Sugar Hill › Development Regulations

Article 8 — Site Grading, Stormwater Management, Culverts and Piped Drainage Systems and Soil Sediment Control Requirements

current as of 2020-12-14verified current · checked 2026-08-24Officialofficial source ↗9 sections · full chapter

§ 8.1

Site Grading.

8.1.1 Grading shall be done in accordance with the lines and grades shown on the approved Grading

Plan.

8.1.2 Grading plans shall show existing and proposed contour lines at an interval of no more than 2

feet. Grading plans shall outline the areas which are required to remain undisturbed (i.e., Tree Protection Areas, buffer, etc.) and shall indicate protective fencing or staking to be placed surrounding such areas.

8.1.3 If the property is within the jurisdiction of the Metropolitan River Protection Act, the grading

shall be consistent with the River Corridor Certificate approved for the project.

8.1.4 Embankments shall be placed in uniform layers not to exceed a compacted thickness of 6 inches

per layer and shall be compacted to a density of 95 percent of the maximum laboratory dry weight per cubic foot as determined by AASHTO Method T-99 in all areas where structure, parking lots and drives, streets, and utilities are to be placed. All other embankments are to be compacted to at least 85 percent.

8.1.5 The maximum slopes for cut or fill shall be 2:1 (two feet of horizontal run for each foot of rise or

fall), except as discussed in Section 8.1.6 below. The depth of cut referred to herein shall be the maximum cut or fill occurring in any one section of cut or fill. The slope of cut or fill shall be uniform throughout for each section of cut or fill except when benching is approved by the City. Cut or fill greater than or equal to 2.5:1 (two and a half feet of horizontal run for each foot of vertical rise or fall) shall incorporate a slope drainage bench at every fifteen (15) feet of slope length. Each slope drainage bench shall incorporate a permanent down drain system and be constructed in accordance with the approved standard drawing. When a cut is made in rock that requires blasting, the slope may be steeper if pre-splitting is employed and upon submission of a geotechnical report which substantiates the integrity of the rock in the steeper condition, subject to the review and approval of the City Manager. (Note: No blasting shall occur without a valid permit issued by the Fire Services Division.) Refer to the Standard Plans for grading section and retaining wall details.

8.1.6 While most soils in the area can be safely stabilized at a 2:1 slope, some soils exhibit a low

shearing resistance and a low cohesiveness. These soils typically are micaceous silts and sandy soils with little or no clay. If the 2:1 slope shows evidence of shearing, non-cohesiveness, sliding, or inability to maintain compaction, the slope shall be stabilized at 3:1 or by using such mechanical methods as needed (such as retaining walls or "grow mats" stapled in place) to maintain slope, height, and integrity.

8.1.7 Slopes greater than four (4) percent shall have a storm water collection system to convey water

from the top of a slope to the lowest point of a slope. Sheet flow drainage shall not be allowed to traverse a graded slope.

8.1.8 A grading plan showing building pad locations shall be submitted for residential subdivisions,

unless a modification application is approved, zoned for a lot size of less than 12,000 square feet or density of 4 units per acre or more. The intent of this regulation is to ensure adequate lot to lot drainage.

Granting a modification will not nullify the intent of these regulations when the layout has a minimum lot area of 14,520 square feet and minimum lot width of 90 feet. The grading plan may be used as a construction document prior to approval of the Final Plat or as a guidance document for individual lot grading after approval of the Final Plat. The grading plan must include the minimum floor elevations, drainage flow arrows and a designation of slab, basement or slab/basement for each lot.

8.1.9 Grading for roads and improved ditches shall be shown.

§ 8.2

Stormwater Management.

8.2.1 Stormwater Management Report Required

a.A Stormwater Management Report shall be prepared for every project. The purpose of this report shall be to formulate a plan to manage stormwater runoff so that stormwater runoff hazards are not created and existing runoff-related problems are not exacerbated, either upstream or downstream from or within the boundaries of the property being developed. The engineer shall be responsible for obtaining all information necessary for the report. Hydrologic analysis and detention pond hydraulics (excluding dams as defined in section 8.6 of these regulations), pipe and open channel hydraulics, culvert hydraulics and water quality best management practices shall be certified by either a professional engineer or landscape architect registered in the State of Georgia. Flood studies for any floodplain or flood prone areas, and hydrologic and hydraulic analysis and design calculations which are performed for the design of a dam as defined in Section 8.6 of these regulations, shall be certified by a professional engineer registered in the State of Georgia.

The Storm Water Management Report shall identify the locations and quantities of storm water runoff entering and exiting the site for both pre- and post-developed conditions.

Analysis of the off-site properties shall anticipate future development in addition to addressing existing conditions.

All culverts, pipe systems, and open channel flow systems shall be sized based on all on-site upstream areas being developed in accordance with the development plans and the off-site upstream areas being fully developed in accordance with the Land Use Plan with no detention. Upstream detention may be included when determining flows, provided the engineer calculates the reduced flows by routing the developed flows through any storm water facility included in the analysis rather than assuming the reduction will occur. The engineer shall show that detention facilities used in the analysis will remain, be properly maintained and the storage volume and outlet structure is based on current conditions.

Detention facilities shall be designed using pre-development flows based on existing conditions for all upstream areas including existing on-site lakes and detention. Post-development flows, except the 100-year flow, shall be based on on-site upstream areas being developed per the development plans and existing conditions for off-site upstream areas. The 100-year flow shall be based on on-site areas being developed per the development plans and the off-site upstream areas being developed per the Land Use Plan with no detention. Upstream detention may be included if it meets the conditions as described for culverts and pipe systems. Existing conditions shall be defined as the conditions of the site at the time of application for a land disturbance permit. The existing condition includes on-site lakes and ponds. Pre-development flows shall be determined by routing the pre-development flows through these storm water facilities. Flows used to size the outlet structures for detention facilities that exceed the 25-year design flow, shall be sized as described for culverts and pipe systems.

When more than 50% of the property of a developed project site is disturbed, the Storm Water Management Report shall be prepared for the entire site and existing impervious areas shall be treated as forest in the pre-developed analysis. When 50% or less of the property is disturbed, detention shall be provided as required by these regulations for the disturbed area and existing impervious areas which are disturbed shall be treated as forest in the pre-developed analysis. For redevelopment, the pre-developed conditions may take into account the existing conditions unless the existing development causes a negative impact on downstream property.

The report shall contain drainage area delineation maps and other exhibits at satisfactory scale and sufficient in quantity and scope to define the boundaries of the site, and off-site areas, relative to watercourses, drainage divides, drainage structures and other pertinent features. The City’s Geographical Information System (GIS) mapping information shall be used where appropriate.

b.For the purposes of these regulations, the words “downstream” and “analysis” shall have the following meanings. The analysis of downstream conditions in the report shall address each and every point or area along the project site’s boundaries at which runoff will exit the property. The analysis shall focus on the portion of the drainageway “immediately”

downstream from the project. This area shall extend downstream from the project to a point in the drainage basin where the project area is 10 percent of the total basin area.

