Gainesville › Unified Land Development Code
Article 11 — Subdivisions and Land Development, Chapter 11-11 — STORMWATER MANAGEMENT
§ 11-11-1
Purposes.
(a)This chapter defines requirements for stormwater management and outlines the water quantity and quality performance criteria for managing stormwater runoff. The majority of technical stormwater criteria and standards are adopted by reference through the use of the latest revision of the Georgia Stormwater Management Manual (GSMM).
(b)The purposes of this chapter are also to protect, maintain and enhance the public health, safety, environment and general welfare by establishing minimum requirements and procedures to control the adverse effects of increased post-development stormwater runoff and nonpoint source pollution associated with new development and redevelopment.
§ 11-11-2
Objectives
This chapter seeks to meet its purposes through the following objectives:
(a)Require that new development and redevelopment maintain the pre-development hydrologic response in their post-development state as nearly as practicable in order to reduce flooding, stream bank erosion, nonpoint source pollution and increases in stream temperature, and maintain the integrity of stream channels and aquatic habitats;
(b)Establish minimum post-development stormwater management standards and design criteria for the regulation and control of stormwater runoff quantity and quality;
(c)Establish design and application criteria for the construction and use of structural stormwater control facilities that can be used to meet the minimum post-development stormwater management standards;
(d)Encourage the use of nonstructural stormwater management and stormwater better site design practices, such as the preservation of greenspace and other conservation areas, to the maximum extent practicable;
(e)Establish provisions for the long-term responsibility for and maintenance of structural stormwater control facilities and nonstructural stormwater management practices to ensure that they continue to function as designed, are maintained, and pose no threat to public safety; and
(f)Establish administrative procedures for the submission, review, approval and disapproval of stormwater management plans, and for the inspection of approved active projects, and long-term follow up.
§ 11-11-3
Definitions
(a)Administrative floodplain: Any land area susceptible to flooding, which would have at least a 1% probability of flooding occurrence in any calendar year based on the basin being fully developed as shown on the projected future land use map.
(b)Administrator: The person appointed to administer and implement this chapter. The Director of the Department of Water Resources, or his/her designee, will serve as Administrator for the purposes of this chapter.
(c)Applicant: A person submitting a land development application for approval.
(d)BMP or best management practice: Both structural devices to store or treat stormwater runoff and non-structural programs or practices which are designed to prevent or reduce the pollution of the waters of the State of Georgia.
(e)BMP landscaping plan: A design for vegetation and landscaping that is critical to the performance and function of the BMP including how the BMP will be stabilized and established with vegetation. It shall include a layout of plants and plant names (local and scientific).
(f)Channel: A natural or artificial watercourse with a definite bed and banks that conducts continuously or periodically flowing water.
(g)Conservation easement: An agreement between a land owner and the city or other government agency or land trust that permanently protects open space or greenspace on the owner's land by limiting the amount and type of development that can take place, but continues to leave the remainder of the fee interest in private ownership.
(h)Construction sequencing plan: A document noting the sequence of construction and identification of infiltration zones for protection during staged installation of permanent post- construction BMPs to ensure suitable site conditions such as avoiding soil compaction by heavy equipment in areas designated for infiltration BMPs.
(i)Decentralized wastewater system: A closed-loop system designed or used to receive sewage from a building sewer and to affect separation and organic decomposition of sewerage solids, and discharging sewage effluent to an absorption field or other management system. Also referred to as an on-site wastewater disposal system or septic tank.
(j)Department of Water Resources: A public agency with authority over the water systems of the city.
(k)Department of Water Resources Director: The Director of the Department of Water Resources of the city, or his or her designee, whose duties include the review and approval of construction plans for water resources for the city.
(l)Design professional: A professional licensed by the State of Georgia in the field of:
engineering, architecture, landscape architecture, forestry, geology, or land surveying, or a person that is a Certified Professional in Erosion and Sediment Control (CPESC) with a current certification by EnviroCert, Inc. Design Professional shall practice in a manner that complies with applicable Georgia law governing professional licensure.
(m)Detention: The temporary storage of stormwater runoff in a stormwater management facility for the purpose of controlling the peak discharge.
(n)Detention facility: A detention basin or structure designed for the detention of stormwater runoff and gradual release of stored water at controlled rates.
(o)Development: New development or redevelopment.
(p)Drainage easement: An easement appurtenant or attached to a tract or parcel of land allowing the owner of adjacent tracts or other persons to discharge stormwater runoff onto the tract or parcel of land subject to the drainage easement. Both streams and storm drainage channels are required to have easements for maintenance purposes as specified in this chapter.
(q)Erosion and Sedimentation Control Plan means a plan that is designed to minimize the accelerated erosion and sediment runoff at a site during land disturbance activities.
(r)Extended detention: The detention of stormwater runoff for an extended period, typically twenty-four (24) hours or greater.
(s)Extreme flood protection: Measures taken to prevent adverse impacts from large low- frequency storm events with a return frequency of one hundred (100) years or more.
(t)Flooding: A volume of surface water that is too great to be confined within the banks or walls of a conveyance or stream channel and that overflows onto adjacent lands.
(u)Greenspace or open space: Permanently protected areas of the site that are preserved in a natural state.
(v)GSMM: The latest edition of the Georgia Stormwater Management Manual, Volume 2:
Technical Handbook, and its Appendices.
(w)Hotspot: A land use or activity on a site that produces higher concentrations of trace metals, hydrocarbons, or other priority pollutants that are normally found in urban stormwater runoff. Examples of hotspots include but are not limited to, gas stations, vehicle service and maintenance areas, industrial facilities such as salvage yards, material storage sites, garbage transfer facilities, and commercial parking lots with high-intensity use.
(x)Hydrologic soil group (HSG): A natural resource conservation service classification system in which soils are categorized into four runoff potential groups. The groups range from group A soils, with high permeability and little runoff produced, to group D soils, which have low permeability rates and produce much more runoff.
(y)Impervious surface: A surface composed of any material that significantly impedes or prevents the natural infiltration of water into soil. Impervious surfaces include, but are not limited to, rooftops, buildings, streets and roads, sidewalks, driveways, parking lots, and any other concrete or asphalt surface. Also called impervious cover.
(z)Improvements: The physical addition and changes to land that may be necessary to produce usable, desirable and acceptable lots or building sites.
(aa)Industrial stormwater general permit: The National Pollutant Discharge Elimination System (NPDES) permit issued by Georgia Environmental Protection Division to an industry for stormwater discharges associated with industrial activity. The permit regulates pollutant levels associated with industrial stormwater discharges or specifies on-site pollution control strategies based on the Standard Industrial Classification (SIC) Code.
(bb)Infiltration: The process of percolating stormwater runoff into the subsoil.
(cc)Inspection and maintenance agreement: A written agreement providing for the long-term inspection, operation, and maintenance of the stormwater management system and its components on a site.
