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(A) Abbreviations. The following abbreviations when used within this subchapter shall have the following designated meanings:
BFE. Base flood elevation.
CLOMR. Conditional Letter of Map Revision.
COE. United States Army Corps of Engineers.
FEMA. Federal Emergency Management Agency.
FIS. Flood Insurance Study.
FPE. Flood protection elevation.
FQI. Floristic Quality Index.
IDNR-OWR. Illinois Department of Natural Resources, Office of Water Resources.
IEPA. Illinois Environmental Protection Agency
NRCS. Natural Resources Conservation Service.
(B) Words and terms. This subchapter contains specific words and terms that shall have the following meanings as set forth, except where otherwise specifically indicated. Words and terms not defined shall have the meanings that are indicated in a common dictionary definition.
ADMINISTRATOR. The Village of Mazon Building and Zoning Officer.
AGRICULTURAL LAND. Land and property defined as agriculture under the zoning code.
AGRICULTURAL SUBSURFACE DRAINAGE. A water management technique driven by economic and safety concerns, where the rate at which surplus ground water should be removed is determined primarily by the moisture/air requirements of the vegetation, and through the use of farm tiles throughout the property.
APPLICABLE ENGINEERING PRACTICE. Procedures, methods or materials recommended in standard engineering textbooks or references as suitable for the intended purpose.
APPLICANT. Any person who submits an application for a permit under this subchapter.
BFE or BASE FLOOD ELEVATION. The elevation in relation to mean sea level of the crest of the base flood.
BASE FLOOD. The flood having a 1% probability of being equaled or exceeded in a given year calculated during a 100-year rain event.
BASEMENT. That portion of a building having its floor subgrade (below ground level) on all sides.
BUFFER. An area of predominantly deep-rooted, native-vegetated land adjacent to channels, wetlands, lakes or ponds for the purpose of stabilizing banks, increasing infiltration, and reducing contaminants (including sediments), in stormwater that flows into such areas.
BUILDING. A walled and roofed structure, including a gas or liquid storage tank that is principally above ground, including manufactured homes, prefabricated buildings and gas or liquid storage tanks. The term also includes recreational vehicles and travel trailers installed on a site from more than 180 days per year.
BULLETIN 70. “Frequency Distributions and Hydroclimatic Characteristics of Heavy Rainstorms in Illinois”, by Floyd Huff and James Angel of the Illinois State Water Survey (1989).
BYPASS FLOWS. Stormwater runoff from upstream properties tributary to a property’s drainage system, but not under its control.
CHROMA. The relative purity, strength or saturation of a color; directly related to the dominance of the determining wavelength of the light and inversely related to the grayness; one of the three variables of color.
CLOMA or CONDITIONAL LETTER OF MAP AMENDMENT. FEMA’s comment on a proposed structure or group of structures that would, upon construction, be located on existing natural ground above the base (1%-annual-chance) flood elevation on a portion of a legally defined parcel of land that is partially inundated by the base flood.
CLOMR or CONDITIONAL LETTER OF MAP REVISIONS. FEMA’s comment on a proposed project that would, upon construction, affect the hydrologic or hydraulic characteristics of a flooding
source and thus result in the modification of the existing regulatory floodway, the effective base flood elevations, or the special flood hazard area (SFHA).
COE. The United States Army Corps of Engineers.
CHANNEL. Any river, stream, creek, brook, branch, flowage, slough, ditch, conduit, culvert, gully, ravine, wash, or natural or manmade drainage way that has a definite bed and bank or shoreline, in or into which surface, ground water, effluent, or industrial discharges flow either perennially or intermittently.
CHANNEL MODIFICATION. Alteration of a channel by changing the physical dimensions or materials of its bed or banks, and includes damming, rip rapping (or other armoring), widening, deepening, straightening, relocating, lining, and significant removal of bottom or woody rooted vegetation, but does not include the clearing of debris or removal of trash or dredging to previously-documented thalweg elevations and side slopes.
COMMERCIAL. Having the qualities associated with the transaction of business with the public at large, where the traffic generated warrants construction of site improvements.
COMMUNITY. The Village of Mazon, Illinois.
COMPENSATORY STORAGE. An excavated, hydrologically and hydraulically equivalent volume of storage created to offset the loss of existing flood storage.
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.
COUNTY. Grundy County, Illinois.
CRITICAL DURATION. The duration of a storm event that results in the greatest peak runoff.
CRITICAL FACILITY. Any facility critical to the health and welfare of a population, and that, if flooded, would create an added dimension to a disaster. Damage to these CRITICAL FACILITIES can impact the delivery of vital services, can cause greater damage to other sectors of the community, or can put special populations at risk. Examples of CRITICAL FACILITIES where flood protection should be required include: emergency services facilities (such as fire and police stations), schools, hospitals, retirement homes and senior care facilities, major roads and bridges, critical utility sites (telephone-switching stations or electrical transformers, and hazardous-material-storage facilities (chemicals, petrochemicals, hazardous or toxic substances).
DAM. Any obstruction, wall embankment or barrier, together with any abutments and appurtenant works, constructed to store or divert water, or to create a pond (not including underground water storage tanks).
DEPRESSIONAL STORAGE. The volume contained below a closed contour on a one-foot-contour-interval topographical map, the upper elevation of which is determined by the invert of a surface gravity outlet.
DESIGN WATER SURFACE ELEVATION. The high water level elevation of a site runoff control facility for a selected storm event, described in terms of the probability of occurring once within a given number of years, for which site runoff control facilities are designed.
DETENTION BASIN. A facility constructed to provide for the temporary storage of stormwater runoff with a controlled release rate.
DEVELOPER. A person who creates or causes a development.
DEVELOPMENT. Any manmade change to the land that includes:
(a) The construction, reconstruction or replacement of a building or an addition to a building;
(b) The installation of utilities, construction of roads, bridges or similar projects;
(c) Drilling and mining;
(d) The construction or erection of levees, walls, fences, dams or culverts;
(e) Channel modifications, filling, dredging, grading, clearing, excavating, paving, or other nonagricultural alterations of the ground surface;
(f) The storage of materials and the deposit of solid or liquid waste;
(g) The installation of a mobile home on a site, the preparation of a site for a mobile home, or the installation of a recreational vehicle on a site for more than 180 days;
(h) Any wetland impact; and
(i) Any other activity of man that might change the direction, height or velocity of stormwater flowing through and from a property.
