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(a) The purpose of this chapter is to establish technically feasible and economically reasonable stormwater management standards in accordance with the Avon Lake Municipal Stormwater Program Manual to achieve a level of stormwater quality and quantity control that will minimize damage to property and stormwater assets along with degradation of water resources and will promote and maintain the health, safety, and welfare of the citizens of the city.
(b) This chapter requires individuals who disturb land or generate debris on land within the city to:
(1) Control stormwater runoff from their property and ensure that all stormwater management practices are properly designed, constructed and maintained;
(2) Reduce water quality impacts to receiving water resources that may be caused by new development or redevelopment activities;
(3) Control the volume, rate and quality of stormwater runoff originating from their property so that surface water and ground water are protected while flooding, debris and erosion potential are not increased;
(4) Minimize the need to construct, repair and replace subsurface storm drain systems and provide a healthy water resource;
(5) Preserve natural infiltration and ground water recharge, and maintain subsurface flow that replenishes water resources;
(6) Incorporate stormwater quality and quantity controls into site planning and design at the earliest possible stage in the development process;
(7) Reduce the expense of maintenance or remedial projects needed to address problems caused by inadequate stormwater management;
(8) Maximize use of stormwater management practices that serve multiple purposes including, but not limited to, flood control, erosion control, fire protection, water quality protection, recreation and habitat preservation;
(9) Design sites to minimize the number of stream crossings and the width of associated disturbance in order to minimize future expenses related to the maintenance and repair of stream crossings; and
(10) Maintain, promote and re-establish conditions necessary for naturally occurring stream processes that assimilate pollutants, attenuate flood flows and provide a healthy water resource.
(c) This chapter shall apply to all work that shall disturb an area in excess of one acre and used or being developed, either wholly or partially, for new or relocated projects involving roads; subdivisions or larger common plans of development; industrial, commercial, institutional or residential projects; building activities on farms; redevelopment activities; grading; and all other uses that are not specifically exempted in § 1060.01
(d) Public entities, including the State of Ohio, Lorain County and the city shall comply with this chapter for roadway projects initiated after the adoption of this chapter and, to the maximum extent practicable, for projects initiated before that time.
(e) This chapter does not apply to activities regulated by, and in compliance with, the Ohio Agricultural Sediment Pollution Abatement Rules.
(f) This chapter does not require a comprehensive stormwater management plan for linear construction projects, such as pipeline or utility line installation, that do not result in the installation of impervious surface as determined by the Stormwater Manager. Such projects must be designed to minimize the number of stream crossings and the width of disturbance. Linear construction projects must comply with the requirements of Chapter 1058 Erosion and Sediment Control.
(g) This chapter does not apply to projects that disturb less than one acre in total area, and are repair or renovation of an existing roadway or improved site as determined by the Stormwater Program Manager.
(Ord. 88-2012, passed 6-25-2012; Ord. 26-2013, passed 3-25-2013)
For the purpose of this chapter, the following definitions shall apply unless the context clearly indicates or requires a different meaning.
ACRE. A measurement of area equaling 43,560 square feet.
AS-BUILT SURVEY. A survey shown on a plan or drawing prepared by a registered surveyor indicating the actual dimensions, elevations and locations of any structures, underground utilities, swales, detention facilities and sewage treatment facilities after construction has been completed.
BEST MANAGEMENT PRACTICES (BMPs). Schedule of activities, prohibitions of practices, operation and maintenance procedures, treatment requirements and other practices to reduce the pollution of water resources and to control stormwater volume and rate.
CLEAN WATER ACT. 33 U.S.C. §§ 1251 et seq. Referred to as the Federal Water Pollution Control Act or the Federal Water Pollution Control Act Amendments of 1972.
COMMUNITY. The City of Avon Lake, its designated representatives, boards or commissions.
COMPREHENSIVE STORMWATER MANAGEMENT PLAN. The written document and plans meeting the requirements of this regulation that sets forth the plans and practices to minimize stormwater runoff from a development area, to safely convey or temporarily store and release post-development runoff at an allowable rate to minimize flooding and stream bank erosion, and to protect or improve stormwater quality and stream channels.
CRITICAL STORM. A storm that is calculated by means of the percentage increase in volume of runoff by a proposed development area. The CRITICAL STORM is used to calculate the maximum allowable stormwater discharge rate from a developed site.
DEBRIS. Any gathered or exposed particulates that are subject to transport by stormwater facilities in whole or part by ordinary stormwater flow.
DETENTION FACILITY. A basin, pond, oversized pipe or other structure that reduces the peak flow rate of stormwater leaving the facility by temporarily storing a portion of the stormwater entering the facility.
DEVELOPMENT AREA. A parcel or contiguous parcels owned by one person or persons, or operated as one development unit, and used or being developed for commercial, industrial, residential, institutional or other construction or alteration that changes runoff characteristics.
DEVELOPMENT DRAINAGE AREA. A combination of each hydraulically unique watershed with individual outlet points on the development area.
DISTURBANCE. Any activity involving the addition or removal of soil or the alteration of existing land surfaces.
DISTURBED AREA. An area of land subject to erosion due to the removal of vegetative cover and/or soil-disturbing activities.
DRAINAGE. The removal of excess surface water or groundwater from land by surface or subsurface drains.
EROSION. The process by which the land surface is worn away by the action of wind, water, ice, gravity or any combination of those forces.
EXTENDED CONVEYANCE. A stormwater management practice that replaces and/or enhances traditional open or closed storm drainage conduits by retarding flow, promoting percolation of runoff into the soil, and filtering pollutants during the stormwater quality event.
EXTENDED DETENTION. A stormwater management practice that replaces and/or enhances traditional detention facilities by releasing the runoff collected during the stormwater quality event over at least 24 to 48 hours, retarding flow and allowing pollutants to settle within the facility.
FINAL STABILIZATION. All soil-disturbing activities at the site have been completed and a uniform perennial vegetative cover with a density of at least 80% coverage for the area has been established or equivalent stabilization practices, such as the use of mulches or geotextiles, have been employed.
GRADING. The process in which the topography of the land is altered to a new slope.
HYDROLOGIC UNIT CODE. A cataloguing system developed by the United States Geological Survey and the Natural Resource Conservation Service to identify watersheds in the United States.
IMPERVIOUS COVER. Any surface that cannot effectively absorb or infiltrate water. This may include roads, streets, parking lots, rooftops, sidewalks and other areas not covered by vegetation.
INFILTRATION. A stormwater management practice that does not discharge to a water resource during the stormwater quality event, requiring collected runoff to either infiltrate into the ground water and/or be consumed by evapotranspiration, thereby retaining stormwater pollutants in the facility.
