For the purpose of this subchapter, the following definitions apply unless the context clearly indicates or requires a different meaning.
ACRE-FOOT (AF). A measure of water volume equal to the inundation of a flat one-acre area to a depth of one foot (43,560 cubic feet).
ADAMS COUNTY DRAINAGE BOARD. The Drainage Board of the county and any subordinate employee to whom they shall specifically delegate a responsibility authorized by this subchapter.
AMORTIZATION PERIOD. The length of time used to repay a debt or mortgage to depreciate an initial cost.
ANTECEDENT RUNOFF CONDITION. The index of runoff potential before a storm event. The index, developed by the Soil Conservation Service (SCS), is an attempt to account for the variation of the SCS runoff curve number (CN) from storm to storm. The ANTECEDENT MOISTURE CONDITION is the moisture found within a soil due to a previous storm event.
BACKFLOW PREVENTER. A device that allows liquids to flow in only one direction in a pipe. BACKFLOW PREVENTERS are used on sewer pipes to prevent a reverse flow during flooding situations.
BACKWATER. The rise in water surface elevation caused by some obstruction such as a narrow bridge opening, buildings, or fill material that limits the area through which the water shall flow. BACKWATER may also be considered as that water elevation found in a tributary that is based on the receiving stream’s existing water elevation.
BASE FLOOD ELEVATION (BFE). The water surface elevation corresponding to a flood having a 1% probability of being equaled or exceeded in a given year.
BASEMENT. Any area of the building having its floor subgrade on all sides.
BENCHMARK. A marked point of known elevation from which other elevations may be established.
BEST MANAGEMENT PRACTICES. Design, construction, and maintenance practices and criteria for stormwater facilities that minimize the impact of stormwater runoff rates and volumes, prevent erosion, and capture pollutants.
BUILDING. See STRUCTURE.
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.
CENTERLINE OF CHANNEL. The middle point or baseline of a channel.
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.
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).
COMPENSATORY STORAGE. An excavated volume of storage within a floodplain used to balance the loss of natural flood storage capacity when fill or substructures are placed within the floodplain. Such excavated volume has to be available for inundation by and accessible to the floodwaters.
CONTIGUOUS. Adjoining or in actual contact with.
CONTOUR. Imaginary line on the earth’s surface which connects points of equal elevation.
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.
CONVOLUTION. The process of translating precipitation excess into a runoff hydrograph.
CRAWL SPACE. Low space below first floor of a house where there has not been excavation deep enough for a basement, but where there is often access for pipes, ducts, and utilities.
CROWN OF PIPE. The elevation of top of pipe.
CROSS-SECTION. A graph or plot of ground elevation across a stream valley or a portion of it, usually along a line perpendicular to the stream or direction of flow.
CUBIC FEET PER SECOND (CFS). Used to describe the amount of flow passing a given point in a stream channel. One cubic foot per second is equivalent to approximately seven and one-half gallons per second.
CULVERT. A closed conduit used for the conveyance of surface drainage water under a roadway, railroad, canal, or other impediment.
CURVE NUMBER (CN). The Soil Conservation Service index that represents the combined hydrologic effect of soil, land use, land cover, hydrologic condition, and antecedent runoff condition.
DAM. All obstructions, wall embankments, or barriers, together with any abutments and appurtenant works, constructed to store, direct water, or create a pool (not including underground water storage tanks).
DAMAGE. Measurable rise in flood heights on buildings currently subject to flooding, flooding of buildings currently not subject to flooding, and increases in volume or velocity to the point where the rate of land lost to erosion and scour is substantially increased.
DATUM. Any level surface to which elevations are referred, usually using mean sea level.
DEPRESSIONAL STORAGE AREAS. Non-riverine depressions in the earth where stormwater collects. The volumes are often referred to in units of acre-feet.
DESIGN STORM. A selected storm event, described in terms of the probability of occurring once within a given number of years, for which stormwater or flood control improvements are designed and built.
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.
DEVELOPMENT.
(1) Any human-made change to improved or unimproved real estate as defined below:
(b) All new business, commercial, and industrial developments more than one acre and up to three acres in size and exceeding 33% impervious surface;
(c) All new business, commercial, and industrial developments over three acres in size; and
(d) Any new highway, street, or road construction that adds impervious surface over and above the existing condition and in the opinion of the County Surveyor adds significantly to the stormwater runoff so as to require the application of this subchapter.
(2) 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. In addition, DEVELOPMENT does not include the reconstruction or maintenance of regulated drains or replacement of existing stream crossings by the County Drainage Board, the County Highway Department, the State Department of Transportation, or other governmental agencies.
