The purpose of this Chapter is to diminish threats to public health and safety caused by floodwaters; reduce economic losses to individuals and the community at large; enhance broader social and economic objectives; protect, conserve, and promote the orderly development of land and water resources; prevent victimizations and fraud; and to comply with the guidelines for the National Flood Insurance Program as published by the Federal Emergency Management Agency (FEMA). This Chapter is adopted to accomplish the following specific purposes:

(A) To meet the requirements of 615 ILCS 5/18g, An Act in Relation to the Regulation of the Rivers, Lakes and Streams of the State of Illinois, approved June 10, 1911, as amended.

(B) To assure that new development does not increase the flood or drainage hazards to others, or create unstable conditions susceptible to erosion.

(D) To protect human life and health from the hazards of flooding.

(E) To lessen the burden on the taxpayer for flood control projects, repairs to flood-damaged public facilities and utilities, and flood rescue and relief operations.

(F) To make federally subsidized flood insurance available for property in the Village by fulfilling the requirements of the National Flood Insurance Program.

(G) To comply with the rules and regulations of the National Flood Insurance Program codified as 44 CFR 59-79, as amended.

(H) To protect, conserve, and promote the orderly development of land and water resources.

(I) To prevent adverse impacts caused by increases in storm water runoff rates and quantities resulting from development and improvement of the land.

Sec. 26-103. Definitions. [back to top]

(A) The following words and terms are found in Title 44 of the Code of Federal Regulations (44 CFR), Section 59.l and are incorporated in this Chapter by reference as though they were fully recited herein:

Agency, Appurtenant Structure, Area of Shallow Flooding, Area of Special Flood Hazard, Basement, Criteria, Critical Feature, Elevated Building, Flood Elevation Determination, Flood Insurance, Floodplain Management, Flood Protection System, Levee, Levee System, Lowest Floor, Person, Principally Above Ground, Variance, and Water Surface Elevation.

Two copies of said Title 44 CFR shall remain on file in the office of the Village Clerk for public inspection and in the office of the Village Engineer.

(B) For the purposes of this Chapter, the following definitions are adopted:

Act - An Act in relation to the regulation of the rivers, lakes, and streams of the State of Illinois, 615 ILCS 5/4.9 et seq.

Adverse impacts - Any deleterious impact on water resources or wetlands affecting their beneficial uses, including recreation, aesthetics, aquatic habitat, quality, and quantity.

Applicant - Any person, firm, or governmental agency who executes the necessary forms to procure official approval of a project or permit to carry out construction of a project from the Village.

Appropriate use - Only uses of the regulatory floodway that are permissible and will be considered for permit issuance. The only uses that will be allowed are as specified in Section 26-304 of this Chapter.

Base flood - The flood having a one percent probability of being equaled or exceeded in any given year. The base flood is also known as the 100-year frequency flood event. Application of the base flood elevation at any location is as defined in Section 26-302 of this Chapter.

Board - The Village Board of Trustees of the Village of Addison, Illinois.

Building - 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, mobile home, or a prefabricated building. This term also includes recreational vehicles and travel trailers to be installed on a site for more than 180 days.

Bulkhead - A retaining wall that protects waterfront property.

Bypass flows - Storm water runoff from upstream properties tributary to a property's drainage system but not under its control.

Capacity of a storm drainage facility - The maximum ability of a storm drainage facility to convey storm water flows without causing substantial damage to public or private property, and in the case of a pipe, without surcharging.

Channel - Any river, stream, creek, brook, branch, natural or artificial depression, ponded area, flowage, slough, ditch, conduit, culvert, gully, ravine, wash, or natural or man-made drainage way, which has a definite bed and banks or shoreline, in or into which surface or groundwater flows, either perennially or intermittently.

Channel modification - Alteration of a channel by changing the physical dimensions or materials of its bed or banks. Channel modification includes damming, riprapping or other armoring, 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).

Commission - The Plan Commission of the Village of Addison, Illinois.

Compensatory storage - An artificially excavated, hydraulically equivalent volume of storage within the special flood hazard area (SFHA) used to balance the loss of natural flood storage capacity when artificial fill or structures are placed within the floodplain. The uncompensated loss of natural floodplain storage can increase off-site floodwater elevations and flows.

Comprehensive Plan - The Official Plan of the Village adopted September 8, 1970, as amended.

