In addition to the definitions in § 153.008, for the purpose of this chapter, the following definitions shall apply unless the context clearly indicates or requires a different meaning.
ADVERSE IMPACTS. Any negative impact on plant, soil, air or water resources affecting their beneficial uses including recreation, aesthetics, aquatic habitat, quality and quantity.
BASE FLOOD ELEVATION or BEE. The elevation at all locations delineating the level of flooding resulting from the 100-year frequency flood event, which has a 1% chance of occurring in any given year.
BEST MANAGEMENT PRACTICES or BMP. A measure used to control the adverse stormwater-related effects of development, and includes structural devices (e.g., pre-treatment grit catch basins, storage tanks, etc.), green infrastructure, (e.g., swales, filter strips, infiltration trenches, and site runoff storage basins designed to remove pollutants, reduce runoff rates and volumes, and protect habitats) and nonstructural approaches, such as public education efforts to prevent the dumping of household chemicals into storm drains.
BUFFER. An area of predominantly vegetated land adjacent to channels, wetlands, lakes, or ponds for the purpose of stabilizing banks and reducing contaminants, including sediments, in stormwater that flows to such areas.
BYPASS FLOWS. Stormwater runoff from upstream properties tributary to a property's drainage system, but not under its control. Many times, this is a pre-existing condition.
CATCH BASIN. A receptacle, located where a street gutter opens into a storm sewer, designed to retain matter that would not readily pass through the sewer and to allow stormwater runoff to enter the sewer.
CHANNEL. Any defined river, stream, creek, on-stream lake or impoundment, ditch, culvert, gully, ravine, or natural or human-made drainageway, which has a definite bed and bank or shoreline, in or into which surface or groundwater flows, either constantly or intermittently.
CHANNEL MODIFICATION. Alteration of a channel by changing the physical dimensions or materials of its bed or banks. CHANNEL MODIFICATION includes damming, riprapping (or other armoring), filling, widening, deepening, straightening, relocating, lining and significant removal of bottom or woody rooted vegetation. CHANNEL MODIFICATION does not include clearing human-made debris or removal of trash.
COMPENSATORY STORAGE. An artificially excavated, hydraulically equivalent volume of storage within the floodplain used to balance the loss of natural flood storage capacity when fill or structure are placed within the floodplain.
CONDUIT. Any pipe, sewer or culvert used for the conveyance or movement of water, whether open or closed.
CRITICAL DURATION STORM. The design storm which provides the highest flood discharges/water surface elevation for the flooding source.
DETENTION BASIN. A facility constructed or modified to provide for the temporary storage of stormwater runoff and the controlled release by gravity of this runoff at a prescribed rate during and after a flood or storm.
DETENTION TIME. The amount of time stormwater is held within a detention basin.
DRAINAGE PLAN. A plan, including engineering drawings and supporting calculations, which describes the existing stormwater drainage system and environmental features, including grading, as well as proposed alterations or changes to the drainage system and environment of a property.
DRAINAGEWAY. A watercourse, gully, swale, dry stream, creek or ditch which naturally carries stormwater runoff or which is fed by street or building gutters or by stormwater sewers.
DRY BASIN. A detention basin designed to drain after temporary storage of stormwater flows and to normally be dry over much of its bottom area.
EROSION. The general process whereby soil or earth is moved by rainfall, flowing water, wind or wave action.
EXCESS STORMWATER RUNOFF. The volume and rate of flow of stormwater discharged from a new development or redevelopment which is or will be in excess of that volume and rate which existed before development or redevelopment.
FLOOD FRINGE. That area as designated by the Federal Emergency Management Agency (FEMA) on either side of the floodway. This area is subject to inundation from the base flood but conveys little or no flow.
FLOOD INSURANCE RATE MAP (FIRM). A map prepared by FEMA that depicts the Special Flood Hazard Area (SFHA) within a community. This map includes insurance rate zones and regulatory floodplains and may or may not depict regulatory floodways.