(dd)Jurisdictional wetland: An area that is inundated or saturated by surface water or groundwater at a frequency and duration sufficient to support a prevalence of vegetation typically adapted for life in saturated soil conditions, commonly known as hydrophytic vegetation.
(ee)Land development: Any land change, including, but not limited to, clearing, digging, grubbing, stripping, removal of vegetation, dredging, grading, excavating, transporting and filling of land, construction, paving, and any other installation of impervious cover.
(ff)Land disturbing activities: Any activity which may result in soil erosion from water or wind and the movement of sediments into State waters or onto lands within the State, including but not limited to clearing, dredging, grading, excavating, and filling of land.
Land disturbing activity does not include agricultural operations as described in O.C.G.A. § 12-7-17(5) or forestry land management practices as described in O.C.G.A.
§ 12-7-17(6) within areas zoned for such activities.
(gg)Land development application: The application for a land development permit on a form provided by the city along with the supporting documentation required by this chapter.
(hh)Land development permit: The authorization necessary to begin construction-related, land- disturbing activity.
(ii)Linear feasibility program: A feasibility program developed by the Department of Water Resources and submitted to the Georgia Environmental Protection Division, which sets reasonable criteria for determining when implementation of stormwater management standards for linear transportation projects being constructed by the city is infeasible.
(jj)Linear transportation projects: Construction projects on traveled ways including but not limited to roads, sidewalks, multi-use paths and trains, and airport runways and taxiways.
(kk)MS4 Permit: The NPDES permit issued by Georgia Environmental Protection Division for discharges from the city’s municipal separate storm sewer system.
(ll)Municipal utility: A utility owned and operated by a local government and providing drinking water, wastewater and stormwater management facilities and services.
(1)Sewer system: A sanitary sewerage system for the collection of water-borne wastes complete with a sewage treatment plant that is owned and operated by the city Department of Water Resources.
(2)Water system: A system for the intake, treatment and distribution of potable water that is owned and operated the city Department of Water Resources.
(3)Stormwater system: A system of structural and nonstructural stormwater management facilities and practices that are used to capture, convey and control the quantity and quality of the stormwater runoff.
(mm)New development: A land development activity on a previously undeveloped site.
(nn)Nonpoint source pollution: A form of water pollution that does not originate from a discrete point such as a sewage treatment plant or industrial discharge, but involves the transport of pollutants such as sediment, fertilizers, pesticides, heavy metals, oil, grease, bacteria, organic materials and other contaminants from land to surface water or groundwater via mechanisms such as precipitation, stormwater runoff, and leaching. Nonpoint source pollution is a by-product of land use practices such as agricultural, silvicultural, mining, construction, subsurface disposal and urban runoff sources.
(oo)Nonstructural stormwater management practice or nonstructural practice: Any natural or planted vegetation or other nonstructural component of the stormwater management plan that provides for or enhances stormwater quantity and/or quality control or other stormwater management benefits, and includes, but is not limited to, stream buffers, open and greenspace areas, overland flow filtration areas, natural depressions, and vegetated channels.
(pp)Off-site facility: A stormwater management facility located outside the boundaries of the site.
(qq)On-site facility: A stormwater management facility located within the boundaries of the site.
(rr)Overbank flood protection: The measures taken to prevent an increase in the frequency and magnitude of out-of-bank flooding (i.e. flow events that exceed the capacity of the channel and enter the floodplain), and that are intended to protect downstream properties from flooding for the two-year through 25-year frequency storm events.
(ss)Owner: The legal or beneficial owner of a site, including but not limited to, a mortgagee or vendee in possession, receiver, executor, trustee, lessee or other person, firm or corporation in control of the site.
(tt)Permit: The permit issued by the city to the applicant which is required for undertaking any land development activity.
(uu)Person: Any individual, partnership, firm, association, joint venture, public or private corporation, trust, estate, commission, board, public or private institution, utility, cooperative, city, county or other political subdivision of the state, any interstate body or any other legal entity, except to the extent exempted from this code.
(vv)Post-construction stormwater management: Stormwater best management practices that are used on a permanent basis to control and treat runoff once construction has been completed in accordance with a stormwater management plan.
(ww)Post-development: The time period, or the conditions that may reasonably be expected or anticipated to exist, immediately after completion of the land development activity on a site as the context may require.
(xx)Practicability policy: The latest edition of the Metropolitan North Georgia Water Planning District’s policy on practicability analysis for runoff reduction.
(yy)Pre-development: The time period, or the conditions that exist, on a site immediately before the implementation of the proposed development. Where phased development or plan approval occurs (preliminary grading, roads and utilities, etc.), the existing conditions at the time prior to the first item being approved or permitted shall establish pre-development conditions.
(zz)Previously developed site: A site that has been altered by paving, construction, and/or land disturbing activity.
(aaa)Professional engineer: An engineer licensed and registered to perform the duties of a professional engineer (P.E.) by the state.
(bbb)Project: A land development project.
(ccc)Redevelopment: Structural development (construction, installation, or expansion of a building or other structure), creation or addition of impervious surfaces, replacement of impervious surfaces not as part of routine maintenance, and land disturbing activities associated with structural or impervious development on a previously developed site. Redevelopment does not include such activities as exterior remodeling.
(ddd)Regional stormwater management facility or regional facility: Stormwater management facilities designed to control stormwater runoff from multiple properties, where the owners or developers of the individual properties may assist in the financing of the facility, and the requirement for on-site controls is either eliminated or reduced.
(eee)Routine maintenance: Activities to keep an impervious surface as near as possible to its currently constructed condition. This includes ordinary maintenance activities, resurfacing paved areas, and exterior building changes or improvements which do not materially increase or concentrate stormwater runoff, or cause additional nonpoint source pollution.
(fff)Runoff: Stormwater runoff.
(ggg)Site: An area of land where development is planned, which may include all or portions of one or more parcels of land. For subdivisions and other common plans of development, the site includes all areas of land covered under an applicable land development permit.
(hhh)Stormwater better site design: Nonstructural site design approaches and techniques that can reduce a site's impact on the watershed and can provide for nonstructural stormwater management. Stormwater better site design includes conserving and protecting natural areas and greenspace, reducing impervious cover, implementing lower impact site design techniques, and using natural features for stormwater management.
(iii)Stormwater concept plan: An initial plan for post-construction stormwater management at the site that provides the groundwork for the stormwater management plan, including the natural resources inventory, site layout concept, initial runoff characterization, and first round stormwater management system design.
(jjj)Stormwater management: The collection, conveyance, storage, treatment and disposal of stormwater runoff in a manner intended to prevent increased flood damage, streambank channel erosion, habitat degradation and water quality degradation, and to enhance and promote the public health, safety and general welfare.
(kkk)Stormwater management facility: Any infrastructure that controls or conveys stormwater runoff.
