ASCE Collaborate has switched to a new platform called Thrive.
We appreciate your patience during the transition. What is Thrive? View more information here. Any questions or feedback? Please contact [email protected]. View Video Tutorials here.
An ASCE membership login is required to participate in discussion forums and ASCE Mentor Match.
I can't remember where I heard it, but at the Congress I heard a brief mention about somebody or some task committee working on/interested in developing curve numbers for either green infrastructure or low impact development. Did I hear that correctly? Is there a group working on this? If so please let me know, and maybe provide a very brief overview of the work that is being done. Thank you!
Nashville's manual has good explanation of how they calculate adjusted curve numbers for retained volume (see section 3.2.5) https://www.nashville.gov/Portals/0/SiteContent/WaterServices/Stormwater/docs/SWMM/2016/Vol5LID/2016_FullVol5LIDManual.pdf
I don't know about that study but here is some relevant information. Several years ago I Developed equations and charts to evaluate allowable Curve Number reduction of impervious and pervious areas due to implementation of various LID techniques. Here is the reference to it (it should be available online):
Zomorodi, K. 2004 “Curve Number and Groundwater Recharge Credits for LID Facilities in New Jersey”, Proceedings of the Conference “Putting the LID on Stormwater Management!” The Inn and Conference Center- Marriott, College Park, Maryland, September 21-23, 2004. Proceedings published electronically on a CD, to reach this paper on the CD first select “Program and BIOS” and then “Read BIOS and papers”. pp. 508-514.
What are curve numbers?
Curve Numbers are approximations of interception and infiltration based upon land use and soil characteristics. It's a popular rainfall-runoff methodology in the United States. The methodology was developed by the US Department of Agriculture's Natural Resource Conservation Service (though when developed it was the Soil Conservation Service or SCS). The paper which outlines the methodology and is still in use today is TR-55 (Technical Release 55) and can be found here: TR-55 Online. It's a little more difficult to implement outside of the United States as some of the input data is developed by the NRCS (Hydrologic Soil Groups being the one I'm thinking of right now).
Hope this helps!
I suppose that there may be a number of folks working on this.
One approach that you may be aware of is the procedure documented by the Maryland Department o the Environment (MDE) in their ESD manual. This approach is based on formulas developed by Dr. Rick McCuen back in 1983 when we were developing the Maryland Stds and Specs for design of infiltration practices. I later adapted the approach in 2000 to estimate the effective CN value when volume based GI practices are used for LID design. I documented this approach in the Queen Anne's County, LID/ESD design manual and also the Charles County LID/ESD design manual. MDE liked the approach and adopted it in their ESD guidance. The way I do it is slightly different from MDE. I just solve the quadratic equation for an adjusted CN based on McCuen's equations while MDE prefers to use tables and interpolation, which I find to be cumbersome and less accurate.
I can provide a copy of the documentation to supplement the description provided in the MDE ESD manual.
Michael Clar, P.E., DWRE
Chair, LID Committee
Ellicott City, MD 21042
Would you be willing to post for all of us the documentation supplement to the MDE ESD manual you mentioned in your reply?
I was at a state stormwater conference in March were there was discussion on changes to the SCS method. Here are some notes I took from the conference (nothing specific regarding CNs and green infrastructure though):
Perhaps downloading the WinTR-55 and playing around with the CNs will answer your question...???
WinTR-55 Watershed Hydrology | NRCS
I am part of a Standards Committee working on the ASCE Manual "Design, Construction, and Maintenance of Permeable Interlocking Concrete Pavement". Attached is DRAFT text on defining CN for this type of pavement system; any feedback is appreciated.