BACKGROUND

The City of Madison has recently finished constructing its second rain garden street in conjunction with a street reconstruction project. The first such project, along Adams Street, has been very popular and well received.

The Adams Street design, due mostly to the unique topography of the area, required an extensive storm pipe network. Underdrains and overflow pipes were installed in each of the gardens. Stormwater gets into the gardens through catch basins, which requires the gardens to be fairly deep. This was one negative aspect of this first design.

For the Eton Ridge Neighborhood, a simple curb casting that has a 4-inch pvc pipe connection is used to direct water into the gardens, and no under-drains or overflow pipes are used. The criteria for placing a rain garden included sites where the overflow will go directly back into the gutter (and not in the direction of the house), adequate distance (10 feet minimum) from trees, and then only if the homeowners wanted them and were willing to pay 25% of the total cost of the rain garden. The new design allows for a depth of about 12 inches at most. Each potential site also required a full 15 feet of length for a rain garden to be considered.

Like Adams Street, involvement in the rain garden program continues to be completely voluntary for the residents. There are 15 households that will be receiving rain gardens; 2 households will be sharing a rain garden, and one homeowner was able to have 2, for a total of 14 rain gardens.

The average size of a garden is 20 feet by 12 feet (1 foot deep). No borings have been completed for this area; however, this neighborhood was developed in the early 1900’s so the soil structure was assumed to be intact.

The rain gardens are expected to have a TSS (total suspended solids) removal efficiency of 22%. Three catch basins were also installed with this project to increase the TSS removal. The combination of rain gardens and catch basins brings the total expected TSS removal to 33%, or 2348.4 pounds of sediment annually.

PLANTING & MAINTENANCE

Homeowners had three options for planting the rain gardens:

1. Select from a list of planting designs and pay a portion of the cost of hiring a landscape contractor to plant the gardens;
2. Select from a list of planting designs and have the plants dropped off by the contractor; or,
3. Purchase and plant the gardens completely on their own.

The rain gardens should be planted by early June at the latest.

FUTURE TERRACE RAIN GARDENS

City Engineering is currently offering rain gardens in terraces in conjunction with street reconstructions, where they are appropriate. In fall 2008, City Engineering staff reviewed each of the proposed street reconstruction projects in 2009, for the possible inclusion of terrace rain gardens. Streets needed to have terraces that met the following criteria to be considered eligible:

1. Have terraces that are at least 10 feet wide;
2. Not be too steep (in any direction); and,
3. No high groundwater issues

Once the possible streets were narrowed down, staff walked each of the streets to determine which properties had adequate room and suitable terraces for possible rain gardens. Homeowners affected by a street reconstruction project receive a letter in the mail that outlines the opportunity for rain gardens, along with other information on the street project. A second post card is also mailed out to remind them about any deadlines for deciding whether they would like to move forward with having a rain gardens installed in the terrace in conjunction with the street project. Currently, the City will pay 75% of the cost of installation and planting of a rain garden in the terrace.