a. Basins shall be constructed to detain temporarily the storm water runoff which exceeds the maximum peak flow rate authorized by this ordinance, as amended from time to time. The volume of storage provided in these basins, together with such storage as may be authorized in other on-site facilities shall be sufficient to control excess runoff from the 100-year storm.
b. The following design principles shall be observed:
1. The maximum volume of water stored and subsequently released at the design release rate shall not result in a storage duration in excess of forty-eight (48) hours unless additional storms occur within the period;
2. The maximum planned depth of storm water stored (without a permanent pool) shall not exceed four (4) feet;
3. All storm water detention facilities shall be separated by not less than twenty (20) feet from any building or structure to be occupied;
4. All excavated excess spoil may be spread so as to provide for aesthetic and recreational features such as sliding hills, sports fields, etc. Slopes no steeper than six (6) feet horizontal to one (1) foot vertical for safety, erosion control, stability and ease of maintenance shall be permitted;
5. Safety screens having a maximum opening of four (4) inches shall be provided for any pipe or opening to prevent children or large animals from crawling in the structures;
6. Danger signs shall be mounted at appropriate locations to warn of deep water, possible flooding conditions during storm periods and other dangers that exist. Fencing shall be provided if deemed necessary by the Department of Planning and Building after review and recommendation of the Plan Commission;
7. Outlet control structures shall be designed to operate as simply as possible and shall require little or no maintenance and/or attention for proper operation. They shall limit discharges into existing or planned downstream channels or conduits so as not to exceed the predetermined maximum authorized peak flow rate;
8. Emergency overflow facilities such as a weir or spillway shall be provided for the release of storm runoffs or in emergency conditions should the normal discharge devices become totally or partially inoperative. The overflow facility shall be of such design that its operation is automatic and does not require manual attention;
9. Grass or other suitable vegetative cover shall be provided throughout the entire basin area. Grass should be cut regularly at approximately monthly intervals during the growing season or as required;
10. Debris and trash removal and other necessary maintenance shall be performed on a regular basis to assure continued operation in conformance to design;
11. Provide a twenty (20) foot vegetative biofilter around the perimeter of the detention pond, including six (6) inches of tilled soil and native plant material, to avoid shade tree and shrub species in favor of native grasses;
12. Provide thirty (30) feet of maintenance easement measured from high water line around perimeter of basin;
13. Provide thirty (30) feet of access easement from public right-of-way to the detention pond.
14. Maximum side slopes of basin shall be three (3) feet horizontal to one (1) foot vertical. Maximum slope of maintenance access ramp shall be six (6) feet horizontal to one (1) foot vertical.
15. A report shall be submitted to the Department of Planning and Building and Plan Commission describing:
A. the proposed development;
B. the current land use conditions;
C. the method of hydraulic and hydrologic analysis used, including any assumptions or special conditions;
D. the results of the analysis;
E. the recommended drainage control facilities; and,
F. include hydraulic and hydrologic calculations, including input and output files, as appendices to the report.
(Ord. No. 1708, 6-13-07)