(lll)Stormwater management measure: Any stormwater management facility or nonstructural stormwater practice.
(mmm)Stormwater management plan: A document describing how existing runoff characteristics will be affected by a land development project and containing measures for complying with the provisions of this Code.
(nnn)Stormwater management system: The entire set of structural and nonstructural site design features and structural BMPs for collection, conveyance, storage, infiltration, treatment, and disposal of stormwater runoff in a manner designed to prevent increased flood damage, streambank channel erosion, habitat degradation and water quality degradation, and to enhance and promote the public health, safety and general welfare.
(ooo)Stormwater retrofit: A stormwater management practice designed for a currently developed site that previously had either no stormwater management practice in place or a practice inadequate to meet the stormwater management requirements of the site.
(ppp)Stormwater runoff: Flow on the surface of the ground, resulting from precipitation.
(qqq)Subdivision: The division of a tract or parcel of land resulting in one or more new lots or building sites for the purpose, whether immediately or in the future, of sale, other transfer of ownership or land development, and includes divisions of land resulting from or made in connection with the layout or development of a new street or roadway or a change in an existing street or roadway.
(rrr)Watercourse: Any natural or artificial surface water conveyance, stream, river, creek, channel, ditch, canal, conduit, culvert, drain, waterway, gully, ravine, or wash in which water flows either continuously or intermittently; a natural watercourse has a definite bed and banks, and includes any area adjacent thereto subject to inundation by reason of overflow or floodwater.
Other terms used but not defined in this chapter shall be interpreted based on how such terms are defined and used in the GSMM and the city’s MS4 permit.
§ 11-11-4
Stormwater Management Report Required
(a)All persons proposing development or construction in the city that meets the applicability requirements of this chapter shall prepare a stormwater management report, unless specifically exempted from the requirements of this chapter. No final subdivision plat shall be approved and no development or building permit shall be issued until and unless the stormwater management report has been reviewed and approved by the administrator, except as exempted below.
(b)This report must be submitted with the stamp and signature of a professional engineer (PE) licensed in the state, who must verify that the design of all stormwater management facilities and practices meet submittal and permitting requirements. The engineer sealing the stormwater management report is responsible for ensuring that all permit requirements related to Section 404 of the Clean Water Act are met.
(c)Stormwater management reports shall not be required for activities that are exempted from the provisions of this chapter by Section 11-11-6.
§ 11-11-5
Applicability
The provisions of this chapter apply to any new development or redevelopment site that meets one or more of the following criteria as determined appropriate by the Director of Water Resources:
(a)New development that creates or adds 5,000 square feet or more of new impervious surface or that involves land disturbing activity of 1 acre of land or more;
(b)Redevelopment (excluding routine maintenance and exterior remodeling) that creates, adds or replaces 5,000 square feet or more of new impervious surface area or that involves land disturbing activity of one acre of land or more;
(c)New development and redevelopment if:
(1)Such new development or redevelopment is part of a subdivision or other common plan of development, and
(2)The sum of all associated impervious surface area or land disturbing activities that are being developed as part of such subdivision or other common plan of development meets or exceeds the threshold in (a) and (b) above;
(3)Hillsides or slopes are 15% or more that are cleared or graded, and
(d)Any commercial or industrial new development or redevelopment, regardless of size, that is a hotspot land use as defined in this chapter; and
(e)Linear transportation projects that exceed the threshold set forth in subsections (a)
or (b) above.
§ 11-11-6
Exemptions
The following activities are exempt from the requirements this chapter:
(a)Land disturbing activity conducted by local, state, authority, or federal agencies, solely to respond to an emergency need to protect life, limb, or property or to conduct emergency repairs;
(b)Land disturbing activity that consists solely of cutting a trench for utility work and related pavement replacement;
(c)Land disturbing activity conducted by local, state, authority, or federal agencies, whose sole purpose is to implement stormwater management or environmental restoration;
(d)Repairs to any stormwater management system deemed necessary by the Department of Water Resources or Department of Community and Economic Development;
(e)Agricultural operations or forestry land management activities or practices as described in O.C.G.A. §§ 12-7-17(5) and 12-7-17(6) within areas zoned for such activities;
(f)Additions or modifications to existing single-family detached or duplex residential structures, except as provided in Section 9-11-11-5;
(g)Single-family detached lots and two family lots that are cleared or disturbed on slopes with a grade of less than 15%;
(h)Single-family detached lots and two-family lots that contain less than 1 acre of disturbed area; however, development of any such lot shall conform to the minimum requirements as set forth in O.C.G.A. 12-7-6, as amended;
(i)Installations or modifications to existing structures solely to implement Americans with Disabilities Act (ADA) requirements, including but not limited to elevator shafts, handicapped access ramps and parking, and enlarged entrances or exits; and
(j)Linear transportation projects being constructed by the city to the extent the administrator determines that the stormwater management standards may be infeasible to apply, all or in part, for any portion of the linear transportation project.
For this exemption to apply, any infeasibility report that is compliant with the city’s linear feasibility program shall first be submitted to the administrator and shall contain adequate documentation to support the evaluation for the applicable portion(s) and any resulting infeasibility determination, if any, by the administrator.
§ 11-11-7
Variances
The Director of Water Resources may grant a variance from the requirements of this chapter if the proposed development activity will not:
(a)Change the rate or volume of runoff significantly, as specified in the GSMM;
(b)Have a significant, negative impact on any wetland, watercourse, or water body as specified in the GSMM; or
(c)Contribute to degradation of water quality; and
(d)The application of the stormwater design sizing criteria is determined to be infeasible to implement based on a feasibility study.
§ 11-11-8
Adoption and Implementation of the GSMM: Conflicts and
Inconsistencies
(a)The latest version of the Georgia Stormwater Management Manual (GSMM) including all related appendices, will provide the primary guidance for the design and evaluation of stormwater management facilities in the city. A copy of the GSMM may be viewed in the Department of Water Resources or may be accessed online.
(b)This chapter is not intended to modify or repeal any other chapter, ordinance, rule, regulation or other provision of law, including but not limited to any applicable stream buffers under state and local laws, and the Georgia Safe Dams Act and Rules for Dam Safety. In the event of any conflict or inconsistency between any provision in the city’s MS4 permit and this chapter, the provision from the MS4 permit shall control. In the event of any conflict or inconsistency between any provision of this chapter and the GSMM, the provision from this chapter shall control. In the event of any other conflict or inconsistency between any provision of this chapter and any other ordinance, rule, regulation or other provision of law, the provision that is more restrictive or imposes higher protective standards for human health or the environment shall control.
(c)If any provision of this chapter is invalidated by a court of competent jurisdiction, such judgement shall not affect or invalidate the remainder of this chapter.
§ 11-11-9
Designation of Administrator
The Director of the Department of Water Resources may from time to time appoint a designee to administer and implement this chapter.
