(A) Permit required, application for permit.
(1) No person, firm, corporation or governmental body not exempted by state law shall commence any development, as defined herein, without first obtaining a stormwater management permit from the village. The Village Clerk shall not issue a permit if the proposed development does not meet the requirements contained herein.
(2) Every application for a stormwater management permit shall be accompanied by a drainage plan as required herein and such other information as may be required by the village for the proper enforcement of this chapter. Each applicant shall submit the following information, depending on development size, to ensure that the provisions of this chapter are met.
(3) 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 stormwater 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.
(B) General stormwater requirements.
(1) No development shall increase flood elevations or decrease flood conveyance capacity upstream or downstream of the site.
(2) Stormwater facilities shall be functional, where practicable, before any other construction begins on a site.
(3) The design of any development shall incorporate the following specific planning principles, where practicable.
(a) Impervious surfaces are the minimum necessary to satisfy the needs of the project and the current zoning regulations.
(b) Where feasible, plans allow sufficient right-of-way and easement widths so that stormwater runoff can be conveyed in vegetated swales. Storm sewers may be used for conveyance of nuisance flows and where conveyance in vegetated swales is impractical.
(c) Retention and infiltration of stormwater runoff should be used to the extent practicable to reduce the volume of stormwater runoff and the quantity of runoff pollutants.
(d) If retention facilities are impractical or are not used, then detention facilities shall be provided.
(e) Drainage plans use best management practices.
(f) Sites are designed to maximize the use of vegetated filter strips and swales to effectively filter stormwater pollutants and promote infiltration of runoff. Wherever practicable, runoff from impervious surfaces is directed onto vegetated filter strips and swales before being routed to a storm sewer or site runoff storage facility.
(C) Site runoff requirements.
(1) Stormwater facilities shall be required and designed so that runoff exits the site at the point where it exited prior to development (unless a change is required and approved in writing by the Village Engineer) 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 without increasing flood damage, erosion or maintenance costs downstream.
(2) Major and minor stormwater facilities shall be sized to convey runoff from the tributary watershed under fully developed conditions.
(3) Major stormwater facilities shall be sized to convey the base flood without causing additional flood damage.
(4) Stormwater facilities shall properly incorporate and be compatible with existing subsurface and surface drainage systems. Designs shall not cause damage to existing drainage systems or to existing adjacent or tributary land uses. The following principles and requirements shall be observed in the design.
(a) Off-site outfall: existing subsurface and surface drainage systems shall be evaluated with regard to their capacity and capability to properly convey site runoff storage facility release without damage to downstream structures and land uses. If the outfall drain tile and surface drainage systems prove to be inadequate, it will be necessary to modify the existing systems or construct new facilities which will not conflict with the existing systems and will not impact existing land uses.
(b) On site: existing agricultural drainage systems shall be mapped to the extent practicable. If any existing agricultural drainage tiles continue to upland watersheds, the developer must maintain drainage service so as not to impede the flow of water from the existing drainage tile. The existing upstream agricultural drainage tile may be connected into the proposed on-site drainage system if the invert of the existing drainage tile is higher than the proposed 100-year high water elevation of the stormwater facilities. The proposed stormwater facilities shall not discharge into existing agricultural drainage systems.
(c) Stormwater and site runoff storage facilities: the stormwater and site runoff storage facilities shall be designed to control the peak rate of discharge from the property for the two-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 allowable peak discharge from events less than or equal to the two-year, 24-hour event shall not be greater than 0.04 cubic foot per second (cfs) per acre of property drained. The allowable peak discharge from events less than or equal to the 100-year, 24-hour event shall not be greater than 0.20 cfs per acre of property drained. In no case shall the release of site runoff water exceed the existing runoff rate from the development area. Redevelopment or expansion of existing development parcels and impervious areas may instead use the alternate method of site runoff storage areas in divisions (C)(4)(l) and (C)(4)(m) below.
(d) The allowable peak discharges for both storms listed in division (C)(4)(c) above shall take into consideration undetainable areas. If areas of the property cannot be detained because of site limitations, the undetained discharge shall be subtracted from the allowable peak discharge to determine the allowable peak discharge from the detention or retention facility.
(e) 1. Design runoff rates shall be determined using event hydrograph methods.
2. Acceptable event hydrograph methods are HEC-HMS, HEC-1 (SCS runoff method), TR-20 or TR-55. Design runoff rates for minor conveyance systems may be calculated using the Rational Method.
(f) All design runoff calculations shall utilize Bulletin 71 rainfall amounts for given storm frequencies. All design runoff calculations, except TR-55, shall utilize Bulletin 71 median time distributions for given storm frequencies. If TR-55 is used, the SCS Type II time distribution shall be used.
