(A) The Board of Commissioners hereby adopts as policy those recommendations made by the Warrick County Drainage Board for stormwater runoff from developed real property.
(B) The following shall be required:
(1) All stormwater drainage systems shall be designed for a minimum 50-year one hour storm. A time concentration for each sub-area, based on post development conditions shall be used to determine the appropriate rainfall intensity for the sizing of all storm sewer pipes, inlets, and catch basins that will be located inside the developed area. All storm sewers shall be installed on proper backfill and with proper cover, as per manufacturer specifications for the particular materials being used.
(2) For the purpose of calculating stormwater retention basins, pre-developed run-off from the site shall be determined as a five-year storm intensity rainfall event release rate. Stormwater storage shall be then calculated as a 50-year storm storage capacity (developed) over a 5-year release rate (undeveloped). Pipes flowing into retention basins shall be designed in such a manner that the design pipe flow capacity is not restricted by the basin pool elevation. All storm water storage basins shall include a controlled discharge structure for the restricted release rate, plus an emergency surface overflow at or equal to the basin design storage elevation.
(3) The Rational Method shall be used for the purpose of calculating pre-development and post- development run-off. Run-off coefficients shall be taken from the Herpic Storm Drainage Manual. A composite coefficient for post-developed conditions shall be determined by using methods described in the Herpic Storm Drainage Manual.
(4) All preliminary drainage plans submitted will show the following information on the plat:
(a) X-sections of all surface drains and waterways.
(b) Surface contour lines at intervals of not more than five feet.
(c) Flow direction arrows on all streets and surface waterways.
(d) All storm sewers within and adjacent to the subdivision by size, length, type, grade, invert and rim elevations.
(e) Locations, storage volumes, release rates, discharge structure details and overflow details for all retention basins.
(f) All sub-drainage areas inside the development shall be delineated. Off-site areas draining through the development site should also be shown.
(g) Certification and signature of the design engineer.
(5) All preliminary drainage plans submitted shall be accompanied by the following:
(a) A copy of the drainage study and calculations for the proposed subdivision.
(b) A letter of certification by the design engineer stating that the drainage plan was prepared in accordance with the criteria as set forth in the Herpic County Storm Drainage Manual and the plan requirements of the Warrick County Drainage Board.
(BC Res. 2000-06, passed 12-18-00)