FLOODPLAIN. The land adjacent to a body of water with ground surface elevations at or below the base flood or the 100-year frequency flood elevation which is subject to inundation.
FLOODWAY. The channel and that portion of the floodplain, including on-stream lakes, adjacent to a stream or watercourse which is needed to store and convey the anticipated existing and future 100-year frequency flood discharge with no more than a 0.1-foot increase in stage due to any loss of flood conveyance or storage and no more than a 10% increase in velocities.
FREEBOARD. An increment of height added to the BFE, groundwater table, or 100-year design water surface elevation to provide a factor of safety for uncertainties in calculations, unknown local conditions, wave action, non-stationary climate, and unpredictable effects such as those caused by debris jams.
GREEN INFRASTRUCTURE. Any stormwater management technique or practice that reduces runoff volume through preserving, restoring, using, or enhancing the processes of infiltration, evapotranspiration, and reuse. Approaches may include green roofs, naturalized detention facilities, trees and tree boxes, rain gardens, vegetated swales, vegetated buffers, wetlands, infiltration planters, porous and permeable pavements, porous piping systems, dry wells, vegetated median strips, reforestation/revegetation, rain barrels, and cisterns, and protection and enhancement of riparian buffers and floodplains.
HYDROGRAPH. A graph showing for a given location on a stream or conduit, the flow rate with respect to time.
ILLINOIS URBAN MANUAL. A publication of best management practices commonly used in an urban setting produced by the Association of Illinois Soil and Water Conservation Districts, published October 2013. http://www.aiswcd.oorg/illinois-urban-manual/
IMPERVIOUS SURFACE. The area of property that is covered by materials other than soil and vegetation and that has no intended capacity to absorb water, such as parking lots, driveways, sidewalks, patios, tennis courts, roofs and other structures.
INFILTRATION. The passage or movement of water into the soil surfaces.
INLET. A receptacle, located where a street gutter opens into a storm sewer, designed to retain matter that would not readily pass through the sewer and to allow stormwater runoff to enter the sewer.
KARST. A type of topography or landscape characterized by features, including but not limited to, surface depressions, sinkholes, rock pinnacles/ uneven bedrock surfaces, underground drainage, and caves. Karst is formed on carbonate rocks, such as limestone or dolomite.
LOESSAL SOIL. A sediment, commonly non-stratified and unconsolidated, composed predominately of silt sized particles with accessory clay and sand.
MAJOR DRAINAGE SYSTEM. That portion of a drainage system needed to store and convey flows beyond the capacity of the minor drainage system generally consisting of storm sewers/ culverts or swales/ ditches that directly connect to a street system in dedicated easements between property lines that directly convey storm water to the street or road storm sewers or detention facilities.
MAXIMUM EXTENT PRACTICABLE. Highest level of runoff volume reduction that is achievable for the development as determined by the applicant and approved by the City Engineer.
MINOR DRAINAGE SYSTEM. That portion of a drainage system designed for the convenience of the public and generally on private property. It consists of yard inlets, pipe drains from downspouts, small open channels, and yard sales and, where manmade, is to be designed to handle the two-year runoff event.
MODIFIED RATIONAL METHOD. As described in the Illinois Department of Transportation “Drainage Manual,” this method is based on the principal that the maximum rate of runoff from a given drainage area occurs at that point in time when all parts of the watershed are contributing to the flow. The rainfall generating the peak flow is assumed to be of uniform intensity for the entire watershed when the rainfall duration is equal to the time of concentration.
NATURAL DRAINAGE. Channels formed in the existing surface topography of the earth prior to changes made by unnatural causes.
NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM (NPDES). The NPDES permit program was created in 1972 by the Clean Water Act, (CWA). The CWA prohibits anybody for discharging “pollutants” through a “point source” into a water of the United States unless they have an NPDES permit. The permit will contain limits on what can be discharged, monitoring and reporting requirements, and other provisions such as erosion control at construction sites to ensure that discharge does not hurt water quality or people's health.
