Loading...
(a) This regulation requires that a Comprehensive Stormwater Management Plan be developed and implemented for all development subject to the regulation as defined by Section 937.01(c) for which 10,000 sf or more of impervious area is added or for all soil disturbing activities disturbing 20,000 sf or more of total land, or less than 20,000 sf if part of a larger common plan of development or sale disturbing one (1) or more acres of total land. The city engineer may require a comprehensive stormwater management plan on any site with new impervious area of less than 10,000 sf or with soil disturbing activities disturbing less than 20,000 sf.
(b) The City of Ontario 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 of Ontario may consult with the Richland County SWCD, state agencies, private engineers, stormwater districts, or other technical experts in reviewing the Comprehensive Stormwater Management Plan.
(Ord. 22-22. Passed 3-16-22.)
(a) Pre-Application Meeting. The applicant shall attend a Pre-Application Meeting with the city engineer and/or zoning inspector to discuss the proposed project, review the requirements of this regulation, 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 (2) sets of a Preliminary Comprehensive Stormwater Management Plan (Preliminary Plan) and the applicable fees to the zoning inspector. 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 city engineer and zoning inspector to determine if the site is laid out in a manner that meets the intent of this regulation and if the proposed SCMs are capable of controlling runoff from the site in compliance with this regulation. The applicant shall submit two (2) 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 the preliminary development plan.
(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 (2) sets of a Final Comprehensive Stormwater Management Plan (Final Plan) and the applicable fees to the zoning inspector 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 Section 937.08 and shall be approved by the city engineer prior to approval of the final plat and/or before issuance of a zoning permit by the Zoning Inspector or building permit by the Building Inspector.
(d) Review and Comment: The city engineer and zoning inspector 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 (2) years from the date of approval.
(Ord. 22-22. Passed 3-16-22.)
Approvals issued in accordance with this regulation 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. Applicants are required to show proof of compliance with these regulations before the City of Ontario will issue a building or zoning permit.
(a) Ohio Environmental Protection Agency (Ohio EPA) National Pollutant Discharge Elimination System (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 certifying and explaining why the NPDES Permit is not applicable.
(b) Section 401 of the Clean Water Act: Proof of compliance shall be a copy of the Ohio EPA Water Quality Certification application tracking number, public notice, project approval, or a letter from the site owner certifying that a qualified professional has surveyed the site and determined that Section 401 of the Clean Water Act is not applicable. Wetlands, and other waters of the United States, shall be delineated by protocols accepted by the U.S. Army Corps of Engineers at the time of application of this regulation.
(c) Ohio EPA Isolated Wetland Permit: Proof of compliance shall be a copy of Ohio EPA's Isolated Wetland Permit application tracking number, public notice, project approval, or a letter from the site owner certifying that a qualified professional has surveyed the site and determined that Ohio EPA's Isolated Wetlands Permit is not applicable. Isolated wetlands shall be delineated by protocols accepted by the U.S. Army Corps of Engineers at the time of application of this regulation.
(d) Section 404 of the Clean Water Act: Proof of compliance shall be a copy of the U.S. Army Corps of Engineers Individual Permit application, public notice, or project approval, if an Individual Permit is required for the development project. If an Individual Permit is not required, the site owner shall submit proof of compliance with the U.S. Army Corps of Engineer's Nationwide Permit Program. This shall include one of the following:
(1) A letter from the site owner certifying that a qualified professional has surveyed the site and determined that Section 404 of the Clean Water Act is not applicable.
(2) A site plan showing that any proposed fill of waters of the United States conforms to the general and special conditions specified in the applicable Nationwide Permit. Wetlands, and other waters of the United States, shall be delineated by protocols accepted by the U.S. Army Corps of Engineers at the time of application of this regulation.
(e) Ohio Dam Safety Law: Proof of compliance shall be a copy of the ODNR Division of Soil and Water Resources permit application tracking number, a copy of the project approval letter from the ODNR Division of Soil and Water Resources, or a letter from the site owner certifying and explaining why the Ohio Dam Safety Law is not applicable.
(Ord. 22-22. Passed 3-16-22.)
(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 completed for every discharge from the site and/or into a water resource or small municipal separate storm sewer system (MS4). The Plan will illustrate the type, location, and dimensions of every structural and non-structural SCM incorporated into the site design, and the rationale for their selection. The rationale must address how these SCMs 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 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 city engineer, a site survey shall be performed by a registered Professional Surveyor to establish boundary lines, measurements, or land surfaces.