(1)The report shall examine the conditions downstream from the project to a point where the project area is 10 percent of the total drainage basin.

(a)The analysis shall include all culverts, obstructions, existing and potential erosion problems, elevations of existing improvements, existing drainage complaints and any other existing modifications to natural conditions. The downstream water courses and receiving conveyance shall be analyzed to ensure that the channel velocities do not exceed values recommended in the Gwinnett County Stormwater Management Manual nor does the pipe system exceed current design criteria of these regulations; and,

(b)If the existing downstream conditions are overburdened by the pre-developed flows in the stream, then the developer and the City shall jointly participate to resolve the problem.

The meaning of “overburdened” shall include but not be limited to situations where 25-year velocities exceed the non-erosive velocity of the stream, habitable structures are shown to be subject to flooding for any frequency up to and including the regulatory flood and storm water facilities that can not carry the design storm in accordance with these regulations; and,

(c)If there are any problems identified downstream that are a result of the development, then the developer shall eliminate the conditions causing the problem.

(2)Hydrographs shall be analyzed at least at two points. One study point shall be at the downstream property line where the watercourse crosses the project site’s downstream property line. The second study point shall be downstream of the project at the point where the project area is 10 percent of the total drainage basin.

(a)The study will compare the pre-developed hydrographs with post-developed hydrographs for the 2, 5, 10, 25, 50, and 100-year flood frequencies; and,

(b)Comparison of peak flows shall include the timing of hydrographs; and

(c)Hydrographs shall be based on a 24-hour storm.

(d)The analysis shall be in accordance with the Gwinnett County Stormwater Management Manual d The following criteria shall be evaluated by the authorized registered professional (refer to Subsection 8.2.1. Paragraph a.) preparing the Storm Water Management Report, and in determining whether or not detention should be required for any portion of any site:

(1)Existing land uses downstream;

(2)Anticipated future land uses downstream;

(3)Magnitude of increase in peak flows due to development;

(4)Presence of existing drainage problems;

(5)Capacity of existing and anticipated drainage systems;

(6)Creation of concentrated flows where none had occurred previously;

(7)Availability of feasible locations for stormwater management facilities;

(8)Existing flows generated off-site which pass through the project site; and

(9)The nature of the receiving watercourse.

e.Where detention for a proposed project is provided in a regional detention facility that was permitted prior to September 1, 2002, the developer shall provide a copy of the original study that met the regulations at the time the facility was permitted. If the approved study can not be found, then the engineer shall provide a recreated study. The project shall be exempt from restudy and any modifications required to meet regulations effective after January 1, 2001, provided the proposed project is in keeping with the intent of the original detention study and the detention facility is maintained.

f.When a development uses an existing facility where the last approved certification and record drawing of the facility was over 18 months prior to the new development’s submittal, the engineer shall provide one of the following.

(a)A new survey, drawing and certification showing that the outlet structure is constructed as approved on the as-built plan and the flood storage and water quality volume of the facility is equal to or greater than the volume required when the facility was approved.

(b)Construction plans and calculations showing that the outlet structure will function as designed and the flood storage and water quality volume of the facility will be equal to or greater than the volume required when the facility was approved once the proposed maintenance has been performed.

(c)A new record survey, drawing, study and certification showing that the facility meets the development requirements when the facility was approved.

(d)Current inspection of existing stormwater management structures with deficiencies noted.

(e)BMP Landscaping Plans if required at the time of BMP construction.

g.Design Criteria – General All design related to storm water shall be in accordance with the Gwinnett County Stormwater Management Manual and the Gwinnett County Storm Sewer Pipe Standards

h.Evidence of Acquisition of Applicable Non-Local Permits The applicant shall certify and provide documentation that all other applicable environmental permits have been acquired for the site prior to approval of the Storm Water Management Report.

8.2.2 Stormwater Management Required

Stormwater management is intended to lessen the impacts of urbanization on the natural hydrology of the site. The goal is to reduce the amount of stormwater runoff and pollutants that are released, provide for natural onsite control and treatment of runoff, and optimize the location of stormwater management facilities. These goals are met through runoff reduction or water quality, channel protection, overbank flood protection and extreme flood protection. The hydrologic methodology used to accomplish these goals for any given project shall conform to the Gwinnett County Stormwater Management Manual.

Runoff reduction practices shall be sized and designed to retain the first 1-inch of rainfall on the site to the maximum extent practicable. Runoff reduction practices are stormwater best management practices (BMPs) used to disconnect impervious and disturbed pervious surfaces from the stormwater drainage system to reduce the post-construction stormwater runoff rates, volumes and pollutant loads. Runoff reduction shall be used where practical, prior to using water quality standards. If the runoff reduction requirements cannot be met in whole or part, then the water quality standards shall be used to treat the remainder.

Stormwater management systems shall be designed to detain or treat the runoff from 85% of the storms that occur in an average year and reduce the average annual post-development total suspended solids loadings by 80% in order to meet the water quality requirement. The water quality requirement can be waived if the entire 100% of runoff reduction is provided. Water quality and runoff reduction can also be provided in conjunction in order to meet the water quality requirements outlined in the Gwinnett County Stormwater Management Manual.

Stream channel protection shall be provided using the following three approaches:

24-hour extended detention storage of the 1-year 24-hour return frequency storm event.

Erosion protection measures such as energy dissipation and velocity control.

Preservation of the applicable stream buffer.

Stormwater management facilities shall be designed so that their peak release rates, when combined with those of all bypass areas in the same basin, produce peak flow rates and flow velocities at the site’s boundary line no greater than those which occurred at the same location for pre-developed conditions unless the project meets the conditions specified in Subsection 8.2.2.b.

a.Whenever a Storm Water Management Report indicates that an adverse impact from storm water runoff is expected to result from the development of a property, that project shall be provided with storm water detention facilities. The meaning of "adverse impact" shall apply when pre-development flows did not cause difficulties and post-development flows do. Difficulties shall include, but not be limited to, situations where 25-year velocities exceed the non-erosive velocity of the stream, habitable structures are shown to be subject to increased depth of flooding for any frequency up to and including the regulatory flood, and storm water facilities that can not carry the design storm in accordance with these regulations.

b.Storm water detention facilities required in Subsection 8.2.2.a shall be provided, unless the authorized registered professional (refer to Subsection 8.2.1. Paragraph a.) certifies and provides certified documentation supporting the conclusion to the City Manager or his/her designee that at least one of the following is true and correct as applicable:

(1)The non-detained, post-development runoff will leave the project site as sheet flow, and will not have an adverse impact upon downstream properties. The increase for a 25-year storm should not exceed 1 cfs over a length perpendicular to the flow of 100 feet.

(2)The effect of detention would be to concentrate flows where sheet flow had occurred under pre-developed conditions, and any impact of increase sheet flow upon downstream properties would be less adverse than that which would result from the concentrated flows from a detention facility even if energy dissipation devices were employed.

