§ 7.5-66. Storm drainage design criteria.

(1)

Storm sewers:

(a)

All storm sewer design calculations shall be certified by a professional engineer, land surveyor or landscape architect currently licensed in the State of Georgia.

(b)

Storm drainage pipes shall be sloped so as to maintain a minimum velocity of three (3) feet per second (fps) during the two-year design storm event in order that sediment will not collect.

(c)

Drainage formulas used in determining size of storm sewer components shall meet all criteria of: "STORMWATER MANAGEMENT MANUAL," Latest Revision, facilitated by the Atlanta Regional Commission, the Georgia Department of Natural Resources-Environmental Protection Division and thirty-five (35) cities and counties across Georgia.

(d)

The 25-year storm event shall be used in designing the storm drains. In cases where the property is traversed by a spring, creek, or other watercourse, the one hundred-year storm event will be used for design.

(e)

Storm sewers shall not be less than fifteen (15) inches in diameter. No storm drain pipe running parallel to the existing primary road shall be located beneath the proposed entrance widening. Relocation of existing storm drainage structures shall be done by the developer.

(f)

Storm drainage structures or drainage ways shall not be located within twenty (20) feet of any existing or proposed building.

(g)

Storm sewers shall extend at least from edge of right-of-way to edge of right-of-way. Residential subdivision storm sewers shall extend at least to the rear of the building on all piping.

(h)

Catch basins, junction boxes, drop inlets and outlet structures shall have a minimum elevation drop from the inlet invert elevation to the outlet invert elevation of at least 0.20 feet.

(i)

Maximum continuous length of pipe without a junction box, drop inlet, or catch basin, shall be three hundred (300) feet for pipes less than forty-two (42) inches in diameter, and five hundred (500) feet maximum for pipe greater than forty-two (42) inches in diameter.

(j)

Storm sewers shall be reinforced concrete pipe (RCP) within the right-of-way of an existing or proposed street.

(k)

Aluminum storm drain piping shall be encased in a polyethylene wrap when it is located within twenty (20) feet of a steel gas line. Contact the City of Cartersville Gas Department for specifications.

(2)

Drainage structures (excluding pipe or culverts):

(a)

The design engineer shall check the hydraulic capacity of each drainage structure designed as an inlet point in the drainage system. The actual stormwater flows shall be compared with the structures flow capacity to insure their capacity is not exceeded.

(b)

Catch basins shall be constructed in accordance with the Georgia Department of Transportation Standard Details 1033D and/or 1034D.

(c)

Catch basins shall be located outside of intersection radii.

(d)

Catch basin spacing from each other shall be limited to a maximum distance as follows:

Two hundred fifty (250) feet on grades up to seven (7) percent.

Four hundred (400) feet on grades from seven (7) percent to ten (10) percent.

Five hundred (500) feet on grades over ten (10) percent.

No curb cuts in lieu of drainage structures will be allowed.

(e)

The outlet end of all storm drain pipes shall have either flared-end sections or concrete headwalls which meet Georgia DOT Standards 1120 or 1125. This same standard applies to the inlet end of storm sewers where an open pipe is designed to collect the runoff. Flared ends shall be of the same material as the storm drain pipe.

(f)

Drop inlets shall be designed to Georgia DOT Standard Detail 1019A. Weir drop inlets shall be provided in landscaped areas. Grated drop inlets shall be provided in paved areas.

(g)

Junction boxes or manholes having access to the pipe shall be constructed to meet the requirements of Georgia DOT Standard Detail 9031U or 1011A. Manholes shall be provided with eccentric cone sections.

(h)

All drainage structures shall have a minimum elevation drop from the inlet invert elevation to the outlet invert elevation of at least 0.20 feet.

(i)

Stormwater management facilities having a depth, including freeboard, greater than or equal to four (4) feet shall be fenced and have a ten-foot wide lockable gate for entrance and maintenance. The fence shall be a minimum of four (4) feet in height and shall be of the vinyl-coated chain link, decorative, or wooden privacy type. If the side slopes are 3 (horizontal) to 1 (vertical) (3:1) or flatter, then safety benches with an average width of fifteen (15) feet may be used in lieu of a fence. If side slopes are 4 (horizontal) to 1 (vertical) (4:1) or flatter, then a fence will not be required.

(j)

Stormwater ditches:

1.

All ditches between storm drain pipes and downstream of storm drain pipe shall be designed by a professional engineer or landscape architect currently licensed in the State of Georgia.

2.

The ditch profile and cross-sections shall be shown on the plans. The plans shall show the velocity and flow for the ditch design. Drainage ditches shall be designed to limit the runoff velocity to less than five (5) fps or the ditch shall have the bottom and sides lined with sod. Ditches shall be designed to limit the runoff velocity to less than eight (8) fps or the ditch shall have a paved invert as shown in section 7.5-70, standard details, details 3.8.17a and 3.8.17b.

3.

In residential subdivisions, all ditches are to be installed and apparent prior to approval of the final plat.

(k)

Subdrainage: When subgrade compaction requirements of these specifications cannot be met, subdrainage will be installed to control the surplus ground water by intercepting side-hill seepage or by lowering or regulating the ground water level.

(l)

Bridges: Bridges shall not be allowed unless otherwise approved by the public works department.

(m)

Existing dams:

1.

It shall be the responsibility of the developer to provide any required information or studies, to include the dam breach analysis, for any dam located on the property proposed to be developed or located on adjacent property upstream of the proposed development, to the City of Cartersville. The design engineer shall search the entire watershed upstream of the property for other dams regulated by the state. The City of Cartersville shall maintain a record of dams reported to the city and their attendant breach zones. The design engineer shall include a statement in the dam breach analysis report whether or not any dams were found upstream and whether or not they affect the property to be developed.

2.

The City of Cartersville shall submit the required information to the Environmental Protection Division of the Georgia Department of Natural Resources for review.

3.

The City of Cartersville shall notify the dam owner in accordance with the procedures set forth in the Georgia Safe Dams Act.

4.

If development is proposed in the breach zone below the dam, then the dam owner shall be required to upgrade the dam to Category I standards, as defined in the Georgia Safe Dams Act, or breach the dam in a safe manner as authorized by the Environmental Protection Division of the Georgia Department of Natural Resources. If the dam owner elects to breach the dam, measures must be taken to ensure that stormwater flows are not increased on downstream property owners.

(n)

Proposed dams: The developer of any proposed new dams which are regulated by the Georgia Safe Dams Act shall obtain necessary permits and approvals from the State of Georgia prior to obtaining a development permit from the City of Cartersville. A development permit shall be required before the construction of said dam.

(Ord. No. 25-07, § 1, 6-7-07; Ord. No. 24-17, § 1, 7-20-17)