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Stormwater Management Abbreviations

BFE – Base Flood Elevation

BMP – Best Management Practice

CFS – Cubic Feet Per Second

FEMA – Federal Emergency Management Agency

FIRM – Flood Insurance Rate Map

FIS – Flood Insurance Study

FPG – Flood Protection Grade

FPS – Feet Per Second

IAC – Indiana Administrative Code

IDEM – Indiana Department of Environmental Management

IDNR – Indiana Department of Natural Resources

INDOT – Indiana Department of Transportation.

LCSO – Lake County Surveyor's Office

MCM – Minimum Control Measure

MS4 – Municipal Separate Storm Sewer System

NAVD – North American Vertical Datum of 1988

NFIP – National Flood Insurance Program

NRCSUSDA – Natural Resources Conservation Service

NPDES – National Pollution Discharge Elimination System

NOI – Notice of Intent, permit application filed with IDEM under provisions of 327 IAC 15-5 and 15-13

NOT – Notice of Termination, certification that all permit provisions have been successfully completed

NOV – Notice of Violation, notice to permittee that provisions of permit have not been satisfied

SFHA – Special Flood Hazard Area

SWCD – Soil and Water Conservation District

SWPPP – Stormwater Pollution Prevention Plan

SWQMP – StormDrainage Control Management Plan

Tc – Time of Concentration

USCS – Unified Soil Classification System

USDA – United States Department of Agriculture

USFWS – United States Fish and Wildlife Service

Stormwater Management Definitions

Base Flood Elevation. The water surface elevation corresponding to a flood having a one-percent (1%) probability of being equaled or exceeded in a given year.

Benchmark. A marked point of known elevation from which other elevations maybe established.

Best Management Practices (BMPs). Design, construction, and maintenance practices and criteria for stormwater facilities that minimize the impact ofstormwater runoff rates and volumes, prevent erosion, and capture pollutants.

Buffer Strip. An existing, variable width strip of vegetated land intended to protect Drainage Control and habitat.

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 drain or subdrain, having at its base a sediment sump designed to retain grit and detritus below the point of overflow.

Channel Improvement. Alteration, maintenance, or reconstruction of the channel area for the purpose of improving the channel capacity or overall drainage efficiency. The noted “improvement” does not necessarily imply Drainage Control or habitat improvement within the channel or its adjacent area.

Channel Modification. Alteration of a channel by changing the physical dimensions or materials of its bed or banks. Channel modification includes damming, rip-rapping or other armoring, widening, deepening, straightening, relocating, lining, and significant removal of bottom or woody vegetation. Channel modification does not include the clearing of dead or dying vegetation,debris, or trash from the channel. Channelization is a severe form of channel modification typically involving relocation of the existing channel (e.g.,straightening).

Channel Stabilization. Protecting the sides and bed of a channel from erosion by controlling flow velocities and flow directions using jetties, drops, or other structures and/or by fining the channel with vegetation,riprap, concrete, or other suitable lining material.

Channel. A portion of a natural or artificial watercourse which periodically or continuously contains moving water, or which forms a connecting link between two (2) 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 substructures are placed within the floodplain.

Contiguous. Adjoining or in actual contact with.

Contour Line. Line on a map which represents a contour or points of equal elevation.

Control Structure. A structure designed to control the rate of flow that passes through the structure, given a specific upstream and downstream water surface elevation.

Council, Town. The Town Council of the Town of St. John, Lake County, Indiana and any duly designated representative, employee or administrative official to whom the Town Council shall specifically delegate a responsibility authorized by this Storm Drainage Control Regulations Ordinance, as amended from time to time.

Cubic Feet Per Second (CFS). Used to describe the amount of flow passing a given point in a stream channel. One (1) cubic foot per second is equivalent to approximately seven and one half (7.5) gallons per second.

Culvert. A closed conduit used for the conveyance of surface drainage water under a roadway, railroad, canal or other impediment.