(3)The undetained flow will pass through downstream properties, in drainage easements obtained by the developer, to an existing detention facility that has been designed to manage the upstream property’s runoff or to the point in the downstream analysis (see 8.2.1.c) which shows that detention is not required.

(4)Where the site runoff will flow directly into a stream or lake without crossing off-site properties:

a.24-hour detention of the 1-year storm is required if water quality protection is required for the project. In this case, the post-development peak flows in the receiving channel may exceed pre-development flows by the smaller value of up to 0.1% of the pre-development flows or 3 cfs in the downstream analysis.

b.Only peak detention for the 2-year though the 25-year storm is not required if the downstream analysis using timing of the hydrographs shows no adverse impact from the exit of the site to the point immediately downstream from the project in the drainage basin where the project area is 10 percent of the total drainage basin area.

c.Should the authorized registered professional conclude that stormwater detention may not be necessary because of anticipated compliance with Section 8.2.2.b., rigid compliance with all of the following criteria is mandatory:

(1)A Stormwater Management Report shall always be required whether or not stormwater detention is required.

(2)If the applicant proposes to show that the detention requirement may be eliminated for all or a portion of a project, then a pre-submittal conference with the City staff is required prior to preparation and submittal of construction plans for the project.

(3)At the pre-submittal conference with the staff, the consultant shall be prepared to discuss the downstream analysis findings as follows:

(a)The affected stream must be analyzed downstream from the project to a point where the project area is 10 percent of the total drainage basin. The analysis must include all culverts, obstructions, existing and potential erosion problems, elevations of existing improvements, and any other existing modifications to natural conditions; and,

(b)If the existing downstream conditions are overburdened by the pre-developed flows in the stream, then detention shall be required unless the developer elects to eliminate the downstream overburdened conditions at his or her expense when the development occurs; and,

(c)If there are any existing drainage complaints downstream, then detention shall be required unless the developer elects to minimize the conditions causing the complaint at his or her expense when the development occurs.

8.2.3 Stormwater Management Facility Design Criteria - General

a.All storm water management facility hydrologic and hydraulic analysis and design calculations shall be certified by the authorized registered professional (refer to Subsection

8.2.1. Paragraph a.).

b.All storm water management facilities shall be designed to detain the 1-year storm runoff, for the area draining to the pond, for 24 hours. For the project, this volume called the channel protection volume, shall be equal to or greater than the 1-year storm runoff volume from the project. In addition, these facilities shall control the peak flow rates associated with storms having 2-year, 5-year, 10-year, and 25-year return frequencies so that flows from the developed site do not exceed those associated with pre-development conditions at the project boundary nor increase the peak flows by more than 5 percent at the point downstream from the project in the drainage basin where the project area is 10 percent of the total basin. Where adverse impacts, as defined in section 8.2.2.a, occur during the 100-year storm, the 100-year storm shall also be regulated.

c.A variety of methods of achieving stormwater management goals shall be acceptable in providing detention facilities. The type of facility provided shall be based on the following criteria:

(1)The type of development which the detention facility is being provided,

(2)The type of development which the detention facility is intended to protect,

(3)Volume of stormwater to be stored,

(4)Origin and magnitude of the flows to be managed,

(5)Topographic opportunities and limitations,

(6)Safety Considerations, but not limited to, installation of fence (solid or other types), berm, vegetation/landscaping, etc. approved by the Director, Department of Planning and Development,

(7)Maintenance requirements,

(8)Aesthetic considerations,

(9)Likelihood of facility operation interfering with access to public or private facilities,

(10)Proximity of facility to property lines, utilities, buffers, etc., and;

(11)Similar site-specific constraints.

d.Detention facilities may be of any of the following types, and two or more types may be used in combination with one another:

(1)Normally-dry basins, whether excavated or created by damming a natural drainage feature, or a combination of both methods,

(2)Lakes and ponds, whether excavated or created by damming a natural drainage feature, or a combination of both methods,

(3)Parking lot facilities,

(4)Underground facilities, and

(5)Roof top facilities.

e.Reservoir routing methods shall be used for all detention facility design.

f.The hydrologic methodology used for any given project shall conform to the Gwinnett County Stormwater Management Manual.

g.Runoff coefficients and runoff Curve Numbers used for pre- and post-development conditions shall be consistent with those shown in the Gwinnett County Stormwater Management Manual. The USGS Method shall be used where applicable to check the magnitude of peak flows when other hydrologic methods recommended in the manual are used.

h.Calculations shall be provided showing how all times of concentration or lag times were computed, both for pre- and post-developed conditions. Likewise, adequate support must be provided for all composite runoff coefficients or curve numbers used.

i.If a computer program is used for hydrologic and hydraulic analysis and design, including generating and routing hydrographs, the output from the program shall be summarized in the Storm Water Management Report, and the name and version of the program shall be indicated. Computer output sheets may be attached to the report if desired by the authorized registered professional (refer to Subsection 8.2.1. Paragraph a.) or if requested by the City.

j.The design of every detention facility of any types shall consider the effects both of inflows in excess of those the facility is designed to accommodate and of malfunctioning of the primary outlet system. A safe path for overflow condition flows shall be provided.

k.Weirs shaped like a “V” (“V” notch weirs) shall be used where practical, considering structural or hydrological concerns.

l.In residential subdivisions, no more than 50% of the basin parameter may be a wall of any type unless the drive is provided to the bottom of the pond. The drive shall be a minimum of 15 feet wide with a maximum slope of 20%.

8.2.4 Stormwater Management Facility Location Criteria

a.For purposes of these Regulations, a detention facility shall be deemed to consist of the area within the maximum design ponding limits, unless a modification application is approved, the dam (if one) including all embankment slopes and wall footings (if applicable), primary and emergency outlet works, any drainage and access easements, and any energy dissipation devices. The intent of these regulations is to ensure that the extent of the facility is defined to allow flooding, access and maintenance. Granting of a modification will not nullify these regulations when the facility is a wet pond or lake, the area within the maximum design ponding limits is reduced to a few feet inside the normal pool elevation, and easements are provided on the perimeter properties to allow for flooding, access and maintenance around the lake. In addition, granting of the modification shall only be considered when the wet pond is an amenity and under no circumstances shall the dam and outlet structure lie on private property.

b.Detention facilities, to the greatest extent feasible, shall be located so as to minimize the amount of flow generated on the project site that bypasses the facility.

c.No portion of any detention facility shall disturb any required (as opposed to voluntary)

buffer, landscape strip, or tree protection area, except that natural bottom detention ponds and their appurtenant structures, which require no grading and removal of trees, may encroach into a required construction buffer.

d.No portion of a private stormwater management facility shall encroach upon a public right-of-way.

e.Detention facilities may be located within utility easements or rights-of-way, or encroach upon utility easements or rights-of-way, upon receipt by the City of written permission from both the property and utility owners.

f.Detention facilities may be constructed within recreation areas required under Section 5.9 of these Regulations, if the following criteria are met:

(1)Ownership of the area will be held by a Qualified Property Owners Association, Homeowners Association, or other private parties.

