Rain gardens are created to collect storm water runoff from house roofs, parking lots and other places. By catching this dirty runoff the garden can help protect streams and lakes from pollutants like lawn fertilizers and pesticides, fluids that leak from cars, and other harmful substances that wash off roofs and paved areas. Rain gardens also filter water and recharge the local aquifer while the plantings in a rain garden support pollinators, birds, butterflies and many useful insects.
By definition a rain garden is not a pond. Standing water will come and go. Chosen plants will tolerate a period of standing water, but they will also be happy when the garden is dry.
This summer I thought of my garden as a rain garden. Of course my garden gains that title by being flooded. Over 30 days we got 17 inches of rain. Because my garden has heavy clay soil that does not drain well, and a high water table the result is flooding. Even though I don’t have an official rain garden I began to wonder if there were any local rain gardens.
As I have been working with other volunteers to plant a meadow pollinator garden in front of the new John Zon Community Center on Pleasant Street, I knew a rain garden had been planted in back of the building. The design of that garden gives it two halves, both similarly planted with plants that do not mind standing in water for a day or three.
The structure of a rain garden is quite simple. It is as wide and long as a site allows. The rules for the depth are fairly consistent. The University of Massachusetts Extension Service gives excellent instructions about creating a rain garden to catch runoff from your house roof.
“If the yard is fairly level, you can just dig out the bowl to the proper depth, which is 6 inches deep (other sites will suggest more depth and a gravel layer of a few inches on the bottom), or a couple of inches deeper if mulch will be used. If the yard is sloped, you may need to construct a small berm (mound) at the down-slope side of the garden to prevent the soil from washing away after a storm. Use the soil that was removed from the upslope side of the garden and add it to the down-slope side. The bottom of the garden should be fairly level to maintain the storage area inside the garden. Slope the edges of the garden, but do not make them too steep. Steep slopes tend to erode easily. Mulch or a ground cover will help to stabilize the soils.” For full information https://ag.umass.edu/landscape/fact-sheets/rain-gardens-way-to-improve-water-quality
Another different sort of rain garden is at the foot of the parking lot between Chapman and School streets. That parking lot slants and rain water runs north, away from Main Street At the end of the parking lot is a curb, but cuts have been made so that water can run into a shallow ditch that acts as a rain garden. Water tolerant plants like joe pye weed, coneflowers and black eyed susans (weeds too) help absorb the runoff. A sign has been placed at the other end of the parking lot to explain the benefits of the tree strip and the trees, as well as the rain garden.
Those who pass the Franklin County Jail will have noticed what I used to call the swamp with cattails and other water loving plants in the area below the jail buildings. That area has changed since the new jail with its big parking lot was built. Now the swamp is confined behind a fence and piping has been installed. I spoke to Joe Fagan, Head of Maintenance, at the jail about the changes. He explained that there are catchment areas for runoff in the parking lot that allows sediment to settle. The water then continues through piping to the retention pond. Periodically that sediment is power vacuumed because eventually sediment sent to the pond would fill it, making it useless. There are also pipes that carry runoff from the jail roof to the retention pond.
In addition large pipes at the south end of the pond allow for overflow if there is really heavy rain. Preventing erosion is an important part of the water management system.
Last week I went to UMass to visit the new prize-winning John W. Olver Design Building for Landscape Architecture and Regional Planning. The building was designed by the Boston architectural firm Leers Weinzapfel.
The landscaping around the building was designed by Stimson Studio. Do not look for a neat lawn. A lush arrangement of trees, shrubs, and grasses surround the building to such an extent that it is just about impossible to see the shaping of the land in ways that manage rainfall and runoff.
The building has parking lots on two sides and sits on a slope. There is a catch basin at the low corner of the parking lot to the north of the building that pipes water into a shallow basin to the west of the building. Rainwater is collected on the roof of the Design Building and channeled off of the east side of the building into two sloped, linear channels called bioswales. The bioswales collect, cleanse, and infiltrate storm water naturally onsite, as opposed to conventional underground sewer systems. The sides and bottom of the bioswales are lined with native vegetation, soil, and rock to filter stormwater and remove harmful pollutants from surface runoff. For more information about this garden https://www.ecolandscaping.org/02/landscape-design/a-walk-through-the-woods/.
We cannot always count on having adequate rainfall. Rain gardens provide a water conservation technique that recharges our local aquifer, helps protect the quality of our streams and rivers, and beautifies an area of our domestic landscape.
Between the Rows August 25, 2018