916.07 STORM WATER MANAGEMENT (SWM) PLAN REQUIREMENTS.
   (a)   Storm Water Management (SWM) plans are intended to provide critical information on all soil erosion and runoff control activities and Best Management Practices (BMPs) to be used and incorporated on the site both during and after site development. This information includes, but is not limited to, site grading, storm water management facilities and practices, erosion and runoff control information, maintenance plans, and other measures that focus on managing the effects of earth-disturbing activities that occur as a result of site development. Said plan shall be prepared and stamped by a Licensed Professional Engineer authorized in the State of Ohio. To minimize duplication, storm water pollution prevention plans developed to meet the requirements of the Ohio EPA may be coordinated and combined with requirements of 916.07 to serve as the applicant's SWM Plan.
   (b)   Each SWM plan shall provide site design that meets the Performance Standards presented in Section 916.05 and provide practical treatment for both water quality and quantity of storm water from the site as appropriate.
   (c)   In general, SWM plans need to address:
      (1)   Erosion and Sediment Control. Provide measures to ensure that earth- disturbing activities at the site during and after development will be managed in a manner that will minimize increased erosion and sedimentation from the site resulting in impacts to water quality and that meet the Performance Standards specified in Section 916.05.
      (2)   Runoff Control. Providing measures to ensure that the rate of surface water runoff from the development site during and after construction will approximate the predevelopment conditions and that meet the Performance Standards specified in Section 916.05. 
      (3)   Non-Structural Preservation Methods. Preserving existing natural conditions as much as feasible.
      (4)   Post Construction Storm Water Management Practices. Providing practices which offer perpetual management of runoff quality and quantity; ensure stream functions are maintained; and ensure receiving stream's physical, chemical, and biological characteristics are protected.
      (5)   Maintenance. Providing a description of maintenance procedures needed to ensure the continued performance of control practices as described in 916.07(d)(2)G.
      (6)   Inspections. Providing procedures for inspection of all on-site controls as specified in Section 916.08(h).
   (d)   A SWM Plan shall specifically include all the following:
      (1)   The minimum elements required in the Site Development Plan described in Section 916.06(b).
      (2)   The contents of the Storm Water Pollution Prevention Plan (SWP3) required by Ohio EPA and incorporated herein by reference. The contents of the Storm Water Management (SWM) plan include, but are not limited to
         A.   A determination of runoff coefficients for both the pre-construction and post construction site conditions.
         B.   Storm Water Quality Control:
            1.   Direct runoff to a BMP: The site shall be designed to direct runoff to one or more of the following storm water 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 storm water runoff; filter and biodegrade pollutants in storm water; promote infiltration and evapotranspiration of storm water; and discharge the controlled runoff to a water resource.
               b.    Extended detention facilities that detain storm water; settle or filter particulate pollutants; and release the controlled storm water to a water resource.
               c.    Infiltration facilities that retain storm water; promote settling, filtering, and biodegradation of pollutants; and infiltrate captured storm water into the ground. The City Engineer 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 (5) acres, but greater than one (1) acre and not part of a common plan of development, where (1) or more acres are disturbed, the City Engineer may approve other BMPs if the applicant demonstrates to the City Engineer 's satisfaction that these BMPs meet the objectives of this regulation.
               e.    For sites greater than five (5) acres, or less than five (5) acres but part of a larger common plan of development or sale which will disturb five (5) or more acres, the City Engineer may approve other BMPs if the applicant demonstrates to the City Engineer's satisfaction that these BMPs meet the objectives of this regulation and has prior written approval from the Ohio EPA.
               f.    For the construction of new roads and roadway improvement projects by public entities (i.e. the state, counties, townships, cities, or villages), the City Engineer may approve BMPs not included in Table 2 of this regulation, but must show compliance with the current version of the Ohio Departments of Transportations "Location and Design Manual, Volume Two Drainage Design".
                  1.   Through the site hydrologic study approved by the City Engineer that uses continuous hydrologic simulation and local long-term hourly precipitation records or
                  2.   Using the following equation:
            
       WQv = C*P*A / 12
                  Were:      
         WQv = water quality volume in acre-feet
         C = runoff coefficient appropriate for storms less than 1 inch
         P = 0.75 inch precipitation depth
         A = area draining into the BMP in acres
         C = 0.858i3 - 0.78i2 + 0.774i+0.04, where:
                   i = fraction of the drainage area that is impervious.
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 the Table below 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:
 
Land Use
Runoff Coefficient
Industrial & 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
 
Post construction BMPs shall be designed such that the drain time is long enough to provide treatment, but short enough to provide storage available for successive rainfall events as described in Table 916.07(d)(2)B. The developer must provide the City Engineer with written approval from the Ohio EPA to use any post-construction BMP not specifically authorized by the Ohio EPA or listed in Table 916.07(d)(2)B.
Table 916.07(d)(2)B.
Target Draw Down (Drain) Times for Structural Post-Construction Treatment
Control Practices
Table 2: Draw Down Times for Storm Water Management Practices
Best Management Practice Drain Time of Wqv.
      