DEVELOPMENT, however, does not include:
(a) Maintenance and repair of existing buildings or facilities that is not considered a substantial improvement;
(b) Repair or replacement of an existing parking lot outside the floodplain, provided that no new impervious surfaces are added, there is no increase in peak flows, and there is no change in the location of the stormwater discharge;
(c) Resurfacing of streets and highways outside the floodplain;
(d) Resurfacing of publicly-owned streets and highways within the floodplain, provided the difference between the elevation of the road surface after resurfacing and the elevation of the road surface on the effective date hereof is not more than two inches;
(e) For agricultural uses, maintenance of existing drainage systems for the limited purpose of maintaining cultivated areas and crop production; or
(f) For agricultural uses and/or improvements undertaken pursuant to a written NRCS conservation plan, not located in a floodplain or floodway.
DRAINABLE WATER. Water that readily drains from soil under the influence of gravity.
DRAINAGE AREA. The land area above a given point that may contribute runoff flow at that point from rainfall.
DWELLING. A building, or portion thereof, designed or used exclusively for residential purposes, including single-family, two-family and multiple-family dwellings, but not including mobile homes or other trailers, or lodging rooms in hotels, motels or lodging houses.
DWELLING, ATTACHED. A dwelling that is joined to another dwelling by any means.
DWELLING, DETACHED. A dwelling surrounded on all sides by open space on the same lot.
DWELLING, MULTIPLE-FAMILY. A dwelling containing three or more dwelling units.
DWELLING, SEMI-DETACHED. A dwelling joined to one other dwelling by a party wall or vertical cavity wall, and aboveground, physically-unifying, horizontal structural elements.
DWELLING, SINGLE-FAMILY. A dwelling containing one dwelling unit.
DWELLING, TWO-FAMILY, DETACHED. A dwelling containing two dwelling units only, one above the other.
DWELLING UNIT. One or more rooms arranged, designed or used as living quarters for one family only. Individual bathrooms and complete single kitchen facilities, permanently installed to serve the entire family, shall always be included within each dwelling unit.
ELEVATION CERTIFICATE. A form published by FEMA, used to certify the base flood elevation and the lowest elevation of usable space to which a building has been constructed.
EPHEMERAL STREAM. A stream whose bed elevation does not intersect the ground water table and carries flow only during and immediately after a runoff-producing rainfall event.
EROSION. The process whereby soil is detached by the action of water or wind.
EXISTING MANUFACTURED HOME PARK OR SUBDIVISION. A manufactured home park or subdivision for which the construction of facilities for servicing the lots on which the manufactured homes are to be affixed, or buildings to be constructed (including, at a minimum, the installation of utilities, the construction of streets, and either final site grading or the pouring of concrete pads) is completed before the effective date of the floodplain management regulations adopted by a community.
EXPANSION TO AN EXISTING MANUFACTURED HOME PARK OR SUBDIVISION. The preparation of additional sites by the construction of facilities for servicing the lots on which the manufactured homes are to be affixed
(including the installation of utilities, the construction of streets, and either final site grading or the pouring of concrete pads).
FARMED WETLANDS. Wetlands that have been identified as fanned wetlands as part of a certified wetland determination performed by the applicant’s engineers according to National Food Security Act Manual methodology.
FEMA. The federal emergency management agency and its regulations at 44 C.F.R. § 9-79, effective September 29, 1989, as amended.
FLOOD. A general and temporary condition of partial or complete inundation of normally dry land areas from overflow of inland or tidal waves or the unusual and rapid accumulation of runoff of surface waters from any source.
FLOOD FREQUENCY. A frequency normally expressed as a period of years, based upon a percent chance of occurrence in any given year from statistical analysis during which a flood of a stated magnitude may be expected to be equaled or exceeded, as in the two-year flood frequency has a 50% chance of occurrence in any given year, and the 100-year flood frequency has one percent 1% chance of occurrence in any given year.
FLOOD FRINGE. That portion of the floodplain outside of the designated floodway.
FLOOD INSURANCE RATE MAP. A map prepared by the Federal Emergency Management Agency that depicts the floodplain or special flood hazard area (SFHA) within a community. This map includes insurance rate zones, and may or may not depict floodways and show base flood elevations.
FLOOD INSURANCE STUDY. An examination, evaluation and determination of flood hazards and, if applicable, corresponding water surface elevations.
FPE or FLOOD PROTECTION ELEVATION. The BFE plus two feet of freeboard or 100-year-design water surface elevation of any adjacent stormwater facility plus two feet of freeboard, whichever is higher.
FLOODPLAIN and SPECIAL FLOOD HAZARD AREA (SFHA). These two terms are synonymous.
FLOODPROOF. Any combination of structural and nonstructural additions, changes or adjustments to structures or property that reduce or eliminate flood damage to real estate, water and sanitary facilities, structures and their contents.
FLOODPROOFING CERTIFICATE. A form published by FEMA that is issued to certify that a building has been designed and constructed to be structurally dry floodproofed to the FPE.
FLOODWAY. That portion of the floodplain required to store and conveys the base flood.
FLOODWAY CONVEYANCE. The measure of the flow-carrying capacity of the floodway section and is defined using Manning’s equation:
K = (1.486 x (AR) )/n
Where:
n = Manning’s roughness factor
A = the effective area of the cross
section
R = the ratio of the wetted area to the
wetted perimeter
FQI or FLORISTIC QUALITY INDEX. The parameter related to the number of native plant species present, as defined by Floyd Swink and Gerald Wilhelm in Plants of the Chicago Region, 4th edition (1994), or by Gerald Wilhelm and Linda Masters in “Floristic Quality Assessment and Application
Computer Programs for the 22-County Chicago Region”, conservation design forum (2000).
FREEBOARD. An increment of elevation added to the base flood elevation to provide a factor of safety for uncertainties in calculations, future watershed development, unknown localized conditions, wave actions and unpredictable effects such as those caused by ice or debris jams.
FUNCTIONAL. Means that a facility performs its primary purpose but may not be completed.
