The following information and data provided by an Illinois licensed professional engineer or land surveyor engaged in storm drainage design shall be submitted to the Council at the time of application for 1) each proposed major subdivision or planned development lying within the Regulated Area prior to Final Plat approval by the Planning Commission, or 2) a building permit for any development, redevelopment, or new construction on real estate which lies within the Regulated Area which has not previously received drainage approval or is not exempt from the requirements of this Ordinance.
(A) Topographic and Soils Maps. A topographic map of the land to be developed and such adjoining land whose topography may affect the layout or drainage of the development. The contour intervals shall be one foot when slopes are less than four percent and shall be two feet when the slope exceeds four percent and shall be five feet when the slope exceeds 10 percent. On this map, the following shall be shown:
(1) The locations of streams and other flood water runoff channels, the extent of the flood plains at the established 100 year flood elevation where available (regulatory floodway), and the limits of the floodway, all properly identified.
(2) The normal shoreline of lakes, ponds, swamps and detention basins, their flood plains, lines of inflow and outflow if any.
(3) The location of regulated drains, farm drains, inlets and outfall, if any of record.
(4) Storm, sanitary and combined sewers and outfall, if any of record.
(5) Septic tank systems and outlets, if any of record.
(6) Seeps, springs, flowing and other wells, that are visible or of record.
(7) Provide soils map of proposed development indicating soil name and their hydrologic classification when Soils Conservation Service (SCS) hydrologic methods are used.
(B) Preliminary Drainage Plan. A comprehensive plan, in preliminary form (or in combined preliminary and final form), designed to handle safely the storm water runoff and to detain the increased storm water runoff must be submitted to the Council. The plan shall provide or be accompanied by maps or other descriptive materials indicating the feasibility of the drainage plan and showing the following:
(1) The extent and area of each watershed affecting the design of detention facilities as shown on United States Geological Survey Quadrangle Maps or other more detailed maps as required by the Council.
(2) The preliminary layout and design of proposed storm sewers, the outfall and outlet locations and approximate elevations, the receiving stream or channel and its 100 year return period water elevation.
(3) The location and design of the proposed street system, especially including depressed pavements used to convey or temporarily store overflow from the heavier rainstorms, and the outlets for such overflow.
(4) The locations, cross sections and profiles of existing streams and flood plains to be maintained, and new channels to be constructed.
(5) The materials, elevations, waterway openings, and the basis for design of proposed culverts and bridges.
(6) Existing detention ponds and basins to be maintained, enlarged, or otherwise altered and new ponds or basins to be built and the basis of their design.
(7) The estimated depth and amount of storage required in the new ponds or basins.
(8) The estimated location and percentage of impervious surfaces existing and expected to be constructed when the development is completed.
(9) Any interim plan which is to be incorporated into the development pending completion of the development and the final drainage plan.
(C) Valley Cross Section. One or more typical cross sections must be provided showing all existing and proposed channels or other open drainage facilities carried to a point above the 100 year high water elevation; showing the elevation of the existing land and the proposed changes thereto, together with the high water elevations expected from the 100 year storm under the controlled conditions called for by this ordinance; and showing the relationship of structures, streets and other facilities.
(D) Site Plan. A plan drawn to scale showing dimensions of the site with existing and proposed facilities must be provided. All plan views shall include, but may not be limited to, the following information when applicable:
(1) A North arrow;
(2) The scale used;
(3) Site location map;
(4) Property boundaries with bearing and distance;
(5) Property owner/developer;
(6) Building setback lines;
(7) Location of all existing and proposed facilities/utilities;
(8) Topography in the area affected by construction.
(E) Final Drainage Plans.
(1) Upon approval of the preliminary drainage plans by the Council, final drainage plans shall be submitted to the Council. The final plans shall provide or be accompanied by calculations, maps and/or other descriptive material showing the following:
(a) The extent and area of each watershed tributary to the drainage channels in the development.
(b) The street storm sewers and other storm drains to be built, the basis of their design, outfall and outlet locations and elevations, the receiving stream or channel and its high water elevation, and the functioning of the drains during high water conditions.
(c) 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.
(d) Existing streams and flood plains to be maintained, and new channels to be constructed, their locations, cross sections and profiles.
(e) Proposed culverts and bridges to be built, their materials, elevations, waterway openings and basis of their design.
(f) Existing detention basins and ponds to be maintained, enlarged, or otherwise altered and new basins or ponds to be built and the basis of their design.
(g) The estimated location and percentage of impervious surfaces existing and expected to be constructed when the development is completed.
(h) The slope, type and size of all sewers and other waterways.
(i) For all detention basins, a plot or tabulation of storage volumes with corresponding water surface elevations and a plot or tabulation of the basin outflow rates for those water surface elevations.
(2) A written report must be included with each preliminary and final drainage plan. The report will contain a summary description of:
(a) The significant drainage problems associated with the project;
(b) The analysis procedure used to evaluate these problems and to propose solutions;
(c) Any assumptions or special conditions associated with the use of these procedures;
(d) The proposed design of the drainage control system; and
(e) The results of the analysis of the proposed drainage control system showing that it does solve the project’s drainage problems.
(3) The following additional documents should be submitted with all applications submitted for approval:
(a) 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 off site drainage entering the site should also be addressed. This report should be comprehensive and detail all the design steps which the design engineer took during the design.
(b) All hydrologic and hydraulic computations should be included in the submittal. These calculations should include, but not be limited to: runoff curve numbers or runoff coefficients; runoff calculation; stage discharge relationships; times of concentration; and storage volume.
(c) Copies of all computer runs. These computer runs should include both the input and the outputs. A floppy diskette with input files will expedite the review process.
(d) A set of plan drawings stamped by a Registered Professional Engineer showing all proposed detention areas, storm sewers, inlets, outfall structures, open ditches, culverts and bridges.
(e) A set of exhibits should be included showing the drainage subareas and a schematic detailing of how any computer model inputs were set up.
(f) A conclusion report summarizing the hydraulic design and detailing how this design satisfies the Mt. Vernon Storm Water and Sediment Control Ordinance.
(F) Submittal and Consideration of Plans. The Council and/or its Engineer shall attempt to approve or disapprove any preliminary plans, final plans and/or construction plans within forty five (45) days of receipt of a complete submittal unless applicant requests to a time extension. All approvals and disapprovals shall be in writing.
(G) Engineering Review Fees.
(1) As a condition of and prior to approval of final drainage plans by the Council, the applicant shall pay to the City of Mt. Vernon the actual costs incurred by the City in respect to the review of all preliminary plans, final plans and/or construction plans by a licensed professional engineer in excess of the first four (4) hours of such review and consultation.
(2) The City shall furnish to the applicant in writing prior to the approval of the applicant’s final drainage plan a written statement specifying the total cost of professional engineering fees incurred by the City in connection with the review of applicant’s plans, including the total hours expended by such professional engineer, and the amount required to be paid by applicant prior to approval of final drainage plans by the Council. As a condition of and prior to approval of final drainage plans, applicant shall pay to the City of Mt. Vernon Clerk the sum set forth in said statement representing the cost of professional engineering services in excess of the following number of hours thereof incurred by the City in connection with the review of applicant’s preliminary and final drainage plans and accompanying information and data: Four (4) hours for individual site plans, subdivisions, and/or other projects that involve storm water drainage plans and/or calculation.
(Prior Code, Art. 20, § 20-7)