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Determining Water Depth

08/14/2010 10:04 PM

Boy, it's been so many years since I last did this that I've forgotten how it's done. Given that I know the length and width of an open channel, the volumetric flow rate of water through it and the inlet and outlet widths, how do I calculate to what depth the water will rise? The water is flowing by gravity alone and the hydraulic gradient is zero i.e. the invert levels at the inlet and outlet ends of the channel are the same. And no, I can't remember where my old school textbook is, otherwise I wouldn't be asking for help here.

Thanks everyone.

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#1

Re: Determining water depth

08/14/2010 11:35 PM

Have you been drinking? If so, it's okay. If not, I am far dumber than I thought and need to leave here. AND STOP CALLING ME BOY!

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#2
In reply to #1

Re: Determining water depth

08/15/2010 12:48 AM

No, alcohol is banned on the Empire's ships and camps anyway. Okay, what would you prefer me to call you then?

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#3
In reply to #2

Re: Determining water depth

08/15/2010 3:55 AM

Call me a cab!

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#4
In reply to #3

Re: Determining water depth

08/15/2010 4:42 AM

As you wish. You're a cab.

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#8
In reply to #2

Re: Determining water depth

08/15/2010 9:14 PM

Bitch. Thank you.

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#5

Re: Determining water depth

08/15/2010 10:47 AM

Oh Lord Vader, so if drinking is banned throughout the Evil Empire, then what are you and your followers "snorting", eh? LOL

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#7
In reply to #5

Re: Determining water depth

08/15/2010 7:53 PM

Nothing. Narcotics are also banned, and in any case considering that I breathe through an activated carbon filter mask, I can't snort anything even if I want to.

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#9
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Re: Determining water depth

08/15/2010 9:29 PM

I was drinking whiskey today. My neighbors came down and I asked them, " what can brown do for you?" I ,of course was referring to the UPS ad. They decided I was an A$$ hole and went home.

We have been repeating various versions of this movie for the past 5 years.

Why do they keep coming back?

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#6

Re: Determining water depth

08/15/2010 12:59 PM

Give us more information, draw a sketch, what is the source of the water coming in, flow rate, depth, head, velocity. How long is the channel, cross section dimensions/geometry, what is the type of surface, concrete, smooth, rough, steel, corrugated, plastic, earthen, etc.. and lastly, what does it dump into, open drop, culvert?

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#10
In reply to #6

Re: Determining water depth

08/16/2010 1:46 AM

Please refer to the sketch.

The water is pumped from a river. The flow is 1.6m3/sec @ 20 m-head. The channels and tank are made of smooth-walled reinforced concrete. The water will discharge into a lake 2000m3 with a depth of 4 meters from a drop of 2 meters from outlet channel.

Thanks for your help.

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#11
In reply to #10

Re: Determining water depth

08/16/2010 10:58 AM

What you provided helps, but still does not give us the needed info to proceed. If you are pumping, how is it being fed to the channel (pipe, chute, chamber, free fall)? What is important is that you have a flow rate coming in, you take it from there. Therefore the hydraulic gradient is not zero, because you have a velocity head starting at the discharge point #1, then it enters the channel, which is the crux of your inquiry. the formula is Q=1.486/nXAXR^(2/3)/S^1/2 =AV. Refer to Open Channel hydraulics, Chow or Handbook of Hydraulics, Brater & King. You can also get some free spreadsheets or low cost programs from Haestads. Your diagrams does not say if its plan view, section or what I'm looking at. It resembles both. It looks like a chamber that you are dumping into from a source (what, where). Is the water building up, it has to build up to build a head to push it through the baffle and up the lift to a delivery chute. Again, I'm speculating from the limited information an crude drawing. Do you have pictures of the sources and delivery, you can email me too.

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#12
In reply to #11

Re: Determining water depth

08/16/2010 11:55 AM

Okay, thanks for the advice. The top drawing is the plan view while the lower one is the side view.

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#13
In reply to #12

Re: Determining water depth

08/16/2010 12:40 PM

I thought so, how does the water get delivered to the inlet on the left? Is it 3.5 m from the baseof the tank? I need to know how much the water has to raise to the outlet on the right side, it appears that it may be 3.2m (5.0-1.8)? For the sake of brevity, we can assume that the water equalizes and flows out on the right with a head as in a reservoir in a chute 5 m long and 2m wide and determine the depth that way. YOu apply bernoulis equation for conservation of energy from the reservoir to the outlet 5m to the right for the depth with a zero channel slope. Z1+D1+fV1^2/(2g) = Z2+fV2^2/(2g)+H Z1=Z2, CANCEL f=LOSS FACTOR V=VELOCITY D=DEPTH OF FLOW g=GRAVITY CONSTANT, 32.2 FPS, 9.2 MPS H=ENERGY SLOPE, DIFFERENCE IN DROP BETWEEN 1 & 2 I calc out 56.5' or 17.2m, too much flow for a small chute

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#14
In reply to #13

Re: Determining water depth

08/17/2010 12:03 AM

Okay, thanks for your help. I'll let my friend know that this is an unfeasible design.

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