(a) General. These standards, specifications and requirements shall serve to supplement Chapter 921 of the Codified Ordinances and the City of Ashland Standard Drawings and Standard Specifications, and all workmanship and materials shall conform to all of the above. All systems shall be designed and constructed in accordance with accepted engineering practice and shall incorporate stormwater management and control, including the conveyance of surface water to an adequate outlet which is capable of carrying the flow, all to the complete satisfaction of the City Engineer and, where applicable, the County Engineer. (See subsection (b) hereof for exceptions.) In addition, in the City within identified flood hazard areas, the subdivider is also subject to Chapter 1333.
(b) Scope and General Requirements. All subdividers or developers shall construct a complete storm sewer and drainage system to ensure complete drainage in and adjacent to the subdivision or development.
All subdividers or developers of areas ten acres or more in aggregate shall conform to all requirements of subsection (i) hereof, except that subdividers or developers of areas for which "preliminary plats" have been approved previously by the Planning Commission may request the Commission to waive or reduce any or all requirements. Where the Commission determines that conformation would pose an unusual hardship, it may waive or reduce the requirements after considering a recommendation by the City Engineer or, where applicable, the County Engineer. Within rights-of-way existing prior to subdivision or development, the City Engineer and, where applicable, the County Engineer may vary and waive these requirements.
(c) Drainage and Grading Plan.
(1) Preliminary. A complete new or revised drainage and grading plan for the entire subdivision or development shall be submitted to and approved by the City Engineer and, where applicable, the County Engineer and the Commission prior to the submission of the preliminary plat. The plan shall show the general runoff pattern of the entire area to be improved, as well as the runoff pattern of adjacent areas which affect, or may be affected, by the proposed improved area. The plan shall also show flood boundaries and base flood elevation data determined by the National Flood Program adopted by the City and other appropriate subdivisions. Sufficient data shall be included for the City Engineer and, where applicable, the County Engineer to check and approve the feasibility of the drainage system and Stormwater Management and Control proposed by the developer.
(2) Final. A final drainage and grading plan showing the entire drainage system and grading plan shall be submitted to the City Engineer and, where applicable, the County Engineer for final approval. The final drainage and grading plan shall conform to these regulations and to any special conditions that were required by the Commission in approving the preliminary plat. The final plan shall include engineering calculations used in determining the design of the drainage courses, the drainage structures, and stormwater runoff control structures and shall include the complete final stormwater management and control plan.
The following shall serve as a minimum requirement for plans and engineering calculations for the on-site drainage:
A. The total tributary drainage areas entering the improved area;
B. Times of concentration, intensity and runoff coefficients used for determining runoff;
C. Discharge volume in cubic feet per second, velocity and additional data needed to establish that the drainage system shall convey the flow to the approved adequate outlet;
D. The plan, profile and capacity of all drainage courses to where the system discharges into the adequate outlet;
E. Size and type of all drainage improvements, including all drainage structures; and
F. Sufficient contours and grading details to show that the proposed improvements shall function adequately.
All drainage construction plans shall be sealed with the stamp of a professional engineer registered in the State of Ohio as required by Ohio R.C. Chapter 4733. The drainage plan shall be submitted to and approved by the City Engineer and, where applicable, the County Engineer prior to the preparation of detailed construction plans for any portion of the drainage system.
Under no circumstances shall any storm drainage system, spouting drain or footer drain be allowed to empty into a sanitary sewer.
(d) Design Criteria and Specific Requirements.
(1) Runoff Coefficients shall be determined in accordance with O.D.O.T. Location and Design Manual, and development of the drainage area for uses and purposes which the City Engineer and, where applicable, the County Engineer determine may be reasonably expected within the next fifty years, allowing for stormwater management and control where appropriate.