Conditional approval of a regulatory floodway map change - Preconstruction approval by Illinois Department of Transportation, Division of Water Resources (DWR) and the Federal Emergency Management Agency of a proposed change to the floodway map. This preconstruction approval, pursuant to this Part, gives assurances to the property owner that once an Appropriate Use is constructed according to permitted plans, the floodway map can be changed, as previously agreed, upon review and acceptance of as-built plans.

Conditional Letter of Map Revision (CLOMR) - A letter which indicates that the Federal Emergency Management Agency will revise base flood elevations, flood insurance rate zones, flood boundaries or floodway as shown on an effective Flood Hazard Boundary Map or Flood Insurance Rate Map, once the as-built plans are submitted and approved.

Conduit - Any channel, pipe, sewer, or culvert used for the conveyance or movement of water, whether open or closed.

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.

Dam - All obstructions, wall embankments or barriers, together with their abutments and appurtenant works, if any, constructed for the purpose of storing or diverting water or creating a pool. Underground water storage tanks are not included.

Detention basin - A facility constructed or modified to restrict the flow of storm water to a prescribed maximum rate through a controlled release by gravity, and to concurrently detain the excess waters that accumulate behind the control structure.

Detention storage - The temporary detaining or storage of storm water in storage basins, in streets, school yards, parks, open space, or other areas under predetermined and controlled conditions with the rate of drainage therefrom regulated by appropriately installed devices.

Detention time - The mean residence time of storm water in a detention basin.

Development - Any man-made change to real estate, including:

(1) Construction, reconstruction, repair, or placement of a building or any addition to a building.

(2) Installing a manufactured home on a site, preparing a site for a manufactured home, or installing a travel trailer on a site for more than 180 days.

(3) Drilling, mining, installing utilities, construction of roads, bridges, or similar projects.

(4) Demolition of a structure or redevelopment of a site.

(5) Clearing of land as an adjunct of construction.

(6) Construction or erection of levees, walls, fences, dams, or culverts; channel modification; filling, dredging, grading, excavating, paving, or other non-agricultural alterations of the ground surface; storage of materials; deposit of solid or liquid waste.

(7) Any other activity of man that might change the direction, height, or velocity of flood or surface water, including extensive vegetation removal.

Development does not include maintenance of existing buildings and facilities such as re-roofing or re-surfacing of roads when there is no increase in elevation, or gardening, plowing, and similar agricultural practices that do not involve filling, grading, or construction of levees or improvements to existing structures and or accessory buildings located on lots of less than 1/3 acre, where the improvements do not exceed 600 square feet in area, or pavement for driveways accessing detached garages. (Ord. 99-65)

Discharge - The rate of outflow of water from detention storage.

Drainage area - The area from which water is carried off by a drainage system; a watershed or catchment area.

Drainage plan - A plan, including engineering drawings and supporting calculations, which describes the existing storm water drainage system and environmental features, as well as the drainage system and environmental features which will be in place after development of a property.

Dry bottom detention basin - A detention basin designed to drain completely after temporary storage of storm water flows and to normally be dry over the majority of its bottom area.

Dwelling - Any building or portion thereof which is designed and used exclusively for residential purposes.

DWR - Illinois Department of Transportation, Division of Water Resources.

Elevation Certificates - A form published by the Federal Emergency Management Agency that is used to certify the elevation to which a building has been elevated.

Erosion - The general process whereby soils are removed by flowing water or wave action.

Excess storm water runoff - The volume and rate of flow of storm water discharged from an urbanized drainage area which is or will be in excess of that volume and rate which pertained before urbanization.

Exempt organization - Organizations which are exempt from this Chapter per the Illinois Compiled Statutes, including state, federal or local units of government.

FEMA - Federal Emergency Management Agency and its regulations at 44 CFR 59-79 effective as of October 1, 1986. This incorporation does not include any later editions or amendments.

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 or runoff of surface waters from any source.

Flood frequency - A period of years, based on a statistical analysis, during which a flood of a stated magnitude may be expected to be equaled or exceeded.

Flood fringe - That portion of the floodplain outside of the regulatory floodway.

Flood Insurance Rate Maps (FIRM) - A map prepared by the Federal Emergency Management Agency that depicts the SFHA within a community. This map includes insurance rate zones and floodplains and may or may not depict floodways.

