§ 8.3. Culverts and piped drainage systems.

8.3.1 Drainage improvements required. Stormwater conveyance facilities, which may include but are not limited to culverts, storm drainage pipes, catch basins, drop inlets, junction boxes, headwalls, gutters, swales, channels, and ditches, shall be provided for the protection of public rights-of-way and private properties adjoining projects sites and/or public rights-of-way.

8.3.2 Standard specifications. Unless otherwise specifically set forth herein or in the Paulding County Standard Details, all of the materials, methods of construction, and workmanship for the work covered in reference to stormwater conveyance facility construction shall conform to the most recent Standard Specifications of the Georgia Department of Transportation (Georgia DOT).

8.3.3 Design criteria; general.

1)

All stormwater conveyance facility design calculations shall be certified by a professional engineer currently registered in the State of Georgia.

2)

Stormwater flows from drainage areas up to 200 acres in size may be calculated using the Rational Method. Flows from drainage areas between ten and 2,000 acres in size may be calculated using the SCS Method or other approved methods. Flows for drainage areas larger than 2,000 acres in size must be calculated using published FEMA data or USGS Regional Regression Analysis.

3)

Runoff coefficients used for pre- and post-development conditions for the rational method shall be consistent with standard engineering practices. For the SCS method the runoff Curve Numbers found in the Manual for Erosion and Sediment Control in Georgia; shall be used. For any stormwater analysis, the composite "C" (rational method) or CN (SCS Method) used for pre-developed conditions shall not exceed 0.3 or 66, respectively, unless prior approval has been obtained through the community development department.

8.3.4 Design criteria; culverts.

1)

Culverts (structures designed to convey water from one side of a public right-of-way to the other and carry the runoff from a contributing drainage area) shall be designed to pass the peak flow associated with a 100-year storm with at least one foot of freeboard between the 100-year ponding elevation and the top of the roadway shoulder, without rising the 100-year flood elevation on upstream properties, and in accordance with article 10 of these regulations.

2)

All pipes are to be designed for inlet and outlet control conditions. Appropriate charts and tables are to be placed on the plans.

3)

The 100-year ponding limits above the culvert shall be shown on the construction plans and on the final plat (if applicable).

4)

The minimum allowable culvert diameter shall be 18 inches.

5)

Culvert design is to be in accordance with the methods contained in the Georgia DOT Drainage manual for highways , chapter 7, and shall include a thorough analysis of both inlet and outlet control structures.

8.3.5 Piped collection systems.

1)

The design (initial pipe sizing and profile design) of piped collection systems required under 8.3.1 herein shall be based upon conveyance of the peak flows associated with a 100-year storm with the hydraulic grade line being at or below the structure throat throughout the system.

2)

Based on the analysis of 100-year conditions, the preliminary design shall be revised where necessary to produce a final design for which the likelihood of dwelling flooding, major property damage, or substantial public access and/or utility interruption shall be less than one chance in 100 years.

3)

Catch basins 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 community development department. This chart may be used for street water in lieu of calculations per structure:

500 feet on grades up to seven percent

400 feet on grades from seven percent to ten percent

250 feet on grades over ten percent

4)

Catch basins shall be spaced so that the spread in the street for a 50-year design flow shall not exceed six feet, as measured from the face of the curb. Gutter spread calculations are required if the above chart is not used.

5)

Complete flow, velocity, and hydraulic grade line computations, shall be provided for all portions of a piped collection system. Hydraulic grade lines shall be shown on the storm drainage profiles contained with the development plans for the 100-year storm.

6)

Should a bridge ever be required it must meet all Georgia DOT standards.

7)

Inverts are required in all structures, leaving no standing water. All inverts are to be constructed of grout or concrete.

8)

All structures are to be precast concrete or brick construction in accordance with Georgia DOT standard details.

9)

On final plats, problem lots will require a residential drainage plan and house location plan prior to obtaining a building permit. Problem lots are to be determined by the community development department. Residential drainage plans shall be drawn at one inch equals 50 feet minimum with two-foot existing and proposed topography. In addition, for each problem lot, an as-built survey of the dwelling, building or structure shall be provided to the community development department prior to final inspections and the issuance of a certificate of occupancy. In the event the as-built survey shows the dwelling does not have proper setbacks, flood standards set forth herein article 10, floor elevations or other discrepancies, the community development department may deny the issuance of the certificate of occupancy.

10)

Maximum continuous length of pipe shall be 300 feet.

11)

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 restricts 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 erosion shall be repaired or corrected before final acceptance by the county.

12)

Trench construction for storm drainage pipe shall be in accordance with State Highway Standards 1030D (or most current).

13)

Storm drainage pipe shall be bedded in No. 57 gravel, if firm soil is not available.

14)

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

15)

Storm drainage pipes shall be sloped so as to maintain a minimum velocity of three FPS (feet per second) so that sediment will not collect.

16)

State Highway Standard 1030D (or most current) shall be used in determining class (concrete) or gauge of pipe underfill, method of backfilling and pipe installation.

8.3.6 Energy dissipation; piped systems and culvert.

1)

Energy dissipation devices, such as splash pads, rip-rap, stilling basins, etc., shall be provided at the outlet of every culvert and piped collection system. (Please refer to the Manual for Erosion and Sediment Control in Georgia.)

2)

Energy dissipation devices shall be located entirely within the project site, and shall not encroach upon any required buffer.

3)

When uniform, graded stone rip-rap is used for energy dissipation, ultraviolet resistant filter fabric (200-pound test) shall be used between the stone layers.

8.3.7 Minimum pipe specifications.

1)

Galvanized corrugated steel pipe and pipe arches shall conform to the requirements of Type I or II pipe per AASHTO M-36 for the specified dimensions and thickness. Corrugated steel pipe shall have a minimum of two ounces per square foot of zinc coating, complying with AASHTO M-218.

(a)

All corrugated galvanized pipe located within a street right-of-way, drainage easement, or detention facility shall be asphalt coated. All corrugated galvanized pipe that will carry a live stream, within a street right-of-way, drainage easement, or in a detention facility shall be either 1) asphalt coated with a paved invert per AASHTO M-190, Type C, or 2) asphalt coated with a concrete lining. The lining shall be plant applied so as to produce a homogeneous nonsegregated lining throughout. The lining shall have a nominal thickness of ¼-inch above the crest of the corrugations.

(b)

See the standard details for minimum acceptable combinations of gages, diameters, and corrugation configurations for corrugated steel pipe and pipe arches (Georgia DOT 1030-D).

(c)

Each end of each pipe section, to be joined by a coupling band, shall have a minimum of two annular corrugations. Coupling bands shall be so constructed as to lap on an equal portion of each of the pipe sections to be connected. The connecting bands shall have a minimum of two annular corrugations and shall fully engage, over the entire pipe periphery, one corrugation on each pipe end. Bands shall be fabricated from the same material as is the pipe, and the gauges shall be as specified in Section 9.2 of AASHTO M-36.

(d)

Gaskets may be required as determined by the department in the field and shall be either sleeve type or 0-ring type, and shall meet the requirements for gaskets as specified in Section 9.3 of AASHTO M-36.

2)

Reinforced concrete pipe shall be required at the entrance of any subdivision containing more than 100 lots. Reinforced concrete pipe shall be in not less than eight foot joint lengths. All joints shall be bell and spigot type, using an 0-ring gasket conforming to ASTM C-443. Pipe shall be manufactured in accordance with AASHTO M-170 and/or ASIM C-6. Class of pipe and wall thickness shall be in accordance with 1030-D, Georgia DOT specification, Table No. 1.

3)

Aluminized steel-coated pipe shall comply with AASHTO M-274 for the coating and AASHTO M-36 for the pipe fabrication. Aluminum alloy pipe shall comply with AASHJ M-196 for material and fabrication.

(a)

See the standard details for the minimum acceptable combinations of gages, diameters, and corrugation configurations for corrugated aluminum pipe and pipe arches, and for corrugated aluminized steel pipe and pipe arches (Georgia DOT 1030-D).