GROUNDWATER. Water that is located within soil or rock below the surface of the earth.
GROUNDWATER CONTROL SYSTEM. A designed system that may consist of tiles, underdrains, French drains or other appropriate stormwater facilities whose purpose is to lower the ground water table to a predictable elevation throughout the year.
HEMI-MARSH. An isolated wetland dominated on the edges by tall, emergent vegetation with an interior area of shallow open water.
HISTORIC STRUCTURE. A structure or site that is:
(a) Listed individually in the National Register of Historic Places, or preliminarily determined by the Secretary of the Interior as meeting the requirements for individual listing in the national register;
(b) Certified or preliminarily determined by the Secretary of the Interior as contributing to a historic district or a district determined by the Secretary to qualify as registered historic district;
(c) Individually listed on the State Inventory of Historic Places by the Illinois Historic Preservation Agency; or
(d) Individually listed on a local inventory of historic places that has been certified by the Illinois Historic Preservation Agency.
HYDRAULICALLY CONNECTED IMPERVIOUS AREAS. Those areas of concrete, asphalt and gravel that, along with building roof surfaces, convey flows directly to an improved drainage system consisting of storm sewers or paved channels. They include roadways drained by curb and gutter and storm sewers, and driveways hydraulically connected to those roadways. However, they do not include roof surfaces discharging to unpaved surfaces that absorb and filter stormwater runoff, or roadways whose primary conveyance is through open ditches and swales.
HYDRAULICALLY EQUIVALENT COMPENSATORY STORAGE. Compensatory storage, either adjacent to the floodplain fill or not located adjacent to the development, but which can be shown by hydrologic and hydraulic analysis to be equivalent to compensatory storage located adjacent to the development.
HYDRAULICS. The science and study of the mechanical behavior of water in physical systems and processes.
HYDROGRAPH. A graph or tabulation showing flow rate with respect to time for a given location on a channel or conduit.
HYDROLOGICALLY DISTURBED. An area where the land surface has been cleared, grubbed, compacted or otherwise modified that changes runoff, volumes, rates or direction.
HYDROLOGY. The science of the behavior of water, including its dynamics, composition and distribution in the atmosphere, on the surface of the earth and underground.
IDNR-OWR. The Illinois Department of Natural Resources, Office of Water Resources, or its duly authorized designee.
IMPERVIOUS SURFACE. Any manmade, hard-surfaced area that does not readily permit the infiltration and absorption of stormwater runoff, including, but not limited to, roofs, roads, drives, parking lots, sidewalks, path and graveled areas.
INFILTRATION. The passage or movement of water into the soil surface.
INTERIM WATERSHED PLAN. A regional study of a specific watershed that does not address the entire range of purposes, goals and objectives outlined in the plan.
INTERMITTENT STREAM. A stream whose bed intersects the ground water table for only a portion of the year on average, or any stream that flows continuously for at least one month out of the year, but not the entire year.
ISOLATED WETLAND. A wetland that does not have an identifiable surface water connection to other waters of the U.S.
LOMA or LETTER OF MAP AMENDMENT. The official determination by FEMA that a specific structure is not in a regulatory floodplain and amends the effective FIRM.
LOMR or LETTER OF MAP REVISION. FEMA’s modification to an effective Flood Insurance Rate Map (FIRM). LOMRs are generally based on the implementation of physical measures that affect the hydrologic or hydraulic characteristics of a flooding source, and thus result in the modification of the existing regulatory floodway, the effective base flood elevations, or the SFHA. The LOMR officially revises the FIRM, and sometimes the Flood Insurance Study (FIS) report, and, when appropriate, includes a description of the modifications. The LOMR is generally accompanied by an annotated copy of the affected portions of the FIRM or FIS report.
LAKE. A body of water, two or more acres in size, that retains water throughout the year.
LINEAL WATERS OF THE U.S. Wetlands along creeks, streams, rivers, ponds, lakes or impoundments that are hydraulically connected to surface water.
LOWEST FLOOR. The lowest floor of the lowest enclosed area (including basement). An unfinished or flood-resistant enclosure usable solely for parking of vehicles, building access or storage, in an area other than a basement area, is not considered a building’s LOWEST FLOOR; provided that such enclosure is not built so as to render the structure in violation of the applicable non-elevation design requirements of this subchapter.
MAJOR STORMWATER SYSTEM. That portion of a stormwater facility needed to store and convey runoff at the 100-year frequency.
MASS GRADING. Development in which the primary activity is a change in topography affected by the movement of earth materials.
MINOR STORMWATER SYSTEM. All infrastructure, including curbs and gutters, storm sewers, culverts, roadside ditches, subsurface drainage systems, intended to convey stormwater runoff at the 100-year frequency.
MITIGATION. Measures taken to offset negative impacts from development in waters of the U.S., including wetlands or the floodplain.
MOBILE HOME (also recognized as a MANUFACTURED HOME). A structure designed for permanent habitation, and so constructed as to permit its transport on wheels, temporarily or permanently attached to its frame, from the place of construction to the location, or subsequent locations, at which it is intended to be a permanent home, and designed to permit the occupancy thereof as a dwelling place for one or more persons.
MOBILE HOME PARK. A lot, parcel or tract of land developed with facilities for
accommodating two or more mobile homes, provided each mobile home contains a kitchen, flush toilet, and shower or bath; and such park shall be for use only by nontransient dwellers remaining continuously for more than one month, whether or not a charge is made. It shall not include a sales lot in which automobiles or unoccupied mobile homes or other trailers are parked for the purpose of inspection or sale, except mobile homes located on a site in the mobile home park that are occupied or vacant for not more than 90 days after occupancy may be sold or offered for sale.
MOTTLED ZONE. A layer that is marked with spots or blotches of different color or shades of color. The pattern of mottling and the size, abundance and color contrast of the mottles may vary considerably and should be specified in soil description.
MUNSELL COLOR SYSTEM. A color designation system that specifies the relative degrees of the three simple variables of color: hue, value and chroma. For example: 10YR is a color of soil with a hue of 10YR, value = 6 and chroma = 4.
NFIP or NATIONAL FLOOD INSURANCE PROGRAM. The federal program codified in Title 44 of the Code of Federal Regulations.
