For the purpose of this chapter, the following definitions shall apply unless the context clearly indicates or requires a different meaning.
   DEVELOPMENT. Any activity, including subdivisions, that alters the surface of the land to create additional impervious surfaces including, but not limited to, pavement, buildings and structures except:
      (1)   Additions to, improvements and repair of existing single-family and duplex dwellings;
      (2)   Construction of any buildings, structures and/or appurtenant service roads, drives and walks on a site having previously provided storm water control as part of a larger unit of development consistent with the original development plan;
      (3)   Remodeling, repair, replacement and improvements to any existing structure or facility and appurtenances that does not increase the impervious area on the site in excess of 10% or add one acre of impervious area; and
      (4)   Construction of any one new single-family or duplex dwelling unit, irrespective of the site area on which the same may be situated.
   EMERGENCY SPILLWAY. A device or devices used to discharge water under conditions of inflow that exceed the design inflow. The EMERGENCY SPILLWAY functions primarily to prevent damage to the detention facility that would permit the sudden release of impounded water. It shall be designed to handle the run-off from a 100-year storm.
   FREEBOARD. The difference in elevation between the top of a structure such as a dam or open channel and the maximum design water surface elevation or high water mark and is an allowance against overtopping by waves or other transient disturbances.
   IPSUSESCM.Illinois Procedures and Standards for Urban Soil Erosion and Sedimentation Control Manual, March 1982.
   PRINCIPAL SPILLWAY. A device, such as an inlet, pipe, weir and the like, to discharge water during operation of the facility under the conditions of a 15-year or less return frequency of the existing conditions, before the proposed development.
   PRIVATE DETENTION FACILITY. Any detention facility located on and controlling discharge from a site wholly owned and controlled by one owner and not platted for future subdivision of ownership. Also, all facilities incorporating detention storage of storm water in or on any of the following:
      (1)   Roofs of buildings or structures also used for other purposes;
      (2)   Paved or surfaced areas also used for other purposes; and
      (3)   Enclosed underground pipes or structures on private property when the surface is used for other purposes.
   PUBLIC DETENTION FACILITY. Any detention facility controlling discharge from a tributary area owned by more than one owner and/or platted for future subdivision of ownership, except as defined as a private detention facility herein.
   RATIONAL METHOD. An empirical formula for calculating peak rates of runoff resulting from rainfall.
   TRIBUTARY AREA. All land draining to the point of consideration, regardless of ownership.
(1999 Code, § 34-5-50)