Best Management Practice (BMP)
Drain Time of Wqv
Extended Conveyance Facilities
(Vegetated Swales, Filter Strips)
-
Infiltration Facilities
24 - 48 hours
Vegetated Filter Strip with Berm
24 hours
Enhanced Water Quality Swale
24 hours
Extended Detention Basin (Dry Basins)***
48 hours
Flow Through Design
**
Retention Basins (Wet Basins)+
24 hours
Constructed Wetlands (above permanent pool)
24 hours
Sand and Other Media Filtration
40 hours
Bioretention*
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 2 hours, peak rainfall intensity of 1 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 City Engineer is necessary to use this practice. For sites greater than five (5) acres or less than five (5) acres but part of a larger common plan of development or sale which will disturb five (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 . ^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.
* Provide both a permanent pool and an extended detention volume above the permanent pool, each size at 0.75 * WQv
 
          C.   For all disturbances of more than one acre but less than five acres of land and is not a part of a larger common plan of development or sale which will disturb five or more acres of land, a description of measures that will be installed during the construction process to control pollutants in storm water discharges that will occur after construction operations have been completed. Structural practices must comply with the requirements of the Ohio EPA.
         D.   An implementation schedule which describes the sequence of major construction operations (i.e., grubbing, excavating, grading, utilities and infrastructure installation) and the implementation of erosion, sediment and storm water management practices or facilities to be employed during each operation of the sequence.
         E.   A detail drawing of a typical individual lot showing standard individual lot erosion and sediment control practices.
         F.   A detailed description of the storm water controls to be incorporated and how these meet or exceed the appropriate Performance Standards presented in Section 916.05.
         G.   A detailed maintenance plan that describes the frequency and type of procedures (i.e., inspection, cleaning, maintenance, repair, and replacement) needed to ensure the continued performance of control practices and the party (e.g., a homeowners' association) that will be responsible for implementing this plan. Such plans must ensure that pollutants collected within structural post-construction practices be disposed of in accordance with local, state, and federal regulations.
         H.   A Site Map including:
            1.   Limits of earth-disturbing activity of the site including associated offsite borrow or spoil areas.
            2.   Soil types on the site, including locations of unstable or highly erodible soils.
            3.   Existing and proposed contours and elevations. A delineation of drainage watersheds expected during and after major grading activities as well as the size of each drainage watershed, in acres.
            4.   Existing and planned locations of buildings, roads, parking facilities and utilities.
            5.   The location of all erosion and sediment control practices, including areas likely to require temporary stabilization during site development.
            6.   Sediment and storm water management basins noting their sediment settling volume and contributing drainage area.
            7.   Permanent storm water management practices to be used to control pollutants in storm water after construction operations have been completed, as applicable.
            8.   Areas designated for the storage or disposal of solid, sanitary, and toxic wastes, including dumpster areas, cement truck washout areas, and vehicle fueling and maintenance.
            9.   The location of designated construction entrances where vehicles will access the site.
            10.   The location of any in-stream activities, including stream crossings.
            11.   Surface water locations including springs, wetlands, streams, lakes, water wells, etc., on or within 200 feet of the site, including the boundaries of wetlands or stream channels and first subsequent named receiving water(s) the permittee intends to fill or relocate for which the permittee is seeking approval from the Army Corps of Engineers and/or Ohio EPA.
         I.   A copy of the written notification from the director of the Ohio EPA that the developer or permittee has been granted permit coverage and is authorized to discharge storm water associated with construction activity under the conditions of the permit and a copy of the Ohio EPA permit under which the permittee has been granted coverage or a copy of the permit requirements.
         J.   The permittee shall reference its Ohio EPA Facility Permit Number on the SWM plan.
   (e)   Determination of Post Development Runoff.
      (1)   Each SWM plan shall include a comparison that quantifies the volume and rate of runoff from the site by subdrainage areas for pre-development conditions and proposed conditions.
This evaluation shall be prepared according to methods prescribed in Rainwater and Land Development or other appropriate sources. The evaluation shall:
         A.   Show delineation and sequence of subdrainage units which comprise the area proposed for development.
         B.   Indicate the hydraulic length of slope per individual subdrainage unit and the length of the natural or manmade watercourse which accommodates the surface runoff from each subdrainage unit.
         C.   Indicate within the legend the average percent slope, erosion factor (K) and runoff curve number (CN) per individual subdrainage areas.
         D.   Include a hydrograph utilizing TR55, "Type II Rainfall Distribution Pattern" over a twenty-four (24)-hour period for the following return intervals: 1, 2, 5, 10, 25, 50, and 100-year storms. Hydrographs for each of the recurrence intervals shall be produced for both the existing and proposed conditions.
         E.   The 24-hour rainfall depths in Schedule 916.07(e)(1)E shall be utilized to quantify the storm water runoff for the existing and proposed conditions.
 