§ 11-11-10
Stormwater Management Standards
Subject to the applicability criteria in Section 11-11-5, exemptions in Section 11-11-6, and variances in Section 11-11-7, the following stormwater management standards apply. Additional details for each standard can be found in the GSMM:
(a)Design of Storm Management System: The design of the stormwater management system shall be in accordance with the applicable sections of the GSMM as directed by the administrator. Any design which proposes a dam shall comply with the Georgia Safe Dams Act and Rules for Dam Safety as applicable.
(b)Natural Resources Inventory: Site reconnaissance and surveying techniques shall be used to complete a thorough assessment of existing natural resources, both terrestrial and aquatic, found on the site. Resources to be identified, mapped, and shown on the Stormwater Management Plan, shall include, at a minimum (as applicable):
(1)Topography (minimum of 2-foot contours) and Steep Slopes (i.e., Areas with Slopes Greater Than 15%);
(2)Natural Drainage Divides and Patterns;
(3)Natural Drainage Features (e.g., swales, basins, depressional areas);
(4)Natural feature protection and conservation areas such as wetlands, lakes, ponds, floodplains, stream buffers, drinking water wellhead protection areas and river corridors;
(5)Predominant soils (including erodible soils and karst areas); and
(6)Existing predominant vegetation including trees, high quality habitat and other existing vegetation.
(c)Better Site Design Practices for Stormwater Management: Stormwater management plans shall preserve the natural drainage and natural treatment systems and reduce the generation of additional stormwater runoff and pollutants to the maximum extent practicable. Additional details can be found in the GSMM Section 2.3.
(d)Stormwater Runoff Quality/Reduction: Stormwater Runoff Quality/Reduction shall be provided by using the following:
(1)For development with a stormwater management plan submitted before December 6, 2020, the applicant may choose either (A) Runoff Reduction or (B)
Water Quality.
(2)For development with a stormwater management plan on or after December 6, 2020, the applicant shall choose (A) Runoff Reduction and additional water quality shall not be required. To the extent (A) Runoff Reduction has been determined to be infeasible for all or a portion of the site using the Practicability Policy, then (B) Water Quality shall apply for the remaining runoff from a 1.2-inch rainfall event and must be treated to remove at least 80% of the calculated average annual post-development total suspended solids (TSS) load or equivalent as defined in the GSMM.
i.Runoff Reduction - The stormwater management system shall be designed to retain the first 1.0 inch of rainfall on the site using runoff reduction methods, to the maximum extent practicable.
ii.Water Quality – The stormwater management system shall be designed to remove at least 80% of the calculated average annual post-development total suspended solids (TSS) load or equivalent as defined in the GSMM for runoff from a 1.2-inch rainfall event.
(3)If a site is determined to be a hotspot, the Department of Water Resources may require the use of specific or additional components for the stormwater management system to address pollutants of concern generated by that site.
(e)Stream Channel Protection: Protection of stream channels from bank and bed erosion and degradation shall be provided by using all of the following three (3) approaches:
(1)24-hour extended detention storage of the one-year, 24-hour return frequency storm event;
(2)Erosion prevention measures such as energy dissipation and velocity control; and
(3)Preservation of any applicable stream buffer;
(f)Overbank flooding protection: Downstream overbank flood protection shall be provided by controlling (attenuating) the post-development peak discharge rate to the pre- development rate for the 25-year, 24-hour storm event.
(g)Extreme flooding protection: Extreme flood protection shall be provided by controlling the 100-year, 24-hour storm event such that flooding is not exacerbated.
(h)Downstream Analysis: Due to peak flow timing and runoff volume effects, some structural components of the stormwater management system fail to reduce discharge peaks to pre-development levels downstream from the site. A downstream peak flow analysis shall be provided to the point in the watershed downstream of the site or the stormwater management system where the area of the site comprises 10% of the total drainage area in accordance with Section 3.1.9 of the GSMM. This is to help ensure that there are minimal downstream impacts from development on the site. The downstream analysis may result in the need to resize structural components of the stormwater management system.
(i)Stormwater Management System Inspection and Maintenance: The components of the stormwater management system that will not be dedicated to and accepted by the city, including all drainage facilities, best management practices, credited conservation spaces, and conveyance systems, shall have an inspection and maintenance agreement to ensure that they continue to function as designed. All new development and redevelopment sites are to prepare a comprehensive inspection and maintenance agreement for the on-site stormwater management system. This plan shall be written in accordance with the requirements in Section 11-11-21.
§ 11-11-11
Pre-Submittal Meeting, Stormwater Concept Plan, and
Stormwater Management Plan Requirements
(a)Before a land development permit application is submitted, an applicant may request a pre-submittal meeting with the Department of Water Resources. The pre-submittal meeting should take place based on an early step in the development process such as before site analysis and inventory (GSMM Section 2.4.2.4) or the stormwater concept plan (GSMM Section 2.4.2.5). The purpose of the pre-submittal meeting is to discuss opportunities, constraints, and ideas for the stormwater management system before formal site design engineering. To the extent applicable, local and regional watershed plans, greenspace plans, trails and greenway plans, and other resource protection plans should be consulted in the pre-submittal meeting. Applicants must request a pre-submittal meeting with the Department of Water Resources when applying for a Determination of Infeasibility through the Practicability Policy set forth by the Department of Water Resources.
(b)The stormwater concept plan shall be prepared using the minimum following steps:
(1)Develop the site layout using better site design techniques, as applicable (GSMM Section 2.3).
(2)Calculate preliminary estimates of the unified stormwater sizing criteria requirements for stormwater runoff quality/reduction, channel protection, overbank flooding protection and extreme flood protection (GSMM Section 2.2).
(3)Perform screening and preliminary selection of appropriate best management practices and identification of potential siting locations (GSMM Section 4.1).
(c)The stormwater concept plan shall contain:
(1)Common address and legal description of the site,
(2)Vicinity map, and
(3)Existing conditions and proposed site layout mapping and plans (recommended scale of 1” = 50’), which illustrate at a minimum:
i.Existing and proposed topography (minimum of 2-foot contours),
ii.Perennial and intermittent streams,
iii.Mapping of predominant soils from USDA soil surveys,
iv.Boundaries of existing predominant vegetation and proposed limits of clearing and grading,
v.Location and boundaries of other natural feature protection and conservation areas such as wetlands, lakes, ponds, floodplains, stream buffers and other setbacks (e.g., drinking water well setbacks, decentralized wastewater system setbacks, etc.),
vi.Location of existing and proposed roads, buildings, parking areas and other impervious surfaces,
vii.Existing and proposed utilities (e.g., water, sewer, gas, electric) and easements,
viii.Preliminary estimates of unified stormwater sizing criteria requirements,
ix.Preliminary selection and location, size, and limits of disturbance of proposed BMPs,
x.Location of existing and proposed conveyance systems such as grass channels, swales, and storm drains,
xi.Flow paths,
xii.Location of the boundaries of the base flood floodplain, future- conditions floodplain, and the floodway (as applicable) and relationship of site to upstream and downstream properties and drainage, and
xiii.Preliminary location and dimensions of proposed channel modifications, such as bridge or culvert crossings.
(d)The stormwater management plan shall contain the items listed in this part and be prepared under the direct supervisory control of either a registered Professional Engineer or a registered Landscape Architect licensed in the state of Georgia. Items (iii), (iv), (v), and (vi) shall be sealed and signed by a registered Professional Engineer licensed in the state of Georgia. The overall site plan must be stamped by a design professional licensed in the State of Georgia for such purpose. (GSMM Section 2.4.2.7):
(1)Natural Resources Inventory
(2)Stormwater Concept Plan
(3)Existing Conditions Hydrologic Analysis
(4)Post-Development Hydrologic Analysis
(5)Stormwater Management System
(6)Downstream Analysis
(7)Erosion and Sedimentation Control Plan
(8)BMP Landscaping Plan
(9)Inspection and Maintenance Agreement
(10)Evidence of Acquisition of Applicable Local and Non-Local Permits
(11)Determination of Infeasibility (if applicable)
(12)Construction Sequencing Plan
(e)For redevelopment and to the extent existing stormwater management structures are being used to meet stormwater management standards the following must also be included in the stormwater management plan for existing stormwater management structures:
(1)As-built Drawings
(2)Hydrology Reports
(3)Current inspection of existing stormwater management structures with deficiencies noted
(4)BMP Landscaping Plans
§ 11-11-12
Application Procedures
Land development applications are handled as part of the process to obtain the land disturbance permit. Before any person begins development on a site, the owner of the site shall first obtain approval in accordance with the following procedure:
(a)File a land development application with the Department of Community and Economic Development with the following supporting materials:
(1)the stormwater management plan prepared in accordance with Section 11-11-11,
(2)a certification that the development will be performed in accordance with the stormwater management plan once approved,
(3)a Preliminary Determination of Infeasibility, as applicable, prepared in accordance with the practicability policy set forth by the Department of Water Resources, and
(4)an acknowledgement that applicant has reviewed the Department of Water Resources form of inspection and maintenance agreement and that applicant agrees to sign and record such inspection and maintenance agreement before the final inspection.
(b)The administrator shall inform the applicant whether the application and supporting materials are approved or disapproved.
(c)If the application or supporting materials are disapproved, the administrator shall notify the applicant of such fact in writing. The applicant may then revise any item not meeting the requirements hereof and resubmit the same for the administrator to again consider and either approve or disapprove.
(d)If the application and supporting materials are approved, the Department of Water Resources may issue the associated land disturbance permit or building permit, provided all other legal requirements for the issuance of such permits have been met.
The stormwater management plan included in such applications becomes the approved stormwater management plan.
§ 11-11-13
Compliance with the Approved Stormwater Management
Plan
(a)All development shall be:
(1)consistent with the approved stormwater management plan and all applicable land disturbance and building permits, and
(2)conducted only within the area specified in the approved stormwater management plan.
(b)No changes may be made to an approved stormwater management plan without review and advanced written approval by the administrator.
§ 11-11-14
Use of Stormwater Quality Site Development Review Tool
Required
(a)An automated spreadsheet tool was developed to facilitate the consistent review of development projects across the 15-county Metropolitan North Georgia Water Planning District (the district), of which the city is a part. The tool was specifically designed to meet the unified sizing and water quality performance criteria outlined in the Georgia Stormwater Management Manual. The overall goal is to provide an effective tool for city review staff and the development community to quickly evaluate the water quality performance of stormwater management plans for development sites. It allows the developer to use a variety of BMPs and provides incentives for leaving key areas, particularly stream buffers, undisturbed.
(b)The city requires every project, unless otherwise exempt, to use the latest stormwater quality site development review tool. A copy of the tool is available upon request from the Department of Water Resources.
§ 11-11-15
Inspections to Ensure Plan Compliance During Construction
Periodic inspections of the stormwater management system during construction shall be conducted by the staff of the Department of Water Resources or conducted and certified by a professional engineer who has been approved by the Department of Water Resources.
Inspections shall use the approved stormwater management plan and the construction sequencing plan for establishing compliance. All inspections shall be documented with written reports that contain the following information:
(a)The date and location of the inspection;
(b)Whether the stormwater management system is in compliance with the approved stormwater management plan;
(c)Variations from the approved stormwater management plan; and
(d)Any other variations or violations of the conditions of the approved stormwater management plan.
§ 11-11-16
Final Inspection; As-Built Drawings; Delivery of Inspection
Section 11-11-16. Final Inspection; As-Built Drawings; Delivery of Inspection and Maintenance Agreement
(a)Upon completion of the development, the applicant is responsible for:
(1)Certifying that the stormwater management system is functioning properly and was constructed in conformance with the approved stormwater management plan and associated hydrologic analysis,
(2)Submitting as-built drawings showing the final design specifications for all components of the stormwater management system as certified by a professional engineer,
(3)Certifying that the landscaping is established and installed in conformance with the BMP landscaping plan, and
(4)Delivering to the Department of Water Resources a signed inspection and maintenance agreement that has been recorded by the owner in the property record for all parcel(s) that make up the site.
(b)The required certification under subsection (1) shall include a certification of volume, or other performance test applicable to the type of stormwater management system component, to ensure each component is functioning as designed and built according to the design specifications in the approved stormwater management plan. This certification and the required performance tests shall be performed by a design professional and submitted to the Department of Water Resources with the request for a final inspection. The Department of Water Resources shall perform a final inspection with applicant to confirm applicant has fulfilled these responsibilities.
§ 11-11-17
Violations and Enforcement
Any violation of the approved stormwater management plan during construction, failure to submit as-built drawings, failure to submit a final BMP landscaping plan, or failure of the final inspection shall constitute and be addressed as violations of, or failures to comply with, the underlying land disturbance permit or the underlying building permit. To address a violation of this chapter, the Department of Water Resources shall have all the powers and remedies that are available to it for other violations of building and land disturbance permits, including without limitation the right to issue notices and orders to ensure compliance, stop work orders, and penalties as set forth in the applicable ordinances for such permits.
§ 11-11-18
Maintenance by Private Parties
On all commercial sites and on residential property where stormwater management facilities exist, the maintenance is the responsibility of the owner or operator of the property. It shall be the responsibility of the owner or operator to repair deficiencies in a timely manner.
§ 11-11-19
Maintenance by Property or Homeowners Associations
When a subdivision or industrial/commercial park has a legally created property or homeowners association, the association will be responsible for maintenance of all drainage easements and all stormwater facilities within the entire development. The association may be required to apply larvicides, stock mosquito fish or take other measures, as required by the Department of Water Resources, to protect the health, safety and welfare of the public. The association shall be formed prior to final plat approval.
