For the purpose of this chapter, the following definitions shall apply unless the context clearly indicates or requires a different meaning.
   ASTM.  American Society for Testing Materials, an association that publishes standards and requirements for materials used in the construction industry.
   BLUE LINE STREAM. Any stream depicted blue in color, solid or dashed, on a USGS Quad Map.
   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.
   CATCH BASIN. A chamber usually built at the curb line of a street for the admission of surface water to a storm sewer or subdrain, having at its base a sediment sump designed to retain grit and detritus below the point of overflow.
   CHANNEL. A portion of 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.
   CONTOUR. An imaginary line on the surface of the earth connecting points of the same elevation.
   CONTOUR LINE. Line on a map, which represents a contour or points of equal elevation.
   CROWN OF PIPE. The elevation of the top of pipe.
   CULVERT. A closed conduit used for the conveyance of surface drainage water under a roadway, railroad, canal or other impediment.
   DATUM. Any level surface to which elevation is referred, usually using mean sea level.
   DENSE GRADED AGGREGATE. Indiana No. 9 Crushed Stone.
   DESIGN STORM. A selected storm event, described in terms of the probability of occurring once within a given number of years, for which drainage of flood control improvements are designed and built.
   DETENTION. Managing stormwater runoff by temporary holding and controlled release.
   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 accumulated behind the outlet.
   DETENTION STORAGE. The temporary detaining of stormwater in storage facilities on rooftops, in streets, parking lots, school yards, parks, open spaces or other areas under predetermined and controlled conditions, with the rate of release regulated by appropriately installed devices. (Refer to § 54.08.)
   DETENTION TIME. The theoretical time required to displace the contents of a tank or unit at a given rate of discharge (volume divided by rate of discharge).
   DISCHARGE. Usually the rate of water flow. A volume of fluid passing a point per unit time commonly expressed as cubic feet per second, cubic meters per second, gallons per minute or millions of gallons per day.
   DRAINAGE AREA. The area draining into a stream at a given point. It may be of different sizes for surface runoff, subsurface flow and base flow, but generally the surface runoff area is considered as the DRAINAGE AREA.
   DRAINAGE BOARD. The Clark County Drainage Board.
   DRAINAGE IMPROVEMENT. An activity within or adjacent to a natural stream or a human-made drain primarily intended to improve the flow capacity, drainage, erosion and sedimentation control, or stability of the drainage way.
   DROP INLET. A structure in which water drops through a vertical riser connected to a discharge conduit or storm sewer.
   EARTH EMBANKMENT. A human-made placement of soil, rock or other material often used to form an impoundment.
   EASEMENT. A right of use over designated portions of the property of another for a clearly specified purpose.
   EMERGENCY SPILLWAY. Usually a vegetated earth channel used to safely convey flood discharges around an impoundment structure.
   FLOOD ELEVATION. The maximum level of high waters for a flood of a given return period and rainfall duration.
   FLOOD or FLOOD WATER. Water that overflows the banks of a lake or watercourse.
   FLOOD HAZARD AREA. Any floodplain, floodway, floodway fringe or any combination which is subject to inundation by the regulatory flood elevation or any floodplain as delineated by Zone A on the current Flood Hazard Boundary Map of the Federal Emergency Management Agency.
   FLOODPLAIN. The area adjoining the river or stream that has been or may be covered by floodwaters. It consists of both the floodway and the floodway fringe.
   FLOODWAY. The channel of a river or stream and those portions of the flood plains adjoining the channel, which is reasonably required to, efficiently carry and discharge the peak flow of the regulatory flood of any river or stream.
   FLOODWAY FRINGE. The portion of the floodplain lying outside the floodplain, which is inundated by the regulatory flood.
      (1)   The slope of a road, a channel or natural ground;
      (2)   The finished surface of a canal bed, roadbed, top of embankment or bottom of excavation; any surface prepared to a design elevation for the support of construction, such as paving or the laying of a conduit; and
      (3)   To finish the surface of a channel bed, roadbed, top of embankment, or bottom of excavation, or other land area to a smooth, even condition.
      (1)   The height of water above any plane of reference; and
      (2)   The energy, either kinetic or potential, possessed by each unit weight of a liquid, expressed as the vertical height through which a unit would have to fall to release the average energy possessed. Used in various compound terms, such as pressure head or velocity head.
   HEAD LOSS. Energy loss due to friction, eddies, changes in velocity, elevation or direction of flow.
      (1)   The source of a stream; and
      (2)   The water upstream from a structure or point on a stream.
   HYDROGRAPH. A graph showing for a given point on a stream the discharge, stage (depth), velocity or other property of water with respect to time.
