I've been tasked w/ routing analysis of 40+ acre urban watershed...
I've been tasked w/ routing analysis of 40+ acre urban watershed...
(OP)
and associated storm sewer using the Rational Method. The purpose of the analysis is to identify any deficiencies in the sizing of the storm sewer. The system consists of about 25 subcatchments/inlets and is quite dendritic in nature.
I understand the Rational Method for smaller, simpler systems, but I am having trouble wrapping my mind around how tc and Q are routed through the system. I've got lots of nodes and lots of pipe.
I've tried modeling the system in UDSEWER, but it is choking on a couple of the larger subcatchments at outer reaches of the system. It's throwing a "backwater solver" error at me.
Intuitively, it seems like the Rational Method is not the appropriate approach to this situation, but it's been what I've been asked to do.
I'm seeking any and all guidance on this matter and appreciate any help. Either in formulating (and justifying) a better way to attack this... or in attacking it with the Rational Method. My H&H is a bit rusty and this is a tall order for something to start warming up that though process again.
I understand the Rational Method for smaller, simpler systems, but I am having trouble wrapping my mind around how tc and Q are routed through the system. I've got lots of nodes and lots of pipe.
I've tried modeling the system in UDSEWER, but it is choking on a couple of the larger subcatchments at outer reaches of the system. It's throwing a "backwater solver" error at me.
Intuitively, it seems like the Rational Method is not the appropriate approach to this situation, but it's been what I've been asked to do.
I'm seeking any and all guidance on this matter and appreciate any help. Either in formulating (and justifying) a better way to attack this... or in attacking it with the Rational Method. My H&H is a bit rusty and this is a tall order for something to start warming up that though process again.





RE: I've been tasked w/ routing analysis of 40+ acre urban watershed...
RE: I've been tasked w/ routing analysis of 40+ acre urban watershed...
For 40 acres, the Rational Method may be okay for your analysis.
StormCAD will conduct the Rational analysis of your system. However, I don't know if they still offer trial software or not.
I believe that Hydraflow (now incorporated with AutoCAD packages) will also analyze your system.
Otherwise, you can also calculate the HGL of the system by hand. Your Tc's will consist of any flow in the drainage areas plus your pipe flow times. The drainage design manual for the City of Fort Worth, TX has a spreadsheet example of how to analyze a SD network using Rational.
Good luck!
RE: I've been tasked w/ routing analysis of 40+ acre urban watershed...
You can develop a spreadsheet from it. The spreadsheet probably only takes about 10 to 20 hours to develop.
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RE: I've been tasked w/ routing analysis of 40+ acre urban watershed...
I just don't believe that you can't do the Rational Method with SWMM.
RE: I've been tasked w/ routing analysis of 40+ acre urban watershed...
Make sense?
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