NRCS. The United States Department of Agriculture, Natural Resources Conservation Service.
NET BENEFIT IN WATER QUALITY. The institution of best management practices as part of a development that, when compared to the pre-development condition, can be judged to reduce downstream sediment of pollutant loadings.
NET WATERSHED BENEFIT. A finding that, when compared to the existing condition, the development will substantially reduce (more than 10%) downstream peak discharges, will reduce downstream flood stages (more than 0.1 feet), or will reduce downstream damage to structures occurring in
the pre-development condition. This finding must be demonstrated by detailed hydrologic and hydraulic analysis of watersheds on a regional scale, as approved by the Administrator.
NEW CONSTRUCTION. Structures for which the start of construction commenced after the effective date of floodplain management regulations adopted by a community, and includes any subsequent improvements of such structures.
NON-RIVERINE. Areas such as isolated depressional storage areas, ponds and lakes.
NUISANCE FLOW. Primarily a dry-weather flow resulting from ground water pumped by individual sump pumps and other human activities not directly related to rainfall events and surface runoff.
OHWM or ORDINARY HIGH WATER MARK. The point on the bank or shore up to which the presence and action of surface water is so continuous as to leave a distinctive mark such as by erosion, destruction or prevention of terrestrial vegetation, predominance of aquatic vegetation, or other easily recognized characteristic.
OBSERVATION STRUCTURES. Structures built on a field tile where the pipe inflow and outflow is visible upon removal of a lid.
OPEN CHANNEL. A conveyance system with a definable bed and banks carrying the discharge from field tiles and surface drainage, but does not include grassed swales within farm fields under agricultural production that are ephemeral in nature.
OPEN WATER. Surface water in lakes, ponds, impoundments and wetlands devoid of vegetative cover.
OVERLAND FLOW PATH. A design feature of the major stormwater system that carries flow 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.
PARCEL. A separate tract of land identified by its own legal description.
PERENNIAL STREAM. A riverine watercourse whose thalweg intersects the groundwater table continuously and flows throughout the year.
PERSON. An individual, partnership, corporation, limited liability company, unincorporated association, trust, municipal corporation, unit of local government or other government agency or authority, or any combination of any of the foregoing.
PLANT COMMUNITIES. Groups of plants with similar habitat requirements and planting regimes.
POND. A body of water, less than two acres in size, that retains a normal water level year round.
PRIMARY GRAVITY OUTLET. The outlet structure designed to meet the release rate requirements of this subchapter, the invert (lowest elevation) of which shall be considered the high water elevation for required stormwater retention.
PROFESSIONAL ENGINEER. An engineer registered in the State of Illinois under the Illinois Professional Engineering Practice Act of 1989, 225 ILCS 325/1 et seq.
PROFESSIONAL LAND SURVEYOR. A land surveyor registered in the State of Illinois under the Illinois Professional Land Surveyors Act of 1989, 225 ILCS 330/1 et seq.
PUBLIC FLOOD EASEMENT. An easement acceptable to the appropriate jurisdictional body that meets the regulations of IDNR-OWR, the
department and the community, and provides legal assurances that all areas subject to flooding in the created backwater of the development will remain open to allow flooding.
RECORD DRAWINGS. Drawings prepared, signed and sealed by a professional engineer or professional land surveyor, representing the final record of the actual in-place elevations, locations of structures and topography.
RECREATIONAL VEHICLE OR TRAVEL TRAILER. A vehicle that is:
(a) Built on a single chassis;
(b) Four hundred square feet or less in size;
(c) Designed to be self-propelled or permanently towable by a light-duty truck; and
(d) Designed primarily not for use as a permanent dwelling, but as temporary living quarters for recreational, camping, travel or seasonal use.
REDEVELOPMENT. Development on a developed site devoted to an existing urban land use from which stormwater either discharges into an existing stormwater facility owned or maintained by a unit of local government, or discharges directly onto a regulatory floodplain. REDEVELOPMENT includes the widening of an existing street or highway owned by a unit of local government.
REGISTERED STRUCTURAL ENGINEER. An engineer licensed under the Illinois Structural Engineering Practice Act of 1989, 225 ILCS 340/1 et seq.
REPETITIVE LOSS. Flood-related damages sustained by a structure on two separate occasions during a ten-year period for which the cost of repairs at the time of each flood event, on the
average, equals or exceeds 25% of the market value of the structure before the damage occurred.
RESTRICTIVE BRIDGE OR CULVERT. A bridge or culvert that crosses a floodplain and cannot convey the base flood without causing increases in the upstream flood profile.
RETENTION FACILITY. A facility that stores stormwater runoff without a gravity release.
RIVERINE. Related to, formed by or resembling a channel, including creeks and rivers.
RUNOFF. The waters derived from melting snow or rain falling within a tributary drainage basin that exceeds the infiltration capacity of the soils of that basin.
SEASONAL HIGH GROUND WATER TABLE. The upper limits of the soil temporarily saturated with water, being usually associated with spring wetness conditions that may be indicated by soil mottles with a Munsell color of two chroma or less.
SEDIMENTATION. The process that deposits hydraulically moved soils, debris and other materials on other ground surfaces or in bodies of water or stormwater drainage systems.
SEDIMENTATION TRAP. A structure or area that allows for the temporary deposit and removal or disposal of sediment materials from stormwater runoff.
SEEPAGE. The movement of drainable water through soil and rock.
SITE. All of the land contemplated to be part of a coordinated development of one or more parcels.
SITE RUNOFF STORAGE FACILITY. A manmade structure for the temporary storage of
stormwater runoff (detention) with a controlled release rate.
SPECIAL MANAGEMENT AREA. An area that consists of a floodplain, regulatory floodplain, wetland, wetlands mitigation area, stream, river or other water body.
START OF CONSTRUCTION. Includes substantial improvement and means the date the building permit was issued, provided the actual start of construction, repair, reconstruction, rehabilitation, addition placement or other improvement, was within 180 days of the permit date. The ACTUAL START means either the first placement of permanent construction of a structure on a site, such as the pouring of slab or footings, the installation of piles, the construction of columns, or any work beyond the stage of excavation or placement of a manufactured home on a foundation. For a substantial improvement, ACTUAL START OF CONSTRUCTION means the first alteration of any wall, ceiling, floor or other structural part of a building, whether or not that alternation affects the external dimensions of the building.