Floodplain - That land typically adjacent to a body of water with ground surface elevations at or below the base flood or the 100-year frequency flood elevation. Floodplains may also include detached SFHA's, ponding areas, etc. The floodplain is also known as the SFHA. The floodplains are those lands within the jurisdiction of the Village that are subject to inundation by the base flood or 100-year frequency flood. The SFHA's of the Village are generally identified as such on the FIRM of the Village prepared by the Federal Emergency Management Agency (or the U.S. Department of Housing and Urban Development) and dated January 18, 1987 and such amendments to such study and maps as may be prepared from time to time. The SFHA's of those parts of unincorporated DuPage County that are within the extraterritorial jurisdiction of the Village or that may be annexed into the Village are generally identified as such on the FIRM prepared for DuPage County by the Federal Emergency Management Agency (or the U.S. Department of Housing and Urban Development) and dated October 18, 1988 and such amendments to such study and maps as may be prepared from time to time.

Flood of Record - An actual historical flood event for which sufficient records are available to establish its extent. No uniform probability of occurrence is associated with floods of record. However, the probability of occurrence may be determined for the event at specific locations.

Floodproofing - Any combination of structural and nonstructural additions, changes or adjustments to structures which reduce or eliminate flood damage to real estate or improved real property, water and sanitary facilities, structures and their contents.

Floodproofing Certificate - A form published by the Federal Emergency Management Agency that is used to certify that a building has been designed and constructed to be structurally dry floodproofed to the flood protection elevation.

Flood Protection Elevation (FPE) - The elevation of the base flood or 100-year frequency flood plus one foot of freeboard at any given location in the SFHA.

Freeboard - An increment of elevation added to the base flood elevation to provide a factor of safety for uncertainties in calculations, unknown localized conditions, wave actions, and unpredictable effects such as those caused by ice or debris jams.

Hydraulic characteristics - The features of a watercourse which determine its water conveyance capacity. These features include but are not limited to size and configuration of the cross-section of the watercourse, texture of materials along the watercourse, alignment of watercourse, gradient of watercourse, amount and type of vegetation within the watercourse, and size, configuration, and other characteristics of structures within the watercourse.

Hydrograph - A graph showing, for a given point on a stream or conduit, the runoff flow rate with respect to time.

Hydrologic and hydraulic calculations - Engineering analysis which determine expected flood flows and flood elevations based on land characteristics and rainfall events.

Infiltration - The passage or movement of water into the soil surfaces.

Lag - The elapsed time between the center of mass of a rain event and the center of mass of the resultant hydrograph at a specific site.

Letter of Map Amendment (LOMA) - Official determination by FEMA that a specific structure is not in a 100-year flood zone; amends the effective Flood Hazard Boundary Map or FIRM.

Letter of Map Revision (LOMR) - Letter that revises base flood or 100-year frequency flood elevations, flood insurance rate zones, flood boundaries, or floodways as shown on an effective FHBM or FIRM.

Major drainage system - That portion of a drainage system needed to store and convey flows beyond the capacity of the minor drainage system.

Manufactured home - A structure, transportable in one or more sections, which is built on a permanent chassis and is designated for use with or without a permanent foundation when connected to the required utilities. The term manufactured homes also includes park trailers, travel trailers, and other similar vehicles placed on site for more than 180 consecutive days.

Manufactured home park or subdivision - A parcel (or contiguous parcels) of land divided into two or more manufactured home lots for rent or sale.

Minor drainage system - That portion of a drainage system designed for the convenience of the public. It consists of street gutters, storm sewers, small open channels, and swales and will be designed to handle at a minimum the 10-year, 24-hour runoff event or more.

Mitigation - Mitigation includes those measures necessary to minimize the negative effects which floodplain development activities might have on the public health, safety, and welfare. Examples of mitigation include compensatory storage, floodproofing, soil erosion and sedimentation control, and channel restoration.

Natural - Conditions resulting from physical, chemical, and biological processes without intervention by man.

NGVD - National Geodetic Vertical Datum of 1929. Reference surface set by the National Geodetic Survey deduced from a continental adjustment of all existing adjustments in 1929.

One hundred year event - A runoff, rainfall, or flood event having a one percent chance of occurring in any given year.

Ordinary High Water Mark (OHWM) - The point on the bank or shore up to which the presence and action of surface water is so continuous so as to leave a distinctive mark such as by erosion, destruction or prevention of terrestrial vegetation, predominance of aquatic vegetation or other easily recognized characteristics.

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.

Property - A parcel of real estate.

