Stormwater Symantics

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    Mike G

    Is anyone aware of an attempt to consolidate terminolgy used to define stormwater infrastructure?
    Specifically I am refering to Rain Gardens and Bio-Infiltration/Detention Basins. Has eny one else seen this difference in design terminolgy around the country. I know the Maryland documents are the standard in use today however I find a few things confusing. Maybe this is because the vast majority of projects I have seen have been efficently designed by engineers.

    So the traditional ‘rain garden’ is a shallow depression and depth is limited by how quickly water can infiltrate in a short period of time. They utilized a more simple soil profile, rely on native plants to define soil structure and increase infiltration.

    Bio-Infiltration basins utilize an engineered soil profile (mostly sand) to store water while infiltration or detention occurs. Native plants do not influence soil aggragation or infiltration (maybe?).

    In my area: engineers seem to design the vast majority of alternative stormwater systems, they only use the term ‘rain garden’, All these systems use the engineered profile.

    I don’t think the terminolgy is as important as much as the real value of plants and native soils are. Any thoughts?

    Andrew Garulay, RLA

    I’ve wondered this myself. We used to simply call them retention ponds. I’ll ask at work, but I think it is a qualitative thing rather than a quantitative one. The term bioretention pond seems to crop up more in front of the regional regulatory authority here and rain garden seems to be the term of choice at the local level. However, the regional authority is generally looking at bigger projects that result in larger retaining areas which may cross some kind of definition threshold that I don’t know about.

    Lawrence Greene

    To add my two cents:
    In Massachusetts, the rain gardens are designed as a pre-treatment unit to treat storm-water before it is infiltrated or discharged.
    Only during the growing season will the plants aid in the absorption of nitrogen, and phosphorous.

    The layered soil profile within the bottom of the rain garden contributes the treatment of the storm water.

    All the soils within the rain garden are imported.
    The growing media is amended with wood chips and leaf compost and below that is a tiered system of sand and crushed stone of varying sizes. This soil profile is sized per the volume of runoff that needs to be treated.

    Andrew Garulay, RLA

    Are you getting different information as to what a “bioretention pond” is here in MA?

    David J. Chirico

    I’m not sure if it will be the same across the country, but the Virginia Department of Conservation and Recreation’s Stormwater Manual has just undergone a massive overhaul in how a site is managed for stormwater. New definitions, new requirements and new calculations across the board. I’m not exactly sure when this will hit, but I believe it will be sometime this year.

    Apparently it will significantly change the way we can plan a site.

    Geoffrey Campbell

    I can only speak to what the Maryland Stormwater Design manual states, but most of these BMP’s/LID Devices/Enivornmental Site Design facilities, are conceptually the same thing with minor differences in soil profile, flow-splitting requirements and drainage area. Raingardens traditionally were for residentail or small-scale applications, and didn’t require over-flow conveyance (although now MDE states that over -flow is required). Bio-filters/Bio-retention facilities were for larger drainage areas and utilized engineered soil profiles with overflow conveyance (underdrain perf. pvc, and elevated control structure, flow-splitters). Also similar are micro-bio-retention facilities, bio-topes, bio-swales (linear applications), landscape infiltration facilities …etc. None of the above mentioned facilities were credited with quantitave management until very recently. Marylands new reg’s look at swm more as a whole instead of quantitative vs. qualititave control. And like David said it drastically changes the way site layout is approached, in my opinion very beneficial to opportunistic LA’s. Bottom line – lots of terms are used that mean virtually the same thing depending on the review agency you’re dealing with and their definitions.

    Mike G

    Is anyone aware of any exceptionally designed, well documented, and public stormwater management projects that completely, or largely, utilize native soils? (Firms, web-resources, documents, etc.)

    I’m trying to get a better understanding of how we can design and construct green infrastructure more closely modeled by ecological systems and just, if not more important, cheaper. Engineered soil profiles are predictible and compact by way more costly. Utilizing on-site soils and existing conditions require more design hours (fees) but can result in less construction costs. In many areas where I see their construction needed, or mandated, surface area is available however only engineered profiles are considerd.

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