STORMWATER FACILITY. All ditches, channels, conduits, bridges, culverts, levees, ponds, natural and manmade impoundments, wetlands, riparian environment, tiles, swales, sewers or other natural or artificial structures or measures that serve as a means of draining or storing surface water and ground water from land.
STORMWATER MANAGEMENT PERMIT. The permit issued under this subchapter
STRUCTURE. A manmade change to the land, constructed on or below the ground, including the construction, reconstruction or placement of a building or any addition to a building.
SUBSTANTIAL DAMAGE. Damage of any origin sustained by a structure whereby the cumulative percentage of damage equals or exceeds 50% of the
market value of the structure before the damage occurred, regardless of actual repair work performed. Volunteer labor and materials must be included in this determination. This term includes structures that have incurred repetitive-loss damages.
SUBSTANTIAL IMPROVEMENT. Any reconstruction, rehabilitation, addition or improvement of a structure taking place subsequent to the adoption of this subchapter, in which the cumulative percentage of improvements:
(a) Equals or exceeds 50% of the market value of the structure before the improvement or repair is started, or
(b) Increases the floor area by more than 20%.
SUBSTANTIAL IMPROVEMENT. Considered to occur when the first alteration of any wall, ceiling, floor or other structural part of the building commences, whether or not that alteration affects the external dimensions of the structure. This term includes structures that have incurred repetitive loss or substantial damage, regardless of the actual repair work done. The term does not include:
(a) Any project for improvement of a structure to comply with existing state or local health, sanitary or safety code specifications that are solely necessary to assure safe living conditions; or
(b) Any alteration of a structure listed on the National Register of Historic Places or the Illinois Register of Historic Places, provided that the alteration does not preclude the structure’s continued historic designation.
SUBSURFACE DRAINAGE. The removal of excess soil water to control water table levels at predetermined elevations, for structural, environmental or other reasons, in areas already developed or being developed for agricultural, residential, industrial, commercial or recreational uses.
SURFACE GRAVITY OUTLET. The point at which stormwater runoff is let out of a basin or depression by flowing via gravity over the surface of the ground or through a conduit that has a direct and open connection to the surface.
THALWEG or VALLEY LINE. The line that is drawn to join the lowest points along the entire length of a streambed or valley in its downward slope, defining its deepest channel.
TOPSOIL. The uppermost part of the soil ordinarily moved in tillage, or its equivalent in uncultivated soils.
TRANSITION SECTION. The reaches of the stream or floodway where water flows from a narrow cross section, or where a narrow cross vice versa.
USABLE SPACE. Space used for dwelling, storage, utilities or other beneficial purposes, including basements.
VILLAGE. The Village of Mazon, Illinois.
VIOLATION. The failure of a structure or other development to be in full compliance with the community’s floodplain management regulations. A structure or other development without the elevation certificate, other certifications or other evidence of compliance is presumed to be in VIOLATION until such time as that documentation is provided.
WATER TABLE. The upper limit of a free water surface in a saturated soil or underlying material.
WATERS OF THE U.S. All interstate and intrastate waters and their tributaries, including lakes, rivers, streams, including intermittent streams, mudflows, sandflats, wetlands, sloughs, prairie potholes, wet meadows, lakes, natural ponds, and all impoundments of the foregoing.
WATERSHED. All land drained by, or contributing water to, the same stream, lake, stormwater facility or draining to a point.
WATERSHED CHARACTERISTICS. The land use, physiology, habitat, climate, drainage system and community profile of a watershed.
WATERSHED PLAN. A study and evaluation of an individual drainage basin’s stormwater management, floodplain management, water quality and flood control needs and capabilities adopted by the county.
WETLAND. As defined by COE in the 1988 Corps of Engineers Wetland Delineation Manual, Technical Report Y-87-1, U.S. Army Corps of Engineers, Waterways Experiment Station, Vicksburg, Mississippi (the “1987 Manual”), or other federally recognized methodology.
WETLAND IMPACT.
(a) The dredging or filling of any wetland having an FQI greater than 25; or
(b) The dredging or filling of any other wetland if:
1. The effect would be that cumulatively, since the effective date hereof, one-tenth acre (4,356 square feet) or more of the wetlands on the site have been dredged or filled, and taking into account all prior dredging or filling of such wetland; and
2. The wetland is not then regulated by COE; or
3. The dredging or filling is not an approved impact under a conservation plan administered by any federal agency under the Food Security Act, as amended (16 U.S.C. § 3801 et seq.).
WETLAND MITIGATION. The creation and long-term maintenance of wetlands to offset wetland impacts from development.
WETLAND MITIGATION BANK. One or more parcels in the county either approved by COE or the Administrator of this plan, where wetlands and/or other aquatic resources are restored, created, enhanced, or in exceptional circumstances, preserved expressly for the purpose of providing compensatory mitigation in advance of authorized impacts to similar resources.
WETLAND MITIGATION FACILITY. A parcel in the county specifically dedicated for the creation and long term maintenance of wetlands and other aquatic resources including any area designated as a compensatory storage facility when such area is used for wetland mitigation.
(Ord. 2019-03, passed 4-15-2019)
No development shall result in any new or additional expense to any person other than the developer for flood protection; or increase flood elevations or decrease flood-conveyance capacity upstream or downstream of the area under the ownership or control of the developer. This requirement shall not prohibit the removal or reduction of built obstructions to flow, such as increasing culvert capacity or lowering roadway elevations.
(A) Analysis and design. Analysis and design of all stormwater facilities for the development shall comply with the standards and criteria established in any applicable watershed plan or interim watershed plan.
(B) Building permits. Stormwater facilities shall be functional before building permits are issued for residential or nonresidential subdivisions. The village may make the determination that building permits may be granted prior to the facilities being functional based on sound engineering.
