Accompanying the final plans of each proposed subdivision or planned unit development, there shall be furnished the following information and data prepared by and bearing the seal of a professional engineer registered in Illinois:
A. Contour Map: As described in subsection 7-4-1A.
B. Comprehensive Drainage Plan: A comprehensive drainage plan is a plan designed to handle safely the stormwater runoff following the rainstorms which exceed the design capacity of storm sewer systems by detention of the increased stormwater runoff. The plan shall provide or be accompanied by maps or other descriptive material showing the following:
1. The extent and area of each watershed tributary to drainage channels in the project;
2. Pavement elevations, roadway ditches, storm sewers and other storm drains to be built, the basis of their design, the outfall and outlet locations and elevations, receiving stream or channel and its high water elevation and the functioning of the drains during high water conditions;
3. Proposed drainage patterns for all lots open space areas. Information shall include ground slopes, nature of drainageway improvements and transitions into channels or drains;
4. Existing streams and flood prone areas to be maintained, enlarged, altered and eliminated; and new channels to be constructed, their locations, cross sections and profiles;
5. Existing culverts and bridges, drainage areas, elevation and adequacy of waterway openings; and new culverts and bridges to be built, their materials, elevations, waterway openings and the basis of their design;
6. Existing detention ponds and basins to be maintained, enlarged and altered and new ponds or basins to be built with dams, if any;
7. The estimated location and extent of impervious surfaces existing and expected to be constructed when the subdivision is completely developed;
8. The slope, type and size of all sewers and other waterways;
9. For all detention basins, a plot or tabulation of storage volumes with corresponding water surface elevations and of the basin outflow rates for those water surface elevations;
10. For all detention basins, design hydrographs of inflow and outflow for the 10-year and 100-year design runoff events for the site under developed conditions and the calculated 10-year and 100-year peak flows from the site under natural and developed conditions;
11. Locations routing, cross sections and capacities of overland flow routes to contain and discharge excess flows into the detention basins. (Ord. 93-498, 11-9-93)