CHAPTER 13

                                                                         STORMWATER MANAGEMENT

SECTION 1:  PURPOSE AND INTENT

a)             The purpose of this chapter is to: 

                1)            Preserve the water resources of the Town, which are critical to the public health, safety and welfare of its citizens.

                2)            To control stormwater runoff so as to prevent erosion, sedimentation and flooding.

                3)            To encourage recharge of the aquifer upon which the public depends for potable fresh water. 

b)            The intent of these design standards is to encourage environmentally sound stormwater management practices; they should go beyond simply providing drainage facilities.  Emphasis should be placed on the use of upland facilities for stormwater control and groundwater recharge.  Developments that sacrifice recharge and upland controls in order to maximize the number of lots will not be allowed.  The Town's stormwater management perspective includes the control of both water quantity and water quality.

c)             The requirements hereafter are designed to allow landowners reasonable use of their property while promoting the following objectives:

                1)            To prevent loss of life and significant loss of property due to flooding.

                2)            To protect, restore, and maintain the chemical, physical and biological quality of ground and surface waters.

                3)            To encourage productive and enjoyable harmony between humanity and nature.

                4)            To prevent individuals, business entities, and governmental entities from causing harm to the community by activities which adversely affect water resources.

                5)            To encourage the protection of wetlands and other natural systems and the use of those natural systems in ways which do not impair their beneficial functioning.

                6)            To minimize the transport of sediments and pollutants to surface waters.

                7)            To protect, restore and maintain the habitat of fish and wildlife.

                8)            To perpetuate natural groundwater recharge.

                9)            To encourage the use of drainage systems which minimize the consumption of electrical energy or petroleum fuels to move water, remove pollutants, or maintain the system.

                10)          To ensure the attainment of these objectives by requiring approval and implementation of water management plans for all activities which may have an adverse affect upon groundwater and surface water.

                11)          To implement the Surface Water Management (SWM) program of the St. Johns River Water Management District (SJRWMD).

SECTION 2:  PERMIT REQUIRED

a)             The requirements of this chapter shall apply to all areas in the Town of Lady Lake and shall be satisfied completely prior to final project approval by the Town.

b)            No person shall conduct a development activity, subdivide, make any change in the use of land, construct any stormwater management system or structure, or change the size of an existing structure or system, except as exempted later in this  chapter, without first obtaining approval from the Town as provided herein.

c)             Approval of the stormwater management plans shall be contingent on approval of any required permit from the St. Johns River Water Management District; however, approval by SJRWMD will not result in automatic approval of the stormwater management plans by the Town.

SECTION 3:  EXEMPTIONS

All activities which are exempt from permitting per SJRWMD regulations shall be exempted from further consideration under the provisions set forth herein.

SECTION 4:  PERFORMANCE CRITERIA

The stormwater management system design shall conform to the following standards:

a)             Projects shall be designed so that stormwater discharges meet, at a minimum, the water quality criteria set forth by the St. Johns River Water Management District, Applicant's Handbook, Management and Storage of Surface Waters, in order to achieve the state water quality standards established by the Florida Department of Environmental Protection in Chapter 17-3, Florida Administrative Code, or as amended.

b)            Wetlands shall only be used for stormwater treatment as allowed by SJRWMD criteria, providing that one-half (1/2) of the required treatment volume is retained in an offline pollution abatement pond in order to skim the first flush prior to discharge into the wetland. The applicant must provide assurance that this offline retention will not deprive the wetland of water which will alter the hydroperiod.

SECTION 5:  DESIGN CRITERIA

a)             Runoff Volume and Peak Rate

                Design Storm (Minimum):

                Rainfall frequency, duration, and distribution for stormwater management systems are to be in accordance with the SJRWMD Applicant's Handbook.

b)            Water Quality

                1)            All developments will treat the required pollution abatement volume prior to discharge to receiving waters.  When pollution abatement volumes and detention volumes to reduce the peak rate of discharge are incorporated into one facility, the volume of water impounded to reduce peak discharges in excess of the pollution abatement volume must be discharged by a positive, non-filtering system.

                2)            The pollution abatement volume and treatment method shall be as required by SJRWMD, 40C-42, except that sites utilizing a Wetlands Stormwater Management System must treat one-half (1/2) of the required volume in an offline detention pond before discharging into the wetland.

c)             Peak Rate and Volume Attenuation

                1)            Peak rate and volume attenuation shall be as required in the SJRWMD regulations.