(C) Overland flow paths. The development shall have an overland flow path at the downstream limit of the site that will pass the base-flood flow without increasing flood damage. If the upstream drainage area is less than 20 acres, a storm sewer pipe and inlet sized for the base flood may be constructed in lieu of providing an overland flow path. Overland flow paths internal to the site shall be considered as part of the major stormwater system, and shall be designed for conveyance of the base flood (critical duration), without use of storm sewer capacity, at a minimum of one cubic foot per second per tributary acre, and without damage to structures.
(D) Protection of buildings. All usable space in new buildings or additions to existing buildings hydraulically connected to a major stormwater system, site runoff storage facility or overland flow path shall be elevated, floodproofed or otherwise protected to the FPE.
(E) Depressional storage. The function of existing onsite depressional storage shall be preserved for both onsite and offsite tributary flows in addition to required detention. When depressional storage is removed, it must be compensated for in the site runoff storage facility at a one-to-one ratio, provided that offsite areas tributary to the existing depressional storage are routed through the site runoff storage facility. This requirement is in addition to the site runoff storage requirements as identified in this subchapter. The village may allow the function of depressional storage to be preserved if the applicant performs detailed pre- and post-project hydrologic and hydraulic modeling to identify the effect of the depressional storage on discharges, using a two-year through 100-year critical duration analysis.
(Ord. 2019-03, passed 4-15-2019)
(A) Erosion and sediment control planning shall be part of the initial site planning process. In the planning process, the applicant shall also address the following:
(1) For projects that involve phased construction, existing land cover for those areas not under current development shall be addressed. If existing land cover does not consist of appropriate dense vegetation, then these phases shall be planted temporarily to reduce erosion from idle land.
(2) In planning the erosion and sediment control strategy, preference shall be given to reducing erosion rather than controlling sediment. In order to accomplish this, details need to be provided that include the construction sequence of the phases such that the amount of land area exposed to erosive forces is the minimum for the completion of the project. Standards and specifications for erosion and sediment control measures shall be in accordance with the latest edition of the Illinois Urban Manual.
(B) Erosion and sediment control plans shall be in accordance with this subchapter and shall include the following:
(1) Detailed construction phasing plan, identifying erosion and sediment control measures to be in place for each phase, shall be provided.
(2) Erosion and sediment control measures are to be installed initially prior to stripping existing vegetation or mass grading. Details of this shall be provided on the plans.
(3) Permanent stabilization measures shall be identified as such.
(4) The expected two-year and ten-year runoff rates from all offsite areas draining into the site shall be identified on the plan.
(5) Methods for conveying flows through the site during construction shall be indicated. These methods shall include the temporary and permanent stabilization measures to be used to reduce velocity and erosion from flow through the construction zone.
(6) A maintenance schedule of each measure used shall be indicated on the plan. As a minimum, all erosion and sediment control measures on site shall be inspected weekly by the applicant, or the applicant’s onsite representative, or after a one-half inch or greater rainfall event, and any required repairs shall be made to keep these measures functional as designed.
(C) Special management areas and any required buffers shall be indicated on the erosion and sediment control plan.
(Ord. 2019-03, passed 4-15-2019)
All developments shall obtain a stormwater management permit, requiring compliance with §§ 151.206 and 151.207 of this subchapter, after the effective date hereof, if one of the following scenarios apply:
(A) Two or more single-family, detached dwellings are to be constructed on a site having five or more acres;
(B) A two-family attached, multi-family attached dwelling, condominium, apartment or other residential building comprised of more than two units is to be constructed on a site one acre or more in size;
(C) Any nonresidential development on a site one acre or more in size, unless the development consists solely of the installation, repair or replacement of the underground or overhead lines of a public utility within a public right-of-way.
(D) Redevelopment on a site one acre or more in size, resulting in 25,000 square feet or more of additional impervious area in aggregate, from the effective date of this subchapter; or
(E) Road development after the effective date hereof in rights-of-way under the ownership or control of a unit of local government, resulting in two acres or more of additional impervious area; or
(F) The repair or replacement of an existing parking lot or privately-owned road within the floodplain results in any additional impervious surface, an increase in peak flows, a change in the location of the stormwater discharge, or an increase in the elevation of the parking or driving surface.
(Ord. 2019-03, passed 4-15-2019)
(A) Stormwater facilities shall be required and designed so that runoff exits the site at the point whereit exited prior to development (unless a change is required and approved in writing by the village), and in a manner so as not to increase flood damage downstream. Concentrated discharges from new developments must enter conveyance systems capable of carrying the design flow rate without increasing flood damage, erosion or maintenance costs downstream.
(B) Minor stormwater systems shall be sized to convey runoff from the tributary watershed under fully developed conditions consistent with the design requirement of the permitting authority.
(C) Major stormwater systems shall be sized to carry the base flood without causing additional flood damage.
(D) Stormwater systems shall properly incorporate and be compatible with existing subsurface and surface discharge systems, including agricultural systems. Designs shall not cause new or increased damage to existing drainage systems, or to existing adjacent or tributary agricultural land uses.
(1) Offsite outfall. Agricultural subsurface and surface drainage systems shall be evaluated with regard to their capacity and capability to properly convey low-flow ground water and site runoff storage facility release without new or increased damage to downstream structures and land uses. If the outfall drain tile and surface drainage systems prove to be inadequate to handle the design release rate, one of the following solutions shall be used:
(a) The site stormwater system and offsite outfall shall be designed so that it does not exceed the existing capacity of the downstream drainage system; or
(b) Modify the existing systems or construct new systems that will not conflict with the existing systems and will not impact existing land uses; or
(c) Alternate solutions may be submitted to the Administrator for approval.
(2) Onsite. Agricultural drainage systems shall be located and evaluated. All existing onsite agricultural drain tiles not serving a beneficial use shall be abandoned by trench removal prior to other development, and recorded on engineering details for the project. If any existing drain tiles continue to drain upland watersheds, the developer must maintain drainage service during construction until new storm sewers can be installed for a permanent connection.
(3) Offsite tributary. Existing drainage systems shall be evaluated with regard to existing capabilities and reasonable future expansion capacities. All existing tributary drain tiles shall be incorporated into the new stormwater system that includes observation structures located at the limits of the site and shall provide a free flow discharge. Agricultural tributary surface conveyance shall be accepted by the new development, with consideration given to the water quality and the ability to filter out sediment.
