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SEC. 91.7013.  EROSION CONTROL AND DRAINAGE DEVICES.
   (Added by Ord. No. 171,175, Eff. 7/25/96.)
 
91.7013.1.  Interceptor Terraces.  (Amended by Ord. No. 185,587, Eff. 7/16/18.)  Paved interceptor terraces shall have a minimum width of 8 feet (2438.4 mm) and shall be installed on the face of all cut and fill slopes at intervals not to exceed 25 feet (7.620 m) measured along a vertical plane.  Where only one terrace is required, it shall be at mid-height.
 
   The cross section of interceptor terraces shall meet the specification shown in Figure A of this division.
 
   The longitudinal slope of interceptor terraces shall not be less than 5% or more than 12%, and any change in rate of grade within these allowable slopes shall increase the grade in the direction of flow.
 
   A single run of an interceptor terrace shall not exceed 150 feet (45.72 m) to a down drain.
 
   Down drain shall be embedded round pipes enclosed in concrete shaped as shown in Section C-C of Figure G of this division, or an alternate design which is prepared by a civil engineer and acceptable to the Department.
 
91.7013.2.  Diverter Terraces.  (Amended by Ord. No. 185,587, Eff. 7/16/18.)  Paved diverter terraces, constructed as shown in Figure B of this division, shall be installed at the top of all graded slopes where the tributary drainage area above has a slope exceeding 1 unit vertical in 10 units horizontal (10% slope) and a horizontal projection of greater than 40 feet (12.192 m).
 
91.7013.3.  Berms.  (Amended by Ord. No. 185,587, Eff. 7/16/18.)  Berms conforming to the provisions of Figure C of this division shall be constructed at the top of all slopes.
 
91.7013.4.  Vee Channels.  (Amended by Ord. No. 171,939, Eff. 4/15/98.)  Where a slough wall is required at the toe of the slope by other provisions of this Code, or a retaining wall is built to support any cut or fill slope, a vee channel shall be constructed behind the wall to carry off the slope waters to interceptors, down drains or other approved drainage devices.
 
91.7013.5  Inlet Structures, Down Drains and Outlet Structures.  (Amended by Ord. No. 171,939, Eff. 4/15/98.)
 
91.7013.5.1.  Inlet Structures.  (Amended by Ord. No. 185,587, Eff. 7/16/18.)  Inlet structures shall be of concrete, galvanized iron hot dipped in asphalt or equivalent.  The inlet structure shall be grated or grilled, or of such entry shape as to prevent entry of objects of greater than 4 inches (101.6 mm) in dimension.  The inlet structure shall be placed on the bench as shown in Section Y-Y of Figure G of this division and shall be so shaped as to provide small entry losses.  An overflow structure into the vee down drains shall be provided.
 
91.7013.5.2.  Down Drains.  (Amended by Ord. No. 185,587, Eff. 7/16/18.)  Down drains shall have paved inverts and shall be of concrete, minimum 18 gauge corrugated galvanized iron hot dipped in asphalt, or corrugated alloy 3004-H-34 aluminum of minimum 16 gauge and hot dipped in asphalt or equivalent.  Pipe down drains shall conform with Section C-C of Figure G of this division and shall have a diameter of a size required by runoff calculations, but no less than 12 inches (304.8 mm).
 
   Open channel down drains shall be designed by a civil engineer and shall have a minimum capacity equal to four times the required pipe size.  The alignment of down drains shall be such as to conserve velocity head.
 
91.7013.5.3.  Outlet Structures.  Outlet structures shall be of concrete, galvanized iron hot dipped in asphalt or equivalent.
 
   Where outletting into street or other approved termination areas, the structure shall be of a design approved by the Department of Public Works.  Where outletting into natural watercourses or other approved locations, the structure shall be provided with adequate velocity reducers, diversion walls, rip-rap, concrete aprons or any similar energy dissipator.  All slope drainage shall be collected and disposed of in the drainage device.
 
91.7013.6.  Runoff Computations.  Runoff shall be based on the proper 50-year isohyetal, and the runoff calculation shall be based on the latest methods adopted by the Bureau of Engineering.
 
91.7013.7.  Drainage Dispersal Wall.  (Amended by Ord. No. 185,587, Eff. 7/16/18.)  A drainage dispersal wall shall be constructed as set forth in Figure F of this division whenever it is necessary to convert channel flow to sheet flow.
 
91.7013.8.  Subdrains.  Subdrains shall be laid under all fills placed in natural watercourses.  Subdrains shall be placed along the watercourse flow line and along the flow line of any branches tributary thereto.  Additional subdrains shall be installed to collect any active or potential springs or seeps which will be covered by the fill.  Subdrains shall be installed after the watercourse has been excavated to firm material in preparation for receiving the fill.  Individual design shall be shown on each plan for city approval, based on recommendations of the soils engineer and geologist to the satisfaction of the Department.
 
91.7013.9.  Gutters.  (Amended by Ord. No. 179,324, Eff. 12/10/07, Oper. 1/1/08.)  Eave or ground gutters shall be provided to receive all roof water and deliver it through a non erosive device via gravity to a street or watercourse, or approved drainage facility, if the slope of the underlying natural ground exceeds three percent or if more than three feet (914 mm) of compacted fill or more than one foot (305 mm) of uncompacted fill is placed on the ground.
 
91.7013.10.  Site Drainage.  (Amended by Ord. No. 179,324, Eff. 12/10/07, Oper. 1/1/08.)  All pads with cut or fill shall slope a minimum of two percent to an approved drainage device or facility, or to a public street.  Where used, the drainage device shall be an adequately designed system of catch basins and drain lines, which conducts the water to a street.
 
   EXCEPTION:  Where the slope of the underlying natural ground does not exceed three percent and the compacted fill is less than three feet (914 mm) in depth, the slope of the pad may be reduced to one percent.
 
91.7013.11.  Drainage Around Buildings.  (Amended by Ord. No. 171,939, Eff. 4/15/98.)  On all building sites, acceptable drainage devices shall be installed to conduct storm water around buildings whenever the distance from the building to the top of any slope is less than five feet (1524 mm).  Where used, the drainage device shall be an adequately designed system of catch basins and drain lines which conducts the water to a street.
 
91.7013.12.  Maintenance of Drainage.  Drainage in conformance with the provisions of this Code shall be maintained during and subsequent to construction.