(A) Location. The subdivider may be required by the Commission to carry away by pipe or open ditch any spring or surface water that may exist either previously to or as a result of the subdivision. Such drainage facilities shall be located in the street rights- of-way where feasible or in perpetual, unobstructed easements of appropriate width.
(B) Accessibility to public storm sewers. Where a public storm sewer is accessible, the applicant shall install storm sewer facilities. If no outlets are within a reasonable distance, then adequate provision shall be made for the disposal of stormwater. However, in subdivisions containing lots of less than 15,000 square feet in area and in business and industrial districts, underground storm sewer systems shall be constructed throughout the subdivision and be conducted to an approved outfall.
(C) Accommodation of upstream drainage areas. A culvert or other drainage facility shall in each case be large enough to accommodate the potential runoff from its entire upstream drainage area, whether inside or outside the subdivision. The Town Engineer shall approve the necessary size of the facility as determined by the subdivider based on the provisions of the required standards of construction and the specifications assuming conditions of maximum potential watershed development permitted by the zoning ordinance.
(D) Drainage design criteria.
(1) The subdivider shall size all storm sewers, inlets, culverts, ditches and other drainage structures based on runoff from a ten-year storm event. The drainage calculations shall also include the effect of the subdivision on the existing downstream drainage facilities outside of the subdivided area. Where it is determined that runoff incidental to the development of the subdivision will overload an existing downstream drainage facility during a five- year storm, the Plan Commission shall not approve the subdivision until provisions have been made for the improvement of said condition.
(2) The storm drainage system will be designed to meet the following conditions.
(a) Storm inlets shall be placed at the low points of roads and shall accept the ten-year storm volume with not more than one-half foot of water pooling above the inlet.
(b) On-site storm runoff detention shall be provided so as to restrict the outlet of stormwater at a ten-year, pre-developed runoff rate for a 100- year, post-developed storm event.
(c) Storm pipes and culverts shall have a minimum diameter of 12 inches.
(d) Drainage swales shall have a minimum longitudinal slope of 1%.
(E) Floodway areas. If a subdivision of land is proposed within the floodplain, then floodways shall be preserved and not diminished in capacity by filling or obstruction except as approved in writing by the state’s Natural Resources Commission. No residential building site may be located within the floodway.
(F) Floodway fringe areas. Where a subdivision is proposed within an area of the floodplain designated as a floodway fringe, the Commission may approve such subdivision provided that:
(1) All streets are elevated sufficiently to be above the regulatory flood elevation;
(2) All lots for residential usage have a flood protection grade that is two feet above the regulatory flood elevation;
(3) Where provided, water and sanitary sewer facilities are constructed to eliminate contamination of or by floodwater;
(4) Approval to fill the area from the state’s Natural Resources Commission has been obtained in writing; and
(5) Lands below the regulatory flood elevation shall not be used for computing the area requirement for any lot.
(G) Floodplain areas. Where a subdivision is proposed within an area of the floodplain for which floodway and floodway fringe designations have not been made, the Commission shall not approve such subdivision unless:
(1) All streets are raised sufficiently to be above the regulatory flood elevation;
(2) All lots for residential usage have a flood protection grade of two feet above the regulatory flood elevation;
(3) Where provided, public water and sanitary sewer facilities are constructed so as to eliminate contamination of or by floodwater;
(4) Filling to achieve the provisions of divisions (G)(1) through (G)(3) above will not raise the level of the regulatory flood elevation more than one-tenth of one foot for that reach of the stream. All filling in the floodplain must be approved in writing by the state’s Natural Resources Commission; and
(5) Lands below the regulatory flood elevation shall not be used for computing the area requirement for any lot.
(H) Recording of plats in the floodplain and floodwav fringe. All final plats having within their boundaries areas whose elevation is below that of the regulatory flood elevation shall show and label the regulatory flood boundary and elevation as of the date the final plat is drawn on the final plat for recording.
(Ord. 2002-13, passed 9-3-2002)