(A) General. Unless otherwise noted on the approved plans, drainage facilities and terracing of graded slopes shall conform to this section.
(B) Terraces.
(1) Mid-slope terraces at least six feet in width shall be established at not more than 30-foot vertical intervals on all cut or fill slopes, except that where only one terrace is required, it shall be at midheight. For cut or fill slopes greater than 60 feet and up to 90 feet in vertical height, one terrace at approximately mid-height shall be 12 feet in width. Terrace widths and spacing for cut and fill slopes greater than 90 feet in vertical height shall be designed by a professional engineer and approved by the City Engineer/Public Works Director. Suitable access shall be provided to permit proper cleaning and maintenance.
(2) Terrace drains shall have a minimum gradient of 2% unless waived by the City Engineer/Public Works Director. The City Engineer/Public Works Director may also allow a lesser gradient for terraces made of acceptable concrete materials, but the gradient shall not be less than 1%. Terrace drains shall have a minimum depth at the deepest point of no less than one foot and a minimum paved width of at least three feet and shall be designed to accommodate all runoff created by the cut or fill slope as well as any tributary runoff which enters the terrace drain.
(C) Subsurface drainage. Cut and fill slopes shall be provided with subsurface drainage as necessary for stability and as recommended by the soil engineer or the engineering geologist.
(D) Stormwater discharge. All drainage facilities shall be designed to carry stormwater runoff to the nearest practicable drainage way approved by the City Engineer/Public Works Director and any other appropriate jurisdiction as an acceptable and safe location to deposit such runoff. Erosion of the ground in the area of discharge shall be prevented by installation of non-erosive down drains, energy dissipaters or other devices approved by the City Engineer/Public Works Director.
(E) Interceptor drains. Concrete interceptor drains (brow ditches) shall be installed along the top of all cut slopes where the tributary drainage area above the cut slope drains toward the cut slope, unless waived by the City Engineer/Public Works Director. The slope gradient for the interceptor drain shall be the same as for terrace drains or as approved by the City Engineer/Public Works Director.
(F) Stormwater runoff. Stormwater runoff shall not be allowed to flow over cut or fill slopes which are steeper than a five to one (5:1) horizontal to vertical slope ratio. Drainage shall be provided by the following methods:
(1) Wherever practicable, each lot shall be graded so that stormwater will drain from the backyard through the side yard and front yard directly to the abutting street or toward approved drainage facilities at a gradient of not less than 1%. Wherever practicable, drainage shall not be directed across other lots or over cut or fill slopes. Cross lot drainage may be permitted provided approved by the City Engineer/Public Works Director and drainage easements are provided.
(2) When the provisions in the above division (F)(2) are not practicable, as determined by the City Engineer/Public Works Director, stormwater shall be collected along the top of slopes or at the rear of graded lots by means of paved gutters and/or French drains and carried to properly sized outfall or area drains, which shall also serve as erosion control devices. Such drainage shall not be allowed to drain across the surface of sidewalks or parkways. Asphalt concrete may not be used for any drainage device. Down drain ditches shall be a minimum of 18 inches deep.
(3) Where slopes are terraced at 30-foot intervals, drainage shall be provided in paved ditches a minimum of 36 inches wide and 12 inches deep. Construction of the ditches shall be as described below and shall be located on the terraces with one side of the ditch two feet from the toe of the slope. Where a terrace is constructed to conform to slope requirements, but is intended to be of a temporary nature, the City Engineer/Public Works Director may waive the drainage ditch requirements, if a satisfactory surety bond or other means to guarantee the improvement is posted with the city.
(4) Down drains, interceptor drains, and terrace drains shall be connected together to collect and transport all stormwater runoff entering the drains. They shall be of sufficient depth, as verified by hydraulic calculations, to allow for unimpeded flow when terraces are crossed. Down drains, interceptor drains, and terrace drains shall be constructed of Portland cement concrete or air blown mortar. They shall be reinforced with wire mesh and/or other appropriate concrete reinforcement as determined by the project engineer and approved by the City Engineer/Public Works Director. If pipe is used for down drains to transport runoff from terrace ditches, it shall be reinforced concrete pipe (RCP), plastic pipe (PVC) or other pipe material approved by the City Engineer/Public Works Director. Anchor lugs or collars may be required by the City Engineer/Public Works Director if the pipe slope is equal to or greater than a two to one (2:1) horizontal to vertical ratio. Pipe specifications shall be approved by the City Engineer/Public Works Director. Special design features shall be provided for abrupt changes in direction of terrace ditches and down drains.
(5) The discharge from any down drain, ditch or pipe shall be controlled so as to prevent erosion of the adjacent grounds. Velocities shall be reduced by means of adequately sized aprons of rock, grouted rip-rap, box-type energy dissipaters or other materials approved by the City Engineer/Public Works Director.
(G) Maintenance of drainage facilities. Where the continuous functioning of a drainage facility is essential to the protection and use of more than one lot within a development project site, a mutual and reciprocal covenant or deed restriction or easement shall be recorded by the owner(s) of the lots on which the drainage facility is located, imposing on each lot owner the responsibility for maintaining that specific portion of the drainage facility located on each lot owner's respective lot.
(H) Off-site drainage easements. All easements necessary for the construction of permanent off-site drainage facilities shall be acquired by the permittee. The easements shall be subject to the approval of the City Engineer/Public Works Director and the City Attorney and recorded prior to the issuance of the grading permit.
(Ord. 2022-364, passed 11-16-2022)