DISCHARGE. Normally, the rate of flow into or out of a sewer, stormwater storage facility, or from a land surface. DISCHARGES are customarily measured in cubic feet per seconds (CFS).
DRAINAGE AREA. The area from which water is carried off by a drainage system, a watershed, or catchment area.
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 FACILITY. A facility 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.
ELEVATION CERTIFICATE. A form published by Federal Emergency Management Agency that is used to certify the 100-year or base flood elevation and the lowest elevation of usable space to which a building has been constructed.
ELEVATION REFERENCE MARK (ERM). Elevation benchmark tied to the National Geodetic Survey Map (NGSM) and identified during the preparation of a flood insurance study prepared for the Federal Emergency Management Agency.
ENERGY DISSIPATOR. A device to reduce the energy of flowing water.
EROSION. Wearing away of the land by running water and waves, abrasion, temperature changes, ice, and wind.
EXTRATERRITORIAL JURISDICTION (ETJ). Areas located outside the corporate limits of a community over which the community has statutory development authority.
FARM OR FIELD TILE. A small diameter clay, plastic, or pipe of some other accepted material installed in an agricultural area to allow drainage of farmland.
FEMA. The Federal Emergency Management Agency.
FLOOD or FLOODWATERS. 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 BOUNDARY AND FLOODWAY MAP (FBFM). A map prepared by the Federal Emergency Management Agency that depicts the FEMA designated floodways within a community. This map also includes the delineation of the 100-year and 500-year floodplain boundaries and the location of the flood insurance study cross-sections.
FLOOD CREST. The maximum stage or elevation reached or expected to be reached by the waters of a specific flood at a given location.
FLOOD DURATION. The length of time a stream is above flood stage or overflowing its banks.
FLOOD EASEMENT. Easement granted to identify areas inundated by the 100-year flood and prohibit or severely restrict development activities.
FLOOD ELEVATION. The elevation at all locations delineating the maximum level of high waters for a flood of given return period.
FLOOD FIGHTING. Actions taken immediately before or during a flood to protect human life and to reduce flood damages such as evacuation, emergency sandbagging, and diking.
FLOOD FORECASTING. The process of predicting the occurrence, magnitude, and duration of an imminent flood through meteorological and hydrological observations and analysis.
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.
FLOOD HAZARD BOUNDARY MAP (FHBM). A map prepared by the Federal Emergency Management Agency that depicts special flood hazard areas as a zone A within a community. There are no study text, base flood elevations, or floodways associated with this map.
FLOOD INSURANCE RATE MAP (FIRM). A map prepared by the Federal Emergency Management Agency that depicts special flood hazard areas within a community. This map also includes the 100-year or base flood elevation at various locations along the watercourses. More recent versions of the FIRM may also show the FEMA designated floodway boundaries and the location of the flood insurance study cross-sections.
FLOOD INSURANCE STUDY (FIS). A study prepared by the Federal Emergency Management Agency to assist a community participating in the National Flood Insurance Program in its application of the program regulations. The STUDY consists of a text which contains community background information with respect to flooding, a floodway data table, a summary of flood discharges, flood profiles, a flood insurance rate map, and a flood boundary and floodway map.
FLOODPLAIN. The channel proper and the areas adjoining any lake or watercourse which have been or hereafter may be covered by the regulatory or 100-year flood. The FLOODPLAIN includes both the floodway and the floodway fringe districts.
FLOODPLAIN MANAGEMENT. The operation of a program of corrective and preventive measures for reducing flood damage, including, but not limited to, flood control projects, floodplain land use regulations, flood-proofing of buildings, and emergency preparedness plans.
FLOODPLAIN REGULATIONS. General term applied to the full range of codes, ordinances, and other regulations relating to the use of land and construction within floodplain limits. The term encompasses zoning ordinances, subdivision regulations, building and housing codes, encroachment laws, and open area (space) regulations.
FLOOD PROFILE. A graph showing the relationship of water surface elevation to a specific location, the latter generally expressed as distance above the mouth of a stream of water flowing in an open channel. It is generally drawn to show surface elevation for the crest of a specific magnitude of flooding, but may be prepared for conditions at any given time or stage.
FLOOD PROTECTION GRADE (FPG). The elevation of the regulatory or 100-year flood plus two feet at any given location in the special flood hazard area or 100-year floodplain.