Design Storm. A selected storm event, described in terms of the probability of occurring once within a given number of years, for which drainage or flood control improvements are designed and built.

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.

Detention Facility. A facility designed to detain a specified amount of stormwater runoff assuming a specified release rate. The volumes are often referred to in units of acre-feet.

Detention Storage. The temporary detaining of storage 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.

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).

Development. Any man-made change to improved or unimproved real estate including but not limited to:

Construction, reconstruction, or placement of a building or any addition to a building;
Construction of flood control structures such as levees, dikes, dams or channel improvements;
Construction or reconstruction of bridges or culverts;
Installing a manufactured home on a site, preparing a site for a manufactured home, or installing a recreational vehicle on a site for more than one hundred eighty (180) days;
Installing utilities, erection of walls, construction of roads, or similar projects;
Mining, dredging, filling, grading, excavation, or drilling operations;
Storage of materials; or
Any other activity that might change the direction, height, or velocity of flood or surface waters.
“Development” does not include activities such as the maintenance of existing buildings and facilities such as painting, re-roofing, resurfacing roads, or gardening, plowing and similar agricultural practices that do not involve filling, grading, excavation, or the construction of permanent buildings.

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.

Ditch. A man-made, open drainageway in or into which excess surface water or groundwater drained from land, stormwater runoff, or floodwaters flow either continuously or intermittently.

Drain. A buried slotted or perforated pipe or other conduit (subsurface drain) or a ditch (open drain) for carrying off surplus groundwater or surface water.

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. The removal of excess surface water or groundwater from land by means of ditches or subsurface drains.

Drop Manhole. 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 dewatered after having provided its planned detention of runoff during a storm event.

Duration. The time period of a rainfall event.

Erosion. The wearing away of the land surface by water, wind, ice, gravity, or other geological agents.

Flood (or Flood Waters). A general and temporary condition of partial or complete inundation of normally dry land areas from the overflow, the unusual and rapid accumulation, or the runoff of surface waters from any source.

Flood Elevation. The elevation at all locations delineating the maximum level of high waters for a flood of given return period.

Flood Frequency. A statistical expression of the average time period between floods equaling or exceeding a given magnitude. For example, a 100-year flood has a magnitude expected to be equalled or exceeded on the average of one (1)time one hundred (100) years; such a flood has a one-percent (1%) chance of being equalled or exceeded in any given year. Often used interchangeably with”recurrence interval”.

Flood Hazard Area. Any floodplain, floodway, floodway fringe, or any combination thereof which is subject to inundation by the regulatory flood; or any flood plain as delineated by Zone X on a Flood Hazard Boundary Map.

Flood Protection Grade (FPG). The elevation of the regulatory or 100-year flood plus two (2) feet at any given location in the Special Flood Hazard Area or 100-year floodplain.

Flood Protection Grade. The elevation of the lowest floor of a building, including the basement, which shall be two (2) feet above the elevation of the regulatory flood.

Floodplain. The channel proper and the areas adjoining the channel which have been or hereafter may be covered by the regulatory or 100-year flood. Any normally dry land area that is susceptible to being inundated by water from any natural source. The floodplain includes both the floodway and the floodway fringe districts.

Floodway Fringe. That portion of the floodplain lying outside the floodway, which is inundated by the regulatory flood.

Floodway. The channel of a river or stream and those portions of the floodplains adjoining the channel which are reasonably required to efficiently carry and discharge the peak flow of the regulatory flood of any river or stream.

Footing Drain. A drain pipe installed around the exterior of a basement wall foundation to relieve water pressure caused by high groundwater elevation.

Freeboard. An increment of height added to the base flood elevation to provide a factor of safety for uncertainties in calculations, unknown local conditions, wave actions and unpredictable effects such as those caused by ice or debris jams. (See Flood Protection Grade).

Gabion. An erosion control structure consisting of a wire cage or cages filled with rocks.