(g) The minor stormwater system shall be designed to safely pass the ten-year recurrence interval up to and including the 24-hour storm event duration as per Bulletin 71. The developer shall provide an overland flow route to pass storms greater than a ten-year frequency. All areas of the property must provide an overland flow route that will pass the runoff from the 100-year event at a stage at least one foot below the lowest foundation grade in the vicinity of the flow path. Overland flow paths designed to handle flows in excess of the minor drainage system capacity shall provide drainage easements at least 20 feet in width.
(h) If streets are to be used as part of the major or minor stormwater systems, ponding depths shall not be greater than the elevation of the top of curbs and shall not remain flooded for more than eight hours for any event less than or equal to the 100-year event.
(i) Culvert crossings shall be designed according to this chapter, unless stricter requirements apply from other governmental agencies. Sizing of culvert crossings shall consider entrance and exit losses as well as headwater and tailwater conditions on the culvert.
(j) Transfers of waters between watersheds (diversions) shall be prohibited except when such transfers will not violate the provisions of division (B) (General Stormwater Requirements) above and are otherwise lawful.
(k) 1. All developments shall incorporate all best management practices required under the Clean Water Act, 33 U.S.C. §§ 1251 through 1376, and as required under § 153.03
(Erosion and Sediment Control) of this chapter.
2. The developer is responsible for obtaining an NPDES permit from the IEPA if the development meets the requirements of this regulation.
(l) 1. Redevelopment or expansion of impervious area, building and/or site coverage on existing development parcels of less than one-half acre in size, with more than 50% existing impervious areas, shall be exempt from the requirements of the site runoff storage facilities in this section except in circumstances where the existing public or private storm sewer or drainage system is incapable of sufficiently handling the increased runoff from this development, a special flood hazard area exists, or the site drains into property or a drainage system under the jurisdiction of a state or federal agency that may require a permit.
2. In such cases detention shall be required to store that portion of the runoff exceeding the outlet capacity or as may be required by the jurisdictional permitting agency.
(m) 1. Redevelopment or expansion of impervious area, buildings and/or site coverage shall be exempt from the requirements of this chapter for parcels with retention areas designed for the entire subdivision or development.
2. In all other cases, the redevelopment or expansion of impervious areas, buildings and/or site coverage shall provide site runoff storage facilities for either:
a. The entire expanded site and/or buildings at a peak discharge rate not to exceed 0.30 cfs per acre of land drained; or
b. Only the increase in impervious area lot coverage and buildings, at a peak discharge rate not to exceed 0.20 cfs per acre drained; whichever is less restrictive.
3. In cases where the existing storm sewer or drainage system is incapable of sufficiently handling the increased development, additional stormwater storage shall be required for that portion of the runoff exceeding the outlet capacity.
(n) Eligible redevelopment or expansion areas are still subject to division (F) (Fee in Lieu of Stormwater Site Runoff Storage Facilities) below.
(D) Site runoff storage requirements (detention/retention).
(1) Event hydrograph routing methods such as HEC-1, HEC-HMS, TR-20 or TR-55 using SCS curve number methodology shall be used to calculate design runoff volumes for all site runoff storage facilities. Event methods shall incorporate the following assumptions:
(a) A normal antecedent moisture condition (AMC=2) shall be assumed as a minimum;
(b) Appropriate rainfall distributions from Bulletin 71 shall be utilized except that SCS Type II distribution is acceptable with TR-55 only;
(c) Twenty-four-hour duration storm with a 50% probability (two-year) of occurrence in any one year as specified by Bulletin 71 sectional rainfall statistics; and
(d) Twenty-four-hour duration storm with a 1% probability (100-year) of occurrence in any one year as specified by Bulletin 71 sectional rainfall statistics.
(2) The design maximum storage to be provided in a site runoff storage facility shall be based on the runoff from the 100-year, 24-hour event and reservoir routing (also called level pool).
(3) Hydraulic computations for the release structure must take into account backwater and tailwater conditions on the site and receiving stream caused by the five-year storm event.
(4) Storage facilities shall be designed and constructed with the following characteristics.
(a) Water surface depths two feet above the base flood elevation will not damage the storage facility or other site improvements.
(b) The storage facilities shall be accessible and easily maintained.
(c) All design site runoff storage volume shall be provided above the seasonal high groundwater table or the invert elevation of the groundwater control system.
(d) Storage facilities shall facilitate sedimentation and catchment of floating material. Unless specifically approved by the Village Engineer, concrete-lined low flow channels shall not be used in the site runoff storage basins.
(e) Storage facilities shall minimize impacts of stormwater runoff on water quality by incorporating best management practices.
(f) Storage facilities shall maximize the distance between site runoff storage inlets and outlets to the maximum extent possible.