(2) Design frequencies shall be as follows:
Description | Frequency (years) |
Spacing and sizing of basins, inlets, laterals, branches and drive pipes | 5 |
Longitudinal pipes, structures, mains and open ditches | 10 |
Crossroad culverts, bridges and sump areas | 50 |
Flood plain structures and areas where overflow or backup could cause property damage (See subsection (i) hereof for possible exceptions.) | 100 |
(3) Quantity and velocity of flow shall be calculated in accordance with O.D.O.T. Location and Design Manual.
(4) All storm sewers shall be designed with hydraulic slopes sufficient to give a mean velocity when flowing full of not less than three feet per second based on value of N = 0.015 for sewers up to and including twenty-seven inches and N = 0.013 for sewers greater than twenty-seven inches. (Clay and concrete pipes. )
(5) Where velocities in conduits exceed fifteen feet per second, special provisions shall be made to protect against erosion and displacement.
(6) Pipe shall be of the size, kind and class to meet the loading requirement and shall conform to all other provisions of these Regulations.
(7) No storm sewer shall be less than ten inches in diameter. Single family house spouting and footer drain connections shall be not less than four inches in diameter. Service connections from other sources shall be of adequate capacity as designed by the Engineer. The minimum grade for all such connections shall be one percent (1%), unless otherwise approved.
(8) Storm sewers constructed within five feet, center-to-center of sanitary sewers, shall have premium joints, that is, meeting A.S.T.M. C433 or C425. This criteria shall apply to mains, as well as connections.
(9) Storm manhole joints shall be of the same type as its incoming sewer, that is, premium joint sewer A.S.T.M. C443 or C425, hence premium joint manhole A.S.T.M. C443.
(10) Manholes or catch basins shall be installed at all changes in grade, size and/or alignment. Radius pipe may be considered for use in changes of alignment of pipe of forty-eight inch diameter and larger.
(11) Maximum spacing for manholes and catch basins shall be 400 feet, as measured horizontally along the centerline of the pipe.
(12) The minimum cover for drainage pipes under pavement shall be twelve inches from the bottom of the pavement base to the crown of the pipe.
(13) A maximum of 200 feet of open trench in advance of pipe laying shall be permitted, unless otherwise approved by the City Engineer and, where applicable, the County Engineer.
(14) All drainage pipes shall be laid and maintained to the required lines and grades, as shown on the plans. Manholes and catch basins shall be installed with the main line, unless otherwise approved by the City Engineer and, where applicable, the County Engineer.
(15) Where connections are to be made to existing sewers, the contractor shall make suitable provisions for handling flow in the existing sewer until the completion of the connection.
(16) All drainage pipes laid by open cut methods under pavement or within two feet of the edge of pavement, shall be bedded and back filled with approved granular material and mechanically compacted.
( 17) Where a storm sewer system is being constructed within a roadway where curbs are installed, catch basins with curb inlets shall be required in accordance with the City of Ashland Specifications and Standard Drawings.
(18) Where a storm sewer system is being constructed and there are no curbs being installed or the sewer system is being installed away from the roadway, there shall be an approved drainage swale over the storm sewer system draining to the inlet basin. All such inlet basins shall be spaced as specified in these regulations and of a type approved by the City Engineer and, where applicable, the County Engineer.
(e) Subsurface Drainage. Adequate facilities shall be constructed to control the flow of ground water to the complete satisfaction of the City Engineer and, where applicable, the County Engineer.
(f) Open Ditches. Ditches shall have a minimum slope of one percent (1%) and shall have a minimum depth of one and one-half feet and a minimum bottom width of two feet. Adequate channel protection shall be provided to accommodate the estimated velocities in accordance with these regulations and O.D.O.T. Location and Design Manual.