§ 11-11-20
Maintenance by Owner of Stormwater Management
Systems Predating Current GSMM For any stormwater management systems approved and built based on requirements predating the current GSMM and that are not otherwise subject to an inspection and maintenance agreement, such stormwater management systems shall be maintained by the owner so that the stormwater management systems perform as they were originally designed.
§ 11-11-21
Inspection and Maintenance Agreements
(a)The owner shall execute an inspection and maintenance agreement with the Department of Water Resources obligating the owner to inspect, clean, maintain, and repair the stormwater management system; including vegetation in the final BMP landscaping plan. The form of the inspection and maintenance agreement shall be the form provided by the Department of Water Resources. After the inspection and maintenance agreement has been signed by the owner and filed with the Department of Water Resources, the City shall promptly record such agreement in the property record for all parcel(s) that make up the site.
(b)The inspection and maintenance agreement shall identify by name or official title the person(s) serving as the point of contact for carrying out the owner’s obligations under the inspection and maintenance agreement. The owner shall update the point of contact from time to time as needed and upon request by the Department of Water Resources. Upon any sale or transfer of the site, the new owner shall notify the Department of Water Resources in writing within 30 days of the name or official title of the new person(s) serving as the point of contact for the new owner. Any failure of an owner to keep the point of contact up to date shall, following 30 days’ notice, constitute a failure to maintain the stormwater management system.
(c)The inspection and maintenance agreement shall run with the land and bind all future successors-in-title of the site. If there is a future sale or transfer of only a portion of the site, then:
(1)The parties to such sale or transfer may enter into and record an assignment agreement designating the owner responsible for each portion of the site and associated obligations under the inspection and maintenance agreement. The parties shall record and provide written notice and a copy of such assignment agreement to the Department of Water Resources.
(2)In the absence of a recorded assignment agreement, all owners of the site shall be jointly and severally liable for all obligations under the inspection and maintenance agreement, regardless of what portion of the site they own.
§ 11-11-22
Right of Entry for Maintenance Inspections
(a)The terms of the inspection and maintenance agreement shall provide for the Department of Water Resources or a designee right of entry for maintenance inspections and other specified purposes. If a site was developed before the requirement to have an inspection and maintenance agreement, or an inspection and maintenance agreement was for any reason not entered into, recorded, or has otherwise been invalidated or deemed insufficient, then the Department of Water Resources shall have the right to enter and inspect property at reasonable times as often as may be necessary to determine compliance with this chapter, pursuant to the city’s general provisions for property access and inspection in this code, including but not limited to chapter 4-7 of the City of Gainesville Code of Ordinances and Chapter 12-1 and Article 16 of this Unified Land Development Code.
(b)Where it is necessary to make an inspection to enforce the provisions of this code, or where the Department of Water Resources has reasonable cause to believe that there exists in a structure or upon a premises a condition which is contrary to or in violation of this code which makes the structure or premises unsafe, dangerous or hazardous, the Department of Water Resources is authorized to enter the structure or premises at reasonable times to inspect or to perform the duties imposed by this code, provided that if such structure or premises are occupied that credentials be presented to the occupant and entry requested. If such structure or premises are unoccupied, the Department of Water Resources shall first make a reasonable effort to locate the owner or other person having charge or control of the structure or premises and request entry. If entry is refused, the Department of Water Resources shall have recourse to the remedies provided by law to gain entry.
§ 11-11-23
Owner’s Failure to Maintain the Stormwater Management
System The terms of the inspection and maintenance agreement shall provide for what constitutes a failure to maintain a stormwater management system and the enforcement options available to the Department of Water Resources. If a site was developed before the requirement to have an inspection and maintenance agreement, or an inspection and maintenance agreement was for any reason not entered into, recorded, or has otherwise been invalidated or deemed insufficient, then:
(a)An owner’s failure to maintain the stormwater management system so that it performs as it was originally designed shall constitute and be addressed as a violation of, or failure to comply with, owner’s property maintenance obligations in code chapters 3-5 or 4-7 of the City Code of Ordinances, Article 16 of this Unified Land Development Code, and this chapter.
(b)To address such a failure to maintain the stormwater management system, the Department of Water Resources shall have all the powers and remedies that are available to it for other violations of an owner’s property maintenance obligations, including without limitation prosecution, penalties, abatement, and emergency measures.
§ 11-11-24
Reference to Unified Stormwater Sizing Criteria
The GSMM has developed a set of unified stormwater sizing criteria that serves as the basis of designing stormwater facilities in the city. These criteria provide an integrated approach for meeting the stormwater runoff quality and quantity management requirements for those applicable developments identified in this section.
The purpose of the unified stormwater sizing criteria is to design a stormwater management system to:
(a)Remove stormwater runoff pollutants and improve water quality;
(b)Prevent downstream stream bank and channel erosion;
(c)Reduce downstream overbank flooding; and
(d)Reduce the runoff from and safely pass extreme storm events.
§ 11-11-25
Stormwater Design Sizing Criteria
Stormwater management typically relies on a system of natural and constructed facilities (practices) for the storage, treatment, and conveyance of runoff. This section provides an overview of the design criteria required for stormwater detention and conveyance facilities in the city.
(a)Stormwater facilities generally. Stormwater facilities in the city must be designed to meet the criteria in the following table using the appropriate runoff calculation methods described in this section. Additional discussion of these criteria can be found in the following subsections and in Volume II, Section 2.2.3 of the Georgia Stormwater Management Manual.
Table 11-6: Summary of the Statewide Stormwater Sizing Criteria for Stormwater Control and
| Sizing Criteria | Description | |
|---|---|---|
| Treatment, WQv (Standard #4) | Retain or treat the runoff from 85% of the storms that occur in an average year. For Georgia, this equates to providing water quality treatment for the runoff resulting from a rainfall depth of 1.2 inches. The water quality treatment goal is to reduce average annual post-development total suspended solids loadings by 80%. | |
| Channel Protection | Provide extended detention of the 1-year, 24-hour storm event released over a period of 24 hours to reduce bankfull flows and protect downstream channels from erosive velocities and unstable conditions. | |
| Overbank Flood Protection | Provide peak discharge control of the 25-year, 24-hour storm event such that the post-development peak rate does not exceed the predevelopment rate to reduce overbank flooding. | |
| Extreme Flood Protection | Evaluate the effects of the 100-year, 24-hour storm on the stormwater management system, adjacent property, and downstream facilities and property. Manage the impacts of the extreme storm event through detention controls and/or floodplain management. | |
| Notes: Source: Georgia Stormwater Management Manual, Volume II, Table 2.2.3-1. |
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§ 11-11-26
Stormwater Runoff Computation
Computations for rate of runoff shall be based on the rainfall intensities for any location across Georgia. Information related to rainfall intensities can be obtained through the National Oceanic and Atmospheric Administration (NOAA) Atlas 14 publication, or online using the Precipitation Frequency Data Server database (http://hdsc.nws.noaa.gov/hdsc/pfds). NOAA precipitation data should be used for all hydrologic analysis at the given locations. Additional information regarding how the values in this database were derived can be accessed using the link above.
