Rain Gardens
Katie Gatzke, Amy Campbell (authors), Keith Hirokawa & Jonathan Rosenbloom (editors)INTRODUCTION
Rain gardens absorb stormwater runoff from roofs, driveways, and other impervious surfaces into a deep-set, planted section.[1] Absorbing this runoff can help divert it from local stormwater systems, reduce costs, and avoid overflow incidents.[2] Rain gardens can reduce the amount of runoff from impervious surfaces by up to 98%.[3]
Rain garden ordinances can be designed in several ways. Most ordinances, such as those citied below, include a definition for “rain garden.” This allows the locality to control or limit what are acceptable types of rain gardens. Ordinances requiring or incentivizing rain gardens should typically include requirements for native water-absorbing plants in the center, with native draught-resistant plants along the edges.[4] Some rain garden ordinances require developers to comply with local stormwater management regulations as well as rain garden-specific stipulations.[5] Some local governments provide stormwater credits for rain gardens or other sustainable structures.[6] Other local governments provide grant money, rebates, or other financing tools to encourage rain garden installation and use.[7] For some of these rain garden incentive or reimbursement programs, local governments require minimum drainage times and installation of a minimum rain garden square footage or minimum stormwater runoff capacity, and commitments to keep and maintain the garden for a minimum number of years.[8] Local governments may also offer stormwater service fee credits based on on-site detention or retention systems.[9]
Installation of rain gardens has in some cases been found to be easier and less expensive than installing bioswales or biocells.[10] However, each jurisdiction should be considered on a case-by-case basis to find the most appropriate balance between rain gardens and “traditional” and other stormwater management practices.[11]
EFFECTS
The installation of rain gardens is important to sustainability and green infrastructure techniques that decrease stormwater and pollution runoff.[12] As mentioned above, rain gardens can dramatically reduce runoff that works its way into local stormwater systems and natural water ways. Reducing runoff can lower a community’s stormwater burden and cost of stormwater management. In addition, it can help mitigate risks associated with flooding. Adding shrubbery and other vegetation to absorb rainwater is an important tactic for reducing fresh-water flooding challenges and rising sea levels.[13]
Rain gardens also filter pet waste, auto fluids, and other pollutants from surplus water.[14] By lowering the amount of pollution found in runoff water, rain gardens can help improve water quality generally.[15] Rain gardens also absorb pathogens, dissolved metals, and small levels of phosphorus and nitrogen.[16]
Rain gardens are not only cost effective, but also bring beauty to the property with varying plant heights and colors.[17] Each rain garden is unique to the property it sits on, so owners have a high amount of control over its shape, size, and appearance.[18] Rain gardens can draw birds, butterflies, and other small wildlife to the area with strategic plantings.[19] This can increase biodiversity and associated environmental and physical and psychological health benefits.
EXAMPLES
Blaine, MN
Blaine’s engineering department must approve plans for each rain garden before construction.[20] Prior to approval, the developer must submit an illustration of the draining area, size and capacity calculations for the draining area, and proof that the rain garden will be able to absorb water within 48 hours.[21] In addition, the developer must indicate the location of the property boundaries, street features, driveways, and other important residential structures.[22] Pursuant to the ordinance, property owners are responsible for maintaining the rain garden. If the rain garden is intended to capture street runoff, there must be a curb cut to allow street water to drain into the garden. Blaine will pay for the curb cut, but all other tasks for the garden are the owner’s responsibility.[23] The ordinance stipulates that city officials have the right-of-entry to inspect rain gardens which collect runoff from public ways (ie. street runoff). Additionally, the location of each rain garden must be recorded as a portion of the city’s stormwater management system.[24] With a permit, rain gardens may sit in the right of way to retrieve street overflow.[25] If a homeowner does not wish street runoff to drain into their rain garden, they must ensure the rain garden takes all of the water from their driveway in addition to 75% of the runoff from the yard and roof.[26]
To view this provision see Blaine, MN Code of Ordinances § 34-541 (2019).
Kennettt Square, PA
In Kennettt Square, rain gardens are synonymous with bioretention areas.[27] Pursuant to the ordinance, specified professional testing must be passed before each rain garden may be installed. Testing must include infiltration abilities and a test pit within the proposed development space.[28] The site plan must include the size of the garden, including its depth. Rain gardens must be at least 18” deep, and may sit with a maximum slope of 3:1. Additionally, rain gardens are required to drain in 72 hours or less.[29] To facilitate drainage, the ordinance requires that rain garden plants should be a mix of various native water-tolerant species. Kennett Square asks rain garden installers to use augmented soil: 50% soil, 30% sand, and 20% compost or woodchips.[30] Owner responsibilities include watering, pruning, and weeding the garden regularly, with emphasis on removing invasive species. Also, space around rain gardens must be kept free of debris from obstructing the flow of runoff. In addition, the owner must inspect the rain garden at least twice per year for erosion or other defects.[31]
To view this provision see Kennett Square, PA Code of Ordinances App. A (2014).
