Normal Depth Calculations - Rectangular channel

[Lashonda]

I have seen a couple of normal depth of flow calculations which use the formal q = 1.71bh^(3/2) where h is the depth of flow and b is width of rectangular channel.

However i don't seem to find this supported in any text book.

I'm reviewing a hydraulic profile of a treatment works and i need to check some depth of flows in some channels.Can anyone help me with the right application of the above formula. I'm not considering channel slope.

Waiting....! thanks

 

[RWF7437]

You must consider both the slope and roughness of the channel as well as the units of measurement ( metric or English).

Try this link:

http://www.haestad.com/library/book...C_RAS&file=Floodplain with HEC-RAS-11-08.html

good luck

 

[Lonelywish]

I agree that you will need to take unit measurements into considerations. But what if I have a channel which has no slope (horizontal) ? I do have an incoming flow rate, Q of lets say 300m3/hr. We will still have a water depth and width right?

 

[Jirrik]

Lashonda,
Since the channel is flat you are dealing with a flow driven by a hydraulic head. It is also called a gradually varied flow as the flow depth gradually changes along the channel.
You need to know the flow depth at a certain section along the channel from which you can calculate flow depths upstream or downstream. This process requires some iterations as you have to determine such water surface slope that drives the particular discharge.

This basic paper gives you the essential background

http://www.efm.leeds.ac.uk/CIVE/CIVE2400/OpenChannelHydraulics2.pdf

and at the same address :

http://www.efm.leeds.ac.uk/CIVE/CIVE2400/

you can even find some spreadsheets to calculate such cases.

There also many on-line calculators that give you the answer but do not believe in all black box generators. I think that the following link provides both the methods and the results.

http://www.lmnoeng.com/Channels/gvf.htm

Good luck