§ 27-519. Stormwater requirements.

(a)

Compliance with state and other regulations. All sites, facilities, and stormwater management systems shall comply with the applicable rules of the Florida Department of Environmental Protection (Ch. 62-330, F.A.C., Ch. 62-621.300, F.A.C., and Ch. 62-624 F.A.C and rules and handbooks of the St. Johns River Water Management District (Ch 40C-4 F.A.C., Ch. 40C-40 F.A.C., Ch. 40C-41 F.A.C., Ch. 40C-42 F.A.C., Ch. 40C-400 F.A.C.). These rules and handbooks are hereby incorporated by reference, but shall not supersede the city's ordinances.

(b)

Conveyance system design:

(1)

The rational method utilizing the FDOT storm tabulation method shall be used unless otherwise approved by the city manager or designee.

(2)

A minimum time of concentration of ten (10) minutes shall be used.

(3)

For minor collection systems, driveway culverts, side drains and subdivision storm sewers the five-year frequency storm shall be used.

(4)

For outfalls from stormwater management systems such as retention or detention systems and cross drains the twenty-five-year frequency storm shall be used.

(5)

The minimum acceptable pipe velocity is 2.5 feet per second (fps) flowing full. If this is a physical impossibility, an absolute minimum hydraulic velocity of 2.0 fps for full flow should be obtained with the prior approval of the city mananger or designee.

(6)

The maximum velocity shall be kept below ten (10) fps.

(7)

The maximum allowable velocity at the point of discharge is 2.5 fps unless energy dissipation is provided. If the outfall discharges into a still body of water, submergence of the outfall by at least two-thirds of the diameter may be considered as energy dissipation.

(8)

When hydraulic calculations do not consider minor energy losses, the elevation of the hydraulic gradient for the design storm condition should be at least 1.0 feet below the gutter, grate elevation or ground elevation. Minor losses will be considered when the hydraulic gradient velocity exceeds six (6) feet per second or lower on critical systems. When minor losses are calculated, it will be acceptable for the hydraulic gradient to reach two-tenths of a foot (0.2') below the gutter elevation, grate elevation, or ground elevation.

(c)

Stormwater management facilities: All stormwater management facilities such as detention and retention systems shall be designed and constructed to control the mean annual, five-year frequency twenty-four hour duration and the twenty-five-year frequency twenty-four hour duration storm events. All stormwater management facilities shall have a positive discharge and outfall except as approved by the city manager or designee. All stormwater management facilities intended for dedication to the city shall provide a minimum twelve (12) feet of clear access on all sides suitable for maintenance vehicles except as approved by the city manager or designee. Project sites less than five (5) acres may use either the rational method or a soils conservation service (SCS) method. Project sites five (5) acres and greater shall use a SCS method. SCS methods shall use the Type II Florida Modified Distributions with rainfall amounts from the St. Johns River Water Management District Technical Publication SJ88-3. All stormwater management facilities must recover to its design low water stage within seventy-two (72) hours. To provide the city with assurances, case permeability test must be performed for every 0.5 acres of retention area and at each retention location at the same elevation as the proposed bottom of the basin and a safety factor of two (2) shall be applied to the design. A groundwater mounding analysis shall be required to demonstrate recovery of all retention areas. All stormwater management systems shall have a one-foot minimum freeboard required at all points for all required storm events, and shall have an emergency overflow which will direct the water to a suitable drainage system. Banks shall be sloped no greater than one (1) unit vertical to five (5) units horizontal, unless privately owned and permanently fenced, in which case the slope may be increased to one (1) vertical per three (3) horizontal units. Steeper slopes shall be bulkheaded with nondeteriorating materials of sufficient strength to support the active and passive earth pressures retained. Pumps used for stormwater shall not be allowed for facilities intended for dedication except as approved by the city manager or designee. Stormwater pumps, forcemains and appurtenances shall be maintained and owned by the property owner or home owners' association, and shall not be intended for dedication to the city. Underground stormwater management facilities such as vault or chamber-type systems shall have suitable provisions for inspection, maintenance, and cleaning. Underground stormwater management facilities shall be maintained and owned by the property owner or home owners' association, and shall not be intended for dedication to the city.

