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ILLINOIS URBAN MANUAL PRACTICE STANDARD

RAIN (feet) CODE 897

Source: Kendall County Soil and Water Conservation District

DEFINITION  Create a unique landscape feature and provide habitat for Rain are small, shallow, flat wildlife such as and insects bottomed depressions constructed to including pollinators. temporarily hold and infiltrate allowing stormwater to soak CONDITIONS WHERE PRACTICE into the ground onsite rather than APPLIES leaving a property as runoff. In developed areas, impervious and Designed to be periodically inundated compacted surfaces increase with water for short periods of time, rain stormwater runoff significantly. Rain gardens are planted with vegetation gardens capture runoff from rooftops, tolerant of being periodically wet and driveways, sidewalks, and other dry. impervious and compacted surfaces.

PURPOSE This practice applies to small locations and locations with soils that Rain gardens are constructed to: will allow adequate unless constructed with engineered soil and/or  Retain stormwater runoff and an underdrain system. facilitate infiltration;  Improve water quality by trapping CRITERIA sediment and debris; Regulations  Remove other pollutants through the biological, chemical and Plan, design and construct stormwater physical properties of , runoff practices to comply with microbes and soils;

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applicable federal, state and local laws negative impacts to wastewater and regulations. treatment systems or wells. Rain gardens shall be a minimum of Utilities and Permits 25 feet from private sewage disposal systems and wells. The landowner and/or contractor shall Avoid areas within a source water be responsible for locating all buried protection area for public drinking utilities (Dial 811 to call JULIE) in the water supply. project area, including drainage tiles and other structural measures.  Rain gardens shall be located a minimum of 10 feet away from The landowner shall obtain all any utilities or building structure necessary permissions from regulatory to prevent infiltrating water from agencies, including, but not limited to, seeping into the foundation. A local, state and federal units of minimum of 35-40 feet separation government, or document that no is preferred. permits are required.  Direct outflow from the rain Vegetation Selection garden away from any building foundation. Stabilize all areas disturbed by construction with vegetation as soon as  The bottom of the rain garden possible after construction and in shall be flat, not exceeding 0.5% accordance with IUM practice standard slope, to facilitate distribution of PERMANENT VEGETATION 880. stormwater runoff and maximize infiltration. Select vegetation tolerant of the site conditions, particularly moisture and sun  Rate and volume of overflow exposure conditions, in which the from the rain garden must not vegetation will be planted. A cause downstream . selection guide can be found in TABLE 897-1. If the rain garden is expected to  Stormwater must be directed to receive pollutants, select vegetation the rain garden through means tolerant of those pollutants. such as topography, swales, or tile connected to downspouts. Location and Design  Soil surface where runoff water  Locate the rain garden so that will enter the rain garden must be the drainage area is less than 2 stable. Include measures such as acres with any impermeable rock to dissipate energy where portion of drainage area no concentrated flow is expected. greater than 1 acre.  Include pretreatment or pollution  Locate the rain garden where soil removal areas such as grass remains stable when saturated. filters or settling areas when runoff is expected to contribute  Locate the rain garden to avoid excessive sediment, trash, debris damage to any structures or

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or other pollutants such as salt or  Design the rain garden to drain oil that would be damaging to the completely between designed system. These areas must be storm events. Any runoff directed adequately designed to handle to the rain garden, such as runoff the expected load capacity. from downspouts, lawns and Locate and build such areas so paved surfaces must be they are easy to access and intermittent. Sump pumps which maintain. discharge continuously shall not be directed to the rain garden.  Provide, at minimum, 2 feet of soil between the bottom of the CONSIDERATIONS rain garden and fractured bedrock or high . The  Illinois rain events are typically 1 target separation should be 3 inch or less. Designing the rain feet. Where there is an increased garden to capture the first 1 inch risk of pollution, an of runoff will capture a significant impermeable liner or layer of amount of stormwater runoff compacted earth may be used to flowing to the rain garden thus separate the rain garden and the treating the pollutants coming water table where there is an into the rain garden. The first increased risk of groundwater flush of runoff carries with it the pollution. majority of the pollutants from a storm event.  Rain gardens are typically between 3 and 9 inches deep,  Soils with a hydrologic group but never exceeding 12 inches in designation of A or B, a USDA depth. soil textural classification of: -  Mound excavated material on the downhill side of the rain garden - Loamy sand no higher than 1 foot above the - Sandy loam bottom of the rain garden. - Loam  Side slopes within the ponding or an infiltration rate of at least 1 area must be 3:1 (H:V) or flatter. inch per hour are preferable for Slopes of any mounded spoil rain gardens. Soils with slower outside of the ponding area must infiltration rates shall be be 5:1 or flatter. amended or modified to increase infiltration. When appropriate,  Design the rain garden to install underdrains where the dewater within 48 hours or less. soils have infiltration rates of ½ The target dewatering time shall inch per hour or less. For soils be 24 hours or less. Locations information see USDA Web Soil with existing soils that do not Survey. meet the criteria above may need a designed underdrain or soil  Avoid compaction in infiltration amendment. areas during construction