(4) Preservation of existing systems. New roadway construction shall preserve existing subsurface systems within the right-of-way. Inspection wells shall be placed in the right-of-way. Tiles found not to be flowing between inspection wells at the end of construction shall be replaced.
(E) Design runoff rates shall be calculated using event hydrograph methods. Design runoff rates for minor stormwater systems may be calculated using the rational method if the design watershed is less than 20 acres.
(F) Any design runoff rate calculation method shall use Bulletin 70, “Northeast Sectional Rainfall Statistics”, and shall calculate flow from all tributary areas upstream of the point of design. Peak discharges for conveyance design purposes shall be based on the critical duration considering the appropriate rainfall distribution.
(G) Major and minor stormwater systems shall be located within easements or rights-of-way, explicitly providing for government access or maintenance of such facilities by the grantee.
(H) Maximum flow depths for new transverse stream crossing shall not exceed one foot at the crown of the road during the base flood condition. The maximum longitudinal flow depth on a roadway shall not exceed six inches at the crown for flow depth (in feet) and velocity (in feet per second) shall not exceed four feet per second for the base flood condition.
(I) Transfers of waters between watersheds (diversions) shall be prohibited, except when such transfers will not violate this subchapter and are otherwise lawful.
(J) Developments shall incorporate best management practices in accordance with the Clean Water Act (33 U.S.C. §§ 1251 et seq., as amended), and as required by the IEPA’s National Pollutant Discharge Elimination System (NPDES) permit program.
(Ord. 2019-03, passed 4-15-2019)
(A) The area of hydrological disturbance on the site shall be used to calculate the required site runoff storage volume. The tributary area of the site at the point of discharge shall be used to calculate the allowable release rates of the primary restrictor for the site runoff storage facility.
(B) The site runoff storage volume required shall be calculated based on maximum release rates of 0.15 cubic feet per second per acre for the 100-year, 24-hour storm event, and 0.04 cubic feet per second per acre for the two-year, 24-hour storm event, according to the methods identified in division (C) below.
(C) Event hydrograph routing methods, such as HEC-1, HEC-HMS, and TR-20 or TR-55 tabular method, using SCS curve number methodology, shall be used to calculate design runoff volumes for site runoff storage facilities. Event methods shall incorporate the following assumptions:
(1) Antecedent moisture condition equals two;
(2) Appropriate Huff rainfall distribution, except that SCS type II distribution is acceptable with TR-55 tabular method only; and
(3) Twenty-four-hour duration storm, with a 1% probability (100-year) of occurrence in any one year as specified by Bulletin 70, “Northeast Sectional Rainfall Statistics”.
(D) For sites where the undeveloped release rate is less than the maximum release rate of this section, the developed release rate and corresponding site runoff storage volume shall be based on the existing undeveloped release rate for the development site.
(E) Hydraulic computations for the release structure must assume backwater conditions up to the ten-year flood elevation on the adjacent receiving watercourse.
(F) Retention requirement.
(1) The runoff from a three-quarter-inch rainfall event over the hydraulically connected impervious area of a new industrial, commercial or multi-family development shall be stored below the elevation of the primary gravity outlet (retention) of the site runoff storage facility. The facility may be designed to allow for evapotranspiration or infiltration of this volume into a subsurface drainage system, and shall not be conveyed through a direct positive connection to downstream areas.
(2) The hydraulically connected impervious area used in the calculation of required retention volume may be reduced by the village if the soils are undisturbed in situ or prepared to maximize infiltration and deep-rooted grasses or other plants that assist in the promotion of infiltration and transpiration are planted in areas appropriately dedicated. The reduction in hydraulically connected impervious area used in the calculation shall be equal to the area of the development meeting the above soils/planting requirement.
(3) Subsurface drainage systems may be designed as a component of the retention portion of the site runoff storage basin to assist in infiltration in accordance with the following criteria:
(a) No such subsurface drainage pipe shall be located within ten feet of drainage pipes directly connected to the site runoff storage basin; and
(b) For purposes of meeting the maximum subsurface drainage requirements, flow control orifices and weirs may be incorporated into the design.
(G) Site runoff storage facilities shall be designed and constructed with the following characteristics.
(1) At least one foot of freeboard above the 100-year design water surface elevation shall be required within the storage facility.
(2) Storage facilities shall be accessible and easily maintained.
(3) All design site runoff storage volume shall be provided above the seasonal high ground water table or the invert elevation of the ground water control system.
(4) Storage facilities shall be designed to control sediment and floating debris. Unless specifically approved by the Administrator, concrete-lined, low-flow ditches shall not be used in site runoff storage basins.
(5) Storage facilities shall minimize the negative impacts of stormwater runoff into the waterquality by incorporating best management practices in the design of the facilities.
(6) Storage facilities shall maximize the distance between site runoff storage inlets and outlets to the extent possible.
(7) Storage facilities shall be designed so as not to exceed the existing pre-development peak runoff rate of the 100-year, critical-duration rainfall, when the primary restrictor is assumed to be blocked.
(8) Storage facilities with single-pipe outlets shall have a minimum inside diameter of 12 inches. If design release rates necessitate a smaller outlet to be constructed, perforated risers or flow control orifices shall be used to prevent smaller openings from clogging.
(H) Storage facilities located within the regulatory floodplain shall:
(1) Comply with this subchapter; and
(2) Store the required amount of site runoff to meet the release rate requirement under all stream flow and backwater conditions, up to the ten-year flood elevation on the adjacent receiving watercourse. The village may approve designs that can be substantiated through hydrologic and hydraulic engineering analysis to provide a new watershed benefit not otherwise realized by strict application of the requirements set forth in this division.
(I) Storage facilities located within the regulatory floodway will be allowed only as a variance and shall:
(1) Meet the requirements for locating storage facilities in the regulatory floodplain; and
(2) Be evaluated by performing hydrologic and hydraulic analysis consistent with the standards and requirements for watershed plans; and
(3) Provide a net watershed benefit.
(J) Site run-off facilities may be located offsite if:
(1) The offsite storage facility meets all of the requirements of this article; and
(2) Adequate storage capacity in the offsite facility is dedicated to the development; and
(3) The development includes a means to convey stormwater within an easement to the offsite storage facility.
