(A)   Alignment of drainage facilities.
      (1)   The diversion of natural drainage will be allowed only within the limits of the proposed improvement. All natural drainage must enter and leave the improved area at its original horizontal and vertical alignment unless an agreement, approved by the Engineer, has been executed with the adjoining property owners.
      (2)   Alignment of drainage facilities must coordinate with other utilities and street designs.
      (3)   Closed conduit must usually be placed straight between manholes. Long radius curves are permitted for pipe 24 inches and larger. The radius of curvature must not be less than 100 feet or the manufacturers recommendation for curved alignment, whichever is greater. Curves, radii and length of pipe joints must be shown on the improvement plans.
   (B)   Easements. Easements for drainage facilities shall meet the requirements of the county improvement standards and the following design standards:
      (1)   Closed conduit. Easements for closed conduits shall meet the following requirements:
         (a)   For pipes 24 inches in diameter and less with trench depth less than or equal to five feet, the minimum width of the easement shall be ten feet with the centerline of the pipe at quarter point; pipe may reverse sides at angle points.
         (b)   Temporary access and working easements must be obtained for work outside of the easement.
         (c)   For pipes exceeding 24 inches in diameter or trenches greater than five feet deep, the easement shall have additional width to provide ample working space as required by the Engineer.
      (2)   Open channels. Easements for open channels shall have sufficient width to contain the open channel with side slopes, fencing where required, and a 15-foot service road when required by the Engineer. Suitable ramps must be provided for access to the bottom when bottom is used for maintenance access.
   (C)   Closed conduit design.
      (1)   Closed conduits shall be either cast-in-place concrete pipe, precast reinforced concrete pipe, non-reinforced concrete pipe, corrugated steel pipe or corrugated aluminum pipe, or other type approved by the County Engineer.
      (2)   The specified type of pipe or alternate pipes must be shown on the plans. Revised plans must be submitted to the county for approval if use of pipe not shown on the plans is desired.
      (3)   Cover requirements shall be as shown on standard drawings. Where the minimum cover requirement cannot be provided, the conduit shall be encased in concrete or provided with a concrete cover or other method of pipe protection approved by the Engineer. These charts are based on Type I bedding and backfill per standard drawing. Type I bedding and backfill shall be used for storm drain conduit unless otherwise specified by the Engineer. Other trench requirements can be found in the standard specifications sections.
      (4)   Where different size pipes meet at a junction, the pipe crown elevations shall be matched unless otherwise approved by the Engineer.
   (D)   Manholes and junction boxes.
      (1)   Standard precast concrete or saddle type manholes per Standard Drawings D-1 and D-2 shall be used where feasible. For cases where special manholes or junction boxes are necessary, the design must be approved by the Engineer. In no case shall manholes or junction boxes be allowed that are smaller than 24 inches inside dimensions. All manholes and junction boxes other than inlets shall have standard manhole covers per standard drawings. Slotted manhole may be used when approved by the Engineer to back up minor drainage in non-traffic areas. These covers will not be allowed in gutters, pedestrian, bicycle or vehicle access areas.
      (2)   Manhole shall be constructed at junction points, angle points greater than 15, changes in grade and changes in pipe size. On curved pipes manholes must be located at the B.C. and E.C. of the curve. Where approved by the Engineer, inlet pipe with diameter 20% or less in size than the main line may not require a manhole at the connection. Manholes located in major intersections shall be avoided wherever possible.
      (3)   Maximum spacing of manholes shall be as follows:
         (a)   For pipe sizes 24 inches or less in diameter the maximum spacing of manholes shall be 500 feet.
         (b)   For pipes greater than 24 inches in diameter the maximum spacing may be up to 600 feet.
         (c)   For curved pipe with radii less than 400 feet, maximum spacing shall be 300 feet.
         (d)   For curved pipe of radii 400 feet or greater, the maximum spacing shall be 400 feet for pipe 24 inches or less in diameter and 500 feet for pipe greater than 24 inches in diameter.
   (E)   Inlets.
      (1)   Drain inlets shall be constructed per standard drawings. Deviations from the standard inlets must be approved by the Engineer.
      (2)   A drain inlet must be placed at all gutter sag points. Inlets located within street crosswalks shall be avoided whenever possible. Spacing of inlets shall meet the hydraulic criteria as set in these standards.
   (F)   Open channels.
      (1)   Natural channels. Natural or grass lined channels shall have a minimum side slope of two to one. For locations of unstable soils, the minimum side slope may be three to one at the discretion of the Engineer. The minimum bottom width shall be six feet with no shrubs or trees within the flow limits of the channel.
      (2)   Concrete lined channels.
         (a)   Concrete lined channels may be constructed if a natural channel is not feasible and one or more of the following conditions are met:
            1.   The capacity of a 66 inch pipe is exceeded;
            2.   The cover requirements for buried pipe cannot be met;
            3.   The required pipe or natural channel grade cannot be maintained; or
            4.   Slope lining is required to maintain the desired channel side slope.
         (b)   Rectangular concrete channels must be structurally designed to retain resultant earth pressures. Calculations must be submitted to the county.
