Brookside Garden's Rain Garden

By Jeff Potter, President, J&G Landscape Design Inc.

A total of 2,000 square feet of concrete sidewalks were removed and replaced with pervious pavers. All of the soil areas within and around the rain gardens were graded to direct the surface water into the gardens. The masonry work shown was constructed after the pavers were installed, and plantings were provided by Brookside Gardens. Photos: Jeff Potter, President, J&G Landscape Design Inc.

J&G Landscape Design of Spencerville, Maryland, built a rain garden for award-winning Brookside Gardens, a 50-acre public garden located within Wheaton Regional Park in Wheaton, Maryland. Originally, the Brookside rain garden was made up of a series of cascading ponds with large boulders and plantings, located in a low lying area on a highly visible section of the public garden. The original garden area frequently flooded due to excess surface water from rainfalls, and the landscape was not thriving despite excellent care. A properly built solution needed to be precise and swift to correct the flow of water, which was damaging both plants and the surrounding busy walking path.

The original boulders were lifted and set aside using a combination of an ASV RC 85 rubber track loader and a Case 580 extend-a-hoe backhoe. J&G Landscape Design removed the desirable plant material by hand and relocated it to other areas of the gardens for future use.

J&G Landscape Design's solution was to build a 2-tired rain garden that would showcase an attractive and environmentally sensitive way to collect and filter surface water run-off prior to water reaching the Chesapeake Bay. Built by J&G Landscape Design, the Brookside rain garden was the first of its kind in Montgomery County, Maryland. All labor and materials necessary for the construction process were donated by J&G, as a way to demonstrate responsibility for the community, and support positive ecological landscape initiatives.

Workers used a backhoe and loader in tandem to keep material for installation process moving smoothly, as they installed the gravel for rain garden water collection. Crews worked by hand simultaneously to level out gravel drainage system to layer create the storage capacity needed. The trench depth and area were determined based on specific site characteristics - such as rainfall amounts, and soil permeability.

In preparation for permeable paver walkway installation, the base course of #2 stones was installed to a depth that allows for ample water storage capacity. Workers dumped in more than 200 tons of coarse stone in the bottom of each bio-retention area to promote infiltration and runoff volume reduction. They installed under-drains, which connect the upper and lower bio-retention areas using 4-inch SDR 21 perforated PVC pipe. This under-drain was covered with #57 stone and a layer of soil separator fabric to keep sediment out of the pipe. Bio-retention soil mix was added atop the gravel in both bio-retention areas ending at the final planting elevation.

Bio-retention

The rain garden design called for an upper bio-retention cell that was connected with a larger lower bio-retention area, a typical rain garden design. The area was first surface graded to create the correct topography to direct and control surface water with in this area. A total of 300 yards of soil was excavated and hauled off-site for the installation of the two bio-retention areas.

The upper bio retention area was excavated down three feet below grade and the lower bio-retention area was excavated 5 feet down below existing grade. Upon completion of the excavation, both retention areas were meticulously graded by hand making sure the sub-grade had the necessary slope to ensure the success of the gardens. This included the installation of a gravel spill way for overflow water between the upper and lower bio-retention areas.

The contractor installed Hanover Aqua-Loc pavers to form the walkway that surrounds the rain garden and connects the conservatory to the upper terrace. These pavers were installed overtop of a layer of clean 3/8-inch gravel that was spread over the #2 stone base.

Pervious Paving

Two pervious paving areas were installed in conjunction with the rain garden. A sitting area complete with pervious pavers and a seat wall with recycled stone from the original feature and limestone caps were installed just above the upper bio-retention area. A trench drain was installed to collect the surface run off from the upper walk and sloped lawn areas. During rainfalls, this water would be drained directly into the upper bio-retention area.

The rain garden was bordered by a second area of 2000 square feet of pervious pavers on the side of the lower bio-retention area. This area was excavated down 18 inches below grade and a series on under-drains were installed to vent any excess water into the lower bio-retention area. The boulders from the original feature were installed as decorative landscape elements throughout the new created garden.

The rain garden was planted with recycled plants from the original garden as well as some new additions. To date, the rain garden and surrounding paver paths has proven successful. The garden's function is illustrated each time it rains. Light and moderate rain water is absorbed quickly, but in times of heavy rain, water flows in a directed manner and gets absorbed correctly, thus eliminating run-off and plant damage. This project has generated significant interest in the community for this type of ecological garden solution. The park stands as a great testament to the beauty of environmentally friendly landscaping.