(c) Community Procedures: The city engineer 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 city engineer based on improvements in engineering, science, monitoring, and local maintenance experience. The city engineer shall make the final determination of whether the practices proposed in the Comprehensive Stormwater Management Plan meet the requirements of this regulation. At a minimum, the following criteria and guidance documents shall be used as minimum standards for design where applicable:
(1) ODNR Rainwater and Land Development Manual, current edition
(2) NRCS CPS Pond Code 378, current edition
(3) ODOT L&D Manual Volume 2 Drainage Design, current edition
The city engineer may also maintain a list of acceptable SCMs that meet the criteria of this regulation to be used in the City of Ontario.
(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 Plan and Inspection and Maintenance Agreement, completed Final Site Plan and Comprehensive Stormwater Management Checklist 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, etc.).
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 imperviousness created by the soil disturbing activity at the beginning and at the conclusion of the project.
E. Selection (source and justification) and/or calculations of runoff coefficients for water quality volume determination, peak discharge control (curve number/critical storm method), and rational method.
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.
I. If applicable, identify the point of discharge to a municipal separate storm sewer system and the location where that municipal separate storm sewer system ultimately discharges to a stream, lake, or wetland. The location and name of the immediate receiving stream or surface water(s) and the first subsequent receiving water(s) and the aerial extent and description of wetlands or other special aquatic sites at or near the site which will be disturbed or which will receive discharges from undisturbed areas of the project.
J. TMDLs applicable for the site; demonstrate that appropriate (SCMs) have been selected to address these TMDLs.
K. For each SCM, identify the drainage area, percent impervious cover within the drainage area, runoff coefficient for water quality volume, peak discharge, and the time of concentration for each subwatershed per Appendix 1 of the current edition of the Rainwater and Land Development Manual. Identify the SCM surface area, discharge and dewatering time, outlet type and dimensions. Each SCM shall be designated with an individual identification number.
L. 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 map units for the entire site, including locations of unstable or highly erodible soils.
C. Existing and proposed one-foot (1') 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 Army Corps of Engineers and/or Ohio EPA.
E. Existing and planned locations of buildings, roads, parking facilities, and utilities.
F. The location of any in-stream activities including stream crossings.
(3) Contact information: Company name and contact information as well as contact name, addresses, and phone numbers for the following:
A. The Professional Engineer who prepared the Comprehensive Stormwater Management Plan.
B. The site owner.
(4) Phase, if applicable, of the overall development plan.
(5) List of sublot numbers if project is a subdivision.
(6) 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, including complete site address and sublot number if applicable.
(8) Location of any easements or other restrictions placed on the use of the property.
(9) A site plan sheet showing:
A. The location of each proposed post-construction SCMs.
B. The geographic coordinates of the site in North American Datum Ohio State Plane 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 also be provided.
(10) Inspection and Maintenance Agreement. The Inspection and Maintenance Agreement required for SCMs under this regulation as a stand-alone document between the City of Ontario and the applicant. A copy of this agreement should be attached to the property deed. The agreement shall contain the following information and provisions:
A. Identification of the landowner(s), organization, or municipality responsible for long-term inspection and maintenance, including repairs, of the SCMs.
B. The landowner(s), organization, or municipality shall maintain SCMs in accordance with this regulation.
C. The City of Ontario has the authority to enter upon the property to conduct inspections as necessary, with prior notification of the property owner, to verify that the SCMs are being maintained and operated in accordance with this regulation.
D. The City of Ontario shall maintain public records of the results of site inspections, shall inform the landowner(s), organization, or municipality responsible for maintenance of the inspection results, and shall specifically indicate in writing any corrective actions required to bring the SCMs into proper working condition.
E. If the City of Ontario notifies the landowner(s), organization, or municipality responsible for maintenance of the maintenance problems that require correction, the specific corrective actions shall be taken within a reasonable time as determined by the City of Ontario.
F. The City of Ontario is authorized to enter upon the property and perform the corrective actions identified in the inspection report if the landowner(s), organization, or municipality responsible for maintenance does not make the required corrections in the specified time period. The City of Ontario shall be reimbursed by the landowner(s), organization, or municipality responsible for maintenance for all expenses incurred within 10 days of receipt of invoice from the City of Ontario, or more with written approval from the city engineer.
G. The method of funding long-term maintenance and inspections of all SCMs.
H. A release of the City of Ontario from all damages, accidents, casualties, occurrences, or claims that might arise or be asserted against the City of Ontario from the construction, presence, existence, or maintenance of the SCMs.