LARGER COMMON PLAN OF DEVELOPMENT. A contiguous area where multiple separate and distinct construction activities may be taking place at different times on different schedules under one plan.
MAXIMUM EXTENT PRACTICABLE. The level of pollutant reduction that operators of small municipal separate storm sewer systems regulated under 40 C.F.R. parts 9, 122, 123 and 124, referred to as NPDES Stormwater Phase II, must meet.
NPDES, NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM. A regulatory program in the Federal Clean Water Act that prohibits the discharge of pollutants into surface waters of the United States without a permit.
NONSTRUCTURAL STORMWATER MANAGEMENT PRACTICE. Stormwater runoff control and treatment techniques that use natural practices to control runoff and/or reduce pollution levels.
POST-DEVELOPMENT. The conditions that exist following the completion of soil-disturbing activity in terms of topography, vegetation, land use and the rate, volume, quality or direction of stormwater runoff.
PRE-CONSTRUCTION MEETING. Meeting prior to construction between all parties associated with the construction of the project including government agencies, contractors and owners to review agency requirements and plans as approved and submitted.
PRE-DEVELOPMENT. The conditions that exist prior to the initiation of soil-disturbing activity in terms of topography, vegetation, land use and the rate, volume, quality or direction of stormwater runoff.
PROFESSIONAL ENGINEER. A professional engineer registered in the State of Ohio with specific education and experience in water resources engineering, acting in conformance with the Code of Ethics of the Ohio State Board of Registration for Engineers and Surveyors.
REDEVELOPMENT. A construction project on land where impervious cover has previously been developed and where the new land use will not increase the runoff coefficient. If the new land use will increase the runoff coefficient, then the project is considered to be a new development project rather than a redevelopment project. (Refer to Table 1 in § 1060.09.)
RIPARIAN AREA. Land adjacent to any brook, creek, river, or stream having a defined bed and bank that, if appropriately sized, helps to stabilize streambanks, limit erosion, reduce flood size flows, and/or filter and settle out runoff pollutants, or performs other functions consistent with the purposes of this regulation.
RIPARIAN AND WETLAND SETBACK. The real property adjacent to a water resource on which soil-disturbing activities are limited, all as defined by the requirements of § 1058.11.
RUNOFF. The portion of rainfall, melted snow or irrigation water that flows across the ground surface and is eventually returned to water resources.
SEDIMENT. The soils or other surface materials that can be transported or deposited by the action of wind, water, ice or gravity as a product of erosion.
SEDIMENTATION. The deposition of sediment in water resources.
SITE OWNER/OPERATOR. Any individual, corporation, firm, trust, commission, board, public or private partnership, joint venture, agency, unincorporated association, municipal corporation, county or state agency, the federal government, other legal entity or an agent thereof that is responsible for the overall construction site.
SOIL-DISTURBING ACTIVITY. Clearing, grading, excavating, filling or other alteration of the earth’s surface where natural or human-made ground cover is destroyed and that may result in, or contribute to, increased stormwater quantity and/or decreased stormwater quality.
STABILIZATION. The use of best management practices that reduce or prevent soil erosion by stormwater runoff, trench dewatering, wind, ice, gravity or a combination thereof.
STORMWATER MANAGER. The employee designated by the Public Works Director to administer the stormwater program for the city in accordance with the Stormwater Pollution Prevention Program Manual.
STRUCTURAL STORMWATER MANAGEMENT PRACTICE. Any constructed facility, structure or device that provides storage, conveyance and/or treatment of stormwater runoff.
SURFACE WATERS OF THE STATE. All streams, lakes, reservoirs, marshes, wetlands or other waterways situated wholly or partly within the boundaries of the state, except those private waters which do not combine or affect a junction with surface water. Waters defined as sewerage systems, treatment works or disposal systems in R.C. § 6111.01 are not included.
TOTAL MAXIMUM DAILY LOAD. The sum of the existing and/or projected point source, non-point source and background loads for a pollutant to a specified watershed, water body or water body segment. A TMDL sets and allocates the maximum amount of a pollutant that may be introduced into the water and still ensures attainment and maintenance of water quality standards.
WATER QUALITY VOLUME. The volume of runoff from a contributing watershed that must be captured and treated, equivalent to the maximized capture volume as defined in the American Society of Civil Engineers (ASCE) Manual and Report on Engineering Practice No. 87 and Water Environment Federation Manual of Practice No. 23 titled Urban Runoff Quality Management.
WATER RESOURCE. Any public or private body of water; including wetlands; the area within the ordinary high water level of lakes and ponds; as well as the area within the ordinary high water level of any brook, creek, river, or stream having a defined bed and bank (either natural or artificial) which confines and conducts continuous or intermittent flow.
WATER RESOURCE CROSSING. Any bridge, box, arch, culvert, truss or other type of structure intended to convey people, animals, vehicles or materials from one side of a watercourse to another. This does not include private, noncommercial footbridges or pole-mounted aerial electric or telecommunication lines, nor does it include below grade utility lines.
WATERSHED. The total drainage area contributing stormwater runoff to a single point.
WETLAND. Those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions, including swamps, marshes, bogs and similar areas (40 C.F.R. part 232; 33 U.S.C. §§ 1251 et seq.).
(Ord. 88-2012, passed 6-25-2012; Ord. 26-2013, passed 3-25-2013; Ord. 43-2014, passed 4-14-2014)
(a) Compliance with the provisions of this chapter shall not relieve any person from responsibility for damage to any person otherwise imposed by law. The provisions of this chapter are promulgated to promote the health, safety and welfare of the public and are not designed for the benefit of any individual or any particular parcel of property.
(b) By approving a comprehensive stormwater management plan under this chapter, the city does not accept responsibility for the design, installation and operation and maintenance of stormwater management practices.
(Ord. 88-2012, passed 6-25-2012; Ord. 26-2013, passed 3-25-2013)
(a) Where this chapter is in conflict with other provisions of law or ordinance, the most restrictive provisions shall prevail.
(b) If any clause, section or provision of this regulation is declared invalid or unconstitutional by a court of competent jurisdiction, the validity of the remainder shall not be affected thereby.
(c) This chapter shall not be construed as authorizing any person to maintain a nuisance on their property, and compliance with the provisions of this regulation shall not be a defense in any action to abate such a nuisance.
(d) Failure of the city to observe or recognize hazardous or unsightly conditions or to recommend corrective measures shall not relieve the site owner from the responsibility for the condition or damage resulting therefrom, and shall not result in the city, its officers, employees or agents being responsible for any condition or damage resulting therefrom.
