For the purpose of this chapter, the following definitions shall apply unless the context clearly indicates or requires a different meaning.
CAPACITY OF A STORM DRAINAGE FACILITY. The maximum flow that can be conveyed or stored by a storm drainage facility without causing damage to public or private property.
CHANNEL. A natural or artificial watercourse which periodically or continuously contains moving water, or which forms a connecting link between two bodies of water. It has a defined bed and banks which serve to confine the water.
COMPENSATORY STORAGE. An artificial volume of storage within a floodplain used to balance the loss of natural flood storage capacity when artificial fill or structures are placed within the floodplain.
CONTIGUOUS. Adjoining or in actual contact with.
COUNTY SURVEYOR. The elected county official responsible for the regulated drain system and this chapter.
CULVERT. A closed conduit used for the passage of surface drainage water under a roadway, railroad, canal or other impediment.
DETENTION BASIN. A facility constructed or modified to restrict the flow of stormwater to a prescribed maximum rate, and to detain concurrently the excess waters that accumulate behind the outlet.
DETENTION STORAGE. The temporary detaining or storage of stormwater in storage basins, on rooftops, in streets, parking lots, school yards, parks, open spaces or other areas under predetermined and controlled conditions, with the rate of drainage there from regulated by appropriately installed devices.
DRAINAGE AREA. The area from which water is carried off by a drainage system; a watershed or catchment area.
DROP MANHOLE. A manhole having a vertical drop pipe connecting the inlet pipe to the outlet pipe. The vertical drop pipe shall be located immediately outside the manhole.
DRY BOTTOM DETENTION BASIN. A basin designed to be completely de-watered after having provided its planned detention of runoff during a storm event.
DURATION. The time period of a rainfall event.
EROSION. Wearing away of the land by running water, waves, temperature changes, ice or wind,
FLOOD or FLOODWATERS. The water of any watercourse which is above the banks of the watercourse. It also means the water of any lake which is above and outside the banks thereof.
FLOOD ELEVATION. The elevation at all locations delineating the maximum level of high waters for a flood of given return period and rainfall duration.
FLOOD HAZARD AREA. Any floodplain, floodway, floodway fringe or any combination thereof which is subject to inundation by the regulatory flood; or any floodplain as delineated by Zone A on a flood hazard boundary map.
FLOOD PROTECTION GRADE. The elevation of the lowest floor of a building. If a basement is included, the basement floor is considered the lowest floor.
FLOODPLAIN. The area adjoining the river or stream which has been or may hereafter be covered by floodwaters.
FLOODWAY. See REGULATORY FLOODWAY.
FLOODWAY FRINGE. The portion of the floodplain lying outside the floodway, which is inundated by the regulatory flood.
FOOTING DRAIN. A drain pipe installed around the exterior of a basement wall foundation to relieve water pressure caused by high groundwater elevation.
GRADE. The inclination or slope of a channel, canal, conduit and the like, or natural ground surface usually expressed in terms of the percentage the vertical rise (or fall) bears to the corresponding horizontal distance.
IMPACT AREAS. Areas defined and mapped by the Plan Commission which are unlikely to be easily drained because of one or more factors, including, but not limited to, any of the following: soil type; topography; land where there is not adequate outlet; a floodway or floodplain; or land within 75 feet of each bank of any regulated drain or within 75 feet from the centerline of any regulated tile ditch.
IMPERVIOUS. A term applied to material through which water cannot pass, or through which water passes with difficulty.
INLET. An opening into a storm sewer system for the entrance of surface stormwater runoff, more completely described as a STORM SEWER INLET.
JUNCTION CHAMBER. A converging section of conduit, usually large enough for a person to enter, used to facilitate the flow from one or more conduits into a main conduit.
LATERAL STORM SEWER. A sewer that has inlets connected to it but has no other storm sewer connected.
MAJOR DRAINAGE SYSTEMS. Drainage systems carrying runoff from an area of one or more square miles.
MANHOLE. Storm sewer structure through which a person may enter to gain access to an underground storm sewer or enclosed structure.
