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# Hydraulic Radius and Area of Multiple Box Culverts.(Chezy Mannings)

## Hydraulic Radius and Area of Multiple Box Culverts.(Chezy Mannings)

(OP)
For a preliminary sizing I have looked at using the Chezy Manning's Equation for box culverts.
1. can you use Chezy Manning's on CBC that are multiple barrels? If yes do you sum up all the areas of each individual box culvert? Do you sum up the hydraulic radius of each individual barrel for the total hydraulic radius?
Q=(1.49/n)(A)(R)^.67(S)^.5

### RE: Hydraulic Radius and Area of Multiple Box Culverts.(Chezy Mannings)

Since your equation is a linear function on area, you can use the combined area, but the hydraulic radius should be for a single barrel. If in doubt, evaluate a singe barrel and multiply by the number of barrels.

Peter Smart

### RE: Hydraulic Radius and Area of Multiple Box Culverts.(Chezy Mannings)

Unless the barrel inverts are at different elevations, or the barrels are non uniform in shape/size, the hydraulic radius should remain the same regardless of the number of barrels

A = area of flow in one barrel
P = wetted perimeter in one barrel
n = number of barrels

r = n*A/(n*P) = A/P

### RE: Hydraulic Radius and Area of Multiple Box Culverts.(Chezy Mannings)

(OP)
So
for example you have a CBC and assume flowing full
IE 5-8x4 CBC assuming flowing full
A=8*4=32 sf
∑A= 32+32+32+32+32= 160 sf
P = 4+4+8+8=24 feet
r=5*32/5*24=1.33
assuming n=.011, S=.0025
Q = (1.49/.011)(160)(1.33)^.67*(.0025)^.5= 1311.79 cfs

### RE: Hydraulic Radius and Area of Multiple Box Culverts.(Chezy Mannings)

all fine except I would not expect n=0.011. for conservative sizing design, I would normally use 0.015 which gives you more like 960 cfs

for instance MDOT says 0.013
https://www.michigan.gov/documents/MDOT_MS4_App_91...

precast.org and INDOT says 0.012 to 0.015
http://www.in.gov/indot/design_manual/files/Ch31_2...

### RE: Hydraulic Radius and Area of Multiple Box Culverts.(Chezy Mannings)

(OP)
One other question why wouldn't you use R = 32/5+32/5+32/5+32/5+32/5= 32 hypothetically doesn't each box have a surface? Just curious?

### RE: Hydraulic Radius and Area of Multiple Box Culverts.(Chezy Mannings)

slange: As you already stated: r= A/P = 5*32/5*24 which reduces to r=32/24

The hydraulic radius for a single barrel is the same as the hydraulic radius for the entire multi-barrel structure. Check the equation - you cannot add the radius for each barrel.

Again, the easy solution is to evaluate the flow for a single barrel and multiply by the number of barrels. Keep it simple.

Peter Smart

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The passage contains a discussion about the application of the Chezy-Manning equation to calculate the flow rate in multiple barrel box culverts. It includes a specific example with calculations and a question about the hydraulic radius.
single_question_with_answer
Given a text passage, determine:
    1. If it contains a mathematical question (including word problems or calculations)
    2. If an answer to that mathematical question is provided in the text

First, describe the content structure you found in 1-2 sentences.

Then provide your analysis in the following format:
TYPE: <one of the following values>
- NO_QUESTION
- SINGLE_QUESTION
- SINGLE_QUESTION_WITH_ANSWER
- MULTIPLE_QUESTIONS
- MULTIPLE_QUESTIONS_WITH_ANSWERS
system
×
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Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# Hydraulic Radius and Area of Multiple Box Culverts.(Chezy Mannings)

## Hydraulic Radius and Area of Multiple Box Culverts.(Chezy Mannings)

(OP)
For a preliminary sizing I have looked at using the Chezy Manning's Equation for box culverts.
1. can you use Chezy Manning's on CBC that are multiple barrels? If yes do you sum up all the areas of each individual box culvert? Do you sum up the hydraulic radius of each individual barrel for the total hydraulic radius?
Q=(1.49/n)(A)(R)^.67(S)^.5

### RE: Hydraulic Radius and Area of Multiple Box Culverts.(Chezy Mannings)

Since your equation is a linear function on area, you can use the combined area, but the hydraulic radius should be for a single barrel. If in doubt, evaluate a singe barrel and multiply by the number of barrels.

Peter Smart

### RE: Hydraulic Radius and Area of Multiple Box Culverts.(Chezy Mannings)

Unless the barrel inverts are at different elevations, or the barrels are non uniform in shape/size, the hydraulic radius should remain the same regardless of the number of barrels

A = area of flow in one barrel
P = wetted perimeter in one barrel
n = number of barrels

r = n*A/(n*P) = A/P

### RE: Hydraulic Radius and Area of Multiple Box Culverts.(Chezy Mannings)

(OP)
So
for example you have a CBC and assume flowing full
IE 5-8x4 CBC assuming flowing full
A=8*4=32 sf
∑A= 32+32+32+32+32= 160 sf
P = 4+4+8+8=24 feet
r=5*32/5*24=1.33
assuming n=.011, S=.0025
Q = (1.49/.011)(160)(1.33)^.67*(.0025)^.5= 1311.79 cfs

### RE: Hydraulic Radius and Area of Multiple Box Culverts.(Chezy Mannings)

all fine except I would not expect n=0.011. for conservative sizing design, I would normally use 0.015 which gives you more like 960 cfs

for instance MDOT says 0.013
https://www.michigan.gov/documents/MDOT_MS4_App_91...

precast.org and INDOT says 0.012 to 0.015
http://www.in.gov/indot/design_manual/files/Ch31_2...

### RE: Hydraulic Radius and Area of Multiple Box Culverts.(Chezy Mannings)

(OP)
One other question why wouldn't you use R = 32/5+32/5+32/5+32/5+32/5= 32 hypothetically doesn't each box have a surface? Just curious?

### RE: Hydraulic Radius and Area of Multiple Box Culverts.(Chezy Mannings)

slange: As you already stated: r= A/P = 5*32/5*24 which reduces to r=32/24

The hydraulic radius for a single barrel is the same as the hydraulic radius for the entire multi-barrel structure. Check the equation - you cannot add the radius for each barrel.

Again, the easy solution is to evaluate the flow for a single barrel and multiply by the number of barrels. Keep it simple.

Peter Smart

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

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The Eng-Tips staff will check this out and take appropriate action.

#### Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

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Register now while it's still free!
user
The passage contains a discussion about the application of the Chezy-Manning equation to calculate the flow rate in multiple barrel box culverts. It includes a specific example with calculations and a question about the hydraulic radius.

TYPE: SINGLE_QUESTION_WITH_ANSWER