(b)

Each end of each pipe section, to be joined by a coupling band, shall have a minimum of two annular corrugations. Coupling bands shall be so constructed to lap on an equal portion of each of the pipe sections to be joined. The connecting bands shall have a minimum of two annular corrugations and fully engage, over the entire pipe periphery, one corrugation on each pipe. Bands shall be fabricated from the same material as the pipe. The minimum band gauges for aluminum pipe and aluminized pipe shall be as specified in AASHTO M-196, Section 19, and AASHTO M-36, Section 9, respectively.

(c)

Gaskets may be required as determined by the department in the field, and shall be either sleeve type or 0-ring type and shall meet the requirements for gaskets as specified in AASHTO M-36, Section 9.3.

4)

Structural plate drainage structures shall conform to the following specifications:

(a)

Corrugated steel structural plate pipe, pipe arches, and arches shall consist of galvanized plates, bolts and nuts of the size, shape and thickness as shown on the approved plans. These structures shall conform to the requirements of AASHTO M-167.

(b)

Corrugated aluminum alloy structural plate pipe, pipe arches and arches shall consist of aluminum plates and galvanized bolts and nuts of the size, shape and thickness as shown on the approved plans. These structures shall conform to the requirements of AASHTO M-219.

8.3.8 Pipe length.

1)

Culverts carrying live streams shall extend to where the crown of the pipe intersects the roadway slope.

2)

Pipes that do not carry live streams shall extend at least 50 feet beyond the front building setback lines, and may be required to extend farther where necessary to provide an adequately protected building site on the property. In nonresidential subdivisions, these pipes may temporarily end at the right-of-way line, but shall be extended as part of a subsequent development permit approved for the individual site.

8.3.9 Pipe installation. Reinforced concrete pipe, corrugated steel pipe, corrugated aluminum pipe and corrugated aluminized steel pipe shall be bedded and backfilled in the same manner.

1)

Bedding. All pipe structures shall be placed on stable earth or No. 57 rock, the characteristics of which would be expected to provide long-term stability. In all live stream pipe installations, in areas of low bearing soils or nonuniform foundations, in areas where rock is encountered at the foundation level, or in other locations where conditions warrant, a minimum of six inches of No. 57 bedding is required.

2)

Geotextiles or geogrids may also be required by the department in problem areas.

3)

Backfilling. Backfill on all pipe installations shall be constructed using foundation backfill material Type I or Type II, as specified in Section 812.01 and 812.02 respectively, in GA. DOT Standard specifications. These materials shall be placed in layers of not more than six inches loose. Compaction of these materials shall be accomplished by hand tamping or machine tamping. Required compaction levels are as follows:

(a)

Backfill within all street rights-of-way shall be compacted to 95 percent maximum density, tested using the AASHT0 Method T-99.

(b)

Backfill in all other areas shall be compacted to 95 percent maximum density, tested using the AASHT0 Method T-99.

4)

Construction loads and minimum covers. If drainage pipe is installed prior to the completion of grading, a minimum of four feet of fill should be provided here needed to adequately protect the drainage structure during the land development phase, unless the structure itself is designed to withstand the anticipated live load during construction.

8.3.10 End finish.

1)

Headwalls or other end treatments are required on all culverts (except under residential driveways) and at the outlet of all piped collection systems.

2)

Headwalls are to be precast concrete, stone masonry with reinforced concrete footings, or poured-in-place, reinforced concrete with reinforced concrete footings.

3)

End treatments that conform to the slope may be masonry, pre-cast concrete end sections, reinforced poured-in-place slope collars, or grouted rip-rap. Concrete end sections shall conform to Georgia DOT Specification 1120. Concrete headwalls are required on all pipes.

8.3.11 Junction boxes and catch basins. Junction boxes having access to the pipe shall be constructed to meet the requirements of the Georgia Department of Transportation standards (or most current). All pipe junctions shall have junction boxes. Junction boxes and catch basins shall have metal manhole frames and lids for access.

8.3.12 Other structures. Natural bottom arches and box culverts may be used in accordance with the latest Standard Specifications of the Georgia DOT.