(d)

Streets and road drainage: Curbs and gutters shall be constructed along the edges of all street pavements for all new development and redevelopment. The distance between curb inlets shall not exceed five hundred (500) feet. The capacity of standard curb inlets shall be no more than 3.5 cubic feet per second (cfs) per throat unless otherwise approved by the city manager or designee. The minimum gutter slope shall be at least 0.005 ft/ft. The city manager or designee may allow, with prior approval, the use of ribbon curb to accommodate road side swales when used as part of a low impact developments (LID) project that incorporate reduction in flow and volume of stormwater, increase in natural hydrology, and adherence to the principles of the Florida Yards and Neighborhoods Program in new landscaping. The maximum side slope for these swales shall be 3:1, the maximum allowable velocity shall be two (2) fps unless soil conditions indicate a lower velocity or structural erosion control protection is provided, and a minimum shoulder width of six (6) linear feet is provided. Rights-of-way with streets and roads without curb and gutter shall be private and will not be dedicated to the city.

(e)

Attenuation: All new developments and redevelopments shall be required to attenuation both peak discharge rate and volume to the historical pre-development flow rates and volume of discharge for the mean annual storm event, five-year frequency twenty-four hour duration storm event and the twenty-five-year frequency twenty-four hour duration storm event.

(f)

Stormwater treatment: All new developments and redevelopments shall provide treatment that meets or exceeds the minimum level of stormwater treatment in Chapter 62-40.432(2), F.A.C. and the applicable design criteria for stormwater management systems established in the rules and handbooks of the SJRWMD. The level of treatment for all new developments and redevelopments located within a basin that discharges to a state listed impaired waterbody shall be equal to "net improvement" as required by Section 373.414(1)(b)(3). This means that the post-development stormwater pollutant loading for the pollutant causing the impairment must be less than the existing stormwater pollutant loading from the site. Pervious and semi-impervious pavements are required to provide treatment. Additional treatment may be required to comply with other state or federal agencies. All new developments and redevelopments shall provide provisions to prevent the escape of floatable materials prior to discharge from the site.

(g)

Illicit discharges and illicit connections: Non-stormwater discharges, illicit discharges and illicit connections such as the discharge of spills and the dumping or disposal of materials other than stormwater into stormwater systems and the city's municipal separate storm sewer systems (MS4) shall be prohibited.

(h)

Stormwater related inspections: All properties and facilities contributing to or discharging into the city's MS4 shall grant city personnel access to the property, buildings, and the facilities to perform inspections, surveillance and monitoring procedures necessary to determine compliance with the city's MS4 permit.

(i)

Adjacent impacts: All new developments and redevelopments shall provide assurance that adjacent or nearby properties not owned or controlled by the applicant will not be adversely affected by drainage or flooding.

(j)

Private stormwater systems: All new developments and redevelopments with private stormwater systems and facilities shall designate an operation and maintenance entity in accordance with the requirements of the SJRWMD that is capable of effectively operating and maintaining such systems and facilities.

(k)

Low maintenance zone: Shall be a minimum of six (6) feet from any pond, stream, watercourse, lake, wetland, swale, retention system, detention system, stormwater inlet, curb inlet or seawall. Appropriate vegetation shall be selected, planted, and maintained to minimize fertilization, watering, erosion, and mowing. Floatable materials such as mulch shall be prohibited in the low maintenance zone. Initial planting shall achieve at least seventy-five (75) percent coverage and shall achieve a ninety-five (95) percent coverage within the first six (6) months after planting to prevent erosion. All exposed soil shall be stabilized to prevent erosion. Cut vegetative material or yard debris shall be not be deposited or left remaining in the low maintenance zone. Fertilizers shall only be minimally used when a soil test and leaf tissue test demonstrate that nutrients are needed for the vegetation to grow and survive. Herbicides, aquatic weed control, and pesticides shall not be used in the low maintenance zone.