(2)Permanent structures, such as buildings and swimming pools, will not be constructed within the boundaries of the stormwater management facility.

(3)Stormwater Management facilities within recreation areas will be approved only if the design of the area includes recreation amenities such as ball fields, tennis courts, grassed open areas or other similar improvements. The intent is to provide recreation facilities with stormwater treatment as a secondary feature.

(4)Permanent stormwater treatment features shall not interfere with the intended used of the recreation amenity, (i.e., a ditch or large swale shall not traverse a ball field, an inlet structure shall not be in a tennis court, etc.).

g.If a residential subdivision is provided within an on-site detention facility not located within a recreation area as specified in 8.2.4.f above, a mandatory property owners’

association shall be established for its ownership and maintenance of all stormwater BMP’s within a residential subdivision. All stormwater BMP’s which are placed on an individual private parcel or which crosses multiple private lots must be located within a private drainage easement, which will include access to the right-of-way, to be maintained by the HOA. If the project is provided with an off-site detention facility, a mandatory property owners’ association shall be established for its maintenance. The association’s bylaws shall be recorded concurrently with the recording of a final subdivision plat. The association’s bylaws shall include the same provisions as specified in subsection 5.9.3, Paragraph b. of this regulation.

The following stormwater BMP’s must be located on a separate lot, owned by the HOA, if not located on a recreation area lot as specified in Section 8.2.4.f:

1.Bio-retention Areas

2.Dry/Dry Extended Ponds

3.Stormwater Ponds 4.Stormwater Wetlands 5.Submerged Gravel Wetlands 6.Underground Detention 7.Multi-purposed Detention Areas

h.A non-residential subdivision is not required to locate an on-site detention facility on a separate lot. The property owners served by a stormwater management facility that provides runoff reduction, water quality, channel protection, overbank flood protection, extreme flood protection or any combination for more than one property owner or is located off-site shall enter into a maintenance agreement with the city for the facility's maintenance. However, if desired by the developer, the facility may be located on a separate lot if it is owned and maintained by a mandatory property owners’ association.

8.2.5 Stormwater Management Facility Easement Requirements

a.In a non-residential subdivision or project, an easement at least 20 feet in width shall be required so as to provide access to all detention facilities from a public street

b.In a residential subdivision, a private drainage easement at least 20 feet in width shall be required to provide access to all linear stormwater BMPs from a public street. The private drainage easements are to be shown on the subdivision’s recorded plat and clearly labeled as a private drainage easement to be maintained by the HOA. c. Access Easement

1.The access easement shall be cleared, grubbed and graded so that it can be utilized by rubber-tired construction vehicles.

2.The minimum drive width shall be 15 feet.

3.The drive shall be grassed or paved.

4.The maximum slope shall be 20% (5H:1V).

5.Access easements may be combined with drainage easements containing an open channel; however, the combined easement shall be a minimum of 30 feet in width and shall be wide enough for the drainage channel and the drive.

d.Every normally-dry detention basin, lake, or parking lot detention facility shall be completely enclosed within a drainage easement. The drainage easement shall extend at least 10 feet beyond the 100-year flooding limits of the detention facility.

8.2.6 Stormwater Management Facility Maintenance

a.The detention storage capacity or function of any detention basin, pond or other impoundment, whether natural or man-made, shall not be removed or diminished without the express approval of the City.

b.In a residential subdivision, it shall be the responsibility of the mandatory property owners’ association to maintain the operational characteristics of any facility constructed on their property for storm water detention pursuant to City requirements, to keep the access drive free of obstructions, and to maintain the facility free of obstruction, silt or debris.

c.In a non-residential subdivision or project served by a detention facility that provides detention for more than one property or by an off-site facility, the property owners shall enter into a maintenance agreement with the City for maintenance of the operational characteristics of the facility pursuant to City requirements, to keep the access drive free of obstructions, and to maintain the facility free of obstruction, silt or debris.

d.In a non-residential project with an on-site stormwater management facility which serves only that project, the property owner shall be responsible to maintain the operational characteristics of the facility pursuant to City requirements, to keep the access drive free of obstructions, and to maintain the facility free of obstruction, silt or debris.

e.Where no maintenance agreement has been recorded, it shall be the responsibility of the property owner to maintain the operational characteristics of any facility constructed on their property for stormwater management pursuant to City requirements, to keep the access drive free of obstructions, and to maintain the facility free of obstruction, silt or debris.

e.Prior to the issuance of a Development Permit, the owner shall submit a detailed schedule of long-term maintenance and inspection activities. This schedule of activities shall be incorporated into a maintenance agreement to be entered into between the City and the owner. The schedule shall describe all maintenance and inspection activities and the parties responsible. The maintenance agreement shall be in a form acceptable to the City Manager and shall be recorded in the deed records of the Clerk of Superior Court of Gwinnett County prior to final plat approval or issuance of a certificate of occupancy as appropriate.

8.2.7 Stormwater Management Facility Construction Standards

a.Stormwater detention facilities shall be constructed in accordance with plans reviewed and approved by the City, and shall be in place and inspected prior to the initiation of other improvements. If the stormwater management is planned to be handled by a lake, a stormwater BMP which shall provide runoff reduction, or any other stormwater management system as determined by the city, a temporary stormwater management facility shall be provided and shall remain in place until such time as the stormwater management facility has become effective in providing stormwater management.

b.Within a detention basin, all stumps are to be cut flush with the ground or removed and all debris is to be removed below the 10-year ponding elevation. Trees or shrubs may be allowed to remain below the 10-year ponding elevation only upon certification of the survivability of the vegetation.

c.Detention slopes which are disturbed are to be grassed. The ground cover within the basin shall be well established with all exposed areas covered prior to the end of the maintenance period.

d.If the developer desires to place a fence around a detention facility, it shall be a minimum 4 foot high fence of durable material, with a 12 foot wide access gate. The fence shall be contained within an easement at least 20 feet wide, shall not encroach upon the detention facility (although their easements may overlap by up to 10 feet), and shall comply with the locational requirements of the Zoning Resolution.

8.2.8 Stormwater Management Facility Engineer's Certification and Record Drawings

A certified record survey of each facility shall be prepared by an authorized registered professional currently registered in the State of Georgia. A certified record drawing of the facility shall be based upon this survey. The authorized registered professional shall certify that the facility functions hydraulically as designed. Documentation demonstrating the required testing outlined in the Gwinnett County Stormwater Management Manual for the proposed stormwater BMP shall also be provided.

Requirements for a certified record survey and applicable addendum as necessary to the Stormwater Management Report shall be the same for water quality facilities as for stormwater management facilities.

a.The survey shall be performed after substantial completion and stabilization of the project has occurred. The record drawing and addendum to the Storm Water Management Report shall be submitted to the City with the certificate of development conformance and approved prior to issuance of a certificate of occupancy or final plat approval as appropriate.