Public flood control project - A flood control project which will be operated and maintained by a public agency to reduce flood damages to existing buildings and structures which includes a hydrologic and hydraulic study of the existing and proposed conditions of the watershed. Nothing in this definition shall preclude the design, engineering, construction or financing, in whole or in part, of a flood control project by persons or parties who are not public agencies.

Publicly navigable waters - All streams and lakes capable of being navigated by watercraft.

Registered Land Surveyor - A land surveyor registered in the State of Illinois, under The Illinois Professional Land Surveyor Act (225 ILCS 330/1 et seq.).

Registered Professional Engineer - An engineer registered in the State of Illinois, under The Illinois Professional Engineering Practice Act (225 ILCS 325/1 et seq.).

Regulatory floodway - The channel, including onstream lakes, and that portion of the floodplain adjacent to a stream or watercourse as designated by DWR, which is needed to store and convey the existing and anticipated future 100- year frequency flood discharge with no more than a 0.l foot increase in stage due to the loss of flood conveyance or storage, and no more than a 10% increase in velocities. The regulatory floodways are designated for Salt Creek and West-wood Creek on the Flood Boundary and Floodway Map prepared by FEMA and dated January 16, 1987 and such amendments to such study and maps as may be prepared from time to time, and for Salt Creek, Westwood Creek, and the South Fork of Westwood Creek, on the Regulatory Floodplain Map prepared by DWR and dated July 1, 1979 and such amendments to such study and maps as may be prepared from time to time. The regulatory floodways for those parts of unincorporated DuPage County that are within the extraterritorial jurisdiction of the Village that may be annexed in the Village are designated for the East Branch of the DuPage River, East Branch Tributary No. l of the DuPage River, and Salt Creek, on the Flood Boundary and Floodway map prepared by FEMA (or Department of Housing and Urban Development) and dated April 15, 1982 and such amendments to such study and maps as may be prepared from time to time. To locate the regulatory floodway boundary on any site, the regulatory floodway boundary should be scaled off the regulatory floodway map and located on a site plan, using reference marks common to both maps. Where interpretation is needed to determine the exact location of the regulatory floodway boundary, the DWR should be contacted for the interpretation.

Repair, remodeling or maintenance - Development activities which do not result in any increases in the outside dimensions of a building or any changes to the dimensions of a structure.

Retention basin - A facility designed to completely retain a specified amount of storm water runoff without gravity release.

Retention/detention facility - A retention facility stores storm water runoff without a gravity release. A detention facility provides for storage of storm water runoff and controlled gravity release of this runoff during and after a flood or storm.

Riverine SFHA - Any SFHA subject to flooding from a river, creek, intermittent stream, ditch, on stream lake system, or any other identified channel. This term does not include areas subject to flooding from lakes, ponding areas, areas of sheet flow, or other areas not subject to overbank flooding.

Runoff - The waters derived from melting snow or rain falling within a tributary drainage basin which are in excess of the infiltration capacity of the soils of that basin, which flow over the surface of the ground or are collected in channels or conduits.

Sedimentation - The processes that deposit soils, debris, and other materials either on other ground surfaces or in bodies of water or watercourses.

Special Flood Hazard Area (SFHA) - Any base flood area subject to flooding from a river, creek, intermittent stream, ditch, or any other identified channel or ponding and shown on a Flood Hazard Boundary Map or Flood Insurance Rate Map as Zone A, AO, A1-30, AE, A99, AH, VO, V30, VE, V, M, or E.

Storm sewer - A closed conduit for conveying collected storm water.

Storm water drainage system - All means, natural or manmade, used for conducting storm water to, through or from a drainage area to the point of final outlet, including but not limited to any of the following: conduits and appurtenance features, canals, channels, ditches, streams, culverts, streets, and pumping stations.

Storm water drainage facility - Any element in a storm water drainage system which is made or improved by man.

Storm water runoff - The waters derived from melting snow or rain falling within a tributary drainage basin, flowing over the surface of the ground or collected in channels or conduits.

Structure - The results of a man-made 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; installing manufactured home on a site; preparing a site for a manufactured home or installing a travel trailer on a site for more than 180 days.

Substantial improvement - Any repair, reconstruction, or improvement of a structure, the cost of which equals or exceeds 50 percent of the market value of the structure either (a) before the improvement or repair is started, or (b) if the structure has been damaged, and is being restored, before the damage occurred. For the purposes of this definition, "substantial improvement" is 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. The term does not, however, include either (l) any project for improvement of a structure to comply with existing state or local health, sanitary, or safety code specifications which are solely necessary to assure safe living conditions, or (2) any alteration of a structure listed on the National Register of Historic Places or a State Inventory of Historic Places.