(g) Storage facilities with single pipe outlets shall have a minimum inside diameter of 12 inches. If design release rates necessitate a smaller outlet, structures such as perforated risers or flow control orifices shall be used. Orifices shall have a minimum diameter of four inches in which case the storage volume of the stormwater facility shall be calculated using the release rate generated by the constructed outlet structure.
(h) Detention facilities shall be designed to remove stormwater pollutants (i.e., but not limited to oil/grease, grit, sediments, organic matter and debris) to be safe, to be aesthetically pleasing and, as much as feasible, available for multiple uses.
(i) Detention facilities shall incorporate velocity dissipation devices to minimize erosion at inlets and outlets and to minimize re-suspension of pollutants.
(j) Detention facilities shall be designed such that the portion of the bottom area which is intended to be dry shall have standing water no longer than 48 hours for any runoff event less than the 100-year event. Underdrains directed to the outlet may be used to accomplish this requirement. Grading plans shall clearly distinguish the wet portion of the basin bottom from the dry portion. Ground slopes in the bottom of dry detention facilities shall be 1.0% or steeper.
(k) Underground detention: stormwater may be detained in underground pipes, tanks or reservoirs meeting the following requirements:
1. Access to all chambers shall be provided for maintenance purposes;
2. Positive gravity outlet shall be provided; and
3. Void space volume of the bedding material shall not be considered as part of the storage volume.
(l) Parking lot detention: parking lots may be used for temporary storage of water, provided vehicles are not endangered and standing water does not exceed six inches for a time not exceeding 24 hours.
(5) Storage facilities located within the regulated floodplain shall comply with all state and federal regulations and shall store the required amount of site runoff to meet the release rate requirement under all streamflow and backwater conditions up to the ten-year flood elevation on the adjacent receiving watercourse.
(6) Storage facilities located within the regulated floodway shall comply with all state and federal regulations and shall be evaluated by performing detailed hydrologic and hydraulic analysis and shall provide a net watershed benefit.
(7) Site runoff facilities may be located off site if the off-site storage facility meets all of the requirements of the chapter, adequate storage capacity in the off-site facility is dedicated to the development and the development includes means to convey stormwater runoff to the off-site storage facility.
(8) Retention facilities shall be designed and constructed with the following characteristics.
(a) Retention facilities shall be designed to remove stormwater pollutants (including, but not limited to, oil, grease, grit, sediments, organic matter, and debris), to be safe, and to be aesthetically pleasing.
(b) The minimum depth shall be at least five feet deep, below normal water level, excluding near shore banks and safety ledges. If fish habitat is to be provided, the minimum depth shall be at least ten feet, below the normal water level over a minimum of 25% of the bottom area to prevent winter freeze-out.
(c) Above the normal water elevation, the side slopes shall be no steeper than five to one (horizontal to vertical).
(d) At normal depth, permanent pool volume shall be equal to or greater than the runoff volume from its watershed for the two-year event.
(e) Safety ledges shall be provided at least four feet in width at a depth not greater than two feet below normal water level.
(f) Subsurface drainage systems may be designed as a component of the retention facility to assist in infiltration in accordance with the following criteria.
1. The retention volume shall be discharged at a rate no greater than that required to empty the calculated retention volume within five days of the storm event.
2. No such subsurface drainage pipe shall be located within ten feet of drainage pipes directly connected to the retention facility.
(g) 1. Wherever the water depth is less than three feet the retention facility shall be constructed by over excavating the required retention volume by one foot and replacing such volume with one foot of topsoil suitable for growing wetland plants (wetland retention area). Topsoil used shall be generally free from nonnative and noxious seed bank.
2. Native wetland plantings shall be introduced and shall not be dominated by or contain cumulatively more than 25% cover of the following species: buckthorn (Rhamunus cathartica or frangula); reed canary grass (Phalaris arundinacea); purple loosestrife (Lythrum salicaria); or giant reed (Phragmites australis). Within six months of the completion of the development ,a qualified wetland review specialist retained by the developer shall verify compliance with this section in a report submitted to the Village Engineer. Wetland retention areas may be provided along 35% of the periphery of the retention area. The buffer width shall not exceed 20 feet and shall have a slope no greater than 5% graded and draining towards the retention facility.
(h) Maintenance of wetland retention areas shall be provided for in the required “maintenance of stormwater facilities agreement”.
(9) The stormwater facilities shall be designed to protect the safety and well-being of all children and adults coming in contact with the system during storm runoff events.
(10) The top of berm or area, not along the sideslopes, surrounding the detention and/or retention facility shall be designed and graded as level as practicable to prevent accidental falls into the basin and for stability and ease of maintenance. Side slopes of detention facilities and open channels shall not be steeper than four to one (horizontal to vertical).
