For the purpose of these regulations, the term Flood Plain or Flood Area is an area subject to flooding due to a Natural Occurrence.
(a) Flood Areas. In order to protect the health, safety and general welfare of the people, the Commission shall reject any proposed subdivision located in an area subject to periodic flooding. If the subdivision is located in an area having poor drainage or other adverse physical characteristics, the Commission may approve the subdivision provided the subdivider agrees to perform such improvements as will render the area safe for the intended use. The subdivider shall furnish a surety covering the total cost of the required improvements. Such surety shall be posted with the Commission.
(b) Regulatory Flood Plain. For the purpose of these regulations, the Regulatory Flood Plain is an area subject to flooding based on the 100 year flood. The 100 year flood is that which has a one percent (1%) chance of occurring in a given location in any single year.
(c) Parts of a Regulatory Flood Plain and Allowed Uses Within Each Part.
(1) Channel. A natural or artificial watercourse that confines and conducts sustained or intermittent streamflow.
(2) Floodway. The Channel and those parts of the adjoining flood plain that are reasonably required to carry and discharge the 100 year flood without a substantial increase in stage.
Allowed Use: Recreational and Open Space.
(3) Floodway fringe. The area within the regulatory flood plain that is out side the floodway. The floodway fringe serves primarily as a backwater storage area.
Allowed Use: Recreational, Open Space and construction of unoccupied structures.
(d) Reason for Controls. To help ensure the general public from loss of life, damage to property and to help create a better environment in which to live.
(e) Responsible Official for Determining Various Parts of a Natural Floodplain. The Mahoning County Engineer shall determine the limits of the various parts of a natural floodplain.
(f) Access. Access to flood control, storm drainage ditches and channels shall be by means of easements whenever dedication of right of way is not possible. Such easements shall be not less than thirty feet in width, exclusive of the width of the ditch or channel and such easement of this type shall be provided on one side of a flood control, storm drainage ditch, channel or similar type facility. (See Section 1107.06
(e)).
(g) Safety. In order to help protect the health, safety and general welfare of the residents within the area of a flood control, storm drainage ditch or channel, the Commission may require the subdivider to construct an appropriate fence or masonry wall adjacent to or surrounding the above mentioned improvements.
(h) National Flood Insurance Program. The National Flood Insurance Program, Section 1910.3(d) for the unincorporated areas of Mahoning County will be utilized by the Commission.
(1) The Single Purpose Flood Plain Management Regulations adopted by the Mahoning County Board of Commissioners on February 15, 1979-Commissioners Journal, Volume 67; Page 116 will be used as a planning tool.
(Ord. 88-1. Passed 6-23-88.)
APPENDIX A: TABLE OF PERMISSIBLE VELOCITIES FOR FLOWING WATER
MAXIMUM VELOCITIES FOR GRASSED WATERWAYS
Permissible Velocity 1/ | |||
Cover | Slope Range 2/ | Erosion Resistant Soils (Ft. Per. Sec.) | Easily Eroded Soils (Ft. Per. Sec.) |
Kentucky bluegrass | 0-5 | 7 | 5 |
Tall fescue | 5-10 | 6 | 4 |
Smooth brome | over 10 | 5 | 3 |
Grass mixtures | 2/0-5 | 5 | 4 |
Reed canary | 5-10 | 6 | 3 |
Redtop | 3/ | ||
Red fescue | 0-5 | 3.5 | 2.5 |
1/ Use velocities exceeding five feet per second only where good cover and proper maintenance can be obtained.
2/ Do not use slopes steeper than ten percent (10%) except for vegetated side slopes in combination with a stone, concrete, or highly resistant vegetative center section.
3/ Do not use slopes steeper than five percent (5%) except for vegetated side slopes in combination with a stone, concrete, or highly resistant vegetative center section.
MAXIMUM VELOCITIES FOR VEGETATED STREAM CHANNELS
Drainage Areas Less Than One Square Mile
The maximum permissible design velocity shall be based on site conditions and shall be such as to result in stability of the ditch bottoms and side slopes. Maximum permissible velocities will be computed using bank-full stage of ten-year frequency stage whichever is lower. The following table will be used as maximum velocity for all drainage main or lateral designs. Vegetation will be established immediately after construction.
SUBSOIL TEXTURE | MAXIMUM VELOCITY 4/ (Ft. Per. Sec.) |
Sand and sandy loam (non colloidal) | 2.5 |
Silt loam (also high lime clay) | 3.0 |
Sandy clay loam | 3.5 |
Clay loam | 4.0 |
Stiff clay, fine gravel and graded loam to gravels | 5.0 |
Graded silt to cobbles (colloidal) | 5.5 |
Shale, hardpan, coarse gravel | 6.0 |
Drainage Areas Greater Than One Square Mile
Channel velocities for newly constructed channels with drainage areas in excess of one square mile shall meet special stability requirements contained in U. S. Soil Conservation Service Technical Guide (Technical Release 25, Planning and Design of Open Channels).
4/ Channels that cannot be designed to meet the maximum velocity limitations must be stabilized with materials other than vegetation. Such materials include crushed rock, concrete, gabions, etc.
PARTS OF A TYPICAL OHIO FLOOD PLAIN
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MAJOR THOROFARE PLAN
MAHONING COUNTY, OHIO
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