Time of concentration - The elapsed time for storm water to flow from the most distant point in a drainage basin to the outlet or point in question.

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 watershed - All of the land surface area that contributes runoff to a given point.

Two-year event - A runoff, rainfall, or flood event having a 50% chance of occurring in any given year.

Village Engineer - The duly appointed engineer of the Village of Addison, Illinois, or his designated representative.

Watercourse - Any stream, creek, brook, branch, natural or artificial depression, slough, gulch, reservoir, lake, pond or natural or man-made drainage way in or into which storm water runoff and floodwaters flow either regularly or intermittently.

Wet bottom detention basin - A basin designed to retain a permanent pool of water after having provided its planned detention of runoff during a storm event.

Wetland - Those transitional lands between terrestrial and aquatic systems where the water table is usually at or near the surface or the land is covered by shallow water. Classification of areas as wetlands shall follow the "Classification of Wetlands and Deepwater Habitats of the United States" as published by the U.S. Fish and Wildlife Service (FWS/OBS-79/31).

Article 2. Drainage System.

Sec. 26-201. Drainage Plan. [back to top]

Each applicant shall submit the following information, depending on development size, showing the following information and data to ensure that the provisions of this Chapter are met. The submittal shall include sufficient information to evaluate the environmental characteristics of the property, the potential adverse impacts of the development on water resources both on-site and downstream, and the effectiveness of the proposed drainage plan in managing storm water runoff. The applicant shall certify on the drawings that all clearing, grading, drainage, and construction shall be accomplished in strict conformance with the drainage plan. The following information shall be submitted for both existing and proposed property conditions.

(A) Properties Smaller than 10 Acres.

(l) Topographic Map - A topographic survey of the property and areas upstream and downstream necessary to determine off-site impacts of the proposed drainage plan at l-foot contours.

(2) Environmental Features - A depiction of environmental features of the property and immediate vicinity including the following:

(a) The limits of wetland areas.

(b) Any proposed channel modifications.

(d) The delineations of floodplains and floodways.

(3) Drainage System - A depiction of drainage system features of the property and immediate vicinity not to exceed 1" = 50' scale, including:

(a) The banks and centerline of streams and channels.

(b) Shorelines of lakes, ponds, and detention basins.

(d) Watershed boundary of the area contributing runoff to the property and sub-area boundaries within the property to determine flow concentration points or inlet locations.

(e) The properties located within stream or river watersheds.

(f) Location, size, and slope of storm water conduits.

(g) Sanitary or combined sewers.

(h) Depressional storage areas.

(i) Detention facilities.

(j) Roads and streets and associated storm water inlets.

(k) 100-year floodplain and floodway for the entire drainage system of the property.

(l) Basis of design for the final drainage network components.

(B) Properties Larger than 10 Acres. The same information as required in Subsection A hereinabove is required for properties larger than 10 acres along with the following additional information:

(l) Mapping of the floodplain for the entire drainage system for the 2-year, 24-hour event.

(2) Mapping of floodplain for the minor drainage system's design event.

(3) Cross-section data for open channel flow paths.

(4) Direction of storm flows.

(5) Flow rates and velocities at critical points in the drainage system.

(6) Mapping of floodplain for the entire drainage system for the 100-year, 24-hour event.

Sec. 26-202. Minimization of Runoff Volumes and Rates. [back to top]

In the selection of a drainage plan for a development, the applicant shall choose a strategy which strives to minimize the increase in runoff volumes and rates from the site. The applicant shall consider and evaluate the following strategies in developing a drainage plan:

(l) Flow attenuation by use of open vegetated swales and retention of natural depression and existing natural stream channels.

(2) Infiltration of runoff on-site.

(3) Storm water retention structures.

(4) Storm water detention structures.

(5) Storm sewers.

Sec. 26-203. Release Rates. [back to top]

The drainage system for a property shall be designed to control the peak rate of discharge from the property for the 2-year, 24-hour and 100-year, 24-hour events to levels which will not cause an increase in flooding or channel instability downstream when considered in aggregate with other developed properties and downstream drainage capacities. The 2-year discharge shall be no greater than 0.04 cfs per acre of property. The 100-year discharge shall be no greater than 0.10 cfs per acre of property.