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.
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.
To finish the surface of a canal bed, roadbed, top of embankment, or bottom of excavation, or other land area to a smooth, even condition.
HEC-22. Federal Highway Administration , Publication No. FHWM-NHI-01-021,August 2001. Urban Drainage Design Manual. Hydraulic Engineering Circular No.22, Second Edition. The document may be downloaded from here

Hydraulics. A branch of science that deals with the practical application of the mechanics of water movement. A typical hydraulic study is undertaken to calculate water surface elevations.

Hydrograph. For a given point on a stream, drainage basin, or a lake, a graph showing either the discharge, stage (depth), velocity, or volume of water with respect to time.

Hydrologic Unit Code. A numeric United States Geologic Survey code that corresponds to a watershed area. Each area also has a text description associated with the numeric code.

Hydrology. The science of the behavior of water in the atmosphere, on the surface of the earth, and underground. A typical hydrologic study is undertaken to compute flow rates associated with specified flood events.

Impact Areas. Areas defined or mapped that 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, land within seventy-five (75) feet of each bank of any regulated drain or within seventy-five (75) feet from the centerline of any regulated tile ditch.

Impervious surface. Surfaces, such as pavement and rooftops, which prevent the infiltration of stormwater into the soil.

Infiltration. Passage or movement of water into the soil.

Inlet. An opening into a storm drain system for the entrance of surface storm water runoff, more completely described as a storm drain inlet.

Invert. The inside bottom of a culvert or other conduit.

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 amain 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 System. Drainage system carrying runoff from an area of one(1) square mile.

Measurable storm event. A precipitation event that results in a total measured precipitation accumulation equal to, or greater than, one-half (1/2)inch of rainfall.

Minimum Control Measure. Minimum measures required by the NPDES Phase II program. The six (6) MCMs are: Public education and outreach, Public participation and involvement, Illicit discharge detection and elimination, Construction site runoff control, Post-construction runoff control, andPollution prevention and good housekeeping.

Minor Drainage Systems. Drainage systems having an area of less than one (1)square mile.

MS4 Operator. Individual(s) appointed by the St. John Town Council to administer and enforce local stormwater regulations.

Municipal Separate Storm Sewer System. An MS4 meets all the following criteria:

is a conveyance or system of conveyances owned by the State, County, Town, or other public entity;
discharges to waters of the U.S.;
is designed or used for collecting or conveying stormwater;
is not a combined sewer; and,
is not part of a Publicly Owned Treatment Works(POTW).
Off-site. Everything not located at or within a particular site.

Off-site Land Areas. Those areas that by virtue of existing topography naturally shed surface water onto or through the developing property.

On-Site. Located within the controlled or urbanized area where runoff originates.

Open Drain. A natural watercourse or constructed open channel that conveys drainage water.

Open Space. Any land area devoid of any disturbed or impervious surfaces created by industrial, commercial, residential, agricultural, or other manmade activities.

Orifice. A device which controls the rate of flow from a detention basin.

Outfall. The point, location, or structure where a pipe or open drain discharges to a receiving body of water.

Outlet. The point of water disposal from a stream, river, lake, tidewater, or artificial drain.

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 Plan Commission of the Town of St. John, Lake County, Indiana.

Radius of Curvature. Length of radius on 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 and/or within the municipal corporate boundaries of the Town of St. John, Lake County, Indiana.

Regulated Drain. A drain subject to the provisions of the Indiana Drainage Code, I.C.-36-9-27, as amended from time to time, and under the jurisdictional authority of the Lake County Surveyor.

Regulatory or 100-Year Flood. The discharge or elevation associated with the 100-year flood as calculated by a method and procedure which is acceptable to and approved by the Indiana Department of Natural Resources (IDNR) and theFederal Emergency Management Agency (FEMA). The “regulatory flood” is also known as the “base flood”.

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 storm water release 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 one (1) time. A flood having a return period of One Hundred (100) years has a one percent (1%) probability of being equaled or exceeded in any one (1) year.

Routing Path. That part of the Storm Drainage System which carries the runoff which exceeds the capacity to carry runoff from a storm with a return period of not less than One Hundred (100) years without causing significant threat to property or public safety.

