(A) Terraces at least eight feet in width shall be established at not more than 30 foot vertical intervals on all cut or fill slopes to control surface drainage and debris; except that where only one terrace is required, it shall be at mid-height. Terrace widths and spacing of cut and fill slopes greater than 90 feet in height shall be designed by the civil engineer upon recommendation of the soil engineer and approved by the Director of Public Works. Suitable access shall be provided to permit proper cleaning and maintenance.
(B) Terrace drains shall be constructed on all terraces, using concrete with suitable reinforcement, with a minimum grading of 5% unless waived by the Director of Public Works due to special circumstances. Construction of the drains shall be such that concrete is a minimum of ½ inch below (and a maximum of four inches below) the surface elevation of the adjacent grade. The terrace drain shall have a minimum depth at the deepest point of one foot and a minimum width of three feet (measured across the top) and shall be designed to accommodate the runoff created.
(C) Unless otherwise approved by the Director of Public Works, a single run of terrace drain shall not collect more than 13,500 square feet of drainage area without discharging into a downdrain or other approved collection device. Approval of alternatively designed terrace drains shall be based on runoff generated by rainfall intensities characteristic of the peak portion of a rainfall hydrograph for a period of time concentration at the discharge point of the terrace drain. Splash walls, velocity reducers, flow spreaders and other structures shall be provided in accordance with good engineering practice.
(D) Construction of the terrace drains shall be as described for gutters and down drains in this chapter, and shall be located on the terraces with one side of the ditch two feet from the toe of slope.
(Ord. 1449, passed 10-19-05)