(l)

Storm sewers and culvers: For all storm sewers, driveway culverts, cross drains and side drains within rights-of-way and intended for dedication to the city shall use reinforced concrete pipe (RCP) class III, IV, or V, precast box culverts, or built-in-place concrete box culverts, terminating with headwalls, mitered end sections, or flared end sections or as approved by the city manager or designee, and shall have a minimum pipe size of fifteen (15) inches round or fifteen (15) inches elliptical equivalent. All storm pipes in paved areas shall have a minimum cover of eighteen (18) inches from the top of the bell to the bottom of the pavement base. All storm pipes in unpaved areas shall have a minimum cover of eighteen (18) inches from the top of the bell to the finished grade. The maximum length of pipe without an access structure shall be four hundred (400) feet. Joints and joint material for reinforced concrete pipe shall be "O-ring" for round pipe or "ram-nek" for elliptical pipe, and shall include a twenty-four-inch band of filter fabric (one (1) foot on each side of joint) wrapped around each joint for all storm sewers intended for dedication to the city. Driveway culverts and cross drains shall extend a minimum of eight (8) feet on each side beyond the edge of pavement of the road. Driveway culverts and side drains not intended for dedication that will be privately maintained may use alternate pipe materials when approved by the city manager or designee. Upon completion of installation, the contractor shall test all flexible pipe for deflection. Pipe deflection shall not exceed five (5) percent. Testing equipment and test supervision will be provided by the contractor. Testing will be done using a mandrel having a diameter equal to ninety-five (95) percent of the inside diameter of the pipe. The test shall be performed without mechanical pulling devices or re-rounders. Any device for measuring deflection must be approved by the city manager or designee. Side drain applications, for lengths less than forty (40) feet, visual inspection methods, such as lamp testing, for deflection may be allowed.

(m)

Operation and maintenance assurances: The legal maintenance entity shall ensure that the "operation and maintenance inspection certification" as required by the SJRWMD is completed in a timely manner, and, a copy is maintained on-site and made available to city inspectors upon request.

(n)

An owner of land that has historically received natural drainage discharges from adjacent higher lands shall be obliged to continue to receive and convey such flows, but the owner of the higher land shall not change the manner, peak flow rates, or location of such historical naturally occurring drainage flows without the express written approval of the owner of the lower land. No obstruction to existing drainage will be permitted unless approved by the city manager or designee. This includes flow in streams, ditches, overland flow, underground flow, flow in pipes, or flow in floodplains. When a development or redevelopment constructs a drainage system to accept the private off-site upstream drainage, unless dedicated and accepted by the city, the property owner, the homeowners association or other acceptable entities as approved by the city, shall maintain the system. Drainage systems downstream of a proposed development or redevelopment shall have the capacity or hydraulic gradient to accept the proposed developments discharge, or that the proposed development improves the downstream drainage system. The city shall not be liability for any damage, drowning or any other personal damages caused by flooding, drainage or discharges including, but not limited to, blockage, dam failure, conveyance failure, structural failures, maintenance issues, wash-outs, erosion or excess flow. When downstream conditions will not accept runoff from the appropriate storm-existing conditions or other special instances, the development will be required to provide a drainage system which will not increase flooding downstream. Accordingly, the city manager or designee may require the developer to analyze the downstream drainage system.

(1)

If there are known flooding problems, approval of off-site stormwater discharge shall be based on:

a.

Maintaining existing peak discharge(s) and stage-discharge relationship(s) at the site discharge location(s) as well as the timing, duration, and volume of existing off-site discharge(s);

b.

A demonstration that peak discharge(s) and volume release(s) from the site will not increase flood stages or velocities off-site; or

c.

Providing improvements along entire discharge path (in recorded easements, unless approved otherwise by the city manager or designee) to the receiving waters.

(2)

Known flooding problems are those which pose an imminent threat to public safety and/or property including loss of human life, blockage of evacuation and/or emergency vehicle routes, and/or flooding of homes, buildings, or roadways as evaluated by the following criteria:

a.

Home/building flooding for any storm;

b.

Overtopping existing conveyance ditches and swales;

c.

Insufficient or lack of positive outfall;

d.

Closed basins or standing water in areas or conveyances for more than twenty-four (24) hours after an event.

e.

Impaired, existing, off-site conveyance systems not designed to handle larger storms flows.

f.

Roads being overtopped by flood stages based on the appropriate design event and over topping of the roadway of greater than one (1) foot based on the 100-year, twenty-four-hour event; or

g.