(e) In the event any provisions of this chapter conflict with provisions of Chapter 1058, the more stringent regulations shall prevail.
(f) In the event any provision of this chapter concerning the location, construction, maintenance, repair, grading or use of a detention facility, non-structural stormwater management practice, structural stormwater management practice, riparian area, water resource or wetland is in conflict with a provision of Chapter 1058 of this code of ordinances, the conflict, to the extent possible, shall be resolved by the Stormwater Program Manager. The Stormwater Program Manager shall consider factors in such decision that are based on permissible provisions that may allow grading, clearing or filling that may be necessary in conjunction with the construction of said practices as part of the overall approved SWP3 plans, and not in violation of other state or federal regulations.
(g) In the event a conflict exists between the provisions of this chapter and the provisions of Chapter 1058 on matters concerning ongoing maintenance, repair, cleaning and use of an existing detention facility, non-structural stormwater management practice, structural stormwater management practice, riparian area, water resource or wetland, the conflict shall be resolved by the Stormwater Program Manager. The Stormwater Program Manager shall resolve conflicts in such a way that requires the least disturbance or interference with the then existing natural elements and features of such practices, yet is reasonable to enable the maintenance, repair or cleaning to be completed.
(Ord. 88-2012, passed 6-25-2012; Ord. 26-2013, passed 3-25-2013)
(a) This chapter requires that a comprehensive stormwater management plan be developed and implemented for soil-disturbing activities disturbing one or more acres of total land, or less than one acre if part of a larger common plan of development or sale disturbing one or more acres of total land, and on which any regulated activity of § 1060.01(c) is proposed.
(b) The city shall administer this regulation, shall be responsible for determination of compliance with this regulation, and shall issue notices and orders as may be necessary. The city may consult with the Lorain County SWCD, private engineers, stormwater districts or other technical experts in reviewing the comprehensive stormwater management plan.
(Ord. 88-2012, passed 6-25-2012; Ord. 26-2013, passed 3-25-2013)
(a) Pre-application meeting. The applicant shall attend a pre-application meeting with the Stormwater Manager to discuss the proposed project, review the requirements of this chapter, identify unique aspects of the project that must be addressed during the review process, and establish a preliminary review and approval schedule.
(b) Preliminary comprehensive stormwater management plan. The applicant shall submit two sets of a preliminary comprehensive stormwater management plan (preliminary plan) and the applicable fees to the Stormwater Manager. The preliminary plan shall show the proposed property boundaries, setbacks, dedicated open space, public roads, water resources, stormwater control facilities and easements in sufficient detail and engineering analysis to allow the Stormwater Manager to determine if the site is laid out in a manner that meets the intent of this regulation and if the proposed stormwater management practices are capable of controlling runoff from the site in compliance with this regulation. The applicant shall submit two sets of the preliminary plan and applicable fees as follows:
(1) For subdivisions. In conjunction with the submission of the preliminary subdivision plan;
(2) For other construction projects. In conjunction with the application for a zoning permit; and
(3) For general clearing projects. In conjunction with the application for a zoning permit.
(c) Final comprehensive stormwater management plan. The applicant shall submit two sets of a final comprehensive stormwater management plan (final plan) and the applicable fees to the Stormwater Program Manager in conjunction with the submittal of the final plat, improvement plans, or application for a building or zoning permit for the site. The final plan shall meet the requirements of § 1060.08 and shall be approved by the Stormwater Program Manager prior to approval of the final plat and before issuance of a zoning permit by the Code Administrator and grading permit issued by the Public Works Department.
The final comprehensive stormwater management plan shall include all post-construction BMPs installed on the site. Details such as inspection and maintenance shall become part of the approved plans. Any documents associated with these responsibilities such as subdivision covenants and restrictions shall be submitted for review and recorded with the final plans. The Stormwater Program Manager shall review the documents to ensure perpetual maintenance of the post-construction BMPs.
(d) Review and comment. The Stormwater Program Manager shall review the preliminary and final plans submitted, and shall approve or return for revisions with comments and recommendations for revisions. A preliminary or final plan rejected because of deficiencies shall receive a narrative report stating specific problems and the procedures for filing a revised preliminary or final plan.
(e) Approval necessary. Land-clearing and soil-disturbing activities shall not begin and zoning and/or building permits shall not be issued without an approved comprehensive stormwater management plan.
(f) Valid for two years. Approvals issued in accordance with this regulation shall remain valid for two years from the date of approval.
(Ord. 88-2012, passed 6-25-2012; Ord. 26-2013, passed 3-25-2013; Ord. 43-2014, passed 4-14-2014)
Approvals issued in accordance with this chapter do not relieve the applicant of responsibility for obtaining all other necessary permits and/or approvals from other federal, state and/or county agencies. If requirements vary, the most restrictive shall prevail. These permits may include, but are not limited to, those listed below.
(a) Ohio EPA NPDES permits authorizing stormwater discharges associated with construction activity or the most current version thereof. Proof of compliance with these requirements shall be the applicant’s notice of intent (NOI) number from Ohio EPA, a copy of the Ohio EPA Director’s authorization letter for the NPDES permit or a letter from the site owner explaining why the NPDES permit is not applicable.
(b) Section 401 of the Clean Water Act, 33 U.S.C. § 1341. The applicant shall provide, if applicable, details relating to the development limitations to be compliant with the Ohio EPA water quality certification.
(c) Ohio EPA isolated wetland permit. The applicant shall provide, if applicable, details relating to the development limitations to be compliant with the Ohio EPA isolated wetland permit.
(d) Section 404 of the Clean Water Act, 33 U.S.C. § 1344. The applicant shall provide, if applicable, details relating to the development limitations to be compliant with the Ohio EPA Clean Water Act.
(Ord. 88-2012, passed 6-25-2012; Ord. 26-2013, passed 3-25-2013)
(a) Comprehensive stormwater management plan required. The applicant shall develop a comprehensive stormwater management plan describing how the quantity and quality of stormwater will be managed after construction is complete for every discharge from the site and/or into a water resource. The plan will illustrate the type, location and dimensions of every structural and non-structural stormwater management practice incorporated into the site design, and the rationale for their selection. The rationale must address how these stormwater management practices will address flooding within the site as well as flooding that may be caused by the development upstream and downstream of the site. The rationale will also describe how the stormwater management practices minimize impacts to the physical, chemical and biological characteristics of on-site and downstream water resources and, if necessary, correct current degradation of water resources that is occurring or take measures to prevent predictable degradation of water resources.
(b) Preparation by professional engineer. The comprehensive stormwater management plan shall be prepared by a registered professional engineer and include supporting calculations, plan sheets, and design details. To the extent necessary, as determined by the Stormwater Program Manager, a site survey shall be performed by a registered professional surveyor to establish boundary lines, measurements, or land surfaces.
