§ 1. Storm drainage.

(a)

Standards to be used in designing a storm drainage system are as follows:

(1)

Development plans shall not increase the natural stormwater discharge rate from the site.

(2)

Storm drainage pipes shall have a minimum cover of three feet between the top of ground and the exterior crown of the culvert.

(3)

Sizing and location of all drainage structures shall be the responsibility of a registered professional engineer, subject to approval by the city engineer.

(4)

Storm drainage pipes shall be a minimum of 15 inches in diameter except where the development is not fed by upstream discharge. In such cases a minimum of 12 inches may be used.

(5)

State highway standard 1030D (or most current) shall be used in determining the class (concrete) or gauge of pipe under fill, method of backfilling, and pipe installation.

(6)

Storm drainage pipes shall have a minimum slope of 1.0 percent for metal pipe and 0.5 percent for concrete pipe, but in no case shall the flow be less than three cubic feet per second.

(7)

The rational method or a similar method approved by the city engineer shall be used in determining the size of drainage structures.

(8)

The rational method shall use a 25-year storm or rain as the stated frequency, except where the development is not fed by upstream discharge. Such cases may use a ten-year storm. A cross drain carrying a watercourse under a street shall use a 100-year frequency.

(9)

A hydrology report shall be submitted to the city engineer. This report shall show all calculations used in sizing ditches, pipes, detention ponds and other drainage structures. A drainage area map delineating all drainage basins pertaining to the site shall be included.

(b)

Drainage easements shall be a minimum of 20 feet wide when used as an open ditch. Piped storm drainage shall have a permanent ten-foot-wide easement.

(c)

Catchbasins and/or drop inlets shall be designed by the developer's engineer or registered surveyor to state highway standards and subject to final approval by the city engineer.

(d)

Street water shall be limited to a maximum distance as follows:

(1)

Five hundred feet on grades up to seven percent;

(2)

Four hundred feet on grades from seven percent to ten percent;

(3)

Two hundred fifty feet on grades over ten percent;

unless otherwise approved by the city engineer.

(e)

Subdrainage will be installed to control the surplus groundwater by intercepting sidehill seepage or by lowering or regulating the groundwater level where such conditions exist.

(f)

A certification of the pipe specifications for each pipe shall be required before installation.

(g)

Bridges shall be designed for a 50-year storm frequency.

(h)

Cross drain pipes shall:

(1)

Be sized for the 100-year storm frequency;

(2)

Be no less than 18 inches in size when under the street;

(3)

Have headwalls of an approved type on inlet and outlet ends of the pipe;

(4)

Extend from edge of right-of-way to edge of right-of-way if larger than 30 inches in diameter;

(5)

Have a maximum continuous length of pipe of 300 feet;

(6)

Have junction boxes having access to the pipe constructed to meet the requirements of state standard 1030D (or most current);

(7)

Be constructed of reinforced concrete when under the street.

(i)

Materials and installation.

(1)

Concrete pipe shall be reinforced within the right-of-way but may be plain pipe outside of the right-of-way. Flat bottom and circular pipe sections shall be laid in a prepared trench with the socket ends pointing upstream. Sections may be joined by mortar joints, bituminous plastic cement joints, rubber-type gasket joints, O-ring gasket joints, or preformed plastic gasket joints. In bituminous plaster cement joints, the annular space shall be filled with joint material and the inside of each joint wiped smooth. Mortar joints shall be thoroughly wetted before filling with joint material. After the initial set, the mortar on the outside shall be protected from the air and sun with thoroughly wet earth or burlap cover. Rubber type, O-ring and preformed plastic gasket joints shall be installed in accordance with the manufacturer's recommendations.

(2)

Metal pipe shall be fully coated inside or outside of the right-of-way.

a.

Workmanship and finish. Culvert pipe on which the spelter coating has been bruised or broken either in the shop or in shipping, or which shows defective workmanship, shall be rejected. Among others, the following defects are specified as constituting poor workmanship, and the presence of any or all of them in any culvert pipe shall constitute sufficient cause for rejection:

1.

Uneven laps;

2.

Elliptical shaping;

3.

Variation from a straight centerline;

4.

Ragged or diagonal sheared edges;

5.

Loose, unevenly lined or spaced rivets;

6.

Poorly formed rivet heads;

7.

Unfinished ends;

8.

Illegible brand;

9.

Lack of rigidity;

10.

Bruised, scaled or broken spelter coating;

11.

Dents or bends in the metal itself.

b.

Coupling bands. Field joints shall be made with bands of the same base metal as the culverts. The bands shall be not less than seven inches wide for diameters of eight inches to 30 inches, inclusive; not less than 12 inches wide for culverts with diameters 36 inches to 60 inches inclusive; and not less than 24 inches wide for culverts with diameters greater than 60 inches. Such bands shall be so constructed as to lap on an equal portion of each of the culvert sections to be connected at the ends by galvanized angles having minimum dimensions of two inches by two inches by 3/16 inches. The seven-inch band shall have at least two galvanized bolts not less than one-half inch in diameter. The one-half-inch band shall have three and the 24-inch band shall have five one-half-inch bolts. Other equally effective methods of connecting the coupling bands may be used if approved by the city engineer.

(j)

Gauge determination and tolerances. The gauge of the culvert metal will be determined from the thickness of the galvanized sheets. The mean thickness and the permissible variations therefrom for each gauge are as shown:

WEIGHT AND GAUGE TOLERANCES

			Permissible Variation in Thickness (in inches) for Coil Width (in inches)
Gauge Number	Weight (ounces per square feet)	Mean Thickness* (inches)	Up to 15	Over 15 to 32, Inclusive
8	112.5	0.1681	0.008	0.009
10	92.5	0.1382	0.008	0.009
12	72.5	0.1084	0.008	0.009
14	52.5	0.0785	0.007	0.007
16	42.5	0.0635	0.007	0.007
18	34.5	0.0516	0.006	0.007

 

*Thickness measured on tangent of corrugation.

_____

(k)

Corrugated aluminum or steel pipe and pipe-arches.

(1)

Pipe sections shall be laid in a prepared trench with outside laps of circumferential joints pointing upstream and with longitudinal joints at the sides. Coupling bands, fastened by two or more bolts, shall join the sections. The space between adjoining sections shall be not more than the width of one corrugation.

(2)

All damaged spots in galvanized coating that expose the base metal shall be repaired before the structure is backfilled. All damaged spots in bituminous coating that expose the base metal shall be recoated with asphalt before the structure is backfilled.

(3)

Elongation of metal pipe shall be as shown on the plans. The contractor shall order the elongation of the vertical axis of the pipe to be done in the shop. Corrugated metal pipe shall be shipped with wire-tie in the pipe ends. Wire-ties shall be removed as soon as possible after the fill is completed.

(l)

Before any traffic over a storm drain is allowed, the developer shall provide an adequate depth and width of compacted backfill to protect the structure from damage or displacement. Any debris or silt that constricts the flow through a pipe shall be removed by the developer as often as necessary to maintain drainage. All pipe structures shall be cleaned before the work is accepted. Any damage or displacement that may occur due to traffic or erosion shall be repaired or corrected at the developer's expense.

(m)

Minimum clearances are:

(1)

Two feet between the bottom of the base, or subbase if used, and the exterior crown of the culvert.

(2)

A minimum of 1.0 foot between underground utilities and exterior crown of culverts.

(n)

Trench construction for storm drainage pipe shall be in accordance with state highway standard 1030D (or most current).

(o)

Storm drainage pipe shall be bedded in Type 57 gravel if firm soil is not available.

(p)

Bridge piling shall be driven to state highway load standards for loading. Certification of pile load shall be by a registered professional engineer.

(q)

Changes in construction plans caused by field conditions shall be made at the direction of the community development department with the cost of such changes to be paid by the developer.