Runoff Coefficient. A decimal fraction relating the amount of rain which appears as runoff and reaches the storm drain 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.

Runoff. That portion of precipitation that flows from a drainage area on the land surface, in open channels, or in stormwater conveyance systems.

Sediment. Solid material (both mineral and organic) that is in suspension, is being transported, or has been moved from its site of origin by air, water, gravity, or ice and has come to rest on the earth’s surface.

Settling Basin. An enlargement in the channel of a stream to permit the settling of debris carried in suspension.

Silt Fence. A fence constructed of wood or steel supports and either natural (e.g. burlap) or synthetic fabric stretched across area of non-concentrated flow during site development to trap and retain on-site sediment due to rainfall runoff.

Silt. (1) Soil fraction consisting of particles between 0.002 and 0.05 mm in diameter. (2) A soil textural class indicating more than 80% silt.

Special Flood Hazard Area. An area that is inundated during the 100-Year flood.

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.

Storm 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 Event. An estimate of the expected amount of precipitation within a given period of time. For example, a 10-yr. frequency, 24-hr. duration storm event is a storm that has a 10% probability of occurring in any one year. Precipitation is measured over a 24-hr. period.

Storm Frequency. The time interval between major storms of predetermined intensity and volumes of runoff–e.g., a 5-yr., 10-yr. or 20-yr. storm.

Storm Sewer. A closed conduit for conveying collected storm water, while excluding sewage and industrial wastes. (Also called a storm drain.)

Stormwater 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, storage facilities, swales, 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.

Subarea/Subbasin. Portion of a watershed divided into homogenous drainage units which can be modeled for purposes of determining runoff rates. The subareas/subbasins have distinct boundaries, as defined by the topography of the area.

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 understudy. 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.

Topographic Map. Graphical portrayal of the topographic features of a land area, showing both the horizontal distances between the features and the irelevations above a given datum.

Topography. The representation of a portion of the earth’s surface showing natural and man-made features of a give locality such as rivers, streams, ditches, lakes, roads, buildings and most importantly, variations in ground elevations for the terrain of the area.

TP-40 Rainfall. Design storm rainfall depth data for various durations published by the National Weather Service in their Technical Paper 40 dated 1961.

TR-20. Soil Conservation Service, 1992. Hydraulics and Hydrology Program. Technical Release No. 20, U.S. Department of Agriculture. As of the fall of 2006, DOS and Windows versions of the computer program are available on-line at https://www.nrcs.usda.gov/wps/portal/nrcs/detailfull/national/water/manage/hydrology/?cid=stelprdb1042793

TR-55. Soil Conservation Service, 1992. Urban Hydrology for Small Watersheds. Technical Release No. 55, U.S. Department of Agriculture. As of the fall of 2006, DOS and Windows versions of the computer program are available on-line at https://www.nrcs.usda.gov/wps/portal/nrcs/detailfull/national/water/?&cid=stelprdb1042901

Trained individual. An individual who is trained and experienced in the principles of storm Drainage Control, including erosion and sediment control as may be demonstrated by state registration, professional certification, experience, or completion of coursework that enable the individual to make judgments regarding storm water control or treatment and monitoring.

Tributary. Based on the size of the contributing drainage area, a smaller watercourse which flows into a larger watercourse.

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.

Water Course or Watercourse. Any river, stream, creek, brook, branch, natural or man-made drainage way in or into which stormwater runoff or floodwaters flow either continuously or intermittently.

Waterbody. Any accumulation of water, surface, or underground, natural or artificial.

Watershed. The region drained by or contributing water to a specific point that could be along a stream, lake or other stormwater facilities. Watersheds are often broken down into subareas for the purpose of hydrologic modeling.

Waterway. A naturally existing or manmade open conduit or channel utilized for the conveyance of water.

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.

Wetlands. Areas that are inundated or saturated by surface water or groundwater at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions.

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