(A) The subdivider shall design and construct a storm drainage system adequate to handle maximum potential flows of water drainage from the subdivision or passing through the subdivision without causing hazard for life or property within the subdivision or surrounding land areas. All storm systems shall be designed and constructed according to the preliminary plat and shall consider the appropriate streets, storm sewers, roadway ditches, grassed swales, natural watercourses, catch basins and inlets, as may be required. All such facilities should be complimentary in design and construction. In general, all areas shall be required to install storm sewers.
(B) Whenever practical, natural open drainage ways shall be utilized as part of the subdivision storm drainage system. Whenever a natural stream or other human-made important surface drainage course or agricultural drainage tiles are located within a subdivision, the subdivider shall dedicate an adequate easement along each side of the stream or tile for purposes of widening, deepening, sloping, improving or protecting the stream or tile for drainage or flood water retention.
(C) The filling, alteration, widening or any other restriction or alteration of a natural stream and flood basin shall be permitted only as shown and approved on the preliminary plat. In areas where stream slopes exceed 12%, such slopes shall either be graded, stabilized by rip-rapping or some sort of planting or shall be dedicated as a natural easement.
(D) Where roadway ditches or swales are permitted, such ditches or swales shall be contained within easements at least ten feet wide and the drainage shall be improved as follows.
(1) With grades to 4%, ditches may have sod bottoms and banks.
(2) With grades from 4% to 8%, ditches or swales must have ditch checks.
(3) With greater than 8% grades, ditches or swales must have rip-rap or be paved.
(4) The filling, alteration, widening or any other restriction or alteration of a roadway ditch or swale shall not be permitted without prior written approval of the Village Board.
(5) No shrubbery, fence or other such structure shall be planted or constructed in or over any drainage ditch or swale in such a manner which would impede the flow of water and storm runoff through these ditches and swales.
(E) (1) Culverts. When allowed, pipe culverts may be used. The minimum length of culverts shall be at least equal to the distance from edge of shoulder to edge of shoulder, plus six times the vertical distance from the edge of should to the flow line of the culvert. No culvert shall have a diameter of less than 12 inches. In no case shall driveway culverts be less than 20 feet in length.
(2) Bridges. All bridges and culverts having a span of more than ten feet shall be approved by the Bridge Engineer, Department of Public Works and Buildings, Division of Highway of the state.
(3) Storm sewers. The sewer system shall be designed by the Rational Method, with self- cleaning velocities as follows. (See § 154.103 of this chapter.)
(a) The part of the system which serves as main or terminal collectors shall be of sufficient capacity to carry the maximum storm water flows which may occur in a ten-year period.
(b) That part of the system which serves as lateral collectors, and which can readily be augmented by future additions, shall be of sufficient capacity to carry maximum storm water flows which may occur in a five-year period.
(c) The engineer shall select coefficients of run-off based on the types of development anticipated in all parts of the watershed affecting the drainage structure. Information regarding future development of the watershed shall be obtained from the Planning Director.
(d) The system shall include all necessary appurtenances such as inlets, catch basins and manholes as may be required for proper operation and maintenance. The sizing of such structures and spacing should provide that encroachment into the street not exceed eight feet from the back curb, and that the head on top of the grate be no higher than the top of the curb or six inches, whichever is the least dimension.
(e) Where the main storm sewer serving a subdivision can be expected to carry a substantial amount of storm water from adjoining lands higher in the drainage area, and where the run- off from these lands can be expected to increase in the future because of more intense development, the developer may be permitted to substitute for such sewer an open ditch. Such ditch shall comply with grading, seeding and sodding specifications of this chapter, and such ditch shall be located on a drainage easement of sufficient width to permit its proper maintenance and to allow the eventual construction of an underground storm sewer adequate to serve the entire drainage area above the subdivision.
(f) All storm sewers shall be at least 12 inches in diameter and shall be of material and construction approved by the Village Engineer.
(g) All materials for the construction of bridges, culverts, storm sewers, catch basins, manholes, inlets and other facilities shall be approved by the Village Engineer.
(4) Over-sized storm sewers. If greater than 24-inch diameter sewers are required to handle the contemplated flows, the cost of such larger sewers shall be shared between the developer and the village. The developer shall be responsible for the cost of furnishing and installing a sewer of an appropriate size for his or her development, and the village will be responsible for the incremental increase in cost to install the larger sewer.
(5) Underdrain system for sump pump discharge. Whenever natural topography does not allow the flow of ground water from individual sump pumps to be directly discharged into a natural watercourse, the developer shall provide an underdrain system at curb side to provide an outlet for the discharges. The drain system shall consist of a six-inch rigid PVC pipe, constructed in a trench immediately behind the curb. The pipe shall be laid to a minimum depth of three feet, six inches from top of pipe of top of curb. The trench shall be backfilled with aggregate to the bottom of the curb. Pipe and aggregate backfill shall be in accordance with the applicable provision of § 607 of the Standard Specifications for Road and Bridge Construction, State of Illinois. Each lot will be provided with a two- inch riser pipe for future connection of a sump pump discharge line. Each riser’s location shall be duly noted on record drawings provided by the developer.
(2007 Code, § 34-7-8)