Recently, we noticed that the most popular article on the Stormwater Web site
was “Rain Gardens Reign” from the May 2008 issue. This article included
information on the Mt. Airy Rain Catchers project that Tetra Tech is
implementing for USEPA’s Office of Research and Development’s Sustainable
Environments Branch. In the process of planning and installing 52 residential
site rain gardens last year and 14 so far this year, we are finding that
this is a different type of work than typical stormwater management systems.
First, some background. Our project is a research study with a standard size
and design for all rain gardens. We developed a conceptual design with
performance and construction specifications, but did not prepare plans and
specifications for each site. Each rain garden is about 150 square feet in
area with an 8- to 10-inch ponding depth, amended onsite soils to at least 18
inches deep, and underdrains. The project is like a design-build approach in
that the contractor installing the gardens is working directly for Tetra
Tech.
Here are some ideas that may be helpful to anyone thinking about installing
rain gardens. They aren’t the final word, but are meant to generate
discussion.
* Each garden site is someone’s yard, making it critical that we work with the
homeowner on the location and the “look” of each garden. We spend time with the
owners in an initial meeting and make time to talk to them in subsequent visits
so that we can explain the work and learn of any concerns early. We have found
that it pays off to spend the extra time up front to establish a good
relationship.
*
Manual excavation would be too time-consuming, but standard excavation
equipment can be too large and heavy to work in backyards. We have found that
gas-powered sod cutters, mini-backhoes, and small excavators are well suited to
our scale of work. Our goal is to complete each garden in less than a day to
minimize disruption to the homeowner and to keep costs down.
* Soil disposal was something we underestimated at first. This will depend on
the depth and method of soil amendment, but sometimes there is more soil
generated than can be incorporated into the berm. Consider having a plan
for soil hauling and disposal.
* Documentation is especially important on this research project so
that we generate useful information for EPA, but also to keep our work organized
and on schedule. Maps, tables, and field data sheets were developed to collect
information; the forms are filed and used for data entry in the office. We
considered using GPS-enabled data collection devices in the field, but decided
to keep it simple. For a larger project, they might work well.
Because we are working on private property and residential areas, our field
workers identify themselves with uniforms and project t-shirts, vehicle
placards, and yard signs. All of our public materials include the project logo
and the name “Mt. Airy Rain Catchers” (see www.mtairyraincatchers.org). We are using native plants for
these gardens and minimal fertilizer. The homeowners like the plants, but we’ve
found that the natives vs. exotic species issue can be more controversial than
expected.
We are tracking survival of species by garden and by species—it takes time
and plant knowledge to survey them, but it’s proving to be helpful.
That’s all for now. What are your experiences, ideas, comments?