Open Channel Flow Question

[civengPE]

This is similar to a problem we worked in our review class. it is probably more difficult than you will see on the exam, but it tests whether you understand the concepts and not just plugging and chugging.

Solve for Q in the attached drawing.

Sorry, The image didn't come out too well.

n1 = .035

n2 = .013

top slope is 3 to 1

bottom slope is 2 to 1

Depth one is 2'

Depth two is 7'

S= 1%

The side slope designations on the drawing were accidentally reversed. :brick:

That's what I get for completely making a question up from scratch.

View attachment 153

 

[civengPE]

I have not done the calculations for Q yet, but this is how it has to be broken down. Check my math.

View attachment 154

 

[civengPE]

You have to cut the channel into "verticle" sections. This is because the friction of the channel lining is waht inhibits flow. I have an example at home. I'll try to scan and post it tonight.

I checked my Wp numbers and believe them to be correct. You only count the perimiter in contact with a surface.

 

[civengPE]

Here's What I got...117.6 CFS :claps:

Here's the work. Don't trust my math or solution! This is just one man's attempt at a problem he made up to amuse himself!

Edited: Removed Solution. ******* me wrote mannings equation incorrectly! :suicide:

 

[civengPE]

I just ran them again and came out with different numbers than last night! :wtf:

I double checked those damn things last night.

I've got to do some work right now, but I will look at it again in a while.

Maybe someone else can weigh in!!

OH Sap, I think you Q2 is double of what it should be. I used both areas in my calculation.

 

[civengPE]

Sap, You are correct. I forgot the Area in Mannings equation.

Damn I'm glad I don't have to take this thing again!!

:drunk:

 

[cantaloup]

NAH ! this is child play. piece of cake . Try to find depth with flow given, do it in 3 minutes!!!

 

[RIP - VTEnviro]

Damn I'm glad I don't have to take this thing again!!
:drunk:

Amen brother.

 

[Road Guy]

:die:

 

[3gorgesdam]

:read:

Here is what I got: Q = 1578.965

I saw one other person got similiar answer. Does that mean we are right?

 

[cantaloup]

I guess I am completely doing this wrong. However, using your same numbers and the same equation, I get
Area A = 3905.6 cfs

Area B = 96.1 cfs

Total = 4001.7 cfs

What am I doing wrong???

I guess that Supperslead's answer is correct. I'll write up a formula for the HP33s for this type of problem just in case , since it's easy to make mistake when calculating area, radius...