Roads being overtopped by flood stages based on the appropriate design event and over topping of the roadway of greater than one-tenth of a foot based on the 25-year, twenty-four-hour event; or

h.

Road being closed to traffic due to flooding; or

i.

Greater than one-half of a foot per one hundred (100) feet of head loss across a stormwater conveyance structure for the appropriate design events.

(o)

Soil borings: Shall be required for all stormwater management systems including all retention and detention systems, and will include one (1) boring per 0.5 acres of system surface area. A minimum of one (1) boring will be required for each stormwater management facility location. The boring shall be taken to a depth at least fifteen (15) feet below the stormwater management facility bottom, and shall include information to show confining layers, encountered groundwater levels, and wet season high-water elevations.

(p)

The minimum finish floor elevation for habitable living spaces should be eighteen (18) inches above the highest adjacent centerline of road or top of curb, whichever is greater, and all other finished floor elevations should be at least twelve (12) inches above the highest adjacent centerline of road or top of curb, whichever is greater.

(q)

Flood zone and flood-prone areas: Any site (including residential lots) adjacent to a stream or river must be evaluated to assure that no blockage occurs in the floodplain. In the event a 100-year flood zone, as shown on current FIRM MAPS, or delineated by the best available data, or ten-year flood zones indicated in current Flood Insurance Study data or by other best available data is to be filled.

(1)

Adequate storage area must be provided to hold the same quantity of water that the flood area did prior to filling;

(2)

Certain channel and improvements downstream must be made to compensate for any storage denial; or

(3)

A combination of No. 1 and 2 unless otherwise approved by the city manager or designee.

Flood-prone areas shall have adequate drainage provided to accommodate stormwater if flood-prone areas are filled. This could be in the form of alternate water storage areas, improvements, or combination of these or other basin changes. Approval from any local, State of Florida, or U.S. Government agency is required and copies forwarded to the city within ten (10) days after commencement of construction on the affected area.

Where base flood elevations have been established, residential and nonresidential structures shall be elevated to or above the base flood elevation plus one (1) foot. In V Zones, the elevation requirement is measured from the bottom of the lowest horizontal structural member. Where base flood elevations have not been established, construction shall be elevated to the depth number specified on the FIRM plus one (1) foot prior to the placement of fill. If no depth number is specified, the lowest floor including the basement, shall be elevated, at least three (3) feet above the highest adjacent natural grade prior to the placement of fill. If no depth number is specified, the lowest floor including the basement, shall be elevated, at least two (2) feet above the highest adjacent natural grade.

Where the special flood hazard area is immediately adjacent to a "floodway" a more stringent base flood elevation is shown in the Flood Insurance Study. Where flood studies have produced floodways that provide a flood elevation based upon the floodway encroachment, these elevations are listed in the "With Floodway" column in the Floodway Data Table in the community's Flood Insurance Study. These higher elevations shall be used as the BFE for that area, and then the freeboard requirement stated above shall be applied.

(r)

Drainage easements: Easement width for drainage pipe shall be twenty-five-foot minimum for five (5) feet of cut or less and two (2) feet additional width for each additional foot of cut below five (5) feet. The pipe shall be located in the center part of any easement. The city shall require unobstructed easements or rights-of-way along rear or side lot lines where necessitated by maintenance requirements. This criteria does not apply for private easements. All stormwater management facilities are to be owned and maintained by the legal operation and maintenance entity as required by the SJRWMD. Rights-of-way or easements must continue through all stormwater management systems. Littoral zones and wetland mitigation areas shall not be located within city easements. Such rights-of-way or easements shall include a hold harmless agreement and a twenty-foot minimum access easement to control structures via land.

(s)

Hold harmless: A "hold harmless" agreement must be executed and approved by the city which will relieve the city of any responsibility of any liability for any damage caused by flooding, including but not limited to, blockage, dam failure, and excess flow, drowning or any other personal damages, and for maintaining all privately owned and operated stormwater management systems. The agreement shall be shown on the final plat.

(t)

Groundwater: In accordance with the test boring data obtained and considering anticipated groundwater changes due to drainage improvements, underