Contra Costa County Municipal Code Ch. 914-8 Conduits

Closed conduits, including under-driveway culverts and street-crossing culverts, shall be of a size adequate to carry the design flow, but shall not be smaller than eighteen inches inside diameter.

(Ords. 89-28, 78-5).

Minimum flow line gradients for closed conduits shall not be less than three one-thousandths foot per foot.

(Ords. 89-28, 78-5).

Closed conduits shall not be designed to operate at high velocities when site conditions may yield an erosive bed load in the facility.

(Ord. 89-28).

Where the outlet velocity from a closed conduit exceeds the maximum allowable velocity for the storm drainage facility receiving the flow, suitable protective works shall be constructed to dissipate the flow. At a minimum, the outlet end of the closed conduit shall be protected by a cutoff wall and the placement of loose riprap. The protective works shall be those specified by a licensed engineer and shall be based on enginering calculations of allowable flow velocities.

(Ords. 89-28, 78-5).

All pipe or culverts intended for use within the roadway shall be of a class or gauge recommended by the manufacturer and approved by the public works department for the cover and service conditions required and shall provide a minimum service life of fifty years. Pipe or culverts for use outside the roadway may be of any approved type and strength to meet field conditions. Metal pipe shall not be used in arterial, thoroughfare or collector streets. Corrugated steel and aluminum pipe shall be bituminous coated unless the soil and drainage water have pH or resistivity values approved by the public works department. Additional protective coating or paving of metal pipes may be required for severe service conditions. The class or gauge of pipe or culvert proposed at each location shall be noted on the improvement plans.

(Ord. 89-28, 78-5).

Storm drain inlets shall be of a design approved by the public works department. Pipelines shall be aligned with the storm drain inlet in such a manner and direction as not to cause a reversal of direction of the flow of the water and as not to enter through a corner of the inlet.

(Ords. 89-28, 78-5).

Water within street areas shall be placed in closed conduits when the maximum depth of computed flow exceeds the capacity of the gutter or creates a traffic hazard or endangers property. Storm water in natural or improved earth channels shall be placed in closed conduits or concrete lined channels, except where the quantity exceeds eighty cubic feet per second, or except as provided otherwise in Chapter 914-4.

(Ords. 89-28, 78-5).

Storm drainage facilities shall allow for tidal action and flood stage where applicable. The hydraulic pressure elevation in any storm drainage facility shall be at least fifteen inches below the top of any inlet grate or manhole.

(Ords. 89-28. 78-5).