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  • 1.  Good Reference for CN for LID applications

    Posted 10-12-2015 10:18 AM

    Karen Kabbes P.E., D.WRE, ENV SP, M.ASCE
    Kabbes Engineering Inc
    Barrington IL
    (847) 842-9663

  • 2.  RE: Good Reference for CN for LID applications

    Posted 10-14-2015 07:59 AM

    You might check with the LID committee for obtaining a "Good Reference for CN for LID applications"?

    Conrad Keyes Jr.
    Chair, MPCES & Secr. SDC
    NMSU Emeritus
    Las Cruces, NM 88005

  • 3.  RE: Good Reference for CN for LID applications

    Posted 10-15-2015 07:35 AM

    Ms. Kabbes-

    You may find these references helpful:

    Design Manuals

    Princegeorgescountymd remove preview
    Design Manuals
    "Stormwater Management Design Manual," September 2014 Appendices This version of the County's Stormwater Management Design Manual may be used by designers for new land development projects. The Manual, as printed, has been approved by the Maryland Department of the Environment and submitted to the Prince George's County Council for review and final adoption.
    View this on Princegeorgescountymd >

    Maryland Stormwater Design Manual

    State remove preview
    Maryland Stormwater Design Manual
    View this on State >

    Stephen Crum P.E., M.ASCE
    Macris Hendricks & Glascock, P.A.
    Jefferson MD
    (301) 670-0840 EXT 1019

  • 4.  RE: Good Reference for CN for LID applications

    Posted 10-15-2015 02:34 PM


    We posted a worksheet to account for BMPs (by rainfall runoff deduction) and their impact on CN's on our website as a design tool.


    Note the text about CN Modification tool.  This is all based upon McCuen's Method.

    Michael Buechter P.E., M.ASCE
    Program Manager
    Webster Grvs MO
    (314) 968-9723

  • 5.  RE: Good Reference for CN for LID applications

    Posted 10-15-2015 02:34 PM

    I am not clear on exactly what this person is looking for.


    Elizabeth Fassman provided guidance on CN values for Green Roofs. For many of the LID practices there is no single CN value,

    However, the volume of runoff that is managed by the practices through infiltration can be used to determine the effective CN value for the drainage area managed by the BMP,

    Or a group of BMPs at a catchment or subwatershed scale.


    I described a procedure (attached) for doing this that is adapted from a procedure developed by Dr. Richard McCuen for the Maryland Department of the Environment(MDE).

    MDE has adopted this approach in developing its Environmental Site Design (ESD) approach to stormwater management.


    It should also be noted that many engineers and academics working with LID practices and sustainable design concepts are questioning the validity of continuing to use the NRCS design storm concept because it is so limited and conservative and tends to overdesign the LID practices as illustrated by Dr. Robert Traver of Villanova(attached). These practitioners recommend using continuous simulation models using actual rainfall data to provide a stronger basis for design.


    There is much, much, more to be said about topic and it would make a good topic for a session in a future LID conference.




  • 6.  RE: Good Reference for CN for LID applications

    Posted 10-15-2015 04:12 PM



    NRCS and ASCE have a MOU to address this question and others and the MOU has a completion date of two years.  The work items include Chapter 8,9,10 and 12 of NEH 630.


    Donald E Woodward F ASCE

    This email has been checked for viruses by Avast antivirus software.

  • 7.  RE: Good Reference for CN for LID applications

    Posted 10-15-2015 07:34 AM

    Karen, I have used the following Portland Cement Association document for pervious concrete curve numbers: http://www.rmc-foundation.org/images/PCRC%20Files/Hydrological%20&%20Environmental%20Design/PC_DesignManual.pdf

    Cristiane Surbeck P.E., M.ASCE
    Associate Professor
    University of Mississippi
    University MS
    (662) 915-5473

  • 8.  RE: Good Reference for CN for LID applications

    Posted 10-15-2015 02:34 PM

    You can check out:

    Christianson, R, S. Hutchinson and G. Brown, 2015. Curve Number Estimation Accuracy on Disturbed and Undisturbed Soils, J. Hydrol. Eng..

    The basic conclusion is that for disturbed soils the normal soil mapping is a poor predictor of the disturbed soil. Instead, you should measure the infiltration with a double ring and compute a CN by the method of:

    Chong, S. K., and Teng, T. M.,1986. “Relationship between the runoff curve number and hydrologic soil properties.” J. Hydrol., 84(1–2), 1–7.

    Of course, that isn't much help in designing before disturbance....

    Glenn Brown P.E., D.WRE, F.EWRI, M.ASCE
    Oklahoma State Univ
    Stillwater OK
    (405) 744-8425