Feel like starting a war...
Feel like starting a war...
(OP)
A city reviewer here ask me to do retention calculation by using "fixed parameters" in the rational method formula (...I know...)
As an example, if someone is planning to extend a parking lot, they ask to use a C of 0.5, a Tc of 15 min and an Intensity related to 100-year frequency as "actual conditions".
Then you have to calculate the "real" parameters for the parking lot for the "proposed conditions" (e.g. C = 0.95, Tc = 5 min and I still related to 100-year).
And Voilà! This dumb procedure leads us to a high retention volume - City reviewer is happy.
Am I the only one thinking this is a pretty stupid procedure?!
I feel like using my own common sense and calculate the retention volume required based on a procedure that makes sense - then arguing with the City reviewer.
As an example, if someone is planning to extend a parking lot, they ask to use a C of 0.5, a Tc of 15 min and an Intensity related to 100-year frequency as "actual conditions".
Then you have to calculate the "real" parameters for the parking lot for the "proposed conditions" (e.g. C = 0.95, Tc = 5 min and I still related to 100-year).
And Voilà! This dumb procedure leads us to a high retention volume - City reviewer is happy.
Am I the only one thinking this is a pretty stupid procedure?!
I feel like using my own common sense and calculate the retention volume required based on a procedure that makes sense - then arguing with the City reviewer.





RE: Feel like starting a war...
RE: Feel like starting a war...
100k population city.
That's the parameters to use - that's it that's all.
RE: Feel like starting a war...
RE: Feel like starting a war...
the city can require retention based on your shoe size, it's their drainage ordinance.
RE: Feel like starting a war...
Bogus
RE: Feel like starting a war...
RE: Feel like starting a war...
I think anyone that has completed and/or used the rational method for a project of similar calibre would sympathize with your frustrations.
I have yet to see a municipality that only accepts the rational method for hydrology. Is it possible to use a more accurate approach? (i.e. modelling with HydroCAD, SWMM, etc)
RE: Feel like starting a war...
Hopefully not too far from the Modified Rational Method results...
RE: Feel like starting a war...
1. predesign to the reviewers "standards",
2. size a detention facility,
3. show the costs to the client.
Then he/she will be onboard for the fight and will anticipate and appreciate your time and expenses.
If you are going to fight, track who has the general NPDES discharge permit from the EPA for your area. They really have the final say on stormwater regulations, since they hold the permit from the EPA. Look on the EPA website to find what agency holds your areas NPDES Stormwater Discharge permit. Then find their approved stormwater manuals. Although towns can still write ordinance that allows them to adopt something more stringent than the EPA, I don't think this is the case here. The Rational method for sizing detention is not accepted by any NPDES permit that I have seen.
Use a hydrologic model/method that is accepted by the regulatory Stormwater Manual under the NPDES permit for flow control. Use it size the detention and submit it to the reviewer along with all the data, and the Section of the NPDES approved Stormwater Manual that says you can use it. If the review refuses it, forward his correspondance and comments to the agency holding the NPDES permit.
RE: Feel like starting a war...
RE: Feel like starting a war...
I will do a cost analysis based on both "procedures" (City Reviewer onboard).
Thanks
RE: Feel like starting a war...
RE: Feel like starting a war...
The guy reviewing isn't an hydrologist (no wonder) and I can't see myself arguing about the fact that the Modified Rational Method shouldn't be applied to retention volume calculation.
Lost the fight
RE: Feel like starting a war...
For what it's worth, a lot of the municipalities in my area have moved from regulations that ask you to "match existing conditions" to regs that make you "match an undeveloped condition," where they specify the CN you've got to pretend was on your site before you got there. Sounds a bit like what you ran into, outside the Rational headaches.
One option you may have, if you're trying to keep your volumes down, is the Dekalb Rational Method. I don't use it anymore, but City of Atlanta used to accept it, and we would sometimes go with a Dekalb analysis on urbanized projects at my last company.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: Feel like starting a war...
I know that we have to follow what the reviewer ask but there's a limit... Mine is when someone tells me to "calculate the required volume with Q=CIA".
This is leading to over-design retetion facilities.
Over-designed + based on a 100-year flood. I mean it's a parking lot...
RE: Feel like starting a war...