.b When a development uses an existing facility without an existing storm water maintenance bond, the facility shall be cleaned out if necessary and a new record survey, drawing, and certification showing that the outlet structure exists as approved and the flood storage and water quality volume of the facility is equal to or greater that the volume required when the facility was approved. As an alternative, a new record survey, drawing, study and certification showing that the facility meets the development requirements when the facility was approved shall be submitted. The survey shall be performed after substantial completion and stabilization of the project has occurred. The certification and supporting data shall be submitted to the City with the certificate of development conformance and approved prior to issuance of a certificate of occupancy or final plat approval as appropriate.

§ 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, gutter, swales, channels, and ditches, shall be provided for the protection of public right-of-way and private properties adjoining projects' sites and/or public rights-of-way. Stormwater conveyance facilities, which are designed to carry runoff from more than one parcel, existing or proposed, shall meet the requirements of these regulations.

8.3.2 Standard Specifications

Unless otherwise specifically set forth herein or in the City of Sugar Hill Standard Drawings, all of the materials, methods of the 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). For roads constructed with public funds, either wholly or in part, or roads classified as Major Thoroughfares, materials which meet the Georgia DOT design standards shall be used unless an alternative is specifically approved by the Gwinnett Department of Transportation.

8.3.3 Design Criteria - General

a.All stormwater conveyance facility design calculations shall be certified by the authorized registered professional (refer to Subsection 8.2.1. Paragraph a.).

b.Methods to calculate storm water flows shall be in accordance with the Gwinnett County Stormwater Management Manual. The USGS Method shall be used where applicable to check the magnitude of peak flows when other hydrologic methods recommended in the manual are used.

c.All portions of a stormwater conveyance system which drain areas falling within the same size category above shall be analyzed using the same methodology.

d.Run-off coefficients used for the Rational Method and runoff Curve Numbers used for the SCS Method shall be consistent with those shown in Gwinnett County Stormwater Management Manual.

e.Smooth interior corrugated polyethylene (PE) pipe shall not be used or installed under the road surface of existing or proposed to be dedicated public streets except where authorized for use by the Georgia DOT.

f.Any pipe or culvert located within a public right of way (R/W) or crossing any street shall be reinforced concrete pipe (RCP).

8.3.4 Design Criteria - Culverts

a.Culverts or pipe systems designed to convey water from one side of a public right-of-way to the other shall be designed to pass the fully developed peak flow associated with a 100-year storm with at least 1.5 feet of freeboard between the 100-year ponding elevation and the centerline of the road, without raising the 100-year flood elevation on upstream properties, and in accordance with Floodplain Management Ordinance. Fully developed flows shall be based on the Land Use Plan adopted by the City of Sugar Hill.

b.The 100-year ponding limits at and upstream of the culvert shall be shown on the Development Plans and on the Final Plat (if applicable).

c.The minimum allowable culvert diameter shall be 18 inches.

d.Culvert design is to be in accordance with the methods contained in the Gwinnett County Stormwater Management Manual and shall include a thorough analysis of both inlet and outlet control conditions.

8.3.5 Piped Collection Systems

a.The preliminary 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 fully developed 25-year storm with the hydraulic grade line (HGL) being one foot or more below the top of each structure, gutter line or proposed final ground surface elevation, whichever is lowest.

b.Once the preliminary design of a piped collection system has been prepared, it shall be analyzed for its behavior during conditions of 100-year flow, with the objective of this analysis being to ascertain the quantities of flow and flowpaths followed by flows exceeding the capacity of the system, whether these pond at inlets or flow along the ground's surface.

c.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.

d.The minimum allowable pipe diameter shall be 15 inches.

e.Catch basins shall be spaced so that the spread in the street for a 10-year design flow shall not exceed the following, as measured from the face of the curb:

(1)8 feet if the street is classified as a Minor Collector or Major Thoroughfare;

(2)16 feet at any given section, but in no case greater than 10 feet on one side of the street, if the street is classified as a Local Street.

Gutter spread calculations shall be submitted to the City for review and approval prior to issuance of a Development Permit.

f.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 25-year storm.

8.3.6 Energy Dissipation - Piped Systems and Culverts

a.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 Standard Drawings.) Velocity protection shall be in accordance with the Gwinnett County Stormwater Management Manual. Velocities for the fully developed 25-year flow shall not exceed the non-erosive velocity as shown in the manual for the receiving conveyance.

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

c.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 and Pipe Coating Requirements

a.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 thicknesses.

Corrugated steel pipe shall have a minimum of 2 ounces per square foot of zinc coating, complying with AASHTO M-218.

(1)All corrugated galvanized pipe not carrying a live stream located within a street right-of-way, drainage easement, or detention facility shall be asphalt coated only. Except for culverts under driveways, all corrugated galvanized pipe which 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 non-segregated lining throughout. The lining shall have a nominal thickness of 1/4 inch above the crest of the corrugations.

(2)See the Standard Drawings for minimum acceptable combinations of gauges, diameters, and corrugation configurations for corrugated steel pipe and pipe arches.

(3)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.

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

b.Reinforced concrete pipe shall be in not less that 8' joint lengths. All joints shall be bell and spigot type, using an O-ring gasket conforming to ASTM C-443. Pipe shall be manufactured in accordance with AASHTO M-170 and/or ASTM C-76. Class of pipe and wall thickness shall be in accordance with 1030-D, Georgia D.O.T. specification, Table No. 1.

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

(1)All corrugated aluminized or aluminum pipe not carrying a live stream located within a street right-of-way, drainage easement, or detention facility may be plain. All corrugated aluminized or aluminum pipe which will carry a live stream within a street right-of-way, drainage easement, or in a detention facility shall have paved inverts pursuant to AASHTO M-190, Type C, except that the pipe need not be fully coated.

(2)See the Standard Drawings 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.

(3)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.

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

d.Structural plate drainage structures shall conform to the following specifications:

(1)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.

(2)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.

e.Smooth Interior Corrugated Polyethylene Pipe

(1)This specification applies to high density polyethylene corrugated pipe with an integrally formed smooth interior. PE pipe manufacturers shall be approved by the Department of Transportation.

(2)This specification is applicable to nominal sizes 15" through 48" diameter. Requirements for test methods, dimensions, and markings of pipe sizes 15" through 36" diameter are those found in AASHTO Designation M-294.

(3)Pipe and fittings shall be made of polyethylene compounds which meet or exceed the requirements of Type III, Category 4 or 5, Grade P33 or P34, Class C per ASTM D-1248 with the applicable requirements defined in ASTM D-1248. Clean reworked material may be used.

(4)The pipe and fittings shall be free of foreign inclusions and visible defects. For pipe sizes 15" diameter and greater, designed drainage perforations shall be permitted in corrugation valleys only. All holes of any kind in the corrugation crests or sidewalls shall be considered unacceptable. The ends of the pipe shall be cut and connected as recommended by the manufacturer.

(5)The normal size for the pipe and fittings is based on the nominal inside diameter of the pipe. Corrugated fittings may be either molded or fabricated by the manufacturer.

Fittings supplied by manufacturers other than the supplier of the pipe shall not be permitted without prior approval from City of Sugar Hill.

(6)Joints shall be made with split couplings, corrugated to engage the pipe corrugations, and shall engage a minimum of 4 corrugations, 2 on each side of the pipe joint. Where required by City of Sugar Hill, a neoprene gasket shall be utilized with the coupling to provide a soil tight joint. Gaskets shall conform to ASTM F-477.

(7)Installation shall be in accordance with ASTM Recommended Practice D-2321 or as specified by City of Sugar Hill.

(8)Certification from the manufacturer that the product was manufactured, tested, and supplied in accordance with this specification shall be furnished to City of Sugar Hill upon request.

8.3.8 Pipe Length

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

b.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.

c.The length requirement, however, shall be subject to requirements for maintaining stream buffers in accordance with Georgia law or County regulations.

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. Smooth interior corrugated polyethylene pipe shall be bedded and backfilled in accordance with the Georgia DOT Standard Specifications or the Gwinnett County Standard Drawings; in addition, prior to approval of a Final Plat, the City may require the submittal of certification from a mandrel testing agency indicating that all such installed pipe does not exceed 7.5% deflection.

a.Bedding:

All pipe structures shall be placed on stable earth or fine granular foundation, the characteristics of which would be expected to provide long-term stability. In all live stream pipe installations, in areas of low bearing solid or non-uniform foundations, in area where rock is encountered at the foundation level, or in other locations where conditions warrant, a minimum of 6" of crushed stone bedding is required, (maximum size of stone shall be 3/4").

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

b.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 Georgia D.O.T.

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:

(1)Backfill within all street rights-of-way shall be compacted to 95% maximum density, tested using the AASHTO Method T-99.

(2)Backfill in all other areas shall be compacted to 95% maximum density, tested using the AASHTO Method T-99.

c.Construction loads and minimum covers:

If drainage pipe is installed prior to the completion of grading, a minimum of 4 feet of fill should be provided where 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

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

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

b.End treatments that conform to the slope may be masonry, pre-cast concrete end sections, metal end sections, PE end sections, reinforced poured-in-place slope collars, or grouted rip-rap. Concrete and metal flared end sections shall conform to Georgia DOT Specifications 1120.

8.3.11 Junction Boxes and Catch Basins

a.Junction boxes and catch basins shall have metal manhole frames and lids for access.

b.Lids for storm drainage facilities shall be engraved in accordance with the Gwinnett County Standard Drawings.

8.3.12 Other Structures

Natural bottom arches and box culverts may be used in accordance with the latest Standard Specifications of the Georgia Department of Transportation.

§ 8.4

Surface Drainage.

8.4.1 Design Standards

a.All new proposed channels shall be designed to carry at least the fully developed 25-year storm with freeboard equal to 20% of the design flow depth.

b.Transition channels shall be provided at the inlet and outlet ends of all culverts and pipe systems, unless otherwise provided herein.

c.The maximum flow velocity at the project site's downstream property line shall not exceed the predeveloped velocity.

d.In cases of potential erosion due to irregular channel alignment, extreme velocities, or excessive slopes, a paved ditch may be required. However, if, in the opinion of the City, the expected long-term maintenance of a surface drainage system could prove impractical, a pipe design may be required. In cases of residential and nonresidential development where a slope exists greater than four percent, a collection system consisting of pipes and pipe inlets shall be designed or a paved ditch with velocity dissipation measures shall be required.

e.The cross-sectional shape of channels shall be as found in the Standard Drawings. "V"

shaped cross-sections are not permitted in grassed channels.

f.If the channel will be affected by backwater from culverts, bridges, other structures or floodplains, backwater curves shall be shown in profiles of the channel.

g.All channels, must be capable of conveying flows sufficient to ensure that overflow of the channel would not result in a likelihood of dwelling flooding, property damage, or public access and/or utility interruption, shall be greater than one (1) chance in 100 years.

h.The piped collection system or drainage easements for the purpose of storm water collection shall be provided to all lots within the proposed development.

i.Private piped collection systems may be utilized by a builder/property owner to connect to the subdivision storm water collection system subject to the design being approved by the City prior to construction. Maintenance of said systems shall be the responsibility of the individual lot owner.

8.4.2 Construction Standards

a.The channel shall be shaped to the dimensions specified on the approved plans and shall be free of overfalls, gullies, or other irregularities.

b.Channels in fills shall be lined.

c.Protective cover in grassed channels shall be installed as soon as the earthwork is completed.

§ 8.5

Erosion Control.

8.5.1 Design Standards

a.The procedures and requirements of the City of Sugar Hill Soil Erosion and Sediment Control Ordinance, as may be revised from time to time, shall be applicable whenever any land disturbance is proposed to occur, and shall continue to apply until the project has been completed. In those instances wherein these Regulations are silent, the "Manual for Erosion and Sediment Control in Georgia" shall apply.

b.No permit shall be issued authorizing any land disturbing activity unless erosion and sediment control plans have first been submitted to and approved by the City in accordance with these Regulations.

8.5.2 Construction Standards

a.All erosion control structures and/or appurtenances as shown on the approved plans shall be in place and operational, and inspected, prior to the beginning of construction, and shall be maintained in operational condition until the phase or project has been completed. (See also requirements for initiation of development activities under Article 11.4.)

b.Temporary and permanent ground covers are required.

c.Upon project completion, erosion control devices and temporary siltation facilities shall be maintained in place while the individual lots are being developed, or until all disturbed areas are fully stabilized.

d.Erosion controls and siltation facilities shall be installed and maintained on each building lot during building construction and site development, as required by the Soil Erosion and Sediment Control Ordinance and consistent with the provisions of the "Manual for Erosion and Sediment Control in Georgia".

8.5.3 Abandoned Projects

Any projects whose permit has lapsed under the terms expressed in Article 4, shall immediately proceed to stabilize all disturbed areas. This responsibility shall fall upon the owner, developer, contractor, or any and all other responsible parties involved in the land disturbance activity.

8.5.4 Stop Work Orders

Except for those activities directly related to compliance with the erosion and sedimentation control ordinance all development activity shall cease while a project is under a stop work order for erosion and sedimentation control violations.

§ 8.6

Dams

Any land disturbing activity that involves a property which is proposed to contain a dam shall comply with the provisions of this Article as well as the provisions contained in Article 3, Section 3.1 of these Regulations.

8.6.1 New Dams Which Become Subject to the Requirements of the Georgia Safe Dams Act and

Rules for Dam Safety.