Sec. 26-204. Water Quality and Multiple Uses. [back to top]

The drainage system should be designed to control pollutants contained in storm water runoff to the maximum extent feasible. If detention basins are used, they shall incorporate design features to capture storm water runoff pollutants. Detention and infiltration of storm water shall be promoted throughout the property's drainage system to reduce the volume of storm water runoff and to reduce the quantity of runoff pollutants.

To the maximum extent feasible, the drainage system should have multiple uses. Uses considered compatible with storm water management include open space, aquatic habitat, recreation (boating, trails, playing fields), and wetlands. The applicant should avoid using portions of the property exclusively for storm water management.

Sec. 26-205. Design Criteria and Standards. [back to top]

(A) Hydrologic Design Procedures. The design of the drainage system shall be developed and evaluated by the applicant based on routing runoff hydrographs for the 2-year, 10-year, and 100-year, 24-hour events through its minor and major components. In addition, a general assessment of the impacts of flows exceeding the 100-year event shall be presented.

(1) Rainfall - Unless a continuous simulation approach to drainage system hydrology is used, all design rainfall events and rainfall distributions shall be based on the Illinois State Water Survey Bulletin 70 (1989). For 24-hour events, 4th quartile average time distributions of heavy rainfalls shall be used as shown in Bulletin 70. SCS Type II rainfall distribution should only be used with the SCS TR-55 hydrograph method.

(2) Hydrograph Required - Runoff hydrographs must be developed as part of the design of the drainage system's minor and major components. The modified rational formula shall not be used for development of a hydrograph.

(3) Antecedent Moisture - All computations of runoff hydrographs which do not rely on a continuous accounting of antecedent moisture conditions shall assume that no more than 80 percent of potential abstraction is available for any event.

(B) Hydraulic Design Procedures. A profile and mapping of floodwater depths and coverage shall be prepared for the property for the 2-year, 10-year, and 100-year events. Direction of flow and velocities shall also be reported for critical points in the drainage system.

(1) Detention - The maximum available storage to be provided in a detention basin shall be based on the runoff from the 100-year, 24-hour event. In lieu of calculating the 100-year, 24-hour event and upon approval by the Village Engineer, the maximum available storage may be equivalent to 4.5 inches over the subject property. Hydrographs for the 2-year, 10-year, and 100-year, 24-hour events shall be routed through any detention structures included in the drainage system and the results displayed as part of Section 26-201, SubSections A and B.

(C) Wet Bottom Detention Basin. Wet bottom detention basins shall be designed to remove storm water pollutants, to be safe, to be aesthetically pleasing, and as much as feasible, to be available for recreational use.

(1) Depths - Wet basins shall be at least 3 feet deep, excluding near shore banks and safety ledges. If fish habitat is to be provided, they shall be at least 10 feet deep over 25 percent of the bottom area to prevent winter freeze-out.

(2) Permanent Pool Volume - The permanent pool volume in a wet basin at normal depth shall be equal to the runoff volume from its watershed for the 2-year event.

(3) Nuisance Control - Wet basins shall be designed in a manner which will reduce as much as practicable nuisance problems such as algae and waterfowl.

(D) Dry Bottom Detention Basins. Dry bottom detention basins shall be designed to remove storm water pollutants, to be safe, to be aesthetically pleasing, and as much as feasible to be available for multiple uses.

(1) Drainage - Dry basins shall be designed so that 80 percent of their bottom areas shall have standing water no longer than 72 hours for any runoff event less than the 100-year event. Basins shall have a minimum two percent bottom slope.

(2) Water Quality - All dry detention basins shall be designed to remove storm water pollutants. At a minimum, dry detention basins should be designed to capture the 2-year, 24-hour runoff event and hold it for at least 24 hours.

(E) Safety. The drainage system components, especially all detention basins, shall be designed to protect the safety of any children or adults coming in contact with the system during runoff events.

(1) Shorelines - The shorelines of all detention basins shall be as level as practicable to prevent accidental falls into the basin and for stability and ease of maintenance.

(2) Banks - The side slopes of the banks of wet bottom detention basins shall not be steeper than 5 horizontal to l vertical above the normal water level and 3 horizontal to l vertical below the normal water level. The side slopes of the banks of dry bottom detention ponds shall not be steeper than 5 horizontal to l vertical.

