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  • 1.  Storm Water Control Measures

    Posted 06-10-2014 04:10 PM

    There is a push to develop stormwater control measures that infiltrate water.  However, too often these infiltration practices do not adequately infiltrate water from day 1, including a rain garden placed next door to my sister-in-law's house.  We need a technique to determine infiltration rates at the planning stage, before designs have been developed.  What would that be?

    John Gulliver
    Minneapolis MN
    (612) 627-4600

  • 2.  RE: Storm Water Control Measures

    Posted 06-11-2014 09:50 AM

    There are storm water low impact development (LID) practices that utilize an underdrain system for when the soil is saturated.  This underdrain is typically placed below engineered soils.  These LID Best Management Practices (BMPs) would not require an in-depth review of the existing soils during planning/design. 

    However, based upon your question, it appears that you are referring to LID practices that do not have an underdrain system or engineered soils.  In that case, during the planning of those types of LID BMPs, I typically use the NRCS Web Soil Survey (WSS) as a resource for general soil infiltration rates.  The WSS provides a good overall picture of the soil types on a site.  For instance, if the soil belongs to Hydrologic Soils Group is "A", the infiltration rate is much higher than a soil belonging to Hydrologic Soils Group "D".  When using the WSS, please be aware of age of the data and level of detail provided within a specific project's WSS report.

    In my opinion, the best resource for obtaining an infiltration rate at a specific location is to perform a soil infiltration test.  This test can be fairly simple and the NRCS has a pretty good field method testing protocol.  There is also an ASTM method for testing soil infiltration rates (ASTM D3385).

    Hope this helps.

    Abbi Dorn P.E., M.ASCE
    Water Resources Mananger
    Ackerman-Estvold Engineering and Management Consulting Inc.
    Minot ND

  • 3.  RE: Storm Water Control Measures

    Posted 06-12-2014 09:47 AM
    The approach we advocate for is consistent robust design that is less sensitive to deviations from assumed conditions.  

    One such approach would be to include up-turned elbows on the under drains that can be removed if the native soils don't infiltrate well. The same thing can be achieved with a manual valve on the under drain system.  Lastly the most advanced approach is to control under drains in real-time using light weight internet-of-things based monitoring and control systems as we have done  as a part of the WERF research "Transforming Our Cities: High Performance Green Infrastructure" in among other places Omaha, NE and Gwinnett County, GA. In the case of controlled systems whether a system is flow through or retain on site is a matter of software.

    (see: http://www.werf.org/a/ka/Search/ResearchProfile.aspx?ReportId=INFR1R11) and www.optirtc.com

    Marcus Quigley, P.E., D.WRE, M.ASCE
    Geosyntec Consultants
    Brookline MA
    (617) 735-9323

  • 4.  RE: Storm Water Control Measures

    Posted 06-18-2014 04:58 PM
    I have noticed an increased interest in using up-turned elbows on the underdrain outlet and I am trying to understand the advantages vs. just elevating the underdrain pipe.  The option to adjust the retention height after the BMP is built is the first explanation of an advantage that I have heard so far.  I have noticed that fine sediment that accumulates below the underdrain tends to never leave, so possibly another advantage is that keeping the underdrain near the bottom of the drainage rock layer and using the upturned elbow to control the detention depth allows the full depth of the rock layer to get routine flushing and thus maintain the design storage volume.   Is anyone aware of any other reasons why an upturned elbow is preferable to the elevated underdrain?  Have people been designing these such that the bioretention soil is partially submerged?  If so, maybe there is an advantage of getting more moisture to the plant roots, possibly increasing transpiration losses, and possibly increasing evaporation by connecting the retained pool to the capillary recharge at the upper depths of soil.

    James Nabong P.E., M.ASCE
    Associate Engineer
    City of San Diego
    San Diego CA

  • 5.  RE: Storm Water Control Measures

    Posted 06-24-2014 09:18 AM

    Sean O'Neill EIT, A.M.ASCE
    Engineer I
    Hyattsville MD

    The upturned underdrain in a bioretention cell can be used to used to create an anaerobic zone, thereby promoting the removal of nitrate from the infiltrated stormwater via denitrification.  Check out the research coming out of Allen Davis' lab at the University of Maryland, or Bill Hunt from NC State.

  • 6.  RE: Storm Water Control Measures

    Posted 06-18-2014 04:58 PM
    Building upon what Abbi has mentioned, another good resource for testing measure to determine infiltration rates during the planning process would be the Western Washington Stormwater Management Manual. In the 2005 version of the manual Volume III Chapeter 3 Section 3.3.4 outlines a simplified approach to infiltration design, with later section going into more detailed design information. The NRCS is a good resource and I use it for a starting point on all my projects, but I've found that the best resource for soils information is to go out and dig a hole so you can see what the exact soil conditions are. Hope this helps.

    Daniel Howe EIT, A.M.ASCE
    Project Engineer
    Cascade Surveying & Engineering Inc.
    Arlington WA