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  • 1.  SWMM vs National Calculator?

    Posted 07-24-2014 07:21 AM
    What are folks' impressions regarding benefits vs drawbacks of using full SWMM vs the new EPA National Calculator? My general impression is that since the National Calculator incorporates a somewhat simplified version of SWMM, detailed design is limited... but for overall site planning it is probably OK and very handy(?) to have the automation of the National Calculator (ie links to the National Weather Service, soils and topography databases, etc.). Thanks in advance for your thoughts. ------------------------------------------- Elizabeth Fassman Ph.D., A.M.ASCE Stevens Institute of Technology Hoboken NJ (201)216-3549 -------------------------------------------

  • 2.  RE: SWMM vs National Calculator?

    Posted 07-25-2014 09:40 AM
    I agree that the detailed design is limited.  The rainfall contribution by rainfall percentile is very handy for sizing BMP's that are stormwater rate based.  I used the EPA calculator on a project located in New York that didn't meet the 90% rainfall percentile for published code of 1.3 inches.  The calculator value for the 75% rainfall percentile was 0.7 inches.  The codes didn't didn't list anything less than 90% rainfall percentile.  On a stormwater retrofit project, I found the EPA calculator very user friendly. 

    Christopher Klingener P.E.,  M.ASCE
    Sr. Civil Engineer
    Waldron Engineering and Construction Inc.
    Exeter NH

  • 3.  RE: SWMM vs National Calculator?

    Posted 07-25-2014 09:41 AM
    We have found the same thing to be true.   The EPA National Stormwater Calculator is an excellent program (especially with its soil and rainfall information).   It is great for conceptual plans.   However, for detailed design, it is very limited.

    A co-worker and I will be doing a presentation at StormCon in a couple of weeks regarding results using the EPA National Stormwater Calculator, the proposed State of Tennessee "Runoff Reduction Analysis Tool," and the City of Chattanooga LID calculator tool.   The EPA program uses the SWMM engine, Tennessee uses the Kostiakov-Lewis method, and Chattanooga uses the "Small Storm Hydrology Method" by Dr. Robert Pitt.   The different methods yield similar, but different results (as one would expect).

    I look forward to seeing comments from others about their experience with the EPA National Stormwater Calculator.

    Tony Kinder P.E., P.L.S., M.ASCE
    Engineering Manager
    City of Chattanooga, Tennessee

  • 4.  RE: SWMM vs National Calculator?

    Posted 07-25-2014 10:06 PM
    Elizabeth See the National Stormwater Calculator User's Guide by Lew Rossman at http://nepis.epa.gov/Adobe/PDF/P100GOQX.pdf SWMM remains the computational engine that the Calculator uses to concentrate on greener BMPs. If he has not retired, Rossman.Lewis@... or Hantush.Mohamed@... are the leading EPA experts on SWMM and the Calculator. As an early advisor to them and the National Risk Mgt Research Lab dating back to the 1990s on scaling SWMM to incorporate BMPs (Best Mgt Practices) they have been very effective over the years and would be outstanding research partners if you can get on their schedules. Both have outstanding records of service to ASCE. During my mid 1990s tenure as Editor-in-chief of J. Environmental Engineering Lew was one of our best associate editors. Mohamed is currently co-editor of J. Hydrologic Engineering for Surface Water and a mainstay of the Task Committee drafting a Manual of Practice for Total Max Daily Load analysis. Congratulations on winning the Horner Award and your service on the EWRI Committee on Low Impact Development. My former faculty advisor Wes Eckenfelder displayed his Horner plaque with pride to illustrate the great company you are in. ------------------------------------------- Steven McCutcheon Ph.D., P.E., D.WRE, F.EWRI, M.ASCE Nat Expert, Sr Envir Engr Athens GA -------------------------------------------