FLOOD RESISTANT CONSTRUCTION (FLOOD-PROOFING). Additions, changes, or adjustments to structures or property that are designed to reduce or eliminate the potential for flood damage.
FLOOD STORAGE AREAS. Depressions, basins, or other areas that normally stand empty or partially empty, but fill with rainfall runoff during storms to hold the runoff and reduce downstream flow rates. The volumes are often referred to in units of acre-feet.
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 efficiently the peak flow of the regulatory flood of any river or stream.
FLOODWAY FRINGE. Those portions of the floodplain lying outside the regulatory floodway.
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).
FRENCH DRAIN. A drainage trench backfilled with a coarse, water-transmitting material; may contain a perforated pipe.
GABION. An erosion control structure consisting of wire cage filled with rocks.
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.
GROUNDWATER RECHARGE. The infiltration of water into the earth. It may increase the total amount of water stored underground or only replenish supplies depleted through pumping or natural discharge.
HIGH WATER. Maximum designed, permitted, or regulated water level for an impoundment.
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.
HYDRAULIC GRADE LINE (HGL). For open channel flow, the HGL is equal to the water surface whereas for pressure flow, it is the piezometric surface.
HYDRODYNAMIC LOADS. Forces imposed on structures by floodwaters due to the impact of moving water on the upstream side of the structure, drag along it sides, and eddies or negative pressures on its downstream side.
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.
HYDROLOGY. The science of the behavior of water, its dynamics, composition, and distribution 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.
HYDROMETEOROLOGIC. Water-related meteorologic date such as rainfall or runoff.
HYDROSTATIC LOADS. Those loads or pressures resulting from the static mass of water at any point of floodwater contact with a structure. They are equal in all directions and always act perpendicular to the surface on which they are applied. HYDROSTATIC LOADS can act vertically on structural members such as floors, decks, and roofs, and can act laterally on upright, structural members such as walls, piers, and foundations.
IMPACT AREAS. Areas defined or mapped by the County Surveyor 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, land within 75 feet of each bank of any regulated drain or within 75 feet from the center line or any regulated tile ditch.
IMPERVIOUS SURFACE. Any hard-surfaced, human-made area that does not readily absorb or retain water, including, but not limited to, building roofs, parking and driveway areas, graveled areas, sidewalks, and paved recreation areas.
IDNR. Indiana Department of Natural Resources.
INFILTRATION. Passage or movement of water into the soil.
INFILTRATION SWALES. A depressed earthen area that is designed to promote infiltration.
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.
LAND SURVEYOR. A person licensed under the laws of the state to practice land surveying.
LATERAL STORM SEWER. A sewer that has inlets connected to it but has no other storm sewer connected.
LIFE CYCLE COST. Cost based on the total cost incurred over the system life including research, development, testing, production, construction, operation, and maintenance. Costs are normally determined on present worth or equivalent annual cost basis.
LOW ENTRY ELEVATION. The elevation in a structure where overbank flooding can enter the structure.
LOWEST FLOOR. Refers to the lowest of the following:
(1) The top of the basement floor;
(2) The top of the garage floor, if the garage is the lowest level of the building;
(3) The top of the first floor of buildings constructed on a slab or of buildings elevated on pilings or constructed on a crawl space with permanent openings; or
(4) The top of the floor level of any enclosure below an elevated building where the walls of the enclosure provide any resistance to the flow of floodwaters unless:
(a) The walls are designed to automatically equalize the hydrostatic flood forces on the walls by allowing for the entry and exit of floodwaters; or
(b) Such enclosed space shall be usable only for the parking of vehicles or building access.
MAJOR DRAINAGE SYSTEM. Drainage system carrying runoff from the drainage 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.
MANNING ROUGHNESS COEFFICIENT or MANNING’S “N” VALUE. A dimensionless coefficient (“n”) used in the Manning’s equation to account for channel wall frictional losses in steady uniform flow.
MINOR DRAINAGE SYSTEM. Drainage system carrying runoff from a drainage area less than one square mile.
NATIONAL FLOOD INSURANCE PROGRAM (NFIP). A federal program enabling property owners to purchase flood insurance. The Federal Emergency Management Agency administers the NFIP in communities throughout the United States. The NFIP is based on an agreement between local communities and the federal government which states that if a community will implement floodplain management measures to reduce future flood risks to new construction and substantially improved structures in flood hazard areas, the federal government will make flood insurance available within the community as a financial protection against flood losses that do occur.
NATIONAL POLLUTION DISCHARGE ELIMINATION SYSTEM (NPDES). Permit system under the authority of the U.S. Environmental Protection Agency regarding point and nonpoint sources of water pollution.
