Provisions shall be made to prevent any surface waters from damaging the cut face of an excavation or the slope surface of a fill. All drainage shall be so designed as to minimize erosion of any slope. Structures shall be constructed of three-inch thick reinforced concrete or air-blown mortar using medium or dark earthen tones (black, tan, sienna, umber, ocher, green). However, subject to the prior approval of the City Engineer, downdrains may be constructed of natural grey concrete or air-blown mortar with a natural riverbed rock surface. All drainage structures shall be of such design as to carry surface water to the nearest street, storm drain or natural watercourse approved by the City Engineer as a safe place to deposit and receive such waters. (Ord. 3411 § 2 (part); April 1, 1975: Ord. 3933 § 1; November 7, 1978: Ord. 3955 § 1; January 9, 1979.)