(c) Community procedures. The Stormwater Program Manager shall prepare and maintain procedures providing specific criteria and guidance to be followed when designing the stormwater management system for the site. These procedures may be updated from time to time, at the discretion of the Stormwater Program Manager, based on improvements in engineering, science, monitoring and local maintenance experience. The Stormwater Program Manager shall make the final determination of whether the practices proposed in the comprehensive stormwater management plan meet the requirements of this regulation. The Stormwater Program Manager may also maintain a list of acceptable best management practices that meet the criteria of this regulation to be used in the city.
(d) Contents of comprehensive stormwater management plan. The comprehensive stormwater management plan shall contain an application, narrative report, construction site plan sheets, a long-term inspection and maintenance agreement, and a site description with the following information provided:
(1) Site description.
A. A description of the nature and type of the construction activity (e.g., residential, shopping mall, highway and the like);
B. Total area of the site and the area of the site that is expected to be disturbed (i.e., grubbing, clearing, excavation, filling or grading, including off-site borrow areas);
C. A description of prior land uses at the site;
D. An estimate of the impervious area and percent of imperviousness created by the soil- disturbing activity at the beginning and at the conclusion of the project;
E. Existing data describing the soils throughout the site, including the soil series and association, hydrologic soil group, porosity, infiltration characteristics, depth to ground water, depth to bedrock and any impermeable layers;
F. If available, the quality of any known pollutant discharge from the site such as that which may result from previous contamination caused by prior land uses;
G. The location and name of the immediate water resource(s) and the first subsequent water resource(s);
H. The aerial (plan view) extent and description of water resources at or near the site that will be disturbed or will receive discharges from the project; and
I. Describe the current condition of water resources including the vertical stability of stream channels and indications of channel incision that may be responsible for current or future sources of high sediment loading or loss of channel stability.
(2) Site map showing.
A. Limits of soil-disturbing activity on the site;
B. Soils types for the entire site, including locations of unstable or highly erodible soils;
C. Existing and proposed one-foot contours. This must include a delineation of drainage watersheds expected before, during, and after major grading activities as well as the size of each drainage watershed in acres;
D. Water resource locations including springs, wetlands, streams, lakes, water wells, and associated setbacks on or within 200 feet of the site, including the boundaries of wetlands or streams and first subsequent named receiving water(s) the applicant intends to fill or relocate for which the applicant is seeking approval from the U.S. Army Corps of Engineers and/or Ohio EPA;
E. Existing and planned locations of buildings, roads, parking facilities and utilities; and
F. The location of any in-stream activities including stream crossings.
(3) Contact information. Company name and contact information as well as contact name, address and phone numbers for the following:
A. The professional engineer who prepared the comprehensive stormwater management plan;
B. The site owner; and
C. Responsible party on-site.
(4) Phase. Phase, if applicable, of the overall development plan;
(5) List. List of sublot numbers if project is a subdivision;
(6) Permit number. Ohio EPA NPDES permit number and other applicable state and federal permit numbers, if available, or status of various permitting requirements if final approvals have not been received;
(7) Location. Location, including complete site address and sublot number if applicable;
(8) Location of easements. Location of any easements or other restrictions placed on the use of the property;
(9) Site plan. A site plan sheet showing:
A. The location of each proposed post-construction stormwater management practice; and
B. The geographic coordinates of the site and each proposed practice in North American Datum Ohio State Plan North.
It is preferred that the entire site be shown on one plan sheet to allow a complete view of the site during plan review. If a smaller scale is used to accomplish this, separate sheets providing an enlarged view of areas on individual sheets should be provided.
(10) An inspection and maintenance agreement. The inspection and maintenance agreement required for post-construction stormwater management practices under this regulation shall be a stand-alone document between the city and the applicant, and, to the extent required, based upon the nature and scope of the project, contain or reference the following information and provisions as the Stormwater Program Manager may deem appropriate:
A. The location of each stormwater management practice, including those practices permitted to be located in, or within 50 feet of, water resources, and identification of the drainage area served by each stormwater management practice;
B. A schedule for regular maintenance for each aspect of the stormwater management system and description of routine and non-routine maintenance tasks to ensure continued performance of the system as is detailed in the approved comprehensive stormwater management plan. This schedule may include additional standards, as required by the Stormwater Program Manager, to ensure continued performance of stormwater management practices permitted to be located in, or within 50 feet of, water resources;
C. The location and documentation of all access and maintenance easements on the property;
D. Identification of the landowner(s), organization or city responsible for long-term maintenance, including repairs, of the stormwater management practices;
E. The landowner(s), organization or city shall maintain stormwater management practices in accordance with this regulation;
F. The city has the authority to enter upon the property to conduct inspections as necessary to verify that the stormwater management practices are being maintained and operated in accordance with this chapter;
G. The city shall maintain public records of the results of site inspections, shall inform the landowner(s), organization or city responsible for maintenance of the inspection results, and shall specifically indicate any corrective actions required to bring the stormwater practices into proper working condition;
H. If the city notifies the landowner(s), organization or city responsible for maintenance of the maintenance problems that require correction, the specific corrective actions shall be taken within a reasonable time frame as determined by the city. If the necessary corrective actions are not taken the city is herein authorized to enter upon the property and to perform the corrective actions identified in the inspection report if the landowner(s), organization or city responsible for maintenance does not make the required corrections in the specified time period. The city shall be reimbursed by the landowner(s), organization, or city responsible for maintenance for all expenses incurred within ten days of receipt of invoice from the city;
I. The method of funding long-term maintenance and inspections of all stormwater management practices; and
J. A release of the city from all damages, accidents, casualties, occurrences or claims that might arise or be asserted against the city from the construction, presence, existence, or maintenance of the stormwater management practices.
Alteration or termination of these stipulations is prohibited without written approval of the Stormwater Program Manager. The applicant must provide a draft of this inspection and maintenance agreement as part of the comprehensive stormwater management plan submittal. Once a draft is approved, a memorandum of agreement shall be recorded with the Lorain County Recorder. A final recorded copy of the agreement, or the memorandum of agreement, must be submitted to the city to receive final inspection approval of the site.