NONPOINT SOURCE POLLUTION. Pollution that enters a water body from diffused origins on the watershed or drainage basin and does not result from discernible, confined, or defined conveyances or discharge points.
OFFSITE. Everything not located at or within a particular site.
OFFSITE LAND AREAS. Those areas which by virtue of existing topography must outlet through the developing property.
100-YEAR FREQUENCY FLOOD. See REGULATORY FLOOD.
ONSITE. Located within the controlled or urbanized area where runoff originates.
OPEN CHANNELS. Include not only those channels which are completely open overhead, but also closed conduits which are flowing partly full. Examples of such closed conduits are tunnels, storm sewers, sanitary sewers, and various types of pipelines. Flow in OPEN CHANNELS involves a free surface.
ORIFICE. A device which controls the rate of flow from a detention basin.
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.
OVERLAND FLOW. Consists of sheet flow, shallow concentrated flow, and open channel flow.
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.
PLANIMETRIC DATA. Horizontal measurements involving distances or dimensions on a diagram, map, plat of survey, or topographic map. Normally in units of feet.
PLAT OF SURVEY. A scaled diagram showing boundaries of a tract of land or subdivision. This may constitute a legal description of the land and be used in lieu of a written description.
PROBABLE MAXIMUM FLOOD. The most severe flood that may be expected from a combination of the most critical meteorological and hydrological conditions that are reasonably possible in the drainage basin. It is used in designing high-risk flood protection works and siting of structures and facilities that shall be subject to almost no risk of flooding. The PROBABLE MAXIMUM FLOOD is usually much larger than the 100-year flood.
PROFESSIONAL ENGINEER. A person licensed under the laws of the state to practice professional engineering.
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. In the Rational Formula, this represents the average rainfall intensity over a duration equal to the time of concentration for the catchment.
REACH. Any length of river, channel, or storm sewer.
RECURRENCE INTERVAL. A statistical expression of the average time between floods equaling or exceeding a given magnitude.
REDEVELOPMENT. See the definition for DEVELOPMENT.
REGULATED AREA. All of the county, except for land areas lying within incorporated areas of the county.
REGULATED DRAIN. A drain subject to the provisions of the State Drainage Code, I.C. 36-9-27.
REGULATORY OR 100-YEAR FLOOD. The flood having a 1% probability of being equaled or exceeded in any given year, as calculated by a method and procedure which is acceptable to and approved by the State Department of Natural Resources and the Federal Emergency Management Agency. If a permit from the State Department of Natural Resources - Division of Water (IDNR-DOW) for construction in the floodway is required, then the regulatory flood peak discharge should be calculated by a method acceptable to the IDNR-DOW. The REGULATORY FLOOD is also known as the BASE FLOOD.
REGULATORY FLOODWAY. See FLOODWAY.
RELEASE RATE. The amount of stormwater released from a stormwater control facility per unit of time.
RESERVOIR. A natural or artificially created pond, lake, or other space used for storage, regulation, or control of water. May be either permanent or temporary. The term is also used in the hydrologic modeling of storage facilities.
RETENTION FACILITY. A facility designed to completely retain a specified amount of stormwater runoff without release except by means of evaporation, infiltration, or pumping. The volumes are often referred to in units of acre-feet.
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.
RIGHT-OF-WAY FOR A COUNTY DRAIN. Land over which a regulated county drain passes and is controlled without restriction or interruption by the property owner.
RIPRAP. Large rock that, when installed along an erodible surface, reduces the erosion potential.
RIVERINE. Relating to, formed by, or resembling a stream (including creeks and rivers).
RUNOFF. The waters derived from melting snow or rain falling within a tributary drainage basin that exceed the infiltration capacity of the soils of that basin, flow over the surface of the ground, or are collected in channels or conduits.
RUNOFF COEFFICIENT. A decimal fraction relating the amount of rain which appears as runoff and reaches the storm sewer system to the total amount of rain falling. A COEFFICIENT of one- half implies that 50% of the rain falling on a given surface appears as stormwater runoff.
SANITARY BACKUP. The condition where a sanitary sewer reaches capacity and surcharges into the lowest area, normally a basement.
SCOUR. The clearing and digging action of flowing water.
SEDIMENT. Material of soil and rock origin transported, carried, or deposited by water.
SEDIMENTATION. The process that deposits soils, debris, and other materials either on the ground surfaces or in bodies of water or watercourses.
