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Chapter 18. General Zoning Ordinance

Sec. 18-135. Standards for Rain Gardens and Bioswales

(1) Definition.

(a) Rain gardens and bioswales can serve both as landscaping and stormwater management features on a building site, where appropriately designed and sited. A rain garden is a shallow, depressed garden that is designed and positioned on a site to capture stormwater runoff and allow for the infiltration of water back into the ground. Rain garden plants are carefully chosen for their ability to withstand moisture extremes and potentially high concentrations of nutrients and sediments that are often found in stormwater runoff. A well designed and maintained rain garden serves as an attractive component of an overall landscaping plan for a development site.

(b) A bioswale is a linear, vegetative stormwater runoff conveyance system that is designed to store and infiltrate water from small storm events back into the ground and direct water from heavy rain events to appropriate storm sewer inlets or other management facilities. The flow of water being conveyed through a bioswale is slowed down, allowing for municipal storm systems to more effectively manage heavier rain events and help reduce the risk of flooding on or off-site. Water being infiltrated or conveyed via a bioswale is also filtered by the vegetation within it, generally improving both ground and surface water quality.

(2) Requirements.

(a) The installation of a rain garden or bioswale may contribute to the overall stormwater management plan for a development site and count toward meeting the City's landscaping guidelines. Rain gardens may count for 20 points for every 20 square feet for yard area, building foundation, and/or paved area requirements, provided the following requirements are met.

(b) Detailed plans shall be provided that show all proposed dimensions of the rain garden or bioswale including length, width, depth, and slope of depression; location of the rain garden or bioswale on the lot relative to hard-surfaced areas, downspouts, and site topography; characteristics of the soil underlying the rain garden or bioswale; description of planting media; the species, number, and size at time of installation of all vegetation proposed for the rain garden or bioswale; and information on any other materials (e.g., rocks) that will be used to line the rain garden or bioswale.

(c) Installation shall not be proposed for any of the following areas of a site:

1. Areas where there is known soil contamination unless the rain garden or bioswale is proposed to be constructed with an under-drain;

2. Areas where the characteristics of the soil would not allow for the proper infiltration of water into the ground; or

3. Areas where there are expected to be high levels of foot traffic.

(d) The owner of the site shall demonstrate that the rain garden or bioswale shall be properly maintained; kept free of trash, weeds, debris, and dead or dying plants; any pipes associated with the rain garden or bioswale will be inspected on an annual basis and kept free of debris; and by the beginning of every spring dead plant materials will be cut back or removed.

(e) Bioswales and rain gardens shall be generously (and appropriately) vegetated to qualify for landscaping points. Bioswales and rain gardens (or portions thereof) that are lined with turf and/or rocks but do not include other vegetation will not count toward meeting landscaping point requirements.

(f) Rain gardens and bioswales may serve as a component of an overall stormwater management plan for a site only if detailed plans, calculations, and specifications are submitted. Detailed plans shall include the location and description of all other stormwater management facilities serving the site, particularly those to which any bioswale will be directed.

(Code 1982, 17.17(6); Ord. No. 1201, 1, 2, 6-14-2011)