(11) Inspection and Maintenance Plan. This plan will be developed by the applicant and reviewed by the City of Ontario. Once the Inspection and Maintenance Plan is approved, a recorded copy of the Plan must be submitted to the City of Ontario as part of the final inspection approval as described in Section 937.12. The plan will include at a minimum:
A. The location of each SCM and identification of the drainage area served by each SCM.
B. Photographs of each SCM, including all inlets and outlets upon completion of construction.
C. Schedule of inspection.
D. 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. A maintenance inspection checklist written so the average person can understand it shall be incorporated. The maintenance plan will include a detailed drawing of each SCM and outlet structures with the parts of the outlet structure labeled. This schedule may include additional standards, as required by the city engineer, to ensure continued performance of SCMs permitted to be located in, or within fifty (50) feet of, water resources.
E. The location and documentation of all access and maintenance easements on the property.
Alteration or termination of these stipulations is prohibited.
(12) Required calculations: The applicant shall submit calculations for projected stormwater runoff flows, volumes, and timing into and through all SCMs for flood control, channel protection, water quality, and the condition of the habitat, stability, and incision of each water resource and its floodplain, as required in Section 937.09 of this regulation. 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 offsite areas have been considered in the calculations.
(13) Existing and proposed drainage patterns: The location and description of existing and proposed drainage patterns and SCMs, including any related beyond the development area and the larger common development area.
(14) For each SCM 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. Final site conditions including stormwater inlets and permanent non-structural and structural SCMs. Details of SCMs shall be drawn to scale and shall show volumes and sizes of contributing drainage areas.
C. Any other structural and/or non-structural necessary to meet the design criteria in this regulation and any supplemental information requested by the city engineer.
D. Each SCM shall be designated with an individual identification number.
(Ord. 22-22. Passed 3-16-22.)
(a) General: The stormwater system, including SCMs for storage, treatment and control, and conveyance facilities, shall be designed to prevent structure flooding during the 100-year, twenty-four (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 system 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 Chapter 1354 Riparian and Wetland Setback requirements.
B. Maintain predevelopment hydrology and groundwater recharge on as much of the site as practicable. Where feasible, bioretention, permeable pavement with infiltration, underground storage with infiltration, infiltration trenches, infiltration basins, and/or rainwater harvesting must be the water quality SCMs used. Separate SCMs may be used for peak discharge control and water quality treatment.
C. Only install new impervious surfaces and compact soils where necessary to support the future land use.
D. Compensate for increased runoff volumes caused by new impervious surfaces and soil compaction by reducing stormwater peak flows to less than predevelopment levels.
E. Be designed according to the methodology included in the most current edition of the Rainwater and Land Development Manual or another design manual acceptable for use by the City of Ontario and Ohio EPA.
SCMs that meet the criteria in this regulation, and additional criteria required by the city engineer, shall comply with this regulation.
(2) Practices designed for final use: SCMs shall be designed to achieve the stormwater management objectives of this regulation, to be compatible with the proposed postconstruction use of the site, to protect the public health, safety, and welfare, and to function safely with routine maintenance.
(3) Stormwater management for all lots: Areas developed for a subdivision, as defined in Chapter 1115 Subdivision Procedures, 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, twenty-four (24)-hour storm; and maintain, to the extent practicable, the pre-development runoff patterns, volumes, and peaks from each lot.
(4) Stormwater facilities in water resources: SCMs 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, and other applicable federal, state, and local agencies as required in Section 937.07 of this regulation, and the activity is in compliance with Chapter 1353 Erosion and Sediment Control Requirements and Chapter 1354 Riparian and Wetland Setback, all as determined by the city engineer.
(5) Stormwater ponds and surface conveyance channels: All surface conveyance designs must provide a minimum of two (2) foot freeboard above the projected peak stage within the facility during the 100-year, twenty-four (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 Section 937.09 if it can be shown to the satisfaction of the city engineer 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 SCMs, 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 city engineer.
(7) Maintenance: All SCMs shall be maintained in accordance with the Inspection and Maintenance Plan and Agreements approved by the city engineer as detailed in Section 937.08.
(8) Ownership: Unless otherwise required by the City of Ontario, SCMs 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 of Ontario. SCMs 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 vegetative buffer strips; phasing of construction operations in order to minimize the amount of disturbed land at any one time, and designation of tree preservation areas or other protective clearing and grubbing practices; and maintaining un-concentrated stormwater runoff to and through these areas. Postconstruction stormwater practices shall provide perpetual management of runoff quality and quantity so that a receiving stream's physical, chemical and biological characteristics are protected and ecological functions are maintained.