                2)            Credit for seepage through the pond bottom to further reduce the peak rate of discharge, or runoff volume, will not be allowed unless accompanied by supporting documentation prepared by a professional engineer.

d)            Development Within Flood Prone Areas (100-Year Flood)

                All development within flood prone areas as delineated on the official National Flood Insurance Program, Flood Insurance Rate Maps, or the latest and best information available, shall comply with the requirements of SJRWMD and the criteria in the Flood Damage Prevention section of the Building and Fire Codes  chapter.

e)             Easements Required

                1)            Ditches, canals, retention areas, storm sewers or any other drainage facility shall have sufficient easements for the facility plus an unobstructed maintenance berm as necessary.  Said easement shall be contiguous to a public right-of-way/easement and shall allow for suitable access by maintenance equipment. 

                2)            Easement size shall be as specified in the Developmental Procedures and Regulations chapter of this Code.

f)             Retention/Detention Pond Requirements

                1)            Side slopes shall be designed per SJRWMD regulations.

                2)            Maintenance berms shall have slopes no steeper than one (1) foot  vertically for every twenty (20) feet horizontally.

                3)            Where retention/detention areas are located on the project periphery, the developer may be required to provide additional landscaping or screening to adequately protect abutting properties, not including right-of-ways.

                4)            Fenced stormwater facilities are discouraged within the Town and shall only be allowed if approved by the Town Manager or Designee.  Stormwater facilities which require fencing due to steep side slopes which potentially endanger human life, must be designed with a six (6) foot high chain link fence or better (i.e., brick wall) around entire perimeter including maintenance berms and provide an access for maintenance vehicles.

                5)            One foot (1') minimum freeboard is required above design storm high water elevation.

g)            Open Channels

                1)            With the exception of "roadside swales" and natural watercourses, open channels shall not be permitted within one-hundred (100) feet of residential lots or school sites unless the open channel is fenced or approved by the  Town Manager or Designee.

                2)            Wherever possible, drainage shall be maintained in an existing open channel with appropriate sodded banks and adequate width for the maximum potential volume of flow.  A closed drainage system may be approved by the Town Manager or Designee.

                3)            The maximum side slopes shall be 3:1 for channels four (4) feet deep or less and 4:1 if greater than four (4) feet deep.

                4)            A roadside ditch shall have a three foot (3') minimum bottom width and a two foot (2') minimum depth, below the shoulder of the road.

                5)            Erosion Protection

SECTION 6:  HYDRAULIC DESIGN CRITERIA

a)             Roadway (Pavement) Design

                1)            General

                               Good pavement drainage design consists of the proper selection of grades, cross slopes, curb types, inlet locations, etc., to remove the design storm rainfall from the pavement in a cost-effective manner while preserving the safety, traffic capacity, and integrity of the highway and street system.  These factors are generally considered to be satisfactory, provided that excessive spreads of the water are removed from the vehicular traveled way and that siltation at pavement low points is not allowed to occur.  The guidelines included herein will accomplish these objectives.

                2)            Minimum Groundwater Clearance

                               A)     The seasonal high groundwater table shall be established by an engineer or professional geologist.

                               B)     All streets should be designed as specified in the Transportation Standards chapter of this Code to provide a minimum clearance to the seasonal high groundwater table, or the artificial water table induced by a road underdrain system.

                               C)     Swales will be permitted only when the seasonal high groundwater table is a minimum of two (2) feet below the invert of the swale.  Swales shall be constructed to allow positive drainage from the pavement to the invert of the swale (i.e., no ponding of water at the edge of pavement).

                3)            Curb and Gutters

                               All roadway drainage not considered suitable for swale and/or ditch type drainage shall be designed with curb and gutter using the criteria in the Transportation Standards of this Code.

                4)            Stormwater Spread into Traveled Lanes

                               The acceptable spread limits for arterial and collector roadways are defined as approximately one-half the traveled lane width.  Acceptable spread limits for local roadways are defined as being below the crown of the road.

b)            Storm Sewer and Culvert Design

                1)            Minimum Pipe Size

                               A)     The minimum size of pipe to be used in storm sewer systems is 15 inches.

                               B)     The minimum size of pipes to be used for culvert installations under roadways shall be 18 inches.  The minimum size of pipes to be used for driveway crossings shall be 15 inches.

                2)            Pipe Grade

                               A)     All storm sewers shall be designed and constructed to produce a minimum velocity of 2.0 feet per second (fps) when flowing full.

                               B)     No storm sewer system or portion thereof shall be designed and constructed to produce velocities in excess of 10 fps for both reinforced concrete pipe and metal pipe.

                               C)     The maximum slope allowable in a culvert shall be a slope that produces a 20 fps velocity within the culvert barrel.

                               D)     A headwall, inlet, manhole, or mitered end section is required at the end of a pipe and erosion protection and/or energy dissipators shall be required to properly control entrance and outlet velocities, unless the outlet is permanently submerged.

                3)            Maximum Lengths of Pipe

                               The following maximum lengths of pipe shall be used when spacing access structures of any type.

