(a) Drainage. A drainage system shall be designed and constructed by the developer to provide for the proper drainage of the surface water of the Development and the drainage area of which it is a part. To this end, the following requirements and methods shall be followed:
(1) Drainage requirements (Grading). No final grading or sidewalk or pavement construction or installation of utilities shall be permitted in any proposed street until the final plat has been approved or conditionally approved. The developer shall grade each Development in order to establish street, block and lot grades in proper relation to each other and to topography, as follows:
A. Block and lot grading.
1. Block grading shall follow the approved Development Grading Plan.
2. Lot grading shall be as follows:
a. Lots shall be graded so that water drains away from each building at a minimum grade of two percent.
b. Surface drainage swales shall have a minimum grade of one-half percent and shall be designed so that surface water will drain into a driveway, street gutter, storm sewer, drain inlet or natural drainage way.
c. The minimum grades of driveways shall be four-tenths percent and a maximum of fifteen percent.
(2) Drainage system requirements. The design criteria for the drainage systems shall be based on the State of Ohio Department of Transportation, Manual of Location and Design. Runoff or design Discharge for sewer design where the contributing area generally consists of pavement and a narrow strip back of the pavement shall be obtained from the rational formula: Q = CIA. The following minimum design frequencies are to be used:
A.
Roadway ditches | 2 years |
Storm sewers | 5 years or 10 years |
Culvert under roadways | 25 years |
Watercourses | 10 years |
B. Runoff Coefficients and rainfall frequencies based on general character of tributary area are set forth in the following table:
Description of Area | Rainfall Frequency (years) | Range of Runoff Coefficient | Coefficient Used Herein |
Open Space - Conservation | 5 | 0.25 - 0.40 | 0.30 |
Rural Residential | 5 | 0.25 - 0.40 | 0.30 |
Low Density Urban Residential | 5 | 0.30 - 0.50 | 0.40 |
Medium Density Urban Residential | 5 | 0.30 - 0.50 | 0.50 |
High Density Urban Residential | 5 | 0.30 - 0.50 | 0.50 |
Multifamily Urban Residential | 5 | 0.40 - 0.60 | 0.60 |
High Density Multifamily Urban Residential | 10 | 0.50 - 0.70 | 0.60 |
High Density Multifamily/Commercial Urban Res. | 10 | 0.50 - 0.70 | 0.60 |
Local Commercial | 10 | 0.50 - 0.70 | 0.50 |
Description of Area |
Rainfall Frequency
(Years)
Range of Runoff
Coefficient
Coefficient Used
Herein
Office and Limited Business
10
0.50 - 0.70
0.50
Community Commercial
10
0.70 - 0.90
0.80
Central Retail - Office
10
0.70 - 0.90
0.90
Intensive and Automotive Oriented Commercial
10
0.70 - 0.90
0.90
Highway Interchange Commercial
10
0.70 - 0.90
0.80
Industrial Research and Office
10
0.50 - 0.70
0.60
Industrial
10
0.40 - 0.90
0.60
Manufacturing, Storage and Disposal
10
0.40 - 0.90
0.60
Railroad Yard Areas
10
0.20 - 0.40
0.30
(b) Post Development runoff shall not exceed pre-development runoff for the 2, 10, 25, and 100 year design storms.
(c) Road Drainage System. The road storm drainage system shall serve as the prime drainage system. It shall be designed to carry roadway, adjacent land and house Storm Water drainage.
(1) Road storm sewers (enclosed). The design Discharged used to determine pavement inlet spacing shall be based on the rational method mentioned in this subsection (e)(2). The gutter flow between inlets shall be calculated by the equation: Q =.56Z/N S1/2 F8/3. (See Manual of Location and Design.)
(2) The inlet spacing shall be based on a ten year frequency, fifteen minutes duration design storm. The spread of water on the pavement shall be limited to two feet into the traveled lane. In addition, standard manholes or combination manhole inlets for cleaning purposes shall be placed no further than 300 feet apart.
(3) Storm sewer laterals. A storm sewer lateral shall be provided for each lot to accommodate footer drains and downspouts. Storm laterals (same material specification as sanitary laterals) should be a minimum of 4" in diameter with an absolute minimum slope of 0.5% and 18" of cover.
(d) Off-Road Drainage Systems. The design of the off-road drainage system shall include the watershed affecting the allotment and shall be extended to a watercourse or ditch adequate to receive the storm drainage.
(1) All watercourses or ditches with a design capacity not exceeding the capacity of a thirty-six inch concrete pipe shall be enclosed. Existing creeks or ditches constructed by the developer which exceed the above limit shall be constructed with a minimum fifteen (15) foot wide continuous earth roadway to provide access for maintenance equipment to all sections of the ditch. The ditch easement may be wide enough to contain such ditch slopes and roadway with ample clearance for the operation of maintenance equipment. Open ditches will have a side slope ratio of 2:1 and a minimum two (2) foot bottom width.
(2) No open ditch shall be constructed within 100 feet of the rear building line of a house, as measured from the house to the edge of the ditch easement.
(3) Any storm drainage courses carried along side lot lines shall be enclosed with approved pipe.
(4) Easements for drainage purposes shall be a minimum of twenty feet in width. Where the watercourse is large, easement widths shall be increased as determined by the Development Engineer.