SEEPAGE. The passage of water or other fluid through a porous medium, such as the passage of water through an earth embankment or masonry wall.
SILT SCREEN FENCE. A fence constructed of wood or steel supports and either natural (e.g. burlap) or synthetic fabric stretched across area of flow during site development to trap and retain onsite sediment due to rainfall runoff.
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.
SPECIAL FLOOD HAZARD AREA (SFHA). Those lands within the jurisdiction of a community which are subject to inundation by the regulatory or 100-year flood. SPECIAL FLOOD HAZARD AREAS are usually designated on a flood hazard boundary map as zone A. After detailed evaluation of local flooding characteristics, the flood insurance rate map will refine this categorization into zones A, AE, AH, AO, and A1-30.
SPILLWAY. A waterway in or about a hydraulic structure, for the escape of excess water.
STANDARD PROJECT FLOOD. A term used by the U.S. Army Corps of Engineers to designate a flood that may be expected from the most severe combination of the meteorological and hydrological conditions that are considered reasonable characteristics of the geographical area in which the drainage basin is located, excluding extremely rare combinations. The peak flow for a STANDARD PROJECT FLOOD is generally 40% to 60% of the probable maximum flood for the same location.
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 SEWER. A closed conduit for conveying collected stormwater.
STORMWATER FACILITY. All ditches, channels, conduits, levees, ponds, natural and human-made impoundments, wetland, tiles, swales, sewers, and other natural or artificial means of draining surface and subsurface water from land.
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.
STRUCTURE. Refers to a structure that is principally above ground and is enclosed by walls and a roof. The term includes a gas or liquid storage tank, a manufactured home, or a prefabricated building. The term also includes recreational vehicles to be installed on a site for more than 180 days.
STRUCTURAL ENGINEER. A person licensed under the laws of the state to engage in the designing or supervising of construction, enlargement, or alteration of structures or any part thereof, for other, to be constructed by persons other than himself or herself.
STRUCTURAL FLOODPLAIN MANAGEMENT MEASURES. Those physical or engineering measures employed to modify the way floods behave, e.g., dams, dikes, levees, channel enlargements, and diversions.
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.
SUBSTANTIAL IMPROVEMENT. Any reconstruction, rehabilitation, addition, or other improvement of a structure, the cost of which equals or exceeds 50% of the market value of the structure at the time of the “start of construction” of the improvement. This term includes structures which have incurred “substantial damage” regardless of the actual repair work performed. The term does not include improvements of structures to correct existing violations of state or local health, sanitary, or safety code requirements, or any alteration of a “historic structure,” provided that the alteration will not preclude the structures continued designation as a “historic structure.”
SUMP FAILURE. A failure of the sump pump that results in inundation of a crawl space or basement.
SUMP PUMP. A small pump that discharges seepage from foundation footing drains.
SURCHARGE. Backup of water in a sanitary or storm sewer system in excess of the design capacity of the system.
TAILWATER. The water surface elevation at the downstream side of a hydraulic structure, i.e. culvert, bridge, weir, dam, and the like.
THALWEG. The deepest point of a channel.
TIME OF CONCENTRATION. 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.
TOPOGRAPHIC MAP. Graphical portrayal of the topographic features of a land area, showing both the horizontal distances between the features and their elevations above a given datum.
TOPOGRAPHY. The representation of a portion of the earth’s surface showing natural and human-made features of a given 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 Services in their Technical Paper 40 dated 1961.
TRANSITION SECTION. Reaches of the stream or floodway where water flows from a narrow cross-section to a wide cross-section or vice-versa.
TRIBUTARY. Based on the size of the contributing drainage area, a smaller watercourse which flows into a larger watercourse.
UNDERDRAIN. A small diameter perforated pipe that allows the bottom of a detention basin to drain.
UNIT HYDROGRAPH. The hydrograph that results from one inch of precipitation excess generated uniformly over the watershed at a uniform rate during a specified period of time.
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 human-made drainage way in or into which stormwater runoff or floodwaters flow either regulatory or intermittently.
WATERSHED. The land area drained by 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.
WATERSHED AREA. The total area from which surface runoff is carried away by a drainage system.
WEIR. A device which is used to restrict the flow of water thereby limiting the discharge rates. A WEIR can also facilitate calculation or measurement of the discharge rates. These are often used to control the rate of flow out of stormwater storage facilities.
WET BOTTOM RETENTION FACILITY. A facility 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 line in saturated soil conditions.
(Ord. 1997-16, passed 12-8-1997; Ord. 2005-01, passed 2-17-2005)