                4)            Allowable Materials

                               Allowable material for storm sewers and structures shall be in accordance with Florida Department of Transportation standards and specifications, and all other applicable Town Codes unless approved by the Town Manager or Designee.  Only reinforced concrete shall be allowed under roads and driveways.  All exposed pipe shall be of similar material.

                5)            Minimum Cover

                               Minimum cover shall be one (1) foot below the final pavement grade.

                6)            Design Tailwater 

                               All storm sewer systems and culverts shall be designed taking into consideration the tailwater of the receiving facility or waterbody.  The tailwater elevation used shall be based on the design storm frequency.

                7)            Design Procedure

                               A)     The Hydraulic Gradient line for the storm sewer system shall be computed taking into consideration the design tailwater on the system and the energy losses associated with entrance into and exit from the system, friction through the system, and turbulence in the individual manholes, catch basins, and junctions within the system.

                               B)     The design storm frequency to be utilized for the design of pavement drainage shall be as follows:

SECTION 7:  CLEARING AND GRADING STANDARDS

a)             The purpose of this section is to provide specific criteria for allowable clearing and grading in order to prevent soil erosion and any impact on adjoining properties.  In addition, the purpose of this section is to comply with Comprehensive Plan Policy 5-1.2.7 Reduce Sediments and Suspended Solids Associated with Shoreline Erosion and Policy 5-1.7.1 Implementing Erosion Control.

b)            Procedures for acquiring a clearing and tree permit, if clearing is to be done prior to receiving a Development Order, shall be as specified in the Developmental Procedures and Regulations chapter of this Code.

c)             Standard practices shall be used to prevent erosion and the depositing of soil off-site per St. Johns River Water Management District regulations.  This shall also include the protection of bare soils from wind forces. 

d)            The burying or depositing of rubbish, logs, lumber, building materials, concrete block, underbrush, trash or other matter which would decompose or allow the land to settle is prohibited.  Duly authorized landfills and limited burying as part of the construction of landscaped berms and similar features in non-buildable areas may be approved.

e)             Shoreline and Wetland Areas

                No such vegetation which is protected as specified in the Environmental Regulations chapter of this Code shall be disturbed without the required state and federal regulatory agency permits.

f)             The property owner or his agent must implement and operate all erosion and sediment control measures required to retain sediment onsite and to prevent violations of water quality standards as specified in Chapters 17-3 and 17-4, F.A.C., or as amended.  The property owner or his agent is encouraged to use appropriate Best Management Practices for erosion and sediment control as described in the Florida Land Development Manual:  A Guide to Sound Land and Water Management, FDEP, latest edition.

SECTION 8:  DEDICATION OF DRAINAGE EASEMENTS AND RIGHTS-OF-WAY

a)             Off-site easements for stormwater management facilities will be required when either of the following conditions exist:

                1)            The discharge is into any man-made facility for which the Town does not have either a drainage easement or right-of-way.

                2)            The discharge is into a natural system such that the rate or character (i.e., sheetflow vs. concentrated flow) of the flow at the property line has been changed.  The easement will be required to a point at which natural conditions are duplicated, and where no adverse impact outside the easement occurs.

b)            When a development is traversed by an existing open channel that is to remain, the applicant shall provide a drainage easement or right-of-way conforming substantially to the lines of such watercourse or open channel. 

SECTION 9:  STORMWATER MANAGEMENT PLAN REQUIREMENTS

a)             It is the responsibility of the applicant to include in the plan application sufficient information for the Town Manager or Designee to evaluate:

                1)            The environmental and hydraulic characteristics of the affected areas.

                2)            The potential and predicted impacts of the proposed activity on community waters.

                3)            The effectiveness and acceptability of those measures proposed by the applicant for eliminating or reducing adverse impacts.

                4)            The ability of an entity to properly maintain the system.

b)            The applicant shall include in the submittal all plans, calculations and supporting information that is to be submitted to SJRWMD.  In addition to this, other information that is to be included with or on the plans includes:

                1)            Proposed subdivision and site layouts with horizontal and vertical controls.

                2)            Overall project grading plan (at 1-foot contours) and individual lot grading plans.

                3)            100-year floodplain compensating calculations, if applicable.

                4)            Recharge demonstration where required.

                5)            Storm sewer, culvert, and open channel tabulations (signed and sealed) including, but not limited to, the following:

                               A)     Dimensions, including length and diameter of pipes.

                               B)     Sub-basin areas tributary to each structure.

                               C)     Runoff coefficient (or curve number if applicable).

                               D)     Time of concentration.

                               E)      Stormwater flow to and from the stormwater structure or junction point.

                               F)      Hydraulic gradient for the applicable storm event, including losses through structures.

                               G)     Estimated receiving water elevation with sources of information.