(11) Calculations required. The applicant shall submit calculations for projected stormwater runoff flows, volumes and timing into and through all stormwater management practices for flood control, channel protection, water quality and the condition of the habitat, stability and incision of each water resource and the floodplain, as required in § 1060.09 of this chapter. These submittals shall be completed for both pre- and post-development land use conditions and shall include the underlying assumptions and hydrologic and hydraulic methods and parameters used for these calculations. The applicant shall also include critical storm determination and demonstrate that the runoff from upper watershed areas have been considered in the calculations;
(12) List of all contractors and subcontractors before construction. Prior to construction or before the pre-construction meeting, provide the list of all contractors and subcontractors names, addresses, and phones involved with the implementation of the comprehensive stormwater management plan, including a written document containing signatures of all parties as proof of acknowledgment that they have reviewed and understand the requirements and responsibilities of the comprehensive stormwater management plan;
(13) Existing and proposed drainage patterns. The location and description of existing and proposed drainage patterns and stormwater management practices, including any related stormwater management practices beyond the development area and the larger common development area; and
(14) Inclusions. For each stormwater management practice to be employed on the development area, include the following:
A. Location and size, including detail drawings, maintenance requirements during and after construction, and design calculations, all where applicable;
B. Any other structural and/or non-structural stormwater management practices necessary to meet the design criteria in this regulation and any supplemental information requested by the Stormwater Program Manager; and
C. Final site conditions including stormwater inlets and permanent nonstructural and structural stormwater management practices. Details of stormwater management practices shall be drawn to scale and shall show volumes and sizes of contributing drainage areas.
(Ord. 88-2012, passed 6-25-2012; Ord. 26-2013, passed 3-25-2013)
(a) General. The stormwater system, including stormwater management practices for storage, treatment and control, and conveyance facilities, shall be designed to prevent structure flooding during the 100-year, 24-hour storm event; to maintain predevelopment runoff patterns, flows, and volumes; and to meet the following criteria.
(1) Integrated practices that address degradation of water resources. The stormwater management practices shall function as an integrated system that controls flooding and minimizes the degradation of the physical, biological and chemical integrity of the water resources receiving stormwater discharges from the site. Acceptable practices shall:
A. Not disturb riparian areas, unless the disturbance is intended to support a watercourse restoration project and complies with § 1058.11;
B. Maintain predevelopment hydrology and ground water recharge on as much of the site as practicable;
C. Only install new impervious surfaces and compact soils where necessary to support the future land use; and
D. Compensate for increased runoff volumes caused by new impervious surfaces and soil compaction by reducing stormwater peak flows to less than pre-development levels.
Stormwater management practices that meet the criteria in this regulation, and additional criteria required by the Stormwater Program Manager, shall comply with this chapter.
(2) Practices designed for final use. Stormwater management practices shall be designed to achieve the stormwater management objectives of this regulation, to be compatible with the proposed post-construction use of the site, to protect the public health, safety and welfare, and to function safely with minimal maintenance.
(3) Stormwater management for all lots. Areas developed for a subdivision, as defined in § 1058.05, shall provide stormwater management and water quality controls for the development of all subdivided lots. This shall include provisions for lot grading and drainage that prevent structure flooding during the 100-year, 24-hour storm; and maintain, to the extent practicable, the pre-development runoff patterns, volumes and peaks from the lot.
(4) Stormwater facilities in water resources. Stormwater management practices and related activities shall not be constructed in water resources unless the applicant shows proof of compliance with all appropriate permits from the Ohio EPA, the U.S. Army Corps of Engineers, and other applicable federal, state and local agencies as required in this chapter, and the activity is in compliance with Chapter 1058 and § 1058.11, all as determined by the Stormwater Program Manager.
(5) Stormwater ponds and surface conveyance channels. All stormwater pond and surface conveyance designs must provide a minimum of one foot freeboard above the projected peak stage within the facility during the 100-year, 24-hour storm. When designing stormwater ponds and conveyance channels, the applicant shall consider public safety as a design factor and alternative designs must be implemented where site limitations would preclude a safe design.
(6) Exemption. The site where soil-disturbing activities are conducted shall be exempt from the requirements of this section if it can be shown to the satisfaction of the Stormwater Program Manager that the site is part of a larger common plan of development where the stormwater management requirements for the site are provided by an existing stormwater management practice, or if the stormwater management requirements for the site are provided by practices defined in a regional or local stormwater management plan approved by the Stormwater Program Manager.
(7) Maintenance. All stormwater management practices shall be maintained in accordance with inspection and maintenance agreements approved by the Stormwater Program Manager as detailed in § 1060.08.
(8) Ownership. Unless otherwise required by the city, stormwater management practices serving multiple lots in subdivisions shall be on a separate lot held and maintained by an entity of common ownership or, if compensated by the property owners, by the city. Stormwater management practices serving single lots shall be placed on these lots, protected within an easement, and maintained by the property owner.
(9) Preservation of existing natural drainage. Practices that preserve and/or improve the existing natural drainage shall be used to the maximum extent practicable. Such practices may include minimizing site grading and compaction; protecting and/or restoring water resources, riparian areas, and existing vegetation; and maintaining unconcentrated stormwater runoff to and through these areas.
(10) Preservation of wetland hydrology. Concentrated stormwater runoff from BMPs to wetlands shall be converted to diffuse flow before the runoff enters a wetland in order to protect the natural hydrology, hydroperiod and wetland flora. The flow shall be released such that no erosion occurs down slope. Practices such as level spreaders, vegetative buffers, infiltration basins, conservation of forest covers, and the preservation of intermittent streams, depressions, and drainage corridors may be used to maintain the wetland hydrology.
If the applicant proposes to discharge to natural wetlands, a hydrological analysis shall be preformed to demonstrate that the proposed discharge matches the pre-development hydroperiods and hydrodynamics.
