This section is adopted for the purpose of controlling accelerated stormwater runoff from development areas and to provide minimum design standards for stormwater management facilities. The development of stormwater management facilities and maintenance of new and existing facilities shall be covered under the following requirements
(a) Storm water retention and/or detention shall be required for the prevention of accelerated flooding and stream channel erosion in conjunction with urban development. The City Engineer is hereby granted and vested with the authority to establish standard design criteria which will be utilized for the review and approval of detention/retention facilities. The purpose of this storm water detention basin design criteria is to:
(1) Permit commercial, industrial and residential development without increasing the flooding of other lands.
(2) Limit and/or reduce the adverse impact on receiving streams, storm sewers, and other drainage facilities caused by accelerated runoff.
(3) Provide a basis of design of storm drainage systems on lands above or below undeveloped areas which will preserve the rights and options of both contributing and receiving property owners and assure the long-term adequacy of storm drainage systems.
(b) The Design Criteria will require that peak discharge flow be controlled in proportion to increased runoff volume. If development does not increase runoff volume, peak flows will not be required to be controlled. However, as development increases the runoff volume due to increased area of impervious surfaces, the criteria will be more stringent.
(1) The design and construction of stormwater management facilities shall require the review and approval of the City Engineer.
(2) Allowable types of stormwater management facilities include but are not limited to:
A. Retention ponds.
B. Detention basins.
C. Underground storage tanks.
D. Rooftop storage areas.
E. Parking lot storage areas.
F. Infiltration/recharge ditches.
G. Swales/buffer strips.
(3) All project sites or development areas required to implement stormwater management practices and facilities shall at a minimum limit the peak rate of discharge from the project site or development area to the downstream receiving water course as follows:
A. Stormwater management measures shall be required to maintain the post-development peak discharge at a level equal to or less than the predevelopment peak discharge rate for a 24-hour duration, two-year frequent storm event, and:
B. Stormwater management facilities shall be designed to control the volume, timing and rate of flows.
(4) Velocity reduction devices must be placed at all outlet points, where necessary, to provide a non-erosive flow velocity to the receiving water course. The City Engineer may waive these requirements if the characteristics of the receiving water course, project site, or development area are such that this type of control would be contrary to accepted engineering practice or detrimental to the environment.
(c) Construction of Storm Water Detention/Retention Facilities.
(1) The construction of a stormwater management facility which impounds water and is made by constructing a dam or an embankment or by excavating a pit or dugout shall be designed and meet the requirements of the United States Department of Agriculture, Soil Conservation Service, Agricultural Handbook Number 590 as supplemented by the standards provided in Soil Conservation Service, State of Ohio Engineering Standard, Technical Guide Section IV, Pond (No.) - 378. The Ohio Dam Safety Laws, Title XV, Chapter 1521 of the Ohio Revised Code, shall be reviewed for compliance. The subdivider shall submit construction plans and details for the storm management facility.
(2) The subdivider shall also submit topographic map showing area served by the stormwater facility with calculations prepared by a registered civil engineer on the design discharge of storm sewers and design criteria for the facility (e.g.. depth, volume, spillway discharge etc.). The plans and calculations shall be checked and approved by the City Engineer.
(d) Maintenance of Storm Water Detention/Retention Facilities and Existing Ponds.
(1) Maintenance of storm water management facilities which impound water and existing ponds are the responsibility of the property owner. For the protection of life, health and property of the general public the City has established the following minimum maintenance requirements for all facilities and ponds located within the City of Twinsburg.
(2) If compliance with minimum maintenance requirements on stormwater facilities or existing ponds is not met the City may enforce penalties listed in Section of the City of Twinsburg Zoning Ordinance.
(3) The following items list minimum maintenance requirements of the City of Twinsburg.
A. Ponds shall be inspected on an annual basis and after heavy rains to determine whether it is functioning properly or needs minor repairs.
B. Repair to walls on the side slopes of the dam and any washes in the spillway immediately with suitable material and compact it thoroughly. Reseed or resod these areas and fertilize as needed.
C. If the upstream face of the earthfill show signs of serious washing or sloughing because of wave action, install protective devices such as booms or riprap.
D. If there is evidence of seepage through or under the dam, consult an engineer at once so that you can take proper corrective measures before there is any serious damage.
E. To maintain the protective plant cover on the dam and on earth spillway, mow it frequently and fertilize when needed.
F. Keep trickle tubes, trash rocks, outlet structures, valves and watering troughs free of trash at all times.
G. Burrowing animals such as badgers, gophers, ground hogs, etc. can cause severe damage to dams or spillways. Such damage shall be immediately repaired. Recommended preventable measures are during construction a heavy layer of sand or gravel on fill may be placed or poultry netting under seeded areas may be installed.
H. Ponds shall be maintained as clean and unpolluted as possible. In ponds that have a significant growth of algae and other forms of plant life and become objectionable because of odors, mosquitoes breeding, etc., the property owners shall initiate management practice to remove these problems. Stocking of ponds with top feeding fish is one possible practice.
I. The recommended minimum pond depth for this area of the country per the United States Department of Agriculture is six (6) to seven (7) feet. Existing ponds which have excessive sediment shall be dredged to maintain the minimum pond depth.
(Ord. 173-2000. Passed 12-17-00.)