§ 35-29.4. Streets and stormwater inlets.

(a)

Design frequency.

(1)

Streets and roadway gutters: conveyance storm event.

(2)

Inlets on-grade: conveyance storm event.

(3)

Parking lots: conveyance storm event.

(4)

Storm drain pipe systems: conveyance storm event.

(5)

Low points: flood mitigation storm event.

(6)

Street ROW: flood mitigation storm event.

(7)

Drainage and floodplain easements: flood mitigation storm event.

(b)

Design criteria.

(1)

Streets and ROW. Depth in the street shall not exceed top of curb or maximum flow spread limits for the conveyance storm. The flood mitigation storm shall be contained on-site or within dedicated right-of-way and easements.

(2)

Parking lots. Parking lots shall be designed for the conveyance storm not to exceed top of curb with maximum ponding at low points of one (1) foot. The flood mitigation storm shall be contained on-site or within dedicated easements.

(3)

Flow spread limits. Inlets shall be spaced so that the spread of flow in the street for the conveyance storm shall not exceed the guidelines listed in Table 35-29E, as measured from the gutter or face of the curb:

Table 35-29E - Flow Spread Limits
Street Classification	Allowable Encroachment
Collectors, Arterial, and Thoroughfares (greater than 2-lanes)	- 8 feet or one travel lane, both sides for a divided roadway
Residential Streets	- curb depth or maximum 6 inches at gutter

 

(4)

Storm drain pipe.

a.

For ordinary conditions, storm drain pipes shall be sized on the assumption that they will flow full or practically full under the design discharge, but will not be placed under pressure head. The manning equation is recommended for capacity calculations.

b.

The maximum hydraulic gradient shall not produce a velocity that exceeds fifteen (15) feet per second (fps). Velocities for storm drainage design must comply with Table 35-29F, unless otherwise approved by the city engineer. Storm drains shall be designed to have a minimum mean velocity flowing full at two and a half (2.5) fps.

Table 35-29F Desirable Velocity in Storm Drains
Description	Maximum Desirable Velocity
Culverts (All types)	15 fps
Storm Drains (Inlet laterals)	No Limit
Storm Drains (Collectors)	15 fps
Storm Drains (Mains)	12 fps

 

;adv=6;c.

The minimum desirable physical slope elevation exceeds one (1) foot below ground elevation for the design flow, the top of the pipe, or the gutter flow line, whichever is lowest, adjustments are needed in the system to reduce the elevation of the hydraulic grade line.

d.

Access manholes are required at intermediate points along straight runs of closed conduits in accordance with the maximum spacing criteria shown in Table 35-29G.

Table 35-29G Access Manhole Spacing Criteria
Pipe Size (inches)	Spacing (feet)
42 and smaller	330 to 650 (MAY)
48 and larger	650 to 1150 (MAY)

 

e.

Pipe hydraulic grade line (HGL) shall be below the throat of inlets.

(5)

Manholes.

a.

The owner shall provide a manhole at all locations where the diameter of the trunk line pipe changes or where the cross-sectional dimensions of the trunk line box changes.

b.

The owner shall provide a manhole at all locations where the spacing between two (2) or more laterals intersecting the trunk line is equal to or less than ten (10) feet.

(Ord. No. 2017-10008, § II, 10-26-17)