"Design storm" means a rainfall event of a size approved by the director, used for the purpose of sizing and designing drainage facilities, stated in terms of a recurrence interval and a time period over which the rainfall amount is measured or analyzed (i.e., a 2-year, 24-hour storm). (Added by Amended Ord. 02-064, Dec. 9, 2002, Eff date Feb. 1, 2003).