ONE HUNDRED-YEAR (100-YEAR) STORM EVENT. A rainfall, runoff or flood event having a 1% chance of occurring in any given year.
OVERLAND FLOW PATH. A design feature of the major stormwater system which carries flows in excess of the minor stormwater system design capacity in an open channel or swale, or as sheet flow or weir flow over a feature designed to withstand the particular erosive forces involved.
PEAK FLOW. The maximum rate of flow of water at a given point in a channel or conduit.
POSITIVE DRAINAGE. Providing overland flow paths for all areas of a property, including depression areas, which drain to channels or storm sewer.
RETENTION BASIN (WET PONDS). A facility designed to completely retain a specified amount of stormwater runoff without release except by means of evaporation, infiltration, emergency bypass or pumping.
RUNOFF. The water or drainage derived from melting snow or rain falling on the land surface, flowing over the surface of the ground, or collected in channels or conduits.
SEDIMENTATION. The process that deposits soils, debris, and other materials - either on other ground surfaces or in bodies of water or stormwater drainage systems.
SINKHOLE (KARST AREAS). A land surface depression or blind valley which may or may not have surface openings to cavernous underground areas and are the result of water movement through silts and jointed limestone. These conditions make the areas unstable and susceptible to subsidence and surface collapse. Fractures in the limestone may channel runoff water to public or private water supplies, making those sources especially susceptible to groundwater contamination.
SLOPE DISTURBANCE LINE. The line which delineates relatively level building areas from areas where slopes exceed one foot vertical in six foot horizontal and where special erosion control precautions must be taken.
STORM SEWER. A closed conduit or pipe for conveying collected stormwater.
STORMWATER. Runoff from the surface of the land resulting from precipitation or snow or ice melt.
STORMWATER DRAINAGE SYSTEM. All means, natural and human-made, used for conveying stormwater to, through or from a drainage area to the point of final outlet from a property. The STORMWATER DRAINAGE SYSTEM includes but is not limited to any of the following: conduits and appurtenance features, canals, channels, ditches, streams, culverts, streets, storm sewers, detention basins, swales and pumping stations.
STORMWATER POLLUTION PREVENTION PLAN (SWPPP). Set of drawings or other documents submitted as a prerequisite to obtaining a stormwater management approval, which contains all information and specifications of drainage systems and environmental features proposed after the development of a property.
STREAM. Any river, creek, branch, or natural or human-made drainageway which has a definite bed and bank or shoreline, in or into which surface or groundwater flows, either constantly or intermittently.
TEN-YEAR (10-YEAR) STORM EVENT. A runoff, rainfall, or flood event having a 10% chance of occurring in any given year.
TIME OF CONCENTRATION. The elapsed time for stormwater to flow from the most hydraulically remote point in a drainage basin to a particular point of interest in that watershed.
TRIBUTARY WATERSHED. All of the land surface area that contributes runoff to a given point.
TWENTY-FIVE YEAR (25-YEAR) STORM EVENT. A runoff, rainfall, or flood event having a 4% chance of occurring in any given year.
TWO-YEAR (2-YEAR) EVENT. A runoff, rainfall or flood event having a 50% chance of occurring in any given year.
VOLUME CONTROL STORAGE. The volume of storage required to detain a specified amount of runoff from the new impervious area of development on the site.
WATER TABLE. The upper limit of a free water surface in a saturated soil or underlying material.
WATERSHED. All land area drained by, or contributing water to, the same stream, creek, ditch, lake, marsh, stormwater facility, groundwater or depressional area.
WATERS OF THE UNITED STATES (WOTUS). The term refers to wetlands, streams, and water bodies that are under the U.S. Army Corps of Engineers regulatory jurisdiction.
WET BASIN. A detention basin designed to maintain a permanent pool of water after the temporary storage of stormwater runoff.
WETLANDS. Defined by regulation as “those areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, and under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions.”
(Ord. 2017-03, passed 3-6-2017)