Bensalem, PA
Similar to many ordinances, Bensalem defines rain gardens as shallow depressions filled with plants intended to filter and trap rain and other water overflow.[32] The most successful location for a rain garden is between the source of runoff and its intended destination (for example, separating driveway runoff from a nearby stream). A garden slope ratio of 3:1 is recommended, as are a 6”-8” depth and a 72-hour or less drain time.[33] The plants for a rain garden need to be native, deep rooted, and either flood resistant or draught resistant. Rain gardens must be regularly pruned, weeded, and inspected for erosion. If the rain garden is on clay soil, the soil should be mixed with compost or other organic materials.[34] Ensuring the rain garden soil level is at least two feet above the water table will prevent the garden from unintentional flooding.[35] For guidelines on “DIY” rain garden installation, see Bensalem’s ordinance (below).[36]
To view this provision see Bensalem, PA Code of Ordinances § 196-148 App. 1 (2019).
ADDITIONAL EXAMPLES
Fontana on Geneva, WI Code of Ordinances § 18-174 (2012) (requiring generously vegetated rain gardens with plants needing nutrients from stormwater and runoff sediment; rain gardens must be maintained by owner, have an underdrain, and cannot sit in contaminated soil; rain gardens can count toward local landscaping requirements and can be considered part of local storm water management plans).
Gladstone, MO Code of Ordinances § 9.2700.080(3) (2011) (permitting sump pumps to be drained into rain gardens; must drain the water from all sump pumps on property; rain gardens must be at least 10-20’ away from the foundation of a home; runoff into the garden must come from the same property, not neighboring properties).
ADDITIONAL RESOURCES
Curtis Hinman, Rain Garden Handbook for Western Washington: A Guide for Design, Installation, and Maintenance, Washington State University Extension (2013), https://perma.cc/64XC-5TE8.
Rain Garden Incentive Program, City of Olympia (2015), https://perma.cc/3ZG6-YLQM.
Stories in New Jersey: Rain Gardens, The Nature Conservancy (last accessed Aug. 1, 2019), https://perma.cc/ZCP7-JS43.
CITATIONS
[1] How and Why to Build a Rain Garden, U. of MN Extension (2018); see Benefits of Rain Gardens, Pleasant Hill, IA (last accessed Aug. 1, 2019).
[2] Id.
[3] Laura Wilson and Mary Gilbertson, Landscapes for Maine: Adding a Rain Garden to Your Landscape, U. of ME Extension (2006).
[4] Id.
[5] See e.g., Blaine, MN Code of Ordinances § 34-541 (2019).
[6] Managing Wet Weather with Green Infrastructure Municipal Handbook: Incentive Mechanisms, Env’l Protection Agency (2009).
[7] Id.
[8] See e.g., Rain Garden Incentive Program, City of Olympia, WA (2015).
[9] National Ass’n of Flood and Stormwater Management Agencies, Guidance for Municipal Stormwater Funding, Environmental Protection Agency, 2-34 (2006).
[10] Benefits of Rain Gardens, supra note 1.
[11] Id.
[12] See How and Why, supra note 1.
[13] Christine Macdonald, Why Every City Should be Planting Rain Gardens, CityLab (2012).
[14] How and Why, supra note 1.
[15] Id.
[16] Id.
[17] Soak Up the Rain: Rain Gardens, Env’l Protection Agency (2018); Wilson, supra note 3.
[18] See Wilson, supra note 3.
[19] How and Why, supra note 1; Soak Up, supra note 17; Macdonald, supra note 13.
[20] Blaine, MN Code of Ordinances § 34-541 (2019).
[21] Id.
[22] Id.
[23] Id.
[24] Id.
[25] Id.
[26] Id.
[27] Kennett Square, PA Code of Ordinances App. A (2019).
[28] Id.
[29] Id.
[30] Id.
[31] Id.
[32] Bensalem, PA Code of Ordinances § 196-148 App. 1 (2019).
[33] Id.
[34] Id.
[35] Id.
[36] Id.