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including compaction from foot those pollutants. Road salts can traffic. Ensure that any be of particular concern. impermeable layer in the infiltration area of the rain garden  Vegetation placed in the is removed or broken up prior to infiltration area of the rain garden planting on sites where must be tolerant of periodically compaction has occurred, dry and periodically inundated particularly where construction conditions. equipment has been used to construct the rain garden.  Vegetation selection and placement is crucial to a  It is important to note, rain successful rain garden. Select gardens shall not be used to vegetation based on position and control construction site erosion. associated moisture regime Additionally, any sediment which within the rain garden. builds up over time shall be removed from the rain garden. Position Moisture Tolerance

 Sediment deposition can create a Low Moist to Average crust on the surface of the rain garden which will begin to limit Medium Average Moisture infiltration. It is important to note removal of sediment build-up High Average to Dry over time is necessary.

 Rain garden size typically ranges  It is important to note rain from 100 to 300 square feet in gardens are not intended to area, commonly 10-30% of the retain permanent water. Avoid drainage area. plants that prefer saturated or wet conditions.  Avoid construction of rain gardens on slopes greater than  Rain gardens can be located in 12%. areas of shade, partial sun or full sun. Partial sun and full sun,  Rain gardens should not be however, are preferable due to located upslope from any building the availability of a larger foundation from which runoff is selection of plant material. Areas being collected such as from beneath should also be downspouts. avoided to prevent root damage  To adequately establish to trees. vegetation, select plants based  Ensure an adequate growing on sun exposure, soils and medium for vegetation. Specified moisture availability at the soil mixes or natural must proposed site location. If the rain be of sufficient depth to support garden is expected to receive pollutants select plants tolerant of

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the root zone of the desired clearance of mulch around new vegetation. plantings to facilitate watering and air exchange. Where  Deep rooted native vegetation phosphorous levels are a should be used and will improve concern, discontinue adding soil infiltration over time. Native mulch once plants are vegetation will typically perform established. better without added fertilizers.  Consider diverting water or  Consider including species lowering the rain garden outlet beneficial for pollinators. until vegetation is established. Pollinator habitat areas consist of Remove the diversion or a sufficient variety of plant complete construction of outlet to species to sustain the target design depth when plants grow pollinators throughout the taller than ponding depth. growing season.  Consider temporarily fencing  Consider grouping plants and around the rain garden to protect including signage to facilitate plantings if herbivore pressure maintenance. exists.

 Successful plant establishment is  A single rain garden will not most easily accomplished during significantly impact flooding spring and fall when soil moisture issues or water quality problems is readily available. During in a community. However, the vegetation establishment ensure cumulative impact of rain adequate maintenance resources gardens in conjunction with other and watering capabilities exist. stormwater management practices has the potential to  Seeding is not recommended as tangibly affect flooding, stream seeds can be washed away and flow, local are slow to establish. Plant the and water quality concerns. infiltration area of the rain garden with dormant or actively growing PLANS AND SPECIFICATIONS nursery stock. Ensure that trees and other vegetation will not Plans and specifications for installing a hinder water from entering the rain garden shall be in compliance with rain garden, create traffic or this standard and shall describe the safety issues, or obstruct utilities. requirements for applying the practice to achieve its intended purpose. At a  Mulch vegetation after planting to minimum include the following items: suppress weeds and conserve moisture. Use shredded 1. Rain garden location hardwood mulch or equivalent non-floatable mulch. Spread 2. Grade, depth, width, length and mulch evenly to a maximum side slope grade depth of 3 inches. Ensure

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3. Rain garden cross-section year’s herbaceous growth which has died back. 4. Material specifications REFERENCES 5. Construction specifications Bannerman, Roger, and E. Considine, All plans shall include the installation, 2003. Rain Gardens: A How-to Manual inspection and maintenance schedules for Homeowners. University of with the responsible party identified. Wisconsin Extension Publication GWQ037 or Wisconsin Department of Natural Resources Publication PUB- WT-776 2003. Madison, WI. OPERATION AND MAINTENANCE Iowa Stormwater Partnership, Rain An operation and maintenance plan Gardens: Iowa Rain and shall be provided for the rain garden to Installation Manual. 2008. eBook. include at a minimum:

 Periodic inspections during Natural Resources Conservation vegetative establishment and Service, Conservation Practice immediately following significant Standard Stormwater Runoff Control: rainfall events. CODE 570. 2013.

 Prompt repair or replacement of Schmidt, Rusty, Dan Shaw, and David damaged components such as Dods, The Blue Thumb Guide to areas subject to wear or erosion, Raingardens. Waterdrop Innovations, as well as, failed plantings. LLC, 2007. Print.

 Periodic inspection to remove USDA-NRCS, Pollinator Biology and accumulated sediment and Habitat: Technical Note 23. 2008. debris. USDA Web Soil Survey  Rain garden vegetation will Natural Resources Conservation require regular watering and Service, United States Department of weeding during plant . Web Soil Survey. Available establishment. online at http://websoilsurvey.nrcs.usda.gov  Prune trees and as needed. Weed rain garden to March 2014 control unwanted vegetation. Annually, in early spring, remove Urbst897.doc or mulch in place the previous

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