         (c)   Trapezoidal concrete sections shall be designed per the standard drawings. The minimum bottom width shall be six feet. A ten-foot wide access road will be required on either bank and will be provided with adequate ramping per standard drawings for access of maintenance equipment to the channel bottom. At the discretion of the Engineer, a bank side road may not be required where channel bottom width is greater than or equal to ten feet and vehicular access to the channel bottom is included.
         (d)   All concrete lined channels shall be enclosed by a minimum six-foot high chain link fence.
      (3)   Rock lined channel. Rock lined channels may be constructed in lieu of concrete channels, but must maintain a minimum two to one side slope and must conform to standards and specifications of the California Department of Transportation.
      (4)   Inlet and outlet structures.
         (a)   Inlets from channels to pipes shall be designed per approved standard drawing. A trash rack will be required in instances where the Engineer deems that significant amounts of debris may occur at the inlet. Trash racks will be designed per approved standard drawing.
         (b)   Outlets from pipes to natural or grass lined channels shall include erosion control provisions per standard drawings.
   (G)   Culverts.
      (1)   The U.S. Bureau of Public Roads nomograph shall be used to compute the capacity of all cross culverts that are not to become a part of a closed conduit system.
      (2)   All headwalls, wingwalls and endwalls shall be considered individually and shall be, in general, designed in accordance with the Standards and Specifications of the California Department of Transportation.
   (H)   Detention and retention systems.
      (1)   General.
         (a)   The maximum side slope for retention ponds or detention basis shall be two to one where adequate side slope stability can be demonstrated. All ponds or basins with depth of 18 inches and with side slopes steeper than five to one shall be completely enclosed by a six-foot high chain link fence. Ponds or basins with slopes five to one or flatter will have no fencing requirements. Where side slopes are steeper than five to one, a vehicular access ramp shall be included into the pond.
         (b)   Vegetation other than trees or landscape shrubs on side slopes and banks of basins and ponds must be mowed, burned or treated with herbicide so as to not reach a height greater than six inches during the non rainy season (March 15 to November 15).
      (2)   Detention basins.
         (a)   Detention basins may be constructed to facilitate other public uses where possible.
         (b)   Detention basins shall be designed with gravity in-flow and gravity out-flow whenever possible. (i.e., large pipe in/smaller pipe out, or overflow in/flap gated outlet). Detention systems requiring pumping facilities must meet the requirements of these standards and must be approved by the Engineer.
         (c)   The bottom of a detention basin shall be sloped at a minimum of 1% towards the outlet works. Whenever possible, a low flow channel or pipe through the basin shall be incorporated into the design.
      (3)   Retention ponds. Retention ponds shall be constructed per standard drawings. Deviation from this design must be approved by the Engineer. The number and depth of percolation pits necessary will be based on recommendations of a certified soil or geotechnical engineer.
   (I)   Pump stations.
      (1)   General.
         (a)   The use of drainage pumps shall be avoided whenever possible and used only with the specific approval of the Engineer.
         (b)   If the use of drainage pumps is permitted, the drainage system shall be so designed as to provide for gravity outfall during the summer months and other periods of low water stages. If a low stage gravity outfall is impossible or impractical, an alternate pump of smaller capacity for low stage flow shall be provided.
         (c)   Pumping installations shall be so designed to accommodate a design storm as specified in these standards. When a station contains gravity discharge, discharge capacity must be equal to the allowable outflow. When the station does not have a gravity discharge, pumping units must be designed to furnish 100% of allowable outflow with any one pump out. Any deviation from this criteria must receive the specific approval of the Engineer.
         (d)   Each pumping installation shall require approval for each of the following items: electrical system, piping system, pumps, housing installation and other miscellaneous design features.
         (e)   For facilities to be maintained by the county, a multi-pump system shall be provided and a pump house shall be required for the electrical control equipment conforming to the improvement standard drawings.
      (2)   Design.
         (a)   Pumping plant sites shall be fenced with a six-foot high chain link fence with three strand barbed wire and a ten-foot minimum width gate. The site shall also be provided with a paved access road. Unpaved areas within the fence boundary shall be sterilized with a soil sterilant.
         (b)   Adequate access shall be provided for cleaning the pump sump.
         (c)   Trash racks shall be provided upstream from the pumping plant. Provisions shall be made for easy cleaning of the trash racks.
         (d)   Hatch covers, where used, shall be of raised pattern aluminum floor plate, or other approved lightweight cover. Dissimilar metals shall be insulated from each other when necessary.
         (e)   Ladder rungs, where used, shall be of a non-slip variety.
   (J)   Temporary drainage diversion.
      (1)   Temporary drainage diversions, such as dams and pipe plugs, shall be located and constructed in such a fashion as to permit their removal during adverse weather.
      (2)   Locations and removal procedures for temporary drainage installations shall be approved by the Engineer, and these installations shall be removed when necessary to prevent damage to adjoining property.
   (K)   Fence requirements.
      (1)   Where required.
         (a)   Improved channels, detention basins and retention ponds in developed areas exceeding one and one half feet in depth and with side slopes steeper than five to one shall be fenced with six-foot chain link fence. In all other areas, fencing shall be placed only upon the recommendation of the Engineer.
         (b)   The fence shall be located six inches within the required drainage easement lines.
      (2)   Access. Double panel access gates shall be required for all vehicular access. The minimum width shall be ten feet and shall be based on the specific application.