(10) Preservation of Wetland Hydrology: Concentrated stormwater runoff from SCMs to wetlands shall be converted to diffuse flow before the runoff enters the wetlands 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 performed to demonstrate that the proposed discharge matches the pre-development hydroperiods and hydrodynamics that support the wetland.
(b) Stormwater Conveyance Design Criteria: All SCMs 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) Surface water protection: The city engineer may allow modification to streams, rivers, lakes, wetlands or other surface waters only if the applicant shows proof of compliance with all appropriate permits from the Ohio EPA, the U.S. Army Corps, and other applicable federal, state, and local agencies as required in Section 937.07 of this regulation, and the activity is in compliance with Section 1353 Erosion and Sediment Control requirements and Chapter 1354 Riparian and Wetland Setback, all as determined by the city engineer. 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 city engineer 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. The sheet flow length shall not exceed seventy-five (75) feet from impervious area or 150 feet from pervious area. Flow shall be directed into an open channel, storm sewer, or other SCMs from areas too long and/or too large to maintain sheet flow, all as determined by the city engineer.
(4) Open channels: Unless otherwise allowed by the city engineer, drainage tributary to SCMs shall be provided by an open channel with vegetated banks and designed to carry the ten (10)-year, twenty-four (24)-hour stormwater runoff from upstream contributory areas.
(5) Storm sewer systems: Storm sewers shall be designed in accordance with the methodology outlined in the current version of the Ohio Department of Transportation Location and Design Manual, Volume 2. In addition, the following criteria shall be used to design storm sewer systems:
A. Storm sewers shall be designed such that they do not surcharge from runoff caused by the ten (10) year, twenty-four (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 twenty-five (25) year, twenty-four (24) hour storm. The system shall be designed to meet these requirements when conveying the flows from the contributing drainage area within the proposed development and existing flows from offsite areas that are upstream from the development.
B. The minimum inside diameter of pipe to be used in public storm sewer systems is twelve (12) inches. Smaller pipe sizes may be used in private systems, subject to the approval of the city engineer.
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. Water resource crossings shall be designed in accordance with the methodology outlined in the current version of the Ohio Department of Transportation Location and Design Manual, Volume 2. In addition, the following criteria shall be used to design structures that cross a water resource in the City of Ontario:
A. Water resource crossings other than bridges shall be designed to convey the stream's flow for the minimum twenty-five (25) year, twenty-four (24) hour storm.
B. Bridges, open bottom arch or spans are the preferred crossing techniques and shall be considered in the planning phase of the development. Bridges and open spans should be considered for all State Scenic Rivers, coldwater habitat, exceptional warmwater 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, twenty-five (25) percent of the cross-sectional area or a minimum of one (1) foot of box culverts and pipe arches must be embedded below the channel bed. The conduit or conveyance must to be sized to carry the twenty-five (25)-year storm under these conditions.
D. The minimum inside diameter of pipes to be used for crossings shall be twelve (12) inches.
E. The maximum slope allowable shall be a slope that produces a ten (10) 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 (5) 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, twenty-four (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, twenty-four (24) hour storm event to an adequate receiving water resource or SCM 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 (1) foot below the finished grade elevation of all structures. 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: In order to preserve floodplain storage volumes and thereby avoid increases in water surface elevations, any filling within floodplains approved by the City of Ontario must be compensated by providing an equivalent storage volume. First consideration for the location(s) of compensatory floodplain volumes should be given to areas where the stream channel will have immediate access to the new floodplain within the limits of the development site. Consideration will also be given to enlarging existing or proposed retention basins to compensate for floodplain fill if justified by a hydraulic analysis of the contributing watershed. Unless otherwise permitted by the City of Ontario, reductions in volume due to floodplain fills must be mitigated within the legal boundaries of the development. Embankment slopes used in compensatory storage areas must reasonably conform to the natural slopes adjacent to the disturbed area. The use of vertical retaining structures is specifically prohibited.
(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: The site shall be designed to direct runoff to one or more of the following SCMs that meet or exceed the criteria in the Construction General Permit.
(1) Additional criteria for extended detention facilities:
A. 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 flatter.
2. The perimeter of all permanent pool areas deeper than four (4) feet shall be surrounded by an aquatic bench that extends at least eight (8) feet and no more than fifteen (15) feet outward from the normal water edge. The eight (8) feet wide portion of the aquatic bench closest to the shoreline shall have an average depth of six (6) inches below the permanent pool to promote the growth of aquatic vegetation. The remainder of the aquatic bench shall be no more than fifteen (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 10 (H) to 1 (V). The aquatic bench shall be planted with native plant species comparable to wetland vegetation that are able to withstand prolonged inundation. The use of invasive plant species is prohibited.
