Rational method application
Rational method application
(OP)
Hello everyone. I am wondering about the rational method applicability. For less than 160ac & retention facilities...
But for more than 160ac. and detention facilities use HEC-1 modeling... ok.
I have seen the rational method where instead of intensity (in/hr), only inches are used. What is the difference of this variation?
What is SCS?
Thank you,
EF
But for more than 160ac. and detention facilities use HEC-1 modeling... ok.
I have seen the rational method where instead of intensity (in/hr), only inches are used. What is the difference of this variation?
What is SCS?
Thank you,
EF





RE: Rational method application
Inches of runoff can't be used in the Rational Method, so that instance you saw was wrong. Rational Method uses intensity to get a peak flow, only.
SCS = Soil Conservation Service, now called the National Resource Conservation Service. They created TR20 and TR55, which is what you should, by and large be using for anything between 10 acres and 1.5 sq mile. TR55 software is free at NRCS website, it is easy to use, if you've had hydrology coursework.
Over 1.5 sq mi, use a statistical flood model.
Remember: The Chinese ideogram for “crisis” is comprised of the characters for “danger” and “opportunity.”
-Steve
RE: Rational method application
There are some quick methods using rational such as assuming a triangular hydrograph using rational peak as max. peak at time equal to time of concentration. This method falls apart for any drainage basin greater than just a few acres.
I recommend using TR-55 or similar method of generating a hydrogragh for your particular design.
regards
KEW
RE: Rational method application
Secondly, what should be used for larger catchments? Am I right in thinking that there are no generic methods and that the specific water course flows should be investigated?
With thanks to all,
Simon
RE: Rational method application
For larger areas, use a statistical model. There is one for PA, USA called PSU-4. It is available here:
http://www.dot.state.pa.us/hh/
Remember: The Chinese ideogram for “crisis” is comprised of the characters for “danger” and “opportunity.”
-Steve