Computing runoff and generating hydrographs must be done by one of the methods outlined in the GSMM, Volume II, Section 5. The table below summarizes the hydrologic calculation methods that will be accepted by the Department of Water Resources and the section reference from the GSMM that explains each. The table also provides guidelines for using the appropriate method based on the size of the drainage area. Additional information relating to the design of conveyance structures can be found in the GSMM. As noted, the rational formula can only be used to design conveyance systems, one of the other methods listed must be used for designing the stormwater detention facilities.
Table 11-7: Methods for Stormwater Runoff Computation
| Computation Task | GSMM Chapter | Rational Formula | SCS | USGS Equations | Water Quality Volume |
|---|---|---|---|---|---|
| Size Limitations for Each Method | 25 acres | 25 to 2,000 acres | 2,000 acres to 25 square miles | Based on BMP | |
| Water Quality Volume (WQv) | 2.2 | X | |||
| Channel Protection Volume (CPv) | 2.2 | X | |||
| Overbank Flood Protection (QP25) | 2.2 | X | X | ||
| Extreme Flood Protection (Qf) | 2.2 | X | X |
Storage Facilities 3.3 X X Outlet Structures 3.4 X X Gutter Flow and Inlets 5.2 X Storm Drain Pipes 5.2 X X X Culverts 5.3 X X X Small Ditches 5.4 X X X Open Channels 5.4 X X Energy Dissipation 5.5 X X Source: Georgia Stormwater Management Manual, Volume II, Table 3.1.1-1.
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§ 11-11-27
Water Quality Performance Criteria
Total suspended solids (TSS) are a key pollutant associated with sediment runoff. It also serves as a "carrier" of other pollutants such as organics, nutrients, and metals. Thus, TSS, a measure of suspended matter-including soils and sediments, will serve as the watershed improvement guideline for managing pollutants.
(a)If using water quality standard #4 from Table 2.2.3-1 of the GSMM, stormwater management systems (which can include both structural stormwater controls and better site design practices) must be designed to remove 80% of the average annual post-development TSS load and be able to meet any other additional watershed- or site-specific water quality requirements. All stormwater detention facilities shall be designed to control the peak flow rates associated with storms having one-, 25- and 100-year storm frequencies as specified in the table above.
(b)If using water quality standard #3 from Table 2.2.3-1 of the GSMM, stormwater management systems (which can include both structural stormwater controls and better site design practices) must retain or reduce the runoff for the first 1.0 inch of rainfall, or to the maximum extent practicable. If the entire 1.0 inch runoff reduction cannot be achieved, the remaining runoff from the 1.2 inch rainfall must be treated as described for standard #4.
(c)A combination of subsections (a) and (b) can be utilized to meet the water quality standard. Any site developed on or after December 6, 2020 must use (b) standard #3 set forth in subsection (b) to meet the water quality criteria
(d)Use of the stormwater quality site development review tool, described in this chapter, provides the developer and reviewer with a summary of the TSS reduction from each of the drainage areas and also presents the overall TSS reduction efficiency of the planned site. Please note that if this overall efficiency is less than 80%, then the site will fail to meet the recommendations of the Georgia Stormwater Management Manual and will not be approved.
§ 11-11-28
Storm Drain Pipe Design
Piped drainage structures shall be designed to meet the following criteria:
(a)Street catch basins, inlets, culverts serving basins of 20 acres or less and longitudinal piping shall be designed for the 25-year storm, shall have a minimum slope of 1%, and shall have a minimum size of 18 inches in diameter.
(b)Inlet and outlet headwalls are required for all pipes.
(c)The 100-year storm frequency shall be used on natural streams, culverts serving basins of 20 acres or larger and any other drainage system receiving and/or transferring offsite drainage flow.
(d)Velocities for all pipes should be kept to a minimum of 2.5 feet per second and outlet velocities, if practical, shall not exceed 4 feet per second when flowing full. However, if outlet velocities exceed 5 feet per second then energy dissipation devices and/or channel protection must be provided.
(e)The downstream end of all storm drain pipe shall be located at a minimum of 50 feet past the building line for pipe sizes up to and including 36 inches in diameter, unless the storm drainage conveys stream flow.
(f)For all pipe design, the designer shall check the 25-year hydraulic grade line to determine that no inlet structures are flooded and that the collection capacity of any structure has not been compromised by the 25-year ultimate hydraulic grade line, and that any street crossing has not been compromised by the 100-year ultimate hydraulic grade line.
(g)Storm drain pipes shall be constructed of class III reinforced concrete or thermoplastic corrugated-smooth lined (HDPE). Aluminized type II corrugated culvert is discouraged but may be accepted on a case-by-case basis as determined by the Department of Water Resources Director. Pipe materials, related connections, and fittings shall meet the following requirements and specifications noted below.
§ 11-11-29
Pipe References and Requirements
Pipe references and requirements are as follows:
(a)Reinforced concrete: AASHTO M170, ASTM C-969, minimum eight-foot joint lengths, bell and spigot with rubber O-ring gasket conforming to ASTM C-361, class of pipe and wall thickness shall be in accordance with 1030D, Georgia GDOT specifications, Table 1.
(b)Aluminized type II corrugated culvert: AASHTO M36, AASHTO M274, AASHTO M196, ASTM C-969, ASTM B74512 gauge minimum.
(c)High density polyethylene: AASHTO M294 Type "S", AASHTO MP7 and type "S", ASTM D-3212, ASTM F-1417, ASTM F-477, ASTM C-969, and shall be certified through the Plastic Pipe Institute Third Party Certification.
(d)Polyvinyl chloride (PVC): AASHTO M304, ASTM D-3212, ASTM F-1417, ASTM F-477, ASTM C-969, ASTM F949, ASTM F794 and F949, and shall be certified through the Plastic Pipe Institute Third Party Certification.
(e)Thermoplastic pipes: All thermoplastic pipes shall have a full circular cross section with an outer corrugated pipe wall and smooth inner wall. Deflection under loads that contributes to local buckling shall not be decreased by more than 5% (AASHTO M294 and MP7 Sec. 7.4) when tested in accordance with ASTM D-2412. The structural design of thermoplastic pipes shall be in accordance with AASHTO Section 12 titled "Buried Structures and Tunnel Liners."