Schedule 916.07(e)(1)E. Sectional Mean Frequency Distributions for Storm Period of
24-Hours and Recurrence Intervals of 1 Year to 100 Years in Ohio
Return Period
(years)
Rainfall (inches) for given
recurrence interval
1
1.98 in.
2
2.44 in.
5
3.06 in.
10
3.55 in.
25
4.35 in.
50
5.08 in.
100
5.92 in.
SOURCE: Huff, Floyd A., and James R. Angel. Rainfall Frequency Atlas of the Midwest. Illinois State Water Survey, Champaign, Bulletin 71, 1992.
 
      (2)   Calculations for the design of storm water management facilities shall demonstrate the following for each subdrainage unit:
         A.   The peak rate of runoff from the critical storm and all more frequent storms occurring on the site does not exceed the peak rate of runoff from a one-year frequency, 24-hour storm occurring on the same site under pre-development conditions.
         B.   Storms of less frequent occurrence than the critical storm, up to the one hundred (100) year storm shall have the proposed peak runoff rates reduced to their respective existing condition peak runoff rates.
      (3)   Calculation of a critical storm for each subdrainage unit of the site shall be determined as follows:
         A.   Calculate by appropriate hydrologic methods, such as the TR55, the total volume of runoff from a one-year frequency, 24-hour storm occurring on the development area before and after development
         B.   From the volumes determined in (4) A. above, determine the percentage increase in volume of runoff due to the proposed development, and using this percentage, select the 24-hour critical storm from the following table:
Table 916.07(e)(4)B.: Twenty-Four Hour Critical Storm Runoff Rate
If the percentage of increase in
runoff volume is:
The Critical Storm
Runoff Rate will Be
Limited to:
Equal to
or greater than
 
And Less Than
0
10
1 year
10
20
2 years
20
50
5 years
50
100
10 years
100
250
25 years
250
500
50 years
500
-
100 years
 
         C.   The City Engineer shall approve or reject any calculation method based on its technical validity for the given situation. Downstream capacity may further reduce maximum discharge requirements.
      (4)   Off-site storm water control facilities. Exceptions to requiring permanent on-site runoff control on the site may be considered by the City Engineer provided the applicant can prove that:
         A.   The intent and standards of this chapter for runoff control can be best achieved by the utilization of off-site storm water control facilities.
         B.   Runoff from the site can be conveyed to off-site storm water facilities in a manner and by means which satisfy or surpass the standards of this chapter.
         C.   The applicant has ownership of or the right to use the off-site facility in question.
   (f)   Storm Water Management (SWM) Plan submission, review and action.
      (1)   The applicant is encouraged to have a pre-submission meeting with the City Engineer.
      (2)   Submission of two sets of the SWM plan and other supporting data required by this regulation to the City Engineer complete the applicant's responsibilities and initiates the review process.
      (3)   The SWM plan shall be reviewed by the City Engineer to:   
         A.   Verify background information furnished by the applicant and evaluate the proposed development in relation to existing site conditions.
         B.   Assess the SWM plan in relation to the Performance Standards and requirements of this chapter.
      (4)   Upon submission of the SWM plan the City Engineer shall complete a review and shall either:
         A.   Approve the SWM plan as submitted by the applicant; or
         B.   Conditionally approve the SWM plan and require the submission of additional and/or revised information by the applicant, in order to fully meet the intent and standards of this chapter; or
         C.   Disapprove the SWM plan based upon a written review noting the reasons.
      (5)   Action by the City Approval Authority and the authorized agent(s) approving or disapproving the SWM plan is a final order for purposes of judicial review.
         (Ord. 11-35. Passed 7-25-11.)