(g) Building Drainage. All building roof drainage and building subsurface drainage shall be conducted in closed conduits to a storm sewer or other approved natural outlet. The conduit shall conform to specifications for A.S.T.M. 3033 (SDR-35) or approved equal and shall be sized in accordance with the following table:
SIZE OF HORIZONTAL STORM DRAINS | |||
Diameter of Drain | Maximum Projected Roof Area For Drains of Various Slopes | ||
1/8 Inch Slope (sq. ft.) | 1/4 Inch Slope (sq. ft.) | ½ Inch Slope (sq. ft.) | |
3 | 822 | 1,160 | 1,644 |
4 | 1,880 | 2,650 | 3,760 |
5 | 3,340 | 4,720 | 6,680 |
6 | 5,350 | 7,550 | 10,700 |
8 | 11,500 | 16,300 | 23,000 |
10 | 20,700 | 29,200 | 41,400 |
12 | 33,300 | 47,000 | 66,600 |
15 | 59,500 | 84,000 | 119,.000 |
An approved clean-out shall be installed at the end of all lines within the right of way and at intervals of 400 feet or less.
Collector lines within the street right of way shall have a minimum inside diameter of six inches. (See subsection (i) hereof for possible exceptions.)
(h) Drainage Easements and Rights of Way. Where ditches, storm sewers or other drainage structures exist or are constructed outside of the dedicated street right of way, written easements of sufficient width, but not less than twenty feet wide, shall be provided to the applicable City, Township or County to ensure proper maintenance and reconstruction.
Where structures are situated essentially within a street right of way, but additional right of way is required to accommodate the structure or provide for proper maintenance, repair, or reconstruction, additional right of way shall be dedicated.
When it is required of the developer to convey surface water outside the limits of the proposed improved area in order to discharge into an approved adequate outlet, it shall be the responsibility of the developer to obtain easements and/or right of way for construction and/or maintenance of such drainage course.
All drainage easements shall be shown on the plat and construction plans. The written drainage easements shall be recorded for public use forever.
(i) Stormwater Management and Control. Stormwater Management and Control for the entire project shall ensure that the peak rate of runoff from the area after development shall not exceed the peak rate of runoff from the same area before development for all storms from a one year to a 100 year frequency, twenty-four hour storm.
(1) The designer shall first determine the total volume of runoff from a one year frequency, twenty-four hour storm, occurring on the area before and after development.
(2) Next, the designer shall determine the percent increase in volume of runoff due to development, and using this percentage, pick the critical storm from the following table:
Table 1
If the percentage of increase in volume of runoff is: | ||
Equal to or greater than: | And less than: | The critical storm for discharge limitation shall be: (years) |
– | 10 | 1 |
10 | 20 | 2 |
20 | 50 | 5 |
50 | 100 | 10 |
100 | 250 | 25 |
250 | 500 | 50 |
500 | – | 100 |
(3) The peak rate of runoff from the critical storm and all more frequent storms occurring on the development area shall not exceed the peak rate of runoff from a one year frequency, twenty-four hour storm occurring on the same area under pre-development conditions. Storms of less frequent occurrence (longer return periods) than the critical storm up to the 100 year storm shall have peak runoff rates no greater than the peak runoff rates from equivalent size storms under pre-development conditions. As an example, if the total volume of runoff is shown to be increased by fifty-eight percent (58%), the critical storm is a ten year storm. The peak rate of runoff for the one, two, five and ten year storms shall be controlled so as not to exceed the peak rate of runoff from a one year frequency storm on the area under pre- development conditions. The runoff from the twenty-five, fifty and 100 year storms need only be controlled to the peak rate of runoff from equivalent size storms under pre-development conditions.
(4) Storage volume does not have to be provided for runoff from off-site upstream areas. Upstream runoff waters should be conveyed through the site in accordance with current runoff conditions.
