With the first development proposal, or prior thereto, there shall be submitted to, and approved by the West Des Moines City Engineer, a complete storm water management plan for all storm sewer and drainage systems to remain a portion of the development. The plan shall be guided by, and adhere to the West Des Moines Subdivision Ordinance, with provision made for conveyance of the 100-year return frequency rainfall (event), including the provision for on-site temporary detention with discharge equivalent to the existing 5-year return frequency storm as required by the City. (Ord. 786, 3-31-1986)