Dams proposed to be 25 feet or more in height and proposed to have an impounding capacity of 100 acre-feet or more at maximum water storage elevation shall be subject to the following:

a.The developer of any new dam in which development exists within the proposed breach zone shall be subject to the requirements of the Georgia Safe Dams Act and Rules for Dam Safety adopted by the Georgia Department of Natural Resources. The developer shall obtain necessary approvals and permits from the Environmental Protection Division of the Georgia Department of Natural Resources for the project and the dam prior to securing a Development Permit from the City. The developer of any new dam as to which development does not exist within the proposed breach zone shall submit construction plans to City of Sugar Hill for review of the project and the dam prior to securing a Development Permit from the City.

b.If the developer elects to construct the new dam in accordance with the design standards for new dams as contained in the Rules for Dam Safety, then new development shall be permitted within the dam breach zone. However, the dam shall meet the design standards for new dams as contained in the Rules for Dam Safety if development currently exists or is proposed in the dam breach zone.

c.If the developer elects not to construct the new dam to the design standards for new dams as contained in the Rules for Dam Safety, then a dam breach analysis for the dam shall be submitted along with the construction plans for review prior to securing a Development Permit from the City. The design engineer shall utilize the computer model entitled "DAMBRK" for the dam breach analysis.

d.Should the new dam not meet the design standards for new dams as contained in the Rules for Dam Safety, then only the following uses and structures shall be permitted within the dam breach easement:

(1)Agriculture which requires no structures for human habitation within the dam breach zone including forestry, livestock raising, and agricultural and forestry access roads.

(2)Fences.

(3)Outdoor advertising signs provided they are located no closer than 100-feet from any residence or place of business.

(4)Roads, driveways and parking areas.

(5)Utility poles, towers, pipelines, water treatment outfalls and facilities, or other similar facilities and structures.

e.For any new dam that is proposed not to meet the design for new dams as contained in the Rules for Dam Safety, the developer shall obtain a dam breach easement, recorded with the Clerk of Superior Court, Gwinnett County from any offsite property owner where it is proposed for the dam breach zone to extend off the property where the dam is being constructed. The developer shall also cause a dam breach easement to be recorded upon the property being developed.

f.Prior to recording of a Final Plat or issuance of a Certificate of Occupancy, as appropriate, an as-built certification from a registered professional engineer shall be submitted to the City. The certification shall state that the dam is constructed in accordance with the provisions of these regulations as well as the authorized construction plans. If the project is for the development on a subdivision, the developer shall also establish a legal entity, acceptable to the City, such as a mandatory Property Owners Association, prior to approval of the Final Plat, responsible for the maintenance of the dam and its impoundment.

8.6.2 New Dams Subject to Regulation by City of Sugar Hill

Dams proposed to be 9 feet or more in height, but less than 25 feet in height, in combination with an impounding capacity proposed to be 20 acre-feet or more at maximum water storage elevation, but less than 100 acre-feet, shall be subject to the following:

a.If the developer elects not to construct the new dam to the design standards for new dams as contained in the Rules for Dam Safety, then a dam breach analysis for the dam shall be submitted with the construction plans for review and authorization prior to securing a Development Permit from the City. The design engineer shall utilize the computer model entitled "DAMBRK" for the dam breach analysis.

b.Should the new dam not meet the design standards for new dams as contained in the Rules for Dam Safety, then only the following uses and structures shall be permitted within the dam breach zone:

(1)Agriculture which requires no structures for human habitation within the dam breach zone including forestry, livestock raising, and agricultural and forestry access roads.

(2)Fences.

(3)Outdoor advertising signs provided they are located no closer than 100-feet from any residence or place of business.

(4)Roads, driveways and parking areas.

(5)Utility poles, towers, pipelines, water treatment outfalls and facilities, or similar facilities and structures.

c.If the developer elects to construct the new dam in accordance with the design standards for new dams as contained in the Rules for Dam Safety, then new development shall be permitted within the dam breach zone. However, the dam shall meet the design standards for new dams as contained in the Rules for Dam Safety if development currently exists or is proposed in the dam breach zone.

d.Construction plans for new dams defined herein shall be submitted to City of Sugar Hill for review for the project and the dam prior to securing a Development Permit from the City.

e.For any dam that is proposed not to meet the design standards for new dams as contained in the Rules for Dam Safety, the developer shall obtain a dam breach easement, recorded with the Clerk of Superior Court, Gwinnett County from any offsite property owner where it is proposed for the dam breach zone to extend off the property where the dam is being constructed. The developer shall also cause a dam breach easement to be recorded upon the property being developed.

f.Prior to recording of a Final Plat or issuance of a Certificate of Occupancy, as appropriate, an as-built certification from a registered professional engineer shall be submitted to the City. The certification shall state that the dam is constructed in accordance with the provisions of these regulations as well as the authorized construction plans. If the project is for the development of a subdivision, the developer shall also establish a legal entity, acceptable to City of Sugar Hill, such as a mandatory Property Owners Association, at time of recording of the Final Plat, responsible for the maintenance of the dam and its impoundment.

8.6.3 Existing Dams

Existing dams that are located on a project site and will remain after construction is complete, shall comply with the provisions of this article and all referenced articles as if they were new dams.

8.6.4 Existing Category II Dams

When an existing Category II dam may be reclassified to a Category I dam because of a proposed development downstream of the dam, the following shall be provided by the developer for review by the Georgia Safe Dams Program.

(a)Location of the Category II dam and the proposed development; and,

(b)A surveyed cross-section of the stream valley at the location of the proposed development including finished floor elevations; and,

(c)A dam breach analysis using the Dambreak computer model to establish the height of the floodwave in the downstream floodplain. The Dambreak modeling shall be completed in accordance with the Safe Dams Program Quality Assurance Program by a qualified registered engineer.

§ 8.7

Extended Detention

8.7.1 Stream Buffers and Impervious Surface Setbacks

Refer to the Stream Buffer Protection Ordinance of the City of Sugar Hill.

8.7.2 Wet and Extended Detention Facility Maintenance

Maintenance requirements shall be as specified in Section 8.2.6 of these regulations.

§ 8.8

Reserved.

§ 8.9

Stormwater Runoff Quality/Reduction

8.9.1 Treatment Runoff

Stormwater runoff quality/reduction can be provided through runoff reduction, water quality, or any combination of the two. Runoff reduction shall be provided in accordance with the requirements of the Stormwater Management Manual. To the extent Runoff Reduction has been determined to be infeasible for all or a portion of the site, then water quality shall apply for the remaining runoff from a 1.2-inch rainfall event. The design professional shall schedule a meeting with the City when requesting removal or reduction of the runoff reduction requirement.

a.All projects, unless exempt pursuant to 8.9.1.d below, that meet one or more of the following criteria shall provide water quality treatment or runoff reduction as outlined in the Stormwater Management Manual. i. New development that involves the creation or addition of 5,000 square feet or more of impervious cover, or that involves other land development activities of 1 acre or more;

ii.Redevelopment that includes the creation, addition or replacement of 5,000 square feet or more of impervious cover, or that involves other lad development activity of 1 acre or more; or

iii.Land development activities that are smaller than the minimum applicability criteria set forth in items i and ii, above, if such activities are part of a larger common plan of development, even though multiple, separate and distinct land development activities may take place at different times on different schedules.

iv.Runoff from any new development or redevelopment, regardless of size, that is defined by the City Manager to be a hotspot land use or activity shall be adequately treated and addressed through the use of structural storm water controls, nonstructural practices and pollution prevention practices.

v.Linear transportation projects that exceed the threshold in i. above.

