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Started by coxy, April 28, 2015, 09:05:57 PM

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coxy

ok you guys and gals can call me all kinds of names :D     but I don't under stand  if you have a 4ft pipe in a brook and there is a flood how come the pipe never runs a solid 4ft stream of water out of it it only runs about half  ??? ???

Holmes

 Venturi effect!
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beenthere

Gravity. Water falls out the end faster than it can fill to the top. (this is a WAG because I'm not real sure from your description just what the situation is... ).  Is 4' the pipe diameter.. or length? Is the pipe horizontal or vertical to the"flood" (assume that is a full head of water before the pipe that is horizontal).
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Ianab

Quote from: Holmes on April 28, 2015, 09:30:34 PM
Venturi effect!

This.

The water at the pipe inlet is slow moving, as it travels through the pipe it accelerates. and so it's effective volume decreases. The inlet of the pipe is what's limiting the water flow in the this case.
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BargeMonkey

 Somewhere we have a erosion control book that has formula's and graphs showing culvert effectiveness. When you start bidding some of these city jobs / federal stream work they specify GPM and GPH on culverts and drainage. Ive got a picture of an 8' culvert flopped out of the ditch laying in a field up the road after Irene,  :D 

thecfarm

I see the same thing around here too.  :)
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coxy

Quote from: beenthere on April 28, 2015, 09:46:30 PM
Gravity. Water falls out the end faster than it can fill to the top. (this is a WAG because I'm not real sure from your description just what the situation is... ).  Is 4' the pipe diameter.. or length? Is the pipe horizontal or vertical to the"flood" (assume that is a full head of water before the pipe that is horizontal)
its diameters   and they are culverts   

tj240

i am guessing here, but you have a 4 foot pipe that is full at one end and only flowing 2 feet?  i would use a 6 foot pipe. like i said just guessing, but if you get a vortex at the head end you wont get a full pipe. go bigger its more money, or just wait it out. good luck
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coxy

tj240  i was just wondering cause I see it all the time when we get extremely high water  don't think I would want to try to put a pipe in a stream of water that was flowing over 4ft of water maybe an interesting time :) ;D 8)

Left Coast Chris

There are several conditions that affect the efficiency of a culvert to pass larger water flows.

The volume of water flow is measured in cubic feet per minute.    The cubic feet per minute rate is affected by slope of the pipe.  The steeper the grade of the pipe the larger the water velocity.  The flatter slope of the pipe the smaller the water velocity.

When a pipe has a steeper slope and faster water velocity the max water flow will generally be controlled by the inlet conditions or inlet controlled.   If there is a flared end section or wing walls on the culvert inlet the flow condition is improved and you will get higher flows through the pipe.   

When a pipe has a flatter slope and slower water velocity often the flow is outlet controlled.  The water coming out of the pipe is likely pushing or backing up from high levels of water on the outlet end. 

Roughness of the pipe will also be a factor.  A corrugated pipe will flow less than a smooth plastic pipe of the same inside diameter as an example.

There are inlet conditions and pipe slope combinations that culverts can flow 3/4 or more full.

Hydraulic formulas and calculations are used to determine flow rates given the parameters mentioned.   
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