(A) All subdivisions shall have an engineer designed and Commission-approved drainage system plan which shall include full details of all surface and/or subsurface improvements. Design of the drainage system plan and stormwater management facilities shall be in accordance with current and best engineering practices. The standards for the design shall be adequate for the soils within the site as well as meet applicable local, state, and federal requirements in existence at the time of subdivision approval.
(B) Proposed final drainage plan for the subdivision, which shall include symbolic representation of direction of flow of surface runoff along all property lines. The plan shall be drawn to the scale of one inch equals 100 feet. The subdivision drainage plan shall include computations indicating all flows currently entering the subdivision, the current runoff from the subdivision area and anticipated runoff when fully developed. Computations shall be made for both ten-year and 100-year flows. Drainage facilities shall be provided to accept and convey existing flows. All on-street drainage shall be captured in inlets or catch basins designed in accordance with the standard practices of the Illinois Department of Transportation of Local Roads and Streets and shall be conveyed by storm sewer capable of carrying the ten-year storm. Easements forbidding permanent structure shall adequately provide for the conveyance of the 100- year storm wherever it may occur within the subdivision. Methods of conveyance may be by combination of storm sewer and open drainageway for the 100-year storm.
(C) Where the proposed construction lies within a subdivision which has an approved final drainage plan, all grading on the property shall be completed in accordance with that plan. A drainage plan shall be submitted for any development requiring a building permit, or construction of a parking lot or other surfaced area exceeding 1,000 square feet, except one- and two-family dwellings. Such plans shall include computations indicating all flows currently entering the lot on which the development is proposed, the current runoff if fully developed. Computations shall be made for both ten-year and 100-year flows. Drainage facilities shall be provided to accept and convey existing flows. Easements forbidding permanent structures shall adequately provide for the conveyance of the 100-year storm wherever it may occur within the development site. No owner, developer, or contractor shall initiate building or parking lot construction prior to receipt and approval of such plans by the city Building Inspection Department.
(D) Whenever agricultural tiles are located within a subdivision which drains an area outside of the subdivision, the developer shall dedicate an easement not less than ten feet in width along each side of the agricultural drainage tile for purposes of maintenance, improvements or replacement of the tile. Tiles may be relocated but shall be placed in easements or contained within public rights-of-way. The developer shall be responsible for relocating all agricultural field tile in the subdivision that services any area located outside the subdivision. New tile must replace all disturbed agricultural tile. Relocated tile shall retain the design flow of the original tile. Agricultural drainage tiles which drain an area outside of the subdivision shall remain a separate system and not incorporated into the subdivision surface and/or subsurface system, except that a connection may be permitted where the flow entering the agricultural tile system is not increased beyond the flow of the site in its present natural undeveloped state. There shall be no connection between a septic system, storm sewer, road drainage system, or sink to any agricultural field tile unless approved by the Coles County Health Department. The Planning Commission may require the subdivider to take those actions necessary for the purposes of discovery of the agricultural drainage tile. Agricultural drainage tiles shall, where possible, be aligned in easements located along property lines. Tiles crossing potential building pads and septic system locations shall be relocated or the lot designed to avoid such potential conflict.
(E) Design flows for roadside ditches shall conform to the requirements of the Illinois Department of Transportation’s Bureau of Design, Design Manual, latest amended edition; however, at a minimum, such ditches shall be designed to accommodate the maximum discharge from a storm of 20-year frequency. Stormwater sewers which serve as main or terminal collectors shall be of sufficient design to accommodate a maximum discharge from a storm of ten-year frequency. Those storm sewers which serve as laterals shall be of sufficient design to accommodate a maximum discharge from a storm of five-year frequency.
(F) The filling, alteration, widening or any other restriction or alteration of a natural stream and flood basin shall be permitted only as shown upon the final approved engineering drawings. Where erosion occurs along stream side slopes, whether caused by alteration or natural occurrence, suitable erosion controls shall be instituted by the developer. All disturbed areas will be seeded, fertilized, and mulched to prevent soil loss in excess of tolerable soil loss limits as defined by the U.S. Soil Conservation Service. Temporary erosion control measures will be used during the time of development to control excess soil erosion caused by development activities. Permanent measures will be installed as well where needed. Where such occurrences exist on stream slopes exceeding 12%, said slopes shall be contained and dedicated in a natural easement.
(G) Where roadway ditches or swales are permitted, such ditches or swales shall be completely included within the road rights-of-way. Where ditch or swale integrity requires additional protection, additional easements may be required either permanently or during construction. Unless lesser standards are approved due to special circumstances, drainage shall be improved as follows:
(1) Slopes: both front slopes and back slopes shall not exceed a four to one ratio slope; and
(2) Grades: with grades to 4%, ditches may have sod bottoms and banks; where ditch grades of 4% to 8% occur, gradient control structures shall be used to maintain the ditch slope at 4% or less; with greater than 8% grades, ditches or swales shall have riprap or be paved.
(H) Where crossroad culverts occur, the rights-of-way shall be sufficient to include any headwall or similar structure.
(I) Floodplain data used in all design work shall be as per Ordinance No. 87-4532, “An Ordinance Regulating Development in Special Flood Hazard Areas.”
(Ord. 88-4582, passed 10-18-1988; Am. Ord. 96- 4850, passed 5-21-1996; Am. Ord. 2011-5341, passed 12-20-2011)