   INDOT. Indiana Department of Transportation. Generally used here to refer to specifications contained in the publication “INDOT Standard Specifications”.
   NGVD. A particular elevation datum known as the National Geodetic Vertical Datum of 1929 (NGVD 1929).
   INLET. An opening into a storm sewer system for the entrance of surface stormwater runoff more completely described as a storm sewer inlet.
   INVERT. The inside bottom of a culvert or other conduit.
   MANHOLE. Storm sewer structure through which a person may enter to gain access to a storm sewer or enclosed structure. A MANHOLE may also be an inlet for the storm sewer system.
   PROFESSIONAL LAND SURVEYOR. A person licensed under the laws of the state to practice land surveying.
   PROFESSIONAL ENGINEER. A person licensed under the laws of the state to practice professional engineering.
   RAINFALL INTENSITY. The rate at which rain is falling at any given instant, usually expressed in inches per hour.
   RATIONAL METHOD. A means of computing storm drainage flow rates (Q) by use of the formula Q = CIA, where C is a coefficient describing the physical drainage area, I is the rainfall intensity and A is the area.
   REGULATORY FLOOD. A flood with a peak having a probability of occurrence of 1% in any given year, which is commonly referred to as a 100-year flood as calculated by a method and procedure, which is acceptable to the Board. If a permit for construction in a floodway is required by the Indiana Department of Natural Resources, the regulatory peak discharge must be calculated by the method and procedure acceptable to the Board and the Indiana Department of Natural Resources.
   REGULATORY FLOODWAY. The channel of a river or stream and those portions of the floodplain adjoining the channel which are reasonably required to carry and discharge the peak flow of the regulatory flood of any river or stream.
   RETENTION FACILITY. A facility designed to completely retain a specified amount of stormwater runoff without release except by means of evaporation, infiltration or pumping.
   RUNOFF. The portion of precipitation that flows from a drainage area on the land surface, in open channels or in stormwater conveyance systems.
   SINKHOLES. A sinkhole is any closed depression in a limestone region formed by the removal of water, surficial soil, rock or other material that is connected to a cavern or underground passage. The SINKHOLE drainage area shall include any area that contributes surface water directly to the SINKHOLE.
   SLOPE. Degree of deviation of a surface from the horizontal, measured as a numerical ratio or percent. Expressed as a ratio, the first number is commonly the horizontal distance (run) and the second is the vertical distance (rise), e.g., 2:1; however, the preferred method for designation of slopes is to clearly identify the horizontal (H) and vertical (V) components (length (L) and width (W) components for horizontal angles). Also note that according to international standards (Metric), the slopes are presented as the vertical or width component shown on the numerator - e.g., IV: 2H. Slope expressions in this handbook follow the common presentation of slopes - e.g., 2:1 with the metric presentation shown in parenthesis - e.g., (IV: 2H). Slopes can also be expressed in A percents=. Slopes given in percents are always expressed as (100V/H); e.g., a 2:1 (IV: 2H) slope is a 50% slope.
   SOIL. The unconsolidated mineral and organic material on the immediate surface of the earth that serves as a natural medium for the growth of land plants. Also see alluvial soil, clay, cohesive soil, loam, permeability (soil), sand, silt, soil horizon, soil profile, subsoil, surface soil, topsoil.
   STORM EVENT. An estimate of the expected amount of precipitation within a given period of time. For example, a ten-year frequency, 24-hour duration storm event is a storm that has a 10% probability of occurring in any one year. Precipitation is measured over a 24-hour period.
   STORM FREQUENCY. The time interval between major storms of predetermined intensity and volumes of runoff; e.g., a five-year, ten-year or 20-year storm.
   STORM SEWER. A sewer that carries stormwater, surface drainage, street wash and other wash waters but excludes sewage and industrial wastes. Also called a STORM DRAIN.
   STORMWATER. Any surface flow, runoff and drainage consisting entirely of water from any form of natural precipitation, and resulting from such precipitation.
   SURFACE RUNOFF. Precipitation that flows onto the surfaces of roofs, streets, the ground and the like, and is not absorbed or retained by that surface but collects and runs off.
   TIME OF CONCENTRATION (TC). The travel time of a particle of water from the most hydraulically remote point in the contributing area to the point under study. This can be considered the sum of an overland flow time and times of travel in street gutters, storm sewers, drainage channels and all other drainage ways.
   WATERSHED AREA. All land and water within the confines of a drainage divide.
   ZONING ORDINANCE. The county zoning ordinance, or any replacement zoning ordinance and its amendments.
(Ord. 2010-11, passed 7-22-2010)