The subdivider shall be required to design and construct an adequate stormwater drainage system. This may be comprised of a natural drainage system, a storm sewer system or a combination natural drainage and storm sewer system. Stormwater drainage systems shall meet the following design standards and shall be shown on the Drainage Plans, as required in § 153.062.
(A) Onsite drainage facilities shall be designed to accommodate:
(1) The effect of water runoff from the parcel after development on downstream drainage areas;
(2) The present water runoff from developed and undeveloped areas upstream; and
(3) That part of the water runoff attributable to future development in undeveloped areas upstream, which is not reasonably likely to be accommodated in such upstream areas.
(B) All stormwater drainage systems shall be separate and independent of any sanitary sewer system.
(C) Natural drainage patterns and natural stream channels shall be maintained wherever possible.
(D) Storm sewers, where required, shall be designed according to accepted engineering practice and the standards of this chapter.
(E) Inlets shall be provided so that surface water is not carried across any intersection, nor for a distance in the gutter greater than that indicated by the design computations submitted with the construction plans. When calculations indicate that curb capacities are exceeded at a point, no further allowance shall be made for flow beyond that point. Surface water drainage patterns shall be shown for each and every lot and block.
(F) All lots, tracts or parcels shall be designed and graded to provide proper drainage away from the buildings and dispose of it without ponding, and all land within the development shall be graded to drain and dispose of surface water without ponding, except where approved by the Administrator. Around each permanent building foundation there shall be a slope with a minimum vertical fall of six inches for the area measured from the foundation to a point ten feet from the building foundation or to the property line, whichever is closer.
(G) (1) All drainage provisions shall be of such design to adequately handle the surface runoff and carry it to the nearest suitable outlet such as a curbed street, storm drain, or natural watercourse.
(2) Where drainage swales are used to divert surface water away from buildings, they shall be sodded or planted as required and shall be of such slope, shape, and size as to conform with the requirements of the Plan Commission.
(H) Concentration of surface water runoff shall only be permitted in swales or watercourses.
(I) Land alteration shall be accomplished in such a way that the grades left at the time that the work is completed will be permanent and stable.
(J) The Plan Commission may require retention ponds to regulate the flow at the outfall. The ponds shall be protected from erosion and shall be designed and constructed to enable adequate access for maintenance. Plans for maintenance shall also be specified.
(K) Excavation and fills shall meet the following standards.
(1) Cut and fill slopes shall not be steeper than a three to one ratio unless stabilized by a retaining wall or cribbing as approved by the Administrator when handled under special conditions.
(2) Provisions shall be made to prevent surface water from damaging the cut face of excavations or the sloping surfaces of fills, by installation of temporary or permanent drainage across or above this area.
(3) Cuts and fills shall not endanger adjoining property.
(4) Fill shall be placed and compacted so as to minimize sliding or erosion of the soil.
(5) Fills shall not encroach or impede flows on natural watercourses or constructed channels.
(6) Fills placed adjacent to natural watercourses or constructed channels shall have suitable protection against erosion during this period of construction.
(7) Grading will not be done in such a way so as to divert water onto the property of another land owner without the expressed consent of the Administrator and other land owner.
(8) During grading operations, necessary measures for dust control will be exercised.
(9) Grading equipment will not be allowed to cross live streams. Provision will be made for the installation of temporary or permanent culverts or bridges.
(L) No subdivider or person, corporation, or other entity shall block, impede the flow of, alter, construct any structure, or deposit any material or thing, or commit any act which will affect normal or flood flow in any communal stream or watercourse or drainage system without having obtained prior approval from the County Drainage Board and/or DNR.
(M) It is the responsibility of the subdivider and any person, corporation, or other entity doing any act on or across a communal stream, watercourse, or swale, or upon the floodplain, floodway, or floodway fringe area of any watercourse during the period of development to return these areas to their original, or equal, conditions upon completion of the activities.
(N) Whenever sedimentation is caused by stripping, vegetation, regrading, or other development activities, it shall be the responsibility of the subdivider, person, corporation or other entity causing such sedimentation to remove it from all adjoining surfaces, drainage systems and watercourses and to repair any damage at his or her expense as quickly as possible.
(O) Connection to a state drainage system is allowed only with written approval from the State Highway Department. Connection to a county legal drain is allowed only with written approval from the County Drainage Board. Connection to a county road ditch is allowed only with written approval from the County Engineer.
(P) The Plan Commission shall not approve any subdivision for which adequate provision for maintenance of drainage systems has not been made. Such provision may include, but is not limited to, acceptance of the system as a rural or urban legal drain by the County Drainage Board, or establishment of a lot owners association with responsibility to set and collect fees for drainage system maintenance.
(Q) (1) If designated as a legal drainage system, all storm sewers, structures, and designated surface drains within the subdivision shall become part of the legal drainage shed.
(2) Subdivision lots shall be assessed an annual drainage maintenance fee by the office of the County Treasurer.
(Prior Code, § 152.098) (Ord. 87, passed 4-18-1988)