MINOR DRAINAGE SYSTEMS. Drainage systems having an area of less than one square mile.
OFF-SITE. Everything not on-site.
ON-SITE. Located within the controlled area where runoff originates.
OUTFALL. The point or location where storm runoff discharges from a sewer or drain. Also applies to the outfall sewer or channel which carries the storm runoff to the point of OUTFALL.
PEAK FLOW. The maximum rate of flow of water at a given point in a channel or conduit resulting from a particular storm or flood.
PLAN COMMISSION. The County Plan Commission.
RADIUS OF CURVATURE. Length of radius of a circle used to define a curve.
RAINFALL INTENSITY. The cumulative depth of rainfall occurring over a given duration, normally expressed in inches per hour.
REACH. Any length of river, channel or storm sewer.
REGULATED AREA. All of the unincorporated land under the jurisdiction of the County Plan Commission. In addition, this will include major and minor residential subdivisions within the two-mile zoning jurisdictions of the Town of Argos and the Town of Bourbon, as well as the City of Plymouth.
REGULATORY FLOOD. The flood having a peak discharge which can be equaled or exceeded on the average of once in a 100-year period, as calculated by a method and procedure which is acceptable to the Plan Commission. If a permit from the National Resources Commission for construction in the floodway is required (see § 153.05), then the regulatory flood peak discharge should be calculated by a method acceptable to the Board and the Natural Resources Commission. This REGULATORY FLOOD is equivalent to a flood having a probability of occurrence of 1% any given year.
REGULATORY FLOODWAY. The channel of a river or stream and those portions of the floodplains adjoining the channel which are reasonably required to carry and discharge the peak flow of the regulatory flood of any river or stream.
RELEASE RATE. The amount of stormwater released from a stormwater control facility per unit of time.
RETURN PERIOD. The average interval of time within which a given rainfall event will be equaled or exceeded once. A flood having a RETURN PERIOD of 100 years has a 1% probability of being equaled or exceeded in any one year.
RUNOFF COEFFICIENT. A decimal fraction relating to the amount of rain which appears as runoff and reaches the storm drainage system to the total amount of rain falling. A coefficient of 0.5 implies that 50% of the rain falling on a given surface appears as stormwater runoff.
SEDIMENT. Material of soil and rock origin, transported, earned or deposited by water.
SIPHON. A closed conduit or portion of which lies above the hydraulic grade line, resulting in a pressure less than atmospheric and requiring a vacuum within the conduit to start flow. A SIPHON utilizes atmospheric pressure to effect or increase the flow of water through a conduit. An inverted SIPHON is used to carry stormwater flow under an obstruction such as a sanitary sewer.
SPILLWAY. A waterway, in or about a hydraulic structure, for the escape of excess water.
STILLING BASIN. A basin used to slow water down or dissipate its energy.
STORAGE DURATION. The length of time that water may be stored in any stormwater control facility, computed from the time water first begins to be stored.
STORM SEWER. A closed conduit for conveying collected stormwater.
STORMWATER DRAINAGE SYSTEM. All means, natural or human-made, used for conducting stormwater to, through or from a drainage area to any of the following: conduits and appurtenant features; canals; channels; ditches; streams; culverts; streets; and pumping stations.
STORMWATER RUNOFF. The water derived from rains falling within a tributary basin, flowing over the surface of the ground or collected in channels or conduits.
TECHNICAL REVIEW COMMITTEE. A committee designated in § 155.02 for the purpose of providing technical review of certain types of petitions and applications.
TRIBUTARY. Contributing stormwater from upstream land areas.
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 river, stream, creek, brook, branch or natural or human-made drainage way in or into which stormwater runoff or floodwaters flow either regularly or intermittently.
WATERSHED. See DRAINAGE AREA.
WET BOTTOM DETENTION BASIN (RETENTION BASIN). A basin designed to retain a permanent pool of water after having provided its planned detention of runoff during a storm event.
(Ord. 2011-03, passed 4-4-2011)