A storm drainage analysis and plat shall be prepared and signed by a professional engineer registered in the state, to include the following:
(A) An up-to-date topographic survey or contour map of the area to be subdivided and contributing watershed showing existing structures and pavement and denoting existing elevations above mean sea level of all land features and improvements that would affect drainage;
(B) An aerial photograph at the scale of one inch equals 100 feet or one inch equals 200 feet showing the area to be subdivided;
(C) A drainage report with a map identifying and locating all rivers, creeks, arroyos, draws, washes or any other channel having definite banks and bed with visible evidence of the occasional flow of water. It shall include computations of the watershed area draining into each watercourse, identification and analysis of permeability of soils in each watershed and calculations based on the S.C.S. Engineering Field Manual procedures for estimating runoff from a 100-year frequency storm of:
(1) The volume and peak discharge of storm surface waters emanating from higher lands and drainage through the area to be subdivided (external drainage); and
(2) The volumes and peak discharge of internal drainage originating from the land to be subdivided prior to and after completion of the proposed development.
(D) A detailed storm drainage plan showing how the runoff from a 100-year storm will be maintained on the property being subdivided. Means of detention basins, retention basins, swales on lots or any other method approved by the Planning and Zoning Commission so as to ensure that the new development will not increase the peak discharge load on the existing drainage system or cause damage to properties at lower elevations. A map submitted with the plan shall indicate all points of entry and discharge of storm runoff prior to and after development, as well as proposed easements and structures provided for containment or controlled discharge of storm drainage. Points of discharge of natural watercourses shall not be altered by the development;
(E) A grading plan showing any proposed alteration, including finished elevations of areas to be graded, paved areas, building sites, retention or detention areas, retaining walls and other structures. It shall be accompanied by a signed agreement by the owner of the lands being platted, binding on his or her heirs or subsequent owners, that no grading, land filling, excavating or other alteration will be done except pursuant to the approved or amended grading plan;
(F) The plan shall show that all property within the subdivision is developed in such a manner that the flood damage will be minimized and that construction and substantial improvements are elevated to the 100-year flood level, if the property lies in an area which has been designated a floodplain under the National Flood Insurance Program. New water and sewer systems (including on-site systems) shall be located to avoid impairment of contamination during flooding;
(G) Areas which will be inundated by runoff from a 100-year or greater frequency storm shall not be divided into lots for sale in any proposed subdivision; and
(H) A copy of the subdivision plat and drainage plan will be provided to any public entity with holdings in the area for their review in order to avoid urban conflicts with the operation and maintenance of utility systems. Their review shall be advisory only.
(Ord. 2013-02, passed 3-19-2013) Penalty, see § 151.999