The Commission shall not approve any subdivision which does not make adequate provision for installation and maintenance of an adequate storm water drainage system. A drainage plan shall be submitted with all computations and backup data describing the storm drainage system. This report shall be reviewed by the County Engineer and County Surveyor who shall make recommendations regarding it to the Commission.
(A) Methodology. The storm water drainage system shall be separate and independent of any sanitary sewer system. The storm water drainage system shall be designed by the Rational Method or other method approved by the County Engineer and a copy of the design computations shall be submitted with the plans. Inlets shall be provided so that surface water is not carried across or around any intersection, nor for a distance of more than 600 feet in a gutter, or when the encroachment of storm water into the street disrupts traffic. When calculations indicate that curb capacities are exceeded at a point, no further allowance shall be made for flow beyond that point and catch basins or inlets shall be used to intercept flow at that point. Surface water drainage patterns shall be shown for each lot and block.
(1) Runoff. Drainage systems shall be designed so that there is no increase in the rate of runoff leaving the property involved in the subdivision after development. The County Engineer shall review the proposed drainage facilities and provide the Commission with an opinion as to whether the system is of sufficient size, based upon the provisions of the required construction standards and specifications assuming conditions of maximum potential watershed development permitted by the Zoning Ordinance.
(2) Downstream areas. The applicant shall provide information for review by the Department and County Engineer regarding the effect of each proposed subdivision on existing drainage facilities outside the area of the subdivision. Where it is anticipated that the additional runoff incident to the development of the subdivision will overload an existing downstream drainage facility, the Commission shall not approve the subdivision until provision has been made for the improvement of the potential condition.
(3) Areas of poor drainage. Areas which are not in designated floodway or floodway fringe areas, but contain soils which are subject to flooding may be approved for subdivision by the Commission; provided that, the applicant fills the affected areas of the subdivision to an elevation sufficient to place building sites (including septic system locations) and streets two feet above ponding levels.
(B) Drainage patterns. Natural drainage patterns and natural stream channels shall be maintained wherever possible.
(C) Blocks and lots. Each block shall be adequately drained, either through the streets or by the use of a ditch, culvert or other approved method. Each lot shall be graded in accordance with the standards set forth in the Erosion Control Handbook.
(D) Streets. All roads abutting or included within property to be subdivided shall be provided with drainage systems in accordance with the standards contained in this chapter.
(E) Erosion control. Any disturbed or graded area shall be protected from erosion in accordance with the Erosion Control Handbook.
(F) Retention ponds. The Commission may require retention ponds to regulate the flow at the outfall. The ponds shall be protected from erosion in accordance with the Erosion Control Handbook. The ponds shall be designed and constructed to enable adequate access for maintenance.
(G) Off-road drainage. Off-road drainage systems shall be extended to a watercourse or ditch of adequate size to receive the storm water.
(H) Connections to existing systems. Connection to a state drainage system is allowed only with written approval from the State Department of Transportation. Connection to a county legal drain is allowed only with written approval in accordance with the Indiana Code requirements for local drains. Connection to a county road ditch is allowed only with written approval from the County Engineer.
(I) Maintenance of drainage systems. The Commission shall not approve any subdivision for which adequate provision for maintenance of drainage systems has not been made. The provision may include, but is not limited to, acceptance of the system by the County Drainage Board or establishment of a lot owners association with responsibility to set and collect fees for drainage system maintenance. Roadside ditches shall not be filled without written approval of the County Engineer.
(J) Drainage report. The drainage report shall identify the applicable areas of concern and problem areas as listed on the selection matrix contained in the Erosion Control Handbook and shall indicate the control strategies for these problem areas. The report shall indicate the existing and proposed drainage conditions and the individual practices to be used to accomplish the objectives of this chapter. Methods selected to control drainage shall be consistent with the Handbook. The report shall evaluate the ability of the proposed water course, channels, drainage tiles, farm tiles, storm sewers, culverts and other improvements to handle the run-off. A registered professional engineer or land surveyor shall prepare this report. The report shall include:
(1) Estimates of the water entering the subdivision. Estimates shall assume that the upper watershed will be fully developed according to the current land use plan;
(2) Conditions of the watershed that may affect run-off such as subsoil type, positive drainage channels, obstructions and so forth;
(3) Quantities of flow at each pickup point or culvert;
(4) Description of minor and major drainage systems. The minor system will usually consist of, but not be limited to, storm sewers, drainage ditches, drainage swales, storm inlets or infiltration structures. The minor system shall be designed to handle a ten-year storm. The major system will usually consist of, but not be limited to, roadways, culverts, bridges or overflow drainage ways. The major system shall be designed to handle a 50-year storm;
(5) The location of all existing subsurface drainage tiles and a plan to preserve or relocate the tiles; and
(6) Proposals which include holding lagoons, storm water ponds or infiltration facilities shall be prepared by a registered professional engineer and shall include data coordinating field tests with design assumptions and estimates of expected annual maintenance costs.
(K) Erosion control plan.
(1) This plan shall identify the applicable areas of concern and problem areas as listed on the selection matrix contained in the Erosion Control Handbook and shall indicate the control strategies for these problem areas. The plan shall indicate the proposed individual practices to be used to accomplish the objectives of this chapter.
(2) Methods selected to control erosion shall be consistent with the Handbook.
(Prior Code, § 8-61) (Ord. 1986-7, passed 10-21-1986; Ord. 4, 2021, passed 6-21-2021)