it.

 

[aspearin1]

Do you have enough information to solve for the area of a hole in the screen? This could allow you to determine a local velocity. You would need to know roughly the number of holes in the screen to divide your flow rate. My appologies, this is the best I can come up with without a picture. Just some extra food for thought.

Aaron A. Spearin
ASQ CSSBB

http://www.Engineering6ss.com

"The only constant in life is change." -Bruce Lee

 

[bimr]

Headloss through a screen =

(1/C)((VV-vv)/2g)

where C= headloss coefficient for clean screen = 0.7

V= velocity through clean screen in m/s

v= approach velocity through clean screen in m/s

C= headloss coefficient for clogged screen = 0.6

Assume that a clogged screen has 50% blockage or twice the velocity.

See Metcalf and Eddy Wastewater Engineering