For the purposes of this Ordinance, the following definitions shall apply:
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 flood plain used to balance the loss of natural flood storage capacity when artificial fill or structures are placed within the flood plain.
CONTIGUOUS. Adjoining or in actual contact with.
COUNCIL. The City Council of Mt. Vernon, Jefferson County, Illinois, and any subordinate employee or agent to whom they shall specifically delegate a responsibility authorized by this Ordinance.
CRITICAL DURATION STORM. The storm duration which requires the greatest detention storage. In the Rational Method, the critical duration storm is equal to the time of concentration being analyzed. For computer modeling, the critical duration storm is equal to or greater than the time of concentration of the watershed being modeled.
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 storm water to a prescribed maximum rate, and to detain concurrently the excess waters that accumulate behind the outlet.
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 greater than two feet between the inlet pipe and the outlet pipe. A vertical drop pipe shall be located immediately outside the manhole.
DRY BOTTOM DETENTION BASIN. A basin designed to be completely dewatered after having provided its planned detention of runoff during a storm event.
DURATION. The time period of a rainfall event.
ENGINEER. A subordinate or agent of the Council to whom the Council has delegated responsibility. The City Engineer serves as a subordinate or agent to the Council having chief engineering responsibilities.
EROSION. Wearing away of the land by running water, waves, temperature changes, ice, or wind.
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 or FLOOD WATERS. 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 HAZARD AREA. Those flood plains which have not been adequately protected from flooding caused by the regulatory flood, and are shown on the Flood Hazard or Floodway Flood Boundary Maps of the Federal Insurance Administration or maps provided to the City by the Federal Emergency Management Agency.
FLOOD PLAIN. The area adjoining the river or stream which has been or may hereafter be covered by flood water from the regulatory floodway and floodway fringe.
FLOODWAY. See REGULATORY FLOODWAY.
FLOODWAY FRINGE. That portion of the flood plain 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, etc., or natural ground surface usually expressed in terms of the percentage the vertical rise (or fall) bears to the corresponding horizontal distance.
HEC-1. U.S. Army Corps of Engineers Flood Hydrograph Package.
IMPACT AREAS. Areas defined and mapped by the Council 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 flood plain, land within 100 feet of each bank of any regulated drain or within 100 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 for the entrance of surface storm water 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.
MANHOLE. Storm sewer structure through which a person may enter to gain access to an underground storm sewer or enclosed structure.
MAJOR DRAINAGE AREA. Drainage system carrying runoff from an area of more than ten square miles Rural classification or one square mile Urban classification. Designs shall be in accordance with the Illinois Department of Transportation Division of Water Resources Standards.
MINOR DRAINAGE SYSTEM. Drainage system carrying runoff from an area of less than ten square miles Rural classification or one square mile Urban classification.
OFF SITE. Everything not on site.
ON SITE. Located within the controlled or Urbanized 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 predetermined storm or flood.
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 land under the jurisdiction of the City of Mt. Vernon. This includes all areas within the corporate limits of the City and all areas within one and one half miles of the corporate limits as existing now or in the future.
REGULATORY FLOOD. That flood having a peak discharge which can be equaled or exceed on the average of once in a one hundred (100) year period, as calculated by a method and procedure which is acceptable to the Council. If a permit from the Illinois Department of Natural Resources Office of Water Resources for construction in the floodway is required (see § 53.06), then the regulatory flood peak discharge should be calculated by a method acceptable to the Council and the Illinois Department of Natural Resources Office of Water Resources. This regulatory flood is equivalent to a flood having a probability of occurrence of one percent (1%) in any given year.
REGULATORY FLOODWAY. The channel of a river or stream and those portions of the flood plains adjoining the channel which are reasonably required to carry and discharge efficiently the peak flow of the regulatory flood of any river or stream.
RELEASE RATE. The amount of storm water released from a storm water 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 one percent probability of being equaled or exceeded in any one year.
RUNOFF COEFFICIENT. A decimal fraction relating the amount of rain which appeared as runoff and reaches the storm sewer system to the total amount of rain falling. A coefficient of 0.5 implies that 50 percent of the rain falling on a given surface appears as storm water runoff.
SEDIMENT. Material of soil or rock origin, transported, carried 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 storm water flow under an obstruction such as a sanitary sewer.
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 storm water control facility, computed from the time water first begins to be stored.
STORM SEWER. A closed conduit for conveying collected storm water.
STORM WATER DRAINAGE SYSTEM. All means, natural or man made, used for conducting storm water to, through or from a drainage area to any of the following: conduits and appurtenant features, canals, channels, ditches, streams, culverts, street and pumping stations.
STORM WATER RUNOFF. The water derived from rains falling within a tributary basin, flowing over the surface of the ground or collected in channels or conduits.
TR-20. Natural Resources Conservation Services Technical Release 20 Project Formulation Hydrology.
TR-55. Natural Resources Conservation Services Technical Release 55 Urban Hydrology for Small Watersheds.
TRIBUTARY. Contributing storm water 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 natural or man made drainageway in or into which storm water runoff or floodwaters flow wither 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.
(Prior Code, Art. 20, § 20-4)