(b) Stormwater conveyance design criteria. All stormwater management practices shall be designed to convey stormwater to allow for the maximum removal of pollutants and reduction in flow velocities. This shall include but not be limited to:
(1) Stream relocation or enclosure. The Stormwater Program Manager may allow the enclosure or relocation of water resources only if the applicant shows proof of compliance with all appropriate permits from the Ohio EPA, the U.S. Army Corps of Engineers, and other applicable federal, state and local agencies as required in § 1060.07 of this regulation, and the activity is in compliance with Chapter 1058, all as determined by the Stormwater Manager. At a minimum, stream relocation designs must show how the project will minimize changes to the vertical stability, floodplain form, channel form, and habitat of upstream and downstream channels on and off the property;
(2) Off-site stormwater discharges. Off-site stormwater runoff that discharges to or across the applicant’s development site shall be conveyed through the stormwater conveyance system planned for the development site at its existing peak flow rates during each design storm. Off- site flows shall be diverted around stormwater quality control facilities or, if this is not possible, the stormwater quality control facility shall be sized to treat the off-site flow. Comprehensive Stormwater Management Plans will not be approved until it is demonstrated to the satisfaction of the Stormwater Program Manager that off-site runoff will be adequately conveyed through the development site in a manner that does not exacerbate upstream or downstream flooding and erosion;
(3) Sheet flow. The site shall be graded in a manner that maintains sheet flow over as large an area as possible. The maximum area of sheet flow shall be determined based on the slope, the uniformity of site grading, and the use of easements or other legally-binding mechanisms that prohibit re-grading and/or the placement of structures within sheet flow areas. In no case shall the sheet flow length be longer than 300 feet, nor shall a sheet flow area exceed one and one-half acres. Flow shall be directed into an open channel, storm sewer, or other stormwater management practice from areas too long and/or too large to maintain sheet flow, all as determined by the Stormwater Program Manager;
(4) Open channels. Unless otherwise allowed by the City Engineer, drainage tributary to stormwater management practices shall be provided by an open channel with landscaped banks and designed to carry the ten-year, 24-hour stormwater runoff from upstream contributory areas;
(5) Open drainage systems. Open drainage systems shall be preferred on all new development sites to convey stormwater where feasible. Storm sewer systems shall be allowed only when the site cannot be developed at densities allowed under zoning or where the use of an open drainage system affects public health or safety, all as determined by the Stormwater Program Manager. The following criteria shall be used to design storm sewer systems when necessary.
A. Storm sewers shall be designed such that they do not surcharge from runoff caused by the five-year, 24-hour storm, and that the hydraulic grade line of the storm sewer stays below the gutter flow line of the overlying roadway, or below the top of drainage structures outside the roadway during a ten-year, 24-hour storm. The system shall be designed to meet these requirements when conveying the flows from the contributory area within the proposed development and existing flows from off-site areas that are upstream from the development.
B. The minimum inside diameter of pipe to be used in public storm sewer systems is 12 inches. Smaller pipe sizes may be used in private systems, subject to the approval.
C. All storm sewer systems shall be designed taking into consideration the tailwater of the receiving facility or water resource. The tailwater elevation used shall be based on the design storm frequency. The hydraulic grade line for the storm sewer system shall be computed with consideration for the energy losses associated with entrance into and exit from the system, friction through the system, and turbulence in the individual manholes, catch basins and junctions within the system.
D. The inverts of all curb inlets, manholes, yard inlets and other structures shall be formed and channelized to minimize the incidence of quiescent standing water where mosquitoes may breed.
E. Headwalls shall be required at all storm sewer inlets or outlets to and from open channels or lakes.
(6) Water resource crossings. The following criteria shall be used to design structures that cross a water resource in the city.
A. Water resource crossings other than bridges shall be designed to convey the stream’s flow for the minimum 25-year, 24-hour storm.
B. Bridges, open bottom arch or spans are the preferred crossing technique and shall be considered in the planning phase of the development. Bridges and open spans should be considered for all state scenic rivers, cold-water habitat, exceptional warm-water habitat, seasonal salmonid habitat streams and Class III headwater streams. The footers or piers for these bridges and open spans shall not be constructed below the ordinary high water mark.
C. If a culvert or other closed bottom crossing is used, 25% of the cross-sectional area, or a minimum of one foot of box culverts and pipe arches, must be embedded below the channel bed.
D. The minimum inside diameter of pipes to be used for crossings shall be 12 inches.
E. The maximum slope allowable shall be a slope that produces a ten-fps velocity within the culvert barrel under design flow conditions. Erosion protection and/or energy dissipaters shall be required to properly control entrance and outlet velocities.
F. All culvert installations shall be designed with consideration for the tailwater of the receiving facility or water resource. The tailwater elevation used shall be based on the design storm frequency.
G. Headwalls shall be required at all culvert inlets or outlets to and from open channels or lakes.
H. Streams with a drainage area of five square miles or larger shall incorporate floodplain culverts at the bankfull elevation to restrict head loss differences across the crossing so as to cause no rise in the 100-year storm event.
I. Bridges shall be designed such that the hydraulic profile through a bridge shall be below the bottom chord of the bridge for either the 100-year, 24-hour storm, or the 100-year flood elevation as determined by FEMA, whichever is more restrictive.
(7) Overland flooding. Overland flood routing paths shall be used to convey stormwater runoff from the 100-year, 24-hour storm event to an adequate receiving water resource or stormwater management practice such that the runoff is contained within the drainage easement for the flood routing path and does not cause flooding of buildings or related structures. The peak 100-year water surface elevation along flood routing paths shall be at least one foot below the finished grade elevation at the structure. When designing the flood routing paths, the conveyance capacity of the site’s storm sewers shall be taken into consideration;
(8) Compensatory flood storage mitigation. All fill proposed to be placed in a designated Flood Hazard Mitigation area shall be in accordance with Chapter 1476; and
(9) Velocity dissipation. Velocity dissipation devices shall be placed at discharge locations and along the length of any outfall to provide non-erosive flow velocity from the structure to a water resource so that the natural physical and biological characteristics and functions of the water resource are maintained and protected.
(c) Stormwater quality control.
(1) Direct runoff to a BMP. The site shall be designed to direct runoff to one or more of the following stormwater management practices. These practices are listed in Table 2 of this regulation and shall be designed to meet the following general performance standards:
A. Extended conveyance facilities that slow the rate of stormwater runoff; filter and biodegrade pollutants in stormwater; promote infiltration and evapotranspiration of stormwater; and discharge the controlled runoff to a water resource;
B. Extended detention facilities that detain stormwater; settle or filter particulate pollutants; and release the controlled stormwater to a water resource;
C. Infiltration facilities that retain stormwater; promote settling, filtering, and biodegradation of pollutants; and infiltrate captured stormwater into the ground. The Stormwater Program Manager may require a soil engineering report to be prepared for the site to demonstrate that any proposed infiltration facilities meet these performance standards;
D. For sites less than five acres, but greater than one acre and not part of a common plan of development, where one or more acres are disturbed, the Stormwater Program Manager may approve other BMPs if the applicant demonstrates that these BMPs meet the objectives of this regulation as stated in division (c)(6) of this section;
E. For sites greater than five acres, or less than five acres but part of a larger common plan of development or sale which will disturb five or more acres, the Stormwater Program Manager may approve other BMPs if the applicant demonstrates to the Stormwater Program Manager’s satisfaction that these BMPs meet the objectives of this regulation as stated in division (c)(6) of this section, and has prior written approval from the Ohio EPA; and
F. For the construction of new roads and roadway improvement projects by public entities (i.e., the state, counties, townships, cities or villages), the Stormwater Program Manager may approve BMPs not included in Table 2 of this regulation, but must show compliance with the current version of the Ohio Departments of Transportation’s Location and Design Manual, Volume Two, Drainage Design.