§ 11-11-30
Pipe Installation Specifications
Pipe installation specifications are as follows:
(a)Foundation and bedding. Unsuitable or unstable foundations shall be undercut and replaced with suitable material. A four-inch to six-inch bedding of class I or II shall be placed and compacted to a minimum of 90% standard proctor density and as per AASHTO T99, AASHTO M145. Haunching materials shall be class I, II, or III and shall be worked under the haunches by hand compaction in eight-inch maximum lifts to 90% standard proctor density. All materials and installation (compaction and bedding) shall meet AASHTO Section 30, AASHTO Section 12, ASTM 2321 and manufacturer's latest specifications. Pipes shall be installed in a dry trench.
(b)Initial backfill. Shall meet the requirements of AASHTO M145, AASHTO Section 12 and shall be one and twenty-four one-hundredths (1.24) inches maximum granular size and minimum compaction of 90% standard proctor density as per AASHTO T99.
(c)Watertight. All joints and connections to drainage structures shall be watertight per ASTM F-1417, inspected and approved by the Department of Water Resources before backfilling.
(d)Street crossings. Thermoplastic corrugated-smooth lined pipe may only be installed in street culverts where the street is classified as a local road, serves 25 or fewer lots, and shall be approved by the Department of Water Resources.
(e)Streams. Stormwater pipes carrying stream flow shall be reinforced concrete or thermoplastic pipe and shall be approved by the Department of Water Resources Director.
(f)Construction. Any storm drainage pipe dedicated to the city shall be constructed using reinforced concrete pipe or thermoplastic pipe.
(g)Easement. Any storm drainage pipe dedicated to the city that extends outside of the street right-of-way shall be located within an easement at least 30 feet in width.
(h)Depth. All storm drainage pipes shall be at least 18 inches below the surface and shall have a slope of at least 1%.
(i)Connection to public system. Development storm drain outlet systems shall connect to a public stormwater conveyance system or to a free-flowing stream, assuming that the post-development stormwater requirements in this chapter are met. The developer shall be required to provide evidence of acceptable capacity to receive additional flow.
(j)Structures. Under no circumstances shall structures be constructed over an existing or proposed storm drain, whether public or private.
(k)Location. All pipes shall be laid in a straight line between structures and longitudinal outside street pavement within the right-of-way or outside right-of-way in dedicated easements. No pipes shall be laid within 4 feet on each side of the center line of any water main or sanitary sewer, unless with the permission of the city engineer. Pipes and fittings will be installed in strict accordance with AASHTO Section 30 and AASHTO Section 12.
(l)Junction boxes. Junction boxes shall be installed where the storm drain changes direction and where one pipe or more intersect. Minimum cover will be 18 inches from finished street elevation to top of pipe.
§ 11-11-31
Headwalls
(a)Headwalls or flared end sections with concrete collars are required at the inlet and outlet on all street culverts and storm drain pipes.
(b)Headwalls are to be precast concrete, stone masonry with reinforced concrete footings, or poured-in-place, reinforced concrete with reinforced concrete footings.
(c)Flared end sections shall be constructed of the same material as the drainage pipe to which they are being connected.
(d)High water elevation contour is to be based on a 25-year storm at the entrance of each head wall.
(e)Energy dissipation devices, such as splash pads, riprap, stilling basins, etc., shall be provided at the outlet of every street culvert and storm drain pipe.
§ 11-11-32
Open Channels
(a)All storm water channels shall be designed to carry at least the 25-year frequency storm with one foot of freeboard.
(b)Velocity at design flow shall be not less than six (6) inches per second but not greater than four (4) feet per second. A higher velocity may be allowed if actions are taken that would avoid erosion or scouring of the channel.
(c)All storm water channels must be designed to convey flows that prevent dwelling flooding, property damage, or public access and/or utility interruption.
(d)The Department of Water Resources may determine that the expected long-term maintenance of a surface drainage system could prove impractical, and a storm water pipe collection system may be required.
(e)Any storm drainage channel that extends outside of the street right-of-way shall be located within a 30-foot wide easement.
(f)In cases in which a subdivision or development is traversed by a stream, there shall be provided an easement extending fifteen (15) feet from the top of each side of the stream bank. A stream protection buffer may be required according to chapter 9-16-3.
(g)All drainage easements, ditches, and drainage areas shall be grassed and/or rip-rapped as necessary to control erosion.
(h)Culverts under driveways shall meet the standards for street culverts.
§ 11-11-33
General Stormwater Design Criteria
(a)The Department of Water Resources may permit several developers to construct joint facilities. The Department of Water Resources shall approve or disapprove the waiver of on-site drainage or detention facilities on the basis of the engineering feasibility of a combined facility.
(b)The Department of Water Resources shall be authorized to approve of alternative methods of stormwater detention based on appropriate engineering studies that do demonstrate equal or better performance in accordance with city storm water management practices. Approved alternatives may include well maintained and landscaped lakes that may be provided to act jointly as detention reservoirs and recreation facilities or aesthetic focal points within forest preserve areas, city or private parks, housing developments, shopping centers, and industrial parks. Other control methods to regulate the rate of stormwater discharge which may be acceptable include, but not [to] be limited to, detention on flat roofs, parking lots, streets, lawns, underground detention, and oversized storm drains with restricted outlets.
(c)Detention facilities and drainage structures shall, where possible, use natural topography and natural vegetation. In lieu thereof, these shall have planted vegetation and permanent ground cover on their borders. All on-site facilities shall be properly maintained by the owner in such a way that they do not become nuisances.
Nuisance conditions shall include: improper storage resulting in uncontrolled runoff and overflow; stagnant water with algae growth, insect breeding, and odors;
discarded debris; and safety hazards created by the facility's operation. Private facilities are the perpetual responsibility of the landowner.
(d)No portion of any detention facility shall be located in any required buffer, street right-of-way or within a flood hazard area.
(e)The 100-year ponding limits of a detention facility shall not encroach upon a public street.
(f)An easement at least twenty-five (25) feet in width shall be required to provide access to the detention facility or other stormwater facility from a street.
(g)Every detention facility or surface impoundment shall be completely enclosed within a drainage easement. The drainage easement shall extend at least ten (10) feet beyond the ponding limits of the 100-year storm for surface impoundments.
(h)Aboveground detention facilities and surface impoundments shall be enclosed with a minimum four-foot high chain link fence and shall be equipped with a minimum four
(4)foot wide access as necessary for maintenance. Any fencing surrounding a stormwater pond that is visible from the public right-of-way shall be decorative in nature, or if chain link fencing is permitted it shall be black vinyl coated.
(i)All graded slopes on aboveground detention facilities or surface impoundments must contain a five (5) foot wide bench for every 20’ in height.
§ 11-11-34
Timing of Installation
Construction of the stormwater system shall be initiated as part of the grading of the site. Storm water detention facilities shall be constructed prior to the installation of any other site improvements, and may be utilized under proper design as sedimentation basins during development. Installation of all other storm drainage pipes, culverts, headwalls, and ditches, shall be coordinated with the construction of streets and other site improvements, as appropriate.