b.The runoff reduction (RR) practices shall be sized and designed to retain the first 1.0 inch of rainfall on the project site. The volume shall be calculated as:

RRv = 1.0(Rv) As /12 (ft2)

Where Rv = 0.05 + I(0.009)

I = percent impervious cover as a whole number As = On-site area to be treated (ft2)

c.The water quality volume (WQV) shall be the runoff from 1.2 inches of rain from the project site. The volume shall be calculated as:

WQV = 1.2(Rv)As/12(ft2)

Where Rv = 0.05 + I(0.009)

I = Percent Impervious as a whole number As = On-site area to be treated (ft2)

d.The following activities are exempt from the providing treatment:

i.Individual single-family or duplex residential lots that are not part of a subdivision or phase development project;

ii.Additions or modifications to existing single-family or duplex residential structures; and

iii.Repairs to any storm water management facility or practice deemed necessary by the City Manager or his/her designee.

iv.Utility line projects such as electrical, gas, water and sanitary sewer line installations.

v.Activities to restore and enhance stream bank stability, vegetation, water quality and/or aquatic habitat, so long as native vegetation and bioengineering techniques are used.

8.9.2 Facility Location Criteria

a.Facility location criteria shall be as specified for stormwater management facilities in Section 8.2.4 of these regulations.

b.In a residential subdivision, the following Best Management Practices must be located on a separate lot in accordance with Section 8.2.4.g if not located on a recreation area lot as specified in 8.2.4.f:

(1)Bio-retention areas;

(2)Dry/Dry Extended Ponds;

(3)Stormwater Ponds;

(4)Stormwater Wetlands;

(5)Submerged Gravel Wetlands;

(6)Underground Detention;

(7)Multi-purpose Detention Areas;

8.9.3 Easement Requirements

(a)Facility easement requirements shall be as specified in Section 8.2.5 of these regulations with the exception that the easement enclosing the facility shall be named a Best Management Practice (BMP) easement.

(b)Stream Buffer Easements shall be shown on the final plat for areas that are claimed in the TSS model as Undisturbed Stream Buffers for the site. These areas shall be left in a natural, undisturbed condition except for walking trails. Trails shall not be allowed within 25 feet of a stream bank without a state waters buffer variance.

(c)Upland Area Easements in non-residential subdivisions that are claimed as undisturbed upland areas for the site, shall be recorded in an easement acceptable to the City. These areas shall be left in a natural, undisturbed condition except for walking trails.

8.9.4 Facility Maintenance

a.Maintenance requirements shall be as specified in Section 8.2.6 of these regulations.

b.Prior to or concurrent with the recording of a Final Plat for a subdivision, or issuance of a Certificate of Occupancy for a non-subdivision project, the developer shall provide acceptable surety such as a bond or letter of credit providing for the maintenance of the facility for a period of not less than 18 months. The amount of the surety shall be the greater of fifty (50) percent of construction costs of the facility or 100 percent of the cost to clean out the facility. At the end of 18 months, the City may require the surety to be renewed due to anticipated maintenance caused by such concerns as future construction activity in the basin draining to the facility. A renewed surety may be required up to a total maximum of ten (10) years. The surety for a facility shall be renewed during the ten years until:

1)The surface water drainage area has undergone final stabilization and all planned construction activity has been completed;

2)All storm water runoff in the surface water drainage area is coming from undisturbed or stabilized areas;

3)At least 90% of the lots in that surface water drainage area of the common development have been sold to an unrelated party, permanent structures completed and final stabilization achieved;

4)The accumulation of acreage of undeveloped lots, lots with no completed permanent structure and no final stabilization, within the surface water drainage area is less than five acres or 10 percent of the total area of the common development draining to the facility, whichever is greater; and

5)Within two (2) months of surety release, the facility shall be cleaned out and a new record survey and certification showing that the facility complies with these regulations as specified in section 8.2.8 shall be submitted. Documentation demonstrating the required testing outlined in the Stormwater Management Manual for the proposed stormwater BMP shall also be provided.

8.9.5 Facility Certification and Record Drawings

Requirements for a certified record survey and addendum to the Storm Water Management Report shall be the same for water quality facilities as for detention facilities in section 8.2.8.

8.9.6 Existing Subdivisions with Regional Water Quality

Where water quality is treated in a regional stormwater management facility approved between April 27, 1999, and January 1, 2001, all lots within the treated area shall either conform to the permit and water quality regulations at the time of approval or conform to the current water quality regulations as stated in section 8.9 A volume verification confirming facility maintenance in accordance with the original design shall be certified by an authorized registered professional and submitted to the City for review and approval.

8.9.7 Existing Subdivisions without Regional Water Quality Facilities

Where drainage is treated in a regional detention facility approved before April 27, 1999, all lots within the treated area shall conform to the current water quality regulations as stated in section 8.9.1 and current channel protection regulations as stated in section 8.2.3. A volume verification confirming facility maintenance in accordance with the original design shall be certified by an authorized registered professional and submitted to the City for review and approval.

8.9.8 Retrofitting of Existing Detention Facilities for Water Quality Treatment

If water quality treatment for a proposed development is to be provided in an existing detention facility, then water quality treatment must be provided for the entire original project basin. A modification to the 25-year detention requirement may be granted for the purpose of retrofitting the stormwater management facility to meet current water quality regulations. Granting of a modification will meet the intent and purpose of these regulations when:

1)The detention requirements of the current regulations are provided in the facility for the 1-year, 2-year, 5-year, and 10-year storm. For a retrofitted facility, the volume of the 1-year storm shall be based on the original project area being detained instead of the total area draining to the basin;

2)The water quality requirements of the current regulations as stated in Section 8.8 are provided for the original project area in the facility;

3)The 25-year ponding limits create a hardship if no modification is granted; and

4)The outlet structure meets the requirements of the current regulations.

8.9.9 Retrofitting of Existing Water Quality Facilities

If water quality treatment for a proposed development is provided in an existing water quality facility then water quality treatment conforming to the current regulations must be provided for the entire original project basin.

8.9.10 Redevelopment

a.When 5,000 square feet or more of impervious surface area is created, added, or replaced, or 1 acre or more of a developed project site is disturbed for redevelopment, and the disturbed area is more than 50% of the property, the water quality requirements of this section must be met for the entire site.

b.When less than 5,000 square feet of impervious surface area is created, added, or replaced, or less than 1 acre of land of a developed project site is disturbed for redevelopment, the project is exempt from having to provide the water quality requirements of this section for the project or for the rest of the site.

c.When 5,000 square feet or more of impervious surface area is created, added, or replaced, or 1 acre or more of a develop project site is disturbed for redevelopment, and the disturbed area is less than 50% of the property, the project shall provide water quality treatment for just the improvements on the site.

8.9.11 Exemptions

In order to avoid excessive regulation on individual residential lots, maintenance and repair efforts, and environmental projects, the city’s storm water management exemptions are the same as Gwinnett County Stormwater Management Manual latest edition.

Article 9. Performance Guidelines.