NOTE: In division (c)(2) of this section, the size of the water quality volume (WQv) orifice can be limited to two and one-half inches in extended detention ponds when drainage areas are too small to allow a practical WQv orifice size.
(2) Criteria applying to all stormwater management practices. Practices chosen must be sized to treat the water quality volume (WQv) and to ensure compliance with Ohio Water Quality Standards (O.A.C. Chapter 3745-1).
A. The WQv shall be equal to the volume of runoff from a 0.75-inch rainfall event and shall be determined according to one of the following methods:
1. Through a site hydrologic study approved by the Stormwater Program Manager that uses continuous hydrologic simulation; site-specific hydrologic parameters, including impervious area, soil infiltration characteristics, slope, and surface routing characteristics; proposed best management practices controlling the amount and/or timing of runoff from the site; and local long-term hourly records; or
2. Using the following equation:
WQv = C*P*A/12
where terms have the following meanings:
WQv = water quality volume in acre-feet
C = runoff coefficient appropriate for storms less than one inch
P = 0.75-inch precipitation depth
A = area draining into the stormwater practice, in acres
Runoff coefficients required by the Ohio Environmental Protection Agency (Ohio EPA) for use in determining the water quality volume can be determined using the list in Table 1 or using the following equation to calculate the runoff coefficient, if the applicant can demonstrate that appropriate controls are in place to limit the proposed impervious area of the development:
C = 0.858i3 - 0.78i2 + 0.774i + 0.04, where:
i = fraction of the drainage area that is impervious
Table 1: Runoff Coefficient Based on the Type of Land Use | |
Land Use | Runoff Coefficient
|
Industrial and commercial | 0.8 |
High-density residential (>8 dwellings/acre) | 0.5 |
Medium-density residential (4 to 8 dwellings/acre) | 0.4 |
Low-density residential (<4 dwellings/acre) | 0.3 |
Open space and recreational areas | 0.2 |
Where land use will be mixed, the runoff coefficient should be calculated using a weighted average. For example, if 60% of the contributing drainage area to the stormwater treatment structure is low density residential, 30% is high density residential, and 10% is open space, the runoff coefficient is calculated as follows (0.6)(0.3) + (0.3)(0.5) + (0.1)(0.2) = (0.35) | |
B. An additional volume equal to 20% of the WQv shall be incorporated into the stormwater practice for sediment storage. This volume shall be incorporated into the sections of stormwater practices where pollutants will accumulate.
C. Stormwater quality management practices shall be designed such that the drain time is long enough to provide treatment and protect against downstream bank erosion, but short enough to provide storage available for successive rainfall events as defined in Table 2.
Table 2: Draw Down Times for Stormwater Management Practices | |
Best Management Practice | Drain Time of WQv |
Infiltration facilities* | 24 - 48 hours |
Extended conveyance facilities (vegetated swales, filter strips) | |
Vegetated filter strip with berm | 24 hours |
Enhanced water quality swale | 24 hours** |
Flow through design | 24 hours |
Extended detention facilities | |
Extended dry detention basins*** | 48 hours |
Wet detention basins + | 24 hours |
Pocket wetland^ | 24 hours |
Constructed wetlands (above permanent pool) | 24 hours |
Bioretention* | 40 hours |
Sand and other media filtration | 40 hours |
* The WQv shall completely infiltrate within 48 hours so there is no standing or residual water pool. ** Sized to pass a hydrograph with a volume equal to the WQv, a duration of two hours, peak rainfall intensity of one inch/hour at a depth of no more than 3 inches and have a minimum hydraulic residence time of 5 minutes. The use of this criterion is limited to sites where the total area disturbed is 5 acres or less. Prior approval from the Stormwater Program Manager is necessary to use this practice. For sites greater than 5 acres or less than 5 acres but part of a larger common plan of development or sale which will disturb 5 or more acres, prior written approval is required from the Ohio EPA. *** The use of a forebay and micropool is required on all extended dry detention basins. Each is to be sized at a minimum 10% of the WQv. + Provide both a permanent pool and an extended detention volume above the permanent pool, each sized with at least 0.75*WQv. ^ A pocket wetland must have a wet pool equal to the WQv, with 25% of the WQv in a pool and 75% in marshes. The EDV above the permanent pool must be equal to the WQv. | |
D. Each practice shall be designed to facilitate sediment removal, vegetation management, debris control, and other maintenance activities defined in the inspection and maintenance agreement for the site.
NOTE: This table is similar to that found in the Ohio EPA Construction General Permit. It has been reordered to match recommended BMP categories and additional description of the “drain time” for vegetated swales and filter strips has been added. The “Flow-Through Design” BMP is an Ohio EPA alternative practice and does require additional approvals from the Community and Ohio EPA depending the development site size, and can be removed from the table if necessary.
(3) Additional criteria applying to infiltration facilities.
A. Infiltration facilities shall only be allowed if the soils of the facility fall within hydrologic soil groups A or B, if the seasonal high water table is at least three feet below the final grade elevation, and any underlying bedrock is at least six feet below the final grade elevation.
B. All runoff directed into an infiltration basin must first flow through a pretreatment practice such as a grass channel or filter strip to remove coarser sediments that could cause a loss of infiltration capacity.
C. During construction, all runoff from disturbed areas of the site shall be diverted away from the proposed infiltration basin site. No construction equipment shall be allowed within the infiltration basin site to avoid soil compaction.
(4) Additional criteria applying to extended conveyance facilities.
A. Facilities shall be lined with fine turf-forming, flood-tolerant grasses.
B. Facilities designed according to the extended conveyance detention design drain time shall:
1. Not be located in areas where the depth to bedrock and/or seasonal high water table is less than three feet below the final grade elevation; and
2. Only be allowed where the underlying soil consists of hydrologic soil group (HSG) A or B, unless the underlying soil is replaced by at least a two and one-half foot deep layer of soil amendment with a permeability equivalent to a HSG A or B soil and an underdrain system is provided.
C. Facilities designed according to the flow through design drain time shall:
1. Only be allowed on sites where:
a. The total area disturbed is five acres or less;
b. The discharge rate from the BMP will have negligible hydrologic impacts to received waters as described in division (c)(6)B. of this section;
c. Prior written approval is given by the Stormwater Program Manager; and
d. For sites greater than five acres or less than five acres but part of a larger common plan of development or sale which will disturb five or more acres, prior written approval has been given by the Ohio EPA.