(K) Site runoff storage volume provided by enlarging existing regulatory floodplain storage (on stream runoff storage) will be allowed only as a variance. The applicant must demonstrate that flood damage will not be increased, and the development will not increase flood flows for both the two-year and 100-year floods.
(L) Structures built across the channel to impound water to meet site runoff storage requirements shall be prohibited on any perennial stream, unless part of a public flood control project with a net watershed benefit. Those streams appearing as blue on a USGS quadrangle map shall be assumed to be perennial, unless better data is provided by the developer. In all cases, it must be demonstrated that all such structures will not cause short-term or long-term instability, and that they are permitted under a joint application to the IDNR, COE and IEPA. Where such facilities are approved, the applicant must also comply with division (F) of this section.
(Ord. 2019-03, passed 4-15-2019)
(A) The BFE shall be delineated on the site topography to establish the regulatory floodplain limits for regulation under this subchapter, using the Flood Insurance Rate Maps (FIRMs) and Flood Insurance Study (FIS) of Grundy County, dated August 2, 2012, by the Federal Emergency Management Agency, in accordance with this subchapter.
(B) The BFE shall be:
(1) In the case of AE Zones on the FIRM, the 1% annual chance flood profile elevation in the FIS; or
(2) In the case of AH Zones on the FIRM, that elevation delineated on the FIRM; or
(3) In the case of a AO Zones on the FIRM, that depth delineated on the FIRM added to the highest adjacent grade or at least two feet above the highest adjacent grade if no depth number is provided; or
(4) For each of the remaining floodplains delineated as A Zones on the FIRM, according to the best data available from federal, state or other sources.
(a) Should no other data exist, the BFE should be determined by an engineering study financed by the applicant, and conducted by a professional engineer using appropriate hydrologic and hydraulic models as follows:
1. Hydrologic models: TR-20, HEC-1, HEC-HMS;
2. Hydraulic models: HEC-2, HEC-RAS, WSP-2; or
3. A technique approved by the Administrator and IDNR-OWR.
(b) Where a channel has a tributary drainage area of 640 acres or more, the above analysis shall be submitted to IDNR-OWR for approval.
(C) Floodway delineation and elevations.
(1) The location of the regulatory floodway shall be as delineated on the FIRM. Where an interpretation is needed to determine the exact location of the regulatory floodway boundary, IDNR-OWR shall be contacted.
(2) General criteria for analysis of flood elevations in the regulatory floodway are as follows:
(a) The flood profiles, flows and data from the current applicable regulatory map must be used for analysis of the base conditions. If the study data appears to be in error or conditions have changed, FEMA and IDNR-OWR shall be contacted for approval and concurrence on the appropriate base conditions data to use. The same Manning’s “n” value shall be used for both existing and proposed conditions, unless a recorded maintenance agreement obligates a public entity to maintain the proposed conditions, or the land cover is changing from vegetative to non-vegetative. The Administrator shall be copied on all related correspondence.
(b) If the BFE at the site is affected by backwater from a downstream receiving stream with a larger drainage area, the proposed development shall be shown to meet the requirements of this section with the receiving stream at both the normal water elevation and the BFE.
(c) If the applicant is informed by IDNR-OWR, a local government or private owner that a downstream or upstream restrictive bridge or culvert is scheduled to be removed, reconstructed or modified, or a regional flood control project is scheduled to be built, removed, constructed or modified within the next five years, the proposed development shall be analyzed and shown to meet the requirements of this section for both the existing conditions and the expected flood profile conditions when the bridge, culvert or flood control project is built, removed or modified.
(d) If the use will result in a change in the location of the regulatory floodway or a change in the BFE, then no development shall take place until a CLOMR has been issued by FEMA. Filling, grading, dredging or excavating may take place upon issuance of a CLOMR by FEMA. No further development activities shall take place or building permit issued in existing or proposed floodplain until a LOMR is issued by FEMA. The Administrator shall be copied on all related correspondence.
(e) In the circumstances listed below and located in a regulatory floodway, at a minimum, the information set forth below shall be submitted to IDNR-OWR for its review and approval.
1. Analysis of the flood profile due to a proposed bridge, culvert crossing or roadway approach.
2. An engineer’s determination that an existing bridge, culvert crossing or roadway approach is not a source of flood damage, and the analysis indicating the proposed flood profile.
3. Alternative transition sections and hydraulically equivalent compensatory storage.
4. Stormwater management permits issued to local units of government for regulatory floodway and floodplain development.
5. IDNR-OWR will issue permits for any IDNR-OWR, state, federal or community projects for activities or developments that are located within the floodway.
(Ord. 2019-03, passed 4-15-2019)
The following general performance standards are applicable to all development in a regulatory floodplain. The standards of this section apply except when superseded by more stringent requirements in the following sections.
(A) All development in the regulatory floodplain shall comply with the compensatory storage volume standards of this subchapter.
(B) For all projects involving a channel modification, fill, stream maintenance or a levee, the flood conveyance and storage capacity of the regulatory floodplain shall not be reduced.
(C) If the proposed development would result in a change in the regulatory floodplain or BFE, the applicant shall obtain a CLOMR from FEMA prior to development, followed by a LOMR from FEMA following development. No buildings may be built in the existing or proposed regulatory floodplain unless the building meets all the building protection standards identified within this subchapter. Proposed changes to the regulatory floodway delineation and the BFE must also be submitted to the IDNR-OWR for its approval.
(D) Prior to the commencement of any construction, modification or removal of a dam, the developer shall obtain an IDNR-OWR dam safety permit or a letter from the IDNR-OWR stating that a permit is not required.
(E) For public flood control projects, the requirements will be deemed met if the applicant demonstrates to IDNR-OWR and the Stormwater Committee:
(1) By hydraulic and hydrologic modeling, that the proposed project will not singularly or cumulatively result in increased flood heights outside the project site, or that any increases will be contained in easements for all flood events, up to and including the base flood event;
(2) That the project will be operated and maintained by a public entity;
(3) That the project will reduce flood damage to an existing building or structure.
(F) Nothing in this section precludes the design, engineering, construction or financing, in whole or in part, of a public flood control project by persons who are not public entities.
(Ord. 2019-03, passed 4-15-2019)
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