(3) Safety Ledge - All wet detention basins shall have a level safety ledge extending 5 feet into the basin from the shoreline and 2 feet below the normal water depth.

(4) Velocity - Velocities throughout the drainage system shall be controlled to safe levels, taking into consideration rates and depths of flow.

(F) Infiltration Practices. Infiltration practices, including basins, trenches, and porous pavement, shall only be allowed in soils considered "A" or "B" by the U.S. Soil Conservation Service. Infiltration practices shall not be located within 75 feet of a water supply well or a building foundation. A sediment settling basin shall be provided to remove coarse sediment from storm water flows before they reach infiltration basins or trenches. Storm water shall not be allowed to stand more than 72 hours over 80 percent of a dry basin's bottom area for the maximum design event to be exfiltrated. The bottom of infiltration facilities shall be a minimum of 4 feet above seasonally high ground water and bedrock.

(G) Detention in Floodplains. Storm water detention facilities are not allowed in the floodway unless permitted by the Illinois Department of Transportation, Department of Water Resources. (Ord. 91-60)

(H) General Detention Considerations.

(1) Overflow Structures - All storm water detention basins shall be provided with an overflow structure capable of safely passing flows in excess of the 100-year event.

(2) Length to Width Ratio - All detention basins should have a length to width ratio of at most 3 to l as measured along the longitudinal axis of flow.

(3) Inlet and Outlet Orientation - As much as feasible, the distance between detention inlets and outlets shall be maximized. If possible, they should be at opposite ends of the basin.

(4) Velocity Dissipation - Baffles or berms should be placed perpendicular to the direction of flow through a detention basin to reduce velocity and prevent scour.

(5) Freeboard - The top of bank shall be a minimum of one foot above the 100-year capacity elevation.

(6) No detention facility shall be constructed within a distance of 10 feet plus one and one-half times the depth of the facility adjacent to any property line unless an easement is established for the purpose of a detention pond across this property line. (Ord. 91-60.)

(I) Maintenance. The storm water drainage system shall be designed to minimize and facilitate maintenance. Turfed side slopes shall be designed to allow lawn mowing equipment to easily negotiate them. Presedimentation basins shall be considered for localizing sediment deposition and removal.

Sec. 26-206. Flows from Tributary Areas. [back to top]

Storm water runoff from areas tributary to the property shall be considered in the design of the property's drainage system. The upstream flows may be routed around the applicant's detention basin through an underground piping system. The upstream flows may be routed through the applicant's detention basin in which case the basin release rate shall be the sum of the allowable release rate for the applicant's property tributary to the basin and the upstream flows.

Sec. 26-207. Early Completion of Detention Facilities. [back to top]

Where detention, retention, or depressional storage areas are to be used as part of the drainage system for a property, they shall be completed before general property grading begins. This is to ensure that if soil erosion and sediment control practices are not adequately implemented, any eroded sediment will be captured in these areas and will have to be removed by the applicant before project completion.

Sec. 26-208. Maintenance. [back to top]

Maintenance of storm water drainage facilities located on private property shall be the responsibility of the owner of that property. Before a permit is obtained from the Village of Addison, the applicant shall execute a maintenance agreement with the Village of Addison guaranteeing that the applicant and all future owners of the property will maintain its storm water drainage system. The maintenance agreement shall also specifically authorize representatives of the Village to enter onto the property for the purpose of inspections of the drainage system. Each agreement shall be recorded with the Recorder of Deeds of DuPage County. The maintenance agreement shall include a schedule for regular maintenance of each aspect of the property's storm water drainage system and shall provide for access to the system for inspection by authorized personnel of the Village of Addison. The maintenance agreement shall also stipulate that if the Village Engineer of the Village of Addison notifies the property owner in writing of maintenance problems which require correction, the property owner shall make such corrections within 30 calendar days of such notification. If the corrections are not made within this time period, the Village may have the necessary work completed and assess the cost to the property owner.

The Village of Addison has the option of requiring a bond to be filed by the property owner for maintenance of the storm water drainage system.

The content of this site is provided as a reference only. Information contained here can be confirmed through the Village of Addison's Village Clerk's Office. The information here is updated approximately every 3 to 6 months and will not include any changes made since the date at the top displayed.

CHAPTER 26. STORMWATER AND FLOODPLAIN MANAGEMENT

VILLAGE OF ADDISON CODE

Chapter 26 – Stormwater and Floodplain Management