(e) Protection of Drainage Systems. The developer shall adequately protect all ditches (roadways and watercourses) to the satisfaction of the Development Engineer or his designee as follows:
(1) All adjoining land where the vegetation has been injured or destroyed or where the land is in need of protection to prevent erosion, deposits in the drainage facilities and/or unsightly conditions shall be restored and protected as directed by the Development Engineer or his designee.
(2) In all cases, any drainage facility shall be in a stable condition, free from either erosion or sedimentation and/or other debris.
(3) No construction shall begin until the developer has complied with all of the provisions of the Kent City Codified Ordinances, and obtained all permits required by the Ohio Environmental Protection Agency and the Army Corp of Engineers.
(4) All storm sewer inlets that accept water runoff from the Development area shall be protected so that sediment-laden water will not enter the storm sewer, unless exempted by the Director or unless the storm system drains to a Sediment Settling Pond. In areas where construction will be ongoing, such as subdivisions, the storm sewer protection shall be maintained until all upsloped areas reach Final Stabilization, as determined by the Director.
(5) The developer shall hydraulically clean the storm sewers at the time of dedication and provide videotape to the satisfaction of the Director. All sediments shall be removed from the system and shall not be flushed downstream.
(6) All storm sewers, footer drains, roof gutter drains and all other drains will be outletted at the bottom of the slope. The slope below the outlet shall be able to control the water being drained through the storm sewer or other drains without causing erosion of the stream or channel banks or channel bottom.
(f) Pipe Policy. The City of Kent Construction Standards and Construction Drawings, as approved by the Service Director.
(g) Storm Water Basins:
(1) Pool Geometry: The minimum length-to-width ratio for the pond is 3:1 (the length will be three (3) times the width).
(2) Riser in Embankment: The riser shall be located within the embankment for purposes of maintenance access. Access to the riser will be by manholes.
(3) Water Drains: Each retention and water quality basin shall have a drainpipe that can completely drain the pond. The drain shall have an elbow within the pond to prevent sediment deposition from plugging the drain.
(4) Principal Spillway: Each principal spillway shall be designed in accordance with the Natural Resources Conservation Service (NRCS) standards and specifications for the office serving Portage County, Ohio. Each principal spillway shall have the capacity to pass the 100 year design storm flows. The inlet or riser size for the pipe drops shall be designed so that the flow through the structure goes from weir flow control to pipe flow control without going into orifice control in the riser. The crest elevation of the primary spillway shall be no less than one foot below the emergency spillway crest. Premium joint pipe is required and a removable trash rack shall be installed at each location. Anti-seep collars shall be provided for all pipe conduits through an embankment.
(5) Emergency Spillway: An emergency spillway shall be provided on each Storm Water management and water quality basin. Emergency spillways shall convey flood flows safely past the embankment, and shall be designed in accordance with NRCS standards and specifications for the office serving Portage County, Ohio. Excavated spillways shall have a 100 year design storm capacity unless exempted in writing by the Director.
(6) Non-Clogging Low Flow Orifice: A non-clogging orifice shall be provided for the Water Quality Basins.
(7) Embankments: Each dam embankment shall be designed in accordance with the NRCS standards and specifications for the office serving Portage County, Ohio. Anti-seep collars shall be provided for all pipe conduits through an embankment.
(8) Safety Features: The perimeter of all water pool areas that are deeper than three (3) feet shall be surrounded by benches that meet the following:
A. A safety bench, with a maximum slope of 3%, which extends outward, on dry land, from the shoreline. This bench will be a minimum of 25 feet wide to provide for the safety of individuals and maintenance vehicles that are adjacent to the water pool. The safety bench may be landscaped to prevent access to the water pool.
B. Side slopes between the safety bench and the aquatic bench shall not be steeper than 3:1 (3 feet horizontal for every 1 foot vertical).
C. An aquatic bench that extends inward from the shoreline far enough to ensure public safety and has a maximum depth of 15 inches below the normal water surface elevations. The aquatic bench may be landscaped to prevent access to the deeper water pool.
D. Side slopes beyond the aquatic bench and below the permanent water level hall not be steeper than 2:1 (2 feet horizontal for every 1 foot vertical).
E. The contours of the pond will be designed and managed to eliminate drop-offs and other hazards. Side slopes getting to the pond shall not exceed 3:1 and shall terminate on a safety bench.
F. The primary spillway opening shall not permit access to the public and other non-maintenance personnel.
(h) These standards are general guidelines and shall not limit the right of the Director to impose at any time additional, more stringent requirements, nor shall the standards limit the right of the Director to waive, in writing, individual requirements.
(i) Methods for controlling increases in Storm Water runoff peaks and volumes may include, but are not limited to:
(1) Retarding flow velocities by increasing friction; for example, grassed road ditches rather than paved street gutters where practical, discharging roof water to vegetated areas, or grass and rock-lined drainage channels.
(2) Grading and use of grade control structures to provide a level of control in flow paths and stream gradients.
(3) Induced infiltration of increased Storm Water runoff into soil, where practical;
(4) Provisions for detention and retention; for example, permanent ponds and lakes with Storm Water basins provided with proper drainage, multiple-use areas for Storm Water detention, recreation, wildlife or transportation, or subsurface storage areas.
(Ord. 2017-17. Passed 3-15-17.)