(A) Upon approval of the preliminary drainage plans by the County Drainage Board, final drainage plans shall be submitted to the Drainage Board.
(B) In addition to data provided on the preliminary drainage plans, the final plans shall provide or be accompanied by calculations, maps, and other descriptive material, including the following:
(1) A set of plan drawings stamped by a state registered professional engineer or a state registered land surveyor showing all proposed detention areas, storm sewers, inlets, outfall structures, open ditches, culverts (including driveway crossings), and bridges. At the minimum, these plan drawings should show or accompany the following:
(a) The extent and area of each watershed area tributary to the drainage channels in the development;
(b) Elevations in the National Geodetic Survey Map (NGSM);
(c) Proposed contours and where they tie into existing contours at the property boundaries;
(d) The street storm sewers and other storm drains to be built, the basis of their design, outfall and outlet locations, and invert elevations, receiving stream or channel, and its 100-year flood conditions;
(e) The parts of the proposed street system where pavements are planned to be depressed sufficiently to convey or temporarily store overflow from storm sewers and over the curb runoff resulting from the heavier rainstorms and the outlets for such overflow;
(f) Existing streams and 100-year floodplains to be maintained, and new channels to be constructed, their locations, cross-sections, and profiles;
(g) Proposed culverts, and bridges to be built, their materials, elevations, waterway openings, and basis of their design;
(h) Existing detention/retention facilities to be maintained, enlarged, or otherwise altered and new facilities to be built and the basis of their design;
(i) The estimated location and percentage of impervious surfaces existing and expected to be constructed when the development is completed; and
(j) The slope, type, and size of all sewers and other waterways.
(2) A written report stamped by a state registered professional engineer or a state registered land surveyor shall be included with each preliminary and final drainage plan. The report will contain a summary description of the following:
(a) The significant drainage problems associated with the project;
(b) The analysis and procedure used to evaluate these problems and propose solutions;
(c) Any assumptions or special conditions associated with the use of these procedures, especially the hydrologic or hydraulic methods;
(d) The proposed design of the drainage control system;
(e) The results of the analysis of the proposed drainage control system showing that it does solve the project’s drainage problems;
(f) As an appendix to the report, a hydraulic report detailing existing and proposed drainage patterns on the subject site. The report should include a description of the present land use as well as proposed land use. Any offsite drainage entering the site should also be addressed. This report should be comprehensive and detail all the steps which the design engineer took during the design process. All hydrologic and hydraulic computations should be included in the submittal. These calculations should include, but not be limited to: development of runoff curve numbers or runoff coefficients; runoff calculations; stage-discharge relationships for detention/retention facility outfalls; times of concentration; and storage volume. A map showing any drainage subareas used in the analysis shall accompany the report;
(g) Copies of the computer models used in the drain analyses may be obtained using disks, USB flash drives, or other means of electronic information transfer and storage devices commonly used; and
(h) For all detention/retention facilities, a plot or tabulation of storage volumes with corresponding water surface elevations and a plot or tabulation of the facility outflow rates for those water surface elevations.
(3) In addition to the criteria and requirements set in this subchapter, the plans and calculations should also meet the following criteria:
(a) If roadside ditches are used rather than storm sewers, the bottom of the ditch should be low enough to install adequately sized driveway culverts without creating “speed bumps;”
(b) Driveway culvert inverts shall be designed to adequately consider upstream and downstream culvert elevations;
(c) Minimum swale and yard slopes are 0.3% unless otherwise approved by the Plan Commission;
(d) Maximum yard slopes are three to one unless otherwise approved by the Plan Commission;
(e) Top of foundation no less than one-half foot above finished grade;
(f) Spot elevations shown at the drainage break points;
(g) Pipes have adequate slope to maintain two and one-half feet per second (fps) velocity (cleaning velocity);
(h) When changing pipe size from a smaller to a larger pipe, match crowns of pipes; and
(i) Inlets are placed such that the tributary flows are in accordance with the grate capacity (i.e., depth of inundation above rim is tolerable in ten-year and 100-year storms).
(Ord. 1997-16, passed 12-8-1997; Ord. 2005-01, passed 2-17-2005) Penalty, see § 153.999