Roadway Stormwater Capacity

[Nick023]

I am having trouble finding the correct method to calculate the stormwater capacity a curbed road can have without overtopping the curb. The roadway is 26' face to face of curb with a 2% straight crown.

All I can find is information on calculating capacity up to the top of the crown on one side of the road. In my situation, I am looking for the capacity of the road in the situation where the crown of the roadway is submerged and the flow is allowed to reach the top of the curb.

Any help would be great.

Thanks,
Nick

 

[cvg]

how about just using Manning's equation?

 

[Nick023]

How is this possible when I essentially have 3 geometric shapes making up the cross section.
(1) Triangle area from the top of the crown to the face of the curb on the left side of the roadway.

(2) Triangle area from the top of the crown to the face of the curb on the right side of the roadway.

(3) Rectangle area across the entire roadway from the top of the crown to the top of the curb.

I can calculate (1) and (2) using Q=0.56(Z/n)*s^(1/2)*d^(8/3) from mannings and add the capacities together but how do I calculate the capacity for area (3)?

 

[cvg]

mannings can be used for any shape channel, even irregular channels.

 

[TerryScan]

How tall is the curb?

 

[civilperson]

Assume two triangles of 0.26' height up to the crown of the road and a rectangle 26'x 0.24' above the crown for cross-section area. Calculate flow Q, at a minimum slope of 0.5% and then at each integer per cent slope and graph for a reusable flow characteristic for roadway section flowing full.

 

[cvg]

try the calculator

http://www.lmnoeng.com/manning.htm

 

[queque]

Sketches of this problem and solution would be helpful.

 

[francesca]

See section 4-2 of the Nashville Stormwater Manual:

http://www.nashville.gov/stormwater/docs/pdfs/stw/vol2/swmanual08_vol2_chapter4.pdf

and the nomograph on page 4-15 has a sketch.

 

[Nick023]

Thanks for all the help... I created a simple spreadsheet that I can use to quickly adjust the characteristics of the road and find the resulting capacity to the top of the curb. (See the attached image)