Culverts shall be a minimum of 12 inches in diameter, 16-gauge corrugated copper bearing steel, hot dipped galvanized and not less than 18 feet long. Longer sections, if necessary, shall be connected with bolted #16-gauge galvanized standard connecting bands not less than 7½ inches wide. Culvert pipe must be installed in such a manner that bottom flow line must be a minimum of 18 inches below edge of traveled portion of adjoining road or street, but in no case higher than flow line of ditch in which culvert is installed.
(O.C. § 4.3)