2. Be designed to slow and filter runoff flowing through the turf grasses with a maximum depth of flow no greater than three inches; and
3. Be designed to have a minimum hydraulic residence time of five minutes.
D. Concentrated runoff shall be converted to sheet flow, or a diffuse flow using a plunge pool, flow diffuser or level spreader, before entering an extended conveyance facility designed according to the flow-through drain time.
(5) Additional criteria for extended detention facilities.
A. The outlet shall be designed to not release more than the first half of the water quality volume in less than one-third of the drain time. The outlet shall be designed to minimize clogging, vandalism, maintenance and promote the capture of floatable pollutants.
B. The basin design shall incorporate the following features to maximize multiple uses, aesthetics, safety and maintainability.
1. Basin side slopes above the permanent pool shall have a run to rise ratio of 3:1 or as approved by the Stormwater Program Manager in order to satisfy the intent of this chapter.
2. The perimeter of all permanent pool areas deeper than four feet shall be surrounded by an aquatic bench that extends at least eight feet and no more than 15 feet outward from the normal water edge. The eight-foot wide portion of the aquatic bench closest to the shoreline shall have an average depth of six inches below the permanent pool to promote the growth of aquatic vegetation. The remainder of the aquatic bench shall be no more than 15 inches below the permanent pool to minimize drowning risk to individuals who accidentally or intentionally enter the basin, and to limit growth of dense vegetation in a manner that allows waves and mosquito predators to pass through the vegetation. The maximum slope of the aquatic bench shall be ten (H) to one (V). The aquatic bench shall be planted with hearty plants comparable to wetland vegetation that are able to withstand prolonged inundation.
3. A forebay designed to allow larger sediment particles to settle shall be placed at basin inlets. The forebay and micropool volume shall be equal to at least 10% of the water quality volume (WQv).
NOTE: Division (c)(6) below identifies the criteria that are currently be used by the Ohio EPA to assess the equivalency of alternative practices that are not listed in Table 2.
(6) Criteria for the acceptance of alternative post-construction BMPs. The applicant may request approval from the Stormwater Program Manager for the use of alternative structural post- construction BMPs if the applicant shows to the satisfaction of the Program Manager that these BMPs are equivalent in pollutant removal and runoff flow/volume reduction effectiveness to those listed in Table 2. If the site is greater than five acres, or less than five acres but part of a larger common plan of development or sale which will disturb five or more acres, prior approval from the Ohio EPA is necessary. To demonstrate the equivalency, the applicant must show the following.
A. The alternative BMP has a minimum total suspended solid (TSS) removal efficiency of 80%, using the Level II Technology Acceptance Reciprocity Partnership (TARP) testing protocol.
B. The water quality volume discharge rate from the selected BMP is reduced to prevent stream bed erosion, unless there will be negligible hydrologic impact to the receiving surface water of the state. The discharge rate from the BMP will have negligible impacts if the applicant can demonstrate one of the following conditions.
1. The entire water quality volume is recharged to ground water.
2. The development will create less than one acre of impervious surface.
3. The development project is a redevelopment project with an ultra-urban setting, such as a downtown area, or on a site where 100% of the project area is already impervious surface and the stormwater discharge is directed into an existing storm sewer system.
4. The stormwater drainage system of the development discharges directly into a large river of fourth order or greater or to a lake, and where the development area is less than 5% of the water area upstream of the development site, unless a total maximum daily load (TMDL) has identified water quality problems in the receiving surface water of the state.
(d) Stormwater quantity control. The comprehensive stormwater management plan shall describe how the proposed stormwater management practices are designed to meet the following requirements for stormwater quantity control for each watershed in the development.
(1) The peak discharge rate of runoff from the critical storm and all more frequent storms occurring under post-development conditions shall not exceed the peak discharge rate of runoff from a one-year, 24-hour storm occurring on the same development drainage area under pre-development conditions.
(2) Storms of less frequent occurrence (longer return periods) than the critical storm, up to the 100-year, 24-hour storm shall have peak runoff discharge rates no greater than the peak runoff rates from equivalent size storms under pre-development conditions. The one-, two-, five-, ten-, 25-, 50- and 100-year storms shall be considered in designing a facility to meet this requirement.
(3) The critical storm for each specific development drainage area shall be determined as follows:
A. Determine, using a curve number-based hydrologic method that generates hydrographs, or other hydrologic method approved by the Stormwater Program Manager, the total volume (acre-feet) of runoff from a one-year, 24-hour storm occurring on the development drainage area before and after development. These calculations shall meet the following standards:
1. Calculations shall include the lot coverage assumptions used for full build out as proposed;
2. Calculations shall be based on the entire contributing watershed to the development area;
3. Curve numbers for the pre-development condition must reflect the average type of land use over the past ten years and not only the current land use; and
4. To account for future post-construction improvements to the site, calculations shall assume an impervious surface such as asphalt or concrete for all parking areas and driveways, regardless of the surface proposed in the site description.
B. From the volume determined in division (d)(3)A. of this section, determine the percent increase in volume of runoff due to development. Using the percentage, select the 24-hour Critical Storm from Table 3.
Table 3: 24-Hour Critical Storm | ||
If the Percentage of Increase in Volume of Runoff is: | The Critical Storm will be: | |
Equal to or Greater Than: | and Less Than: | |
— | 10 | 1 year |
For example, if the percent increase between the pre- and post-development runoff volume for a one-year storm is 35%, the critical storm is a five-year storm. The peak discharge rate of runoff for all storms up to this frequency shall be controlled so as not to exceed the peak discharge rate from the one-year frequency storm under pre-development conditions in the development drainage area. The post-development runoff from all less frequent storms need only be controlled to meet pre- development peak discharge rates for each of those same storms. | ||
(e) Stormwater management on redevelopment projects. Comprehensive Stormwater Management Plans for redevelopment projects shall reduce existing site impervious areas by at least 20%. A one-for-one credit towards the 20% net reduction of impervious area can be obtained through the use of pervious pavement and/or green roofs.
(1) Where site conditions prevent the reduction of impervious area, stormwater management practices shall be implemented to provide stormwater quality control facilities for at least 20% of the site’s impervious area.
(2) When a combination of impervious area reduction and stormwater quality control facilities are used, the combined area shall equal or exceed 20% of the site.
(3) Where projects are a combination of new development and redevelopment, the total water quality volume that must be treated shall be calculated by a weighted average based on acreage, with the new development at 100% water quality volume and redevelopment at 20%.
(4) Where conditions prevent impervious area reduction or on-site stormwater management for redevelopment projects, practical alternatives as detailed in § 1060.10 may be approved by the Stormwater Program Manager.
(Ord. 88-2012, passed 6-25-2012; Ord. 26-2013, passed 3-25-2013)
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