(A) Storm drain hydraulics.
(1) The hydraulic design of storm drain systems includes the determination of flow peaks, the evaluation of street and gutter flow, capacity and spacing of inlets and hydraulic grade line computations for the underground conduits. The procedures provided within §§ 152.30 - 152.39 shall be used for determining flow peaks for the design of storm drain systems. A number of widely distributed manuals are available which provide hydraulic design procedures for evaluation of street and gutter flow, inlet design and hydraulic grade line calculations, as listed below.
Urban Storm Drainage Criteria Manual (Vol. 1, 2, & 3, June 2001), Denver Regional Council of Governments.
Drainage of Highway Pavements (HEC-12) (1984), Federal Highway Administration.
Design of Urban Highway Drainage - The State of the Art, Federal Highway Administration (1979).
Drainage Design Manual for Maricopa County, Arizona, Volume II - Hydraulics (August, 2013).
(2) A number of computer programs are available for performing hydraulic grade line (HGL) calculations. The use of appropriate computer programs are acceptable; however, in order to facilitate review and approval by the Public Works Department, the results of any HGL computation should be compiled on a standard Hydraulic Grade Line Calculation Sheet such as is provided on Figure 7.2. In addition, a profile plot of the hydraulic grade line shall be provided which, at a minimum, provides pipe invert elevations, the hydraulic grade line, energy grade line, ground surface, pipe sizes, junctions, curves, angle points, man-holes, laterals and the downstream controlling tail water.
(B) Inlet clogging design factors. The following guidelines shall be followed to provide an appropriate factor of safety against clogging of pavement inlets:
(1) Grates.
(a) Sump conditions.
1. Orifice flow: required area = 2 x calculated area.
2. Weir flow: required perimeter = 2 x calculated perimeter.
(b) Continuous-grade conditions: Required length of opening = 2 x calculated length.
(2) Curb opening inlets.
(a) Sump conditions: required length of opening = 1.5 x calculated length.
(b) Continuous-grade conditions: Required length of opening = 1.25 x calculated length.
(3) Combination grate and curb opening.
(a) Sump conditions.
1. Orifice flow: required area = 2 x calculated area for grate; required length = 1.25 x calculated length for curb inlet.
2. Weir flow: required perimeter = 2.0 x calculated perimeter for grate; required length = 1.25 calculated length for curb inlet.
(b) Continuous-grade conditions: required length of opening = 1.5 x calculated length for grate; required length = 1.25 x calculated length for curb inlet.
(4) Slotted drains.
(a) Sump conditions: required length = 2 x calculated length.
(b) Continuous-grade conditions:
1. Parallel to flow: required length = 1.5 x calculated length.
2. Perpendicular to flow: Do not use.
(C) General guidelines. These general guidelines shall be used unless more detailed information related to clogging for a specific grate type is available from the manufacturer. All storm drain inlet grates shall be designed to prevent bicycle tire penetration (i.e. "bicycle-safe" grates).
(Res. 1637, passed 2-28-02; Am. Res. 2871, passed 9-17-15; Am. Ord. 872, passed 9-17-15)