3. Detention basins shall be provided with an emergency drain, where practicable, so that the basin may be emptied if the primary outlet becomes clogged and/or to drain the permanent pool to facilitate maintenance. The emergency drain should be designed to drain by gravity where possible.
4. Detention basins shall be provided with an emergency spillway and associated freeboard, designed in accordance with the methodology outlined in the current edition of NRCS 378.
(d) Stormwater Quantity Control: The Comprehensive Stormwater Management Plan shall describe how the proposed SCMs 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 (1)-year, twenty-four (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, twenty-four (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 (1), two (2), five (5), ten (10), twenty-five (25), fifty (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 or other hydrologic method approved by the city engineer, the total volume (acre-feet) of runoff from a one (1)-year, twenty-four (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. Model pervious, directly connected impervious and disconnected impervious areas as subwatersheds.
4. Drainage area maps shall include area, curve number, time of concentrations. Time of concentration shall also show the flow path and the separation in flow type.
5. Rainfall Depth - For the most accurate, up-to-date, location-specific rainfall data for stormwater design, use the Precipitation-Frequency Atlas of the United States, NOAA Atlas 14, Vol 2(3). available online: http://hdsc.nws.noaa.gov/hdsc/pfds/.
6. Temporal Distribution - Use the SCS Type II rainfall distribution for all design events with a recurrence interval greater than one (1) year. Include lot coverage assumptions used for full build out of the proposed condition.
7. Curve numbers for the pre-development condition shall reflect the average type of land use over the past ten (10) years and not only the current land use.
i. Pre-development Curve Numbers - For wooded or brushy areas, use listed values from TR-55 NRCS USDA Urban Hydrology for Small Watersheds, 1986 in good hydrologic condition. For meadows, use listed values. For impervious area that has been in place prior to the implementation of the City of Ontario Stormwater Management Ordinance of 1986, use listed values. For all other areas (including impervious area added after 1986 and all types of agriculture), use pasture, grassland, or range in good hydrologic condition.
2. Post-development Curve Numbers - Open space areas shall use post-construction HSGs from the current edition of the Rainwater and Land Development Manual unless the soil is amended. All undisturbed areas or open space with amended soils shall be treated as "open space in good condition."
8. Time of Concentration - Use velocity based methods from (TR-55 NRCS USDA Urban Hydrology in Small Watersheds, 1986) to estimate travel time (Tt) for overland (sheet) flow, shallow concentrated flow and channel flow.
i. Maximum sheet flow length is 100 feet.
ii. Use the appropriate "unpaved" velocity equation for shallow concentrated flow from Soil Conservation National Engineer Handbook Section 4- Hydrology (NEH-4)
9. The volume reduction provided by permeable pavement, bioretention, or other LID SCMs may be subtracted from the post development stormwater volume. Volume reductions for these practices may be demonstrated using methods outlined in the current edition of the Rainwater and Land Development Manual or a hydrologic model acceptable to the city engineer.
B. 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 except in instances of engineered permeable pavement systems. From the volume determined in Section 937.09(d)(3)A., determine the percent increase in volume of runoff due to development. Using the percentage, select the twenty-four (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 |
10 | 20 | 2 year |
20 | 50 | 5 year |
50 | 100 | 10 year |
100 | 250 | 25 year |
250 | 500 | 50 year |
500 | --- | 100 year |
For example, if the percent increase between the pre- and post-development runoff volume for a 1-year storm is 35%, the Critical Storm is a 5-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 1-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.
(1) SCMs on previously developed sites must meet the criteria in the Construction General Permit.
(Ord. 22-22. Passed 3-16-22.)
(a) When the City of Ontario determines that site constraints compromise the intent of this regulation, off-site alternatives may be used that result in an improvement of water quality and a reduction of stormwater quantity. Such alternatives shall meet the standards in the Construction General Permit and shall achieve the same level of stormwater quantity control that would be achieved by the on-site controls required under this regulation. The City Engineer may require proof of Ohio EPA review and approval for any alternative action proposed.
(b) Alternative actions may include, but are not limited to the following. All alternative actions shall be approved by the city engineer:
(1) Fees, in an amount specified by the City of Ontario to be applied to community-wide SCMs.
(2) Implementation of off-site SCMs and/or the retrofit of an existing practice to increase quality and quantity control.
(3) Stream, floodplain, or wetland restoration.
(4) Acquisition or conservation easements on protected open space significantly contributing to stormwater control such as wetland complexes.
(Ord. 22-22. Passed 3-16-22.)
Loading...