(5) The following and other approved means may be employed to accomplish the desired Stormwater management and control:
A. Construction of on-site and off-site retention basins or detention basins with restricted outlets or pumps. These basins should, where possible, be constructed to provide for multiple purposes including stormwater control, sedimentation control, fire protection, aesthetics and recreation facilities;
B. Construction of surface storage basins such as backyard and roadway drainage ditches, parking lots, rooftops, etc., with restricted outlets;
C. Construction of subsurface storage structures such as oversized drainage pipes, subbasements, etc;
D. Direct discharge of roof drainage to lawn areas where the flow can be adequately accommodated by an orderly and comprehensive stormwater management program;
E. Retarding flow velocities by increasing friction; for example, grassed road ditches rather than paved street gutters where practical, or grass and rock-lined drainage channels;
F. Grading and use of grade control structures to provide a level of control in flow paths and stream gradients;
G. Induced infiltration of increased stormwater runoff into the soil where practical; for example, constructing special infiltration areas where veils are suitable, retaining topsoil for all areas to be vegetated or providing good infiltration areas with proper emergency overflow facilities;
H. On-stream retention basins with gravity operation of regulated outlets;
I. Side-stream retention basins with gravity operation by regulated outlets or pumped return;
J. Large retention basins with permanent recreation basins either on stream or side-stream with gravity operation by regulated outlets or pumped return with or without drainage area diversion;
K. Stream flow regulation and/or control devices, backwater retention weirs, etc;
(6) The purpose of these required procedures is to:
A. Permit development without increasing the flooding of other lands;
B. Minimize damage to receiving streams caused by accelerated runoff;
C. Provide a basis for design of storm drainage systems or lands above or below undeveloped areas which shall preserve the rights and options of both contributing and receiving property owners and assure the long-term adequacy of storm drainage systems; and
D. Eliminate the need for oversizing storm drainage facilities in anticipation of what may be developed upstream in the future.
(7) A final stormwater management and control plan shall be submitted to the City Engineer and, where applicable, the County Engineer for final approval. Before the final plan is completed, it is encouraged that the design engineer consult the appropriate Engineers so that the plan can be developed in accordance with currently accepted policy and criteria. The final plan shall include all the engineering data required in subsection (a) through (i)(6) hereof, and shall also include:
A. The predevelopment rate of runoff and intensity for the various rainfall frequencies used in the analysis;
B. The hydrologic data of the tributary area, including time of concentration, intensity and runoff coefficients;
C. The location of the proposed retention or detention facility in relation to the tributary area;
D. The inflow hydrographs for the tributary area prior to development for the various rainfall frequencies used in the analysis outlined herein;
E. The critical storm hydrograph based on the criteria outlined herein;
F. The storm hydrographs of the less frequent occurrences to check peak runoff rates;
G. The maximum permitted release rate from the retention or detention facility, that is the outflow hydrograph;
H. The storage volume required for the retention or detention facility;
I. The design of a spillway or other means for release of stored water and for bypassing excess flows of exceedingly rare rainfalls that cannot be accommodated by the storage facility;
J. Provide method for complete and timely drainage of stored runoff by provision of sufficient basin slope, adequate pumping facilities and/or alternate release mechanisms for stored runoff without causing secondary problems;
K. Types of facility for retention or detention such as rooftop, parking lot, park pond, etc; and
L. Safety precautions which shall include fencing, guard railing, maximum side slopes, vegetation and control.
(8) The appropriate County, Township or City shall assume responsibility for permanent maintenance of the major structures and facilities designed to control and manage stormwater runoff. The maintenance of minor detention areas, generally grassed areas which are portions of individual lots, shall be the responsibility of individual owners. Special covenants shall be written into the title of individual lots so that the owners are aware that portions of their property shall be used for temporary water storage.
(9) Ownership and/or easements for the purpose of maintenance shall be granted to the appropriate governmental subdivision for access to all major stormwater control structures and facilities for which the subdivision is assuming permanent maintenance responsibility.
(10) Financing of the permanent maintenance of the major stormwater control structures and facilities shall be handled through a "perpetual maintenance agreement" whereby all *benefitting property owners in the drainage area shall be assessed their proportionate share of the maintenance costs. These assessments shall be certified in accordance with appropriate sections of the Ohio Revised Code. (Ord. 39-81. Passed 10-7-81.)
*Legal definition.