(11) All detention or retention facilities shall be provided with an overflow structure capable of safely passing excess flows at a stage at least two-feet above the base flood elevation. The design flow rate of the overflow structure shall be equivalent to the 100-year inflow rate.
(12) Velocities throughout the stormwater facilities shall be controlled to safe and non-erosive levels taking into consideration rates and depths of flow.
(13) The stormwater facilities shall be designed to minimize and facilitate maintenance.
(14) To effectively reduce runoff volumes, infiltration practices including basins and trenches may be utilized according to the following practices.
(a) Infiltration practices should be located on soils in hydrologic soil group “A” or “B” as designated by the United States Natural Resources Conservation Service.
(b) Infiltration basins and trenches designed to recharge groundwater shall not be located within 75 feet of a water supply well or a building foundation.
(c) A sediment settling basin shall be provided to remove coarse sediment from stormwater flows before they reach the infiltration basins or trenches. Stormwater shall not be allowed to stand more than 48 hours over 80% 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 four feet above seasonally high groundwater and bedrock.
(E) Accommodating flows from upstream tributary areas.
(1) Stormwater runoff from areas tributary to the property shall be considered in the design of the property’s stormwater facilities. Whenever practicable, flows from upstream areas that are not to be detained should be routed around the basin being provided for the site being developed.
(2) When there are upstream tributary areas not meeting the storage and release rates of this chapter, regional detention on the applicant’s property shall be explored by the applicant by following the following steps:
(a) Compute the storage volume needed for the applicant’s property using the release rates, the property area and the procedures described in this chapter;
(b) Identify the upstream areas tributary to the applicant’s property that do not meet the storage and release requirements of this chapter;
(c) Compute the storage volume needed for the applicant’s property plus the upstream tributary area. If tributary areas are not developed, then a reasonable fully developed land cover, based on local zoning, shall be assumed for the purposes of computing storage;
(d) Once the necessary storage is computed, the village may choose to pay for oversizing the applicant’s site runoff storage facility to bring the upstream areas into compliance, thereby making the applicant’s site runoff storage facility a regional storage facility; and
(e) If regional storage is selected by the village, then the storage facility shall be designed according to the combined property area. The applicant’s responsibility shall be limited to the storage volume computed for his or her property only. If regional storage is not selected by the village, then the storage facility shall be designed according to just the applicant’s property and all flows from the upstream area shall be routed around the applicant’s storage facility. If the applicant must route flows from the upstream tributary area through his or her storage facility and the upstream tributary areas exceed one square mile in size, the storage facility shall be considered as an on-stream storage facility.
(3) When there are upstream tributary areas meeting the storage and release rates of this chapter, the upstream flows shall be bypassed around the applicant’s storage facility, or be routed through the applicant’s storage facility if it is the only practicable alternative. The required storage for the applicant’s property shall be computed in accordance with this chapter. However, if the village decides to route upstream tributary flows through the applicant’s storage facility, the final design of the storage facility shall be based on the combined total of the applicant’s property plus the tributary areas draining through it. The applicant shall demonstrate using hydrologic and hydraulic modeling that at no time will the release rate from the applicant’s property exceed the allowable release rate for his or her property alone.
(F) Fee in lieu of stormwater site runoff storage facilities.
(1) The developer may pay a fee in lieu of constructing the stormwater runoff detention/retention facilities, required by this section, when authorized by the Village Engineer. The fee shall be $92,000 per acre foot (volume) of the required site runoff storage facility and may increase from time to time as approved by the Village Board. The developer shall submit to the Village Engineer, for approval, a professional engineer’s drainage analysis and report of the site runoff storage requirements in accordance with this chapter associated with the detention/retention improvements.
(2) The developer will not have the option to pay a fee in lieu of constructing the stormwater detention facility if, in the opinion of the Village Engineer, undetained runoff from the development may adversely impact an adjacent or downstream property(s) or the other requirements of divisions (C)(4)(l) and (C)(4)(m) above have not been met.
(3) All fees paid in lieu of constructing stormwater site runoff storage facilities shall be payable to the village prior to the recording of the final plat, or if no plat is required, prior to the issuance of a building or development permit. The funds collected in accordance with this division (F) shall be held by the village to be used for the construction of stormwater management or special flood hazard area mitigation projects designed to serve the immediate or future needs of the village to reduce stormwater flooding, control or mitigate erosion, enhance stormwater quality, maintain or improve existing or future stormwater facilities, drainage or conveyance systems. Furthermore, these funds may be used for other costs associated with stormwater management projects such as land acquisition, and professional service fees, including, but not limited to, engineering studies, design and inspection.
(Prior Code, § 4-4-2) (Ord. 2015-17, passed 8-3-2015)