Birchwood Woodland Restoration Rain Garden
Garden Magic has designed and installed another Next Generation Rain Garden in Mountain Lakes, New Jersey, believed to be the first rain garden incorporating both advanced rain garden concepts and woodland restoration practices into a single project.
The advanced rain garden applies natural systems to reduce the negative impacts of stormwater runoff, improve water quality, and enhance biodiversity. Rapidly flowing rainwater from the Birchwood Lake parking lot is interrupted and captured in the constructed basin, allowing water to filter into the ground instead of eroding the bank and washing pollutants into the adjacent Crystal Lake. Plants help keep the soil porous, soak up water, and remove nutrients and some chemical impurities. The planted native perennials and shrubs help restore the woodland understory, while providing habitat for local wildlife and pollinators.
The rain garden was made possible with funding and support from the New Jersey Conservation Foundation (a Franklin Parker Conservation Excellence Grant), Borough of Mountain Lakes, and the Whippany River Watershed Action Committee.
For many years, excess stormwater runoff from the Birchwood Lake parking lot was causing serious bank erosion, carrying sediment and other contaminants (nutrients, oils, chemicals) into Crystal Lake. Installation of this rain garden has interrupted rapidly flowing rainwater, along with the contaminants it carries, from going down the hill and directly into the lake below. Instead, runoff from the parking lot is disconnected from the lake and captured in a constructed rain garden basin built adjacent to the roadway. Over several hours, the water collected in the rain garden filters into the ground, is taken up by plants, or returned to the atmosphere through evapo-transpiration.
Preventing soil erosion and catching sediment at this site is particularly important for protecting lake water quality, because much of the phosphorus getting into freshwater lakes today comes attached to eroded soil and sediment particles, and excess phosphorus can be the driving force behind aquatic algal (phytoplanktonic, cyanobacterial) blooms.
The Birchwood Rain Garden was installed on an extremely complex site, including: 1) a narrow strip of land sandwiched between the roadway and a steep bank leading down to the lake, 20 feet below; 2) old and new erosion cuts in the bank that needed correcting; 3) half of the site was filled with buried waste gravel and cut rocks that required removal; 4) presence of existing large trees that were already stressed by the gravel and rock fill; 5) a heavily shaded site, requiring a special selection of rain garden plants.
Approaching the rain garden design concurrently as a “woodland restoration” (minimizing existing root disruption, while planting additional native woodland vegetation) provided a unique solution to a difficult site while enhancing both watershed and habitat benefits.
The rain garden and woodland restoration aspects of this project complement each other. The constructed rain garden provides improved soil and water conditions, so that plants can thrive. At the same time, the native woodland perennials and shrubs provide stability to the rain garden, ensure long-term infiltration, and aid in the removal of water, nutrients and chemical impurities. Together, they produce a natural-looking restored woodland understory, while providing habitat for local wildlife and pollinators.
Over 125 native plants can be found in the rain garden, including: Berry-producing shrubs (arrowwood viburnum, blueberry, chokeberry, redosier dogwood, silky dogwood, winterberry); ferns (cinnamon, lady, marsh, ostrich, royal, sensitive); and perennials (blackeyed Susan, boneset, cardinal flower, golden zizia, great blue lobelia, mayapple, red columbine, Solomon’s seal.)
