# NORMAL DEPTH

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### #1 winner9459

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Posted 02 April 2011 - 01:01 AM

I am not able to figure out how to use charts to arrive at normal depth for open channel problems with a circular cross section.

I am able to use the chart in Appendix 19-C and table 19.3 in CERM to arrive at Q/Qfull, but I am kind of stuck in there. Should I be just using the mannings equations to calculate depth and would it be equal to normal depth....

If so, why isn't it working for flowing full and full half-full when I tried to derive the equations given in CERM, by modifying the mannings equations.

The basic question: how do I calculate normal depth for circular channels using the graph ?????????

### #2 maximus808

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Posted 02 April 2011 - 04:16 AM

Hey winner, it's been a while since I dived into water resources but I'll try to help you out. I took the Oct. Exam and passed in the trans depth so hopefully I can help you. Let's see.......the way I look at these types of problems is to see what are they asking first....then what I'm given or what I can find. Typically you are given a pipe diameter with parameters to find it's flow using mannings. This represents Qfull. Most likely you are given the partial flowrate which represents Q. You begin to see the set up of Q/Qfull. You need to find d/Dfull. You have Dfull which is the diamter......use q/Qfull and I'm not certain but you either go left and down or up and right to intersect the curve for flow or velocity for a constant n or varying n. Most times it will be constant if the material of the pipe does not change....does this make sense guys. You will be able to find a value for d/Dfull. Multiply that value by Dfull and you will get d. Be sure to check your units of what Dfull is as that is what your d will be in. I hope that helps a little bit. I always found the tables better than the graph though. You look for the number of d/Dfull based on your value of q/Qfull.

### #3 winner9459

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Posted 05 April 2011 - 01:25 AM

I figured out a better way. I found ASCE water PE materil which has charts plotting yn/d for various k values. That would be the fastest way to solve for the normal depth in circular pipes.

Toanswer my first Q, I think we can just use ythe manning equation to solve for Yn.

### #4 PEmarsh

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Posted 06 April 2011 - 02:32 AM

I always solve for depth using Manning's equation. As long as you can do the math, I find it easier than using the table. Also, if you are given the flow rate and it does not say "critical flow rate," you can assume you are solving for the normal depth. This sounds like a uniform flow problem.

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