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For the purpose of this chapter, the following definitions shall apply unless the context clearly indicates or requires a different meaning.
ALLOWABLE DISCHARGE. The restricted discharge from a site after development or redevelopment as calculated in accordance with the Stormwater Management Plan.
100-YEAR FLOOD ELEVATION. The elevation delineating the flood level having a 1% probability of being equaled or exceeded in any given year (also known as the base flood elevation), as determined from Flood Insurance Rate Maps (FIRMs) or the best available information.
BEST MANAGEMENT PRACTICES (BMP). Structural, vegetative, or managerial practices used to protect and improve the quality of surface water and groundwater.
BIO-FILTRATION. A soil filtration system. Common components of the system include:
(1) Grass filter strip;
(2) Surface planting with woody and herbaceous plant species;
(3) Mulch layer two to three inches thick;
(4) Sandy loam or loamy sand soil-textured planting soil media (two feet minimum depth);
(5) Sand layer (six inches minimum depth); and
(6) Perforated PVC pipe under-drainage within a gravel bed protected with geo-textiles (15 inches depth).
BIO-SWALE. Drainage channels that divert runoff water from the storm sewer into a natural area where native plants help absorb and recycle it. Plants like grasses, rushes, native plants, other water and drought tolerant flowers and bushes are commonly found in bio-swales to trap and absorb water. These systems are dry most of the time and do not have standing water.
CONDUIT. Any channel, pipe, sewer, or culvert used for the conveyance or movement of water whether open or closed.
DESIGN DISCHARGE RATE. Unit allowable discharge rate per acre of land proposed for development or redevelopment. Design discharge rates will vary between drainage districts based on existing drainage system capacity. The city drainage map outlines drainage district lines and design discharge rates.
DESIGN IMPERVIOUSNESS FACTOR (IMP). The actual proposed percentage of impervious surface for a proposed development or redevelopment. The IMP is used to calculate the design discharge (Qd). The design discharge is used to determine storm sewer sizes and required detention volumes. A minimum IMP for various zoned land uses must be established in a pre-design meeting prior to a complete stormwater discharge permit submittal. Minimum IMP's are established per zoning district.
DETENTION FACILITY. A facility constructed or modified to restrict the flow of stormwater to a prescribed maximum rate and to concurrently detain the excess waters that accumulate behind the outlet.
DEVELOPER/OWNER ENGINEER. The engineering person, firm, or corporation formally designated by the developer/owner to act as its engineer.
DEVELOPMENT. The construction of a building, parking lot, structure, and the like, on a piece of land, or otherwise changing the use of a piece of land. Typically, development occurs to property which is vacant of any significant infrastructure or building.
DISCHARGE. The release or outflow of water from any source.
DRAINAGE AREA. The area from which stormwater runoff is conveyed to a single outlet (for example, a watershed or catchment area).
EXCESS STORMWATER RUNOFF. The volume and rate of flow of stormwater discharged from a drainage area, which is in excess of the allowable discharge.
EMERGENCY OVERFLOW. A hydraulic control structure used to control the location and flow direction of stormwater which is either in excess of the required detention storage or is due to a failure in the site's stormwater management system. The emergency overflow shall be directed to a public road right-of-way or to an available municipal storm drainage system.
ENGINEER. A civil engineer that is licensed to work in the State of Michigan or a person who is working under the direct supervision of a civil engineer licensed to work in Michigan.
FIRST FLUSH. The first 0.5 inch of a rain or precipitation event from the entire site or contributing watershed. By capturing and treating the first 0.5 inch of runoff, pollutants that are washed off of the land can be removed from the stormwater before it leaves the site (required by MDEQ before discharge into any waters of the state).
FLOODPLAIN. The special flood hazard lands adjoining a water-course, the surface elevation of which is lower than the base flood elevation and is subject to periodic inundation determined from Flood Insurance Rate Maps (FIRMs) or the best available information. A parcel of land can be located within a floodplain without being shown on a FIRM map.
IMPERVIOUS SURFACE. A surface, which does not easily allow the infiltration or penetration of water. During rainstorm events a large percentage of water will runoff. (For example, rooftops, paved walks, roadways, driveways, sidewalks, and the like.)
LOW IMPACT DESIGN (LID). Implementation of developmental strategies or best management practices in a manner that maintains pre-development hydrology, or decreases runoff quantity, and improves runoff quality.
NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM (NPDES). In 1987 the Clean Water Act was amended and required to implement a program that would address pollutants being discharged into the nation's waters. This now includes stormwater discharges into waters of the nation/state.
PEAK FLOW. The maximum rate of flow of stormwater runoff at a given location.
PERCENT IMPERVIOUS. Percentage of total site area, which is, or is proposed to be, an impervious surface.
PERVIOUS SURFACE. A surface, which allows infiltration or penetration of water. During rainstorm events a percentage of water will infiltrate into the surface with the remaining stormwater running off. The percentage wooded areas, golf courses, and the like.
RAIN GARDEN. A depressed area of a size that was determined by specified engineering guidelines with amended soils and specific plants, shrubs, and trees that has a specific volume to store stormwater runoff.
REAR LOT DRAINAGE. A stormwater system designed to provide drainage in rear lot areas to prevent water from ponding for extended periods of time. It must be noted that these systems are not designed to convey stormwater in a rapid manner. It is a deliberately designed system that can provide additional detention capabilities during severe runoff conditions.
REDEVELOPMENT. Altering, improving, reconstructing or otherwise changing the use of an existing developed property. A site will be considered a redevelopment for this chapter when an area greater than or equal to 5% of the existing developed portion of the site (for example, roof, gravel, and/or paved surfaces) or, an area greater than 5,000 square feet is constructed or reconstructed with roof, pavement, or any other impervious surface.
RESTRICTOR. A hydraulic control structure used to restrict the stormwater discharge from the site to the allowable discharge of the site as determined by this plan.
RETENTION STORAGE. The permanent retaining or storage of stormwater in a storage basin, on rooftops, in streets, parking lots, school yards, parks, open space, or other areas under predetermined and controlled conditions. The only discharge of stormwater from the retention storage area is by ground infiltration, evaporation, and the like.
STORMWATER RUNOFF. The water from a rainstorm or snowmelt, which flows over the surface of the ground or is collected in a drainage system.
SUBSURFACE DETENTION STORAGE. Detention storage that is provided in underground storage facilities such as pipes, arch systems, engineered stone with voids, or tanks.
TEN-YEAR DESIGN STORM. A precipitation event with a duration equal to the time of concentration, having a 10% probability of occurring in any given year or occurring once every ten years on average.
TIME OF CONCENTRATION. The elapsed time for stormwater runoff to flow from the most distant point in a drainage area to the outlet or other predetermined point.
UNIT ALLOWABLE DISCHARGE. Unit allowable discharge rate per acre of land proposed for development or redevelopment. Design discharge rates will vary between drainage districts based on existing drainage system capacity.
UPLAND AREA. Land located in the upper portion of a watershed whose surface drainage flows toward the area being considered for development.
URBANIZATION. The development, change, or improvement of any parcel of land consisting of one or more lots for residential, commercial, industrial, institutional, recreational, or public utility purposes.
WATERCOURSE. Any natural or artificial stream, river, creek, channel, ditch, canal, conduit, culvert, drain, waterway, gully, ravine, street, roadway, swale, or wash in which water flows in a definite direction, either continuously or intermittently.
WATERS OF THE STATE. Any of the following: the Great Lakes bordering the state and their connecting waters; and all inland lakes, rivers, streams, impoundments, open drains, and other surface bodies of water within the jurisdiction of the state, including wetlands as defined by Part 303 of PA 451 of 1994.
(Ord. 644, passed 6-25-2018)