The Best Urban BMP in the Bay Awards contest (BUBBAs) recognizes the best practices and programs being implemented in the urban environment across the Chesapeake Bay watershed. The BUBBAs shine a light on innovators in the field who are using new and creative techniques to treat runoff and restore local watersheds.

The Vernal Pool (A Different Approach to “Fixing” Drainage) was chosen by jurors as one of the 3 best projects in the Residential category. The category recognizes exceptional stormwater practices installed on a residential property. The project description follows below.

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Welspryng was retained by the homeowner in the Spring of 2019 to address drainage issues on their property. The homeowner’s lawn service was making a mess of large wet areas of turf in the backyard. A flat area held surface water, implying a grading problem, but test pits showed groundwater nearly at the surface, indicating a seasonally high water table. The homeowner was fully onboard with getting rid of some lawn and creating habitat, but with the site being so wet in the spring and then drying out in the summer, it would be challenging to implement a typical rain garden plant palette.

The proposed solution: Make it wetter.

Vernal pools are small, shallow, ephemeral water bodies. They fill each spring by rain and snow melt and are drier for a period of time during the summer. They support several species of animals that require these temporary wetland habitats. Approaching the drainage “problem” as an opportunity, additional runoff was directed towards the project area. The goal was to increase the hydro-period (i.e., the timing and duration of inundation) to extend the seasonal surface ponding and increase the sub-surface moisture level during the drier months. This permitted the use of a wetter community of plants that could better tolerate the seasonal ponding and fluctuations in water level, in essence creating a vernal pool.

To that end, three downspouts (975 square feet of roof area representing 20% of site impervious) were piped from the house to an 18-inch catch basin modified to filter out fine and coarse debris. The initial flush passes through the filter then enters a series of sub-surface detention chambers (480 gallons), placed adjacent to the ponding area and embedded in pea gravel. Runoff that is detained in the perforated chambers slowly percolates into the sub-grade under the ponding area through a sand-filled trench to supplement soil moisture and irrigate plants from the bottom up during drier periods. The project functions similar to a submerged gravel wetland in this respect, with the chambers providing the detention volume that is normally created by the voids in the gravel. The advantage of this innovative approach is that it eliminates the need to excavate and dispose of a large volume of soil and replace it with tons of imported gravel during construction.

When the chambers are full, gravity forces excess water up and out of the top of the catch basin to fill the ponding area. The basin functions like a conventional rain garden, with the ponding water infiltrating directly to the plant roots. An overflow at the far end filters water through a vegetated swale along the rear property line before reaching a county storm drain inlet in a nearby yard.

A unique approach to planting

Two dumpsters of sod were removed and 1,500 square feet of the back yard were planted with a native plant community based palette. Using data from USDA, Maryland DNR, NatureServe, the U.S. National Vegetation Classification (USNVC), VegBank and the Maryland Plant Atlas, Welspryng has developed a reference database for generating plant palettes based on natural plant community analogs that are likely to occur in Anne Arundel County. Most accepted definitions of a plant community include four central ideas: 1) uniform physical structure, 2) uniform habitat, 3) shared floristic composition, and 4) recurring distribution across a landscape. An advantage of this approach is that it can produce plant species palettes that are intrinsically tailored to the anticipated site conditions.

The USNVC is a standard process for identifying and cataloging plant communities. In this case, a list of species found in plots from CEGL006499 – Coastal Plain / Outer Piedmont Seepage Bog was cross-referenced with plant records for Anne Arundel County from the Maryland Plant Atlas to create a reference palette that informed plant species selections. This method is distinctly different from the conventional practice of assembling palettes per the subjective preferences of the designers, which commonly result in arbitrary collections of native plant species.

Many popular natives were present in the reference palette, such as Magnolia virginiana, Clethra alnifolia, Aster novi-belgii, Solidago rugosa, Juncus effusus and Carex crinita. However there were also many less commonly used natives in the reference palette which are commercially available but otherwise may not have been considered, such as Vaccinium corymbosum, Solidago fistulosa, Rhexia virginica, Ludwigia alternifolia, Triadenum virginicum, Woodwardia areolata, Dichanthelium clandestinum, Panicum anceps, Juncus canadensis and Eleocharis obtusa. The palette that resulted from this unique process features a more diverse selection of plants that looks more like a native habitat that may be found locally.

Lastly, it can’t go without saying that having the full support of the client made a huge difference in the success of this project. A simple drainage project was reimagined to also detain/retain impervious runoff, express the beauty of a native plant community and establish habitat. During the first growing season there were monarch butterflies, a ton of dragonflies and tadpoles, believed to be wood frogs, were observed in the vernal pool. What would perhaps have otherwise been addressed with a conventional, one-dimensional drainage solution by some has instead been allowed to fulfill its potential as an extraordinary stewardship opportunity.

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Presented by the Chesapeake Stormwater Network, the virtual awards ceremony for the 5^th edition of the Best Urban BMP in the Bay Awards will be held on March 10^th from 3-5pm. The 1^st place winner in each category will be announced during the 10^th edition of the Bay-wide Stormwater Retreat and the ceremony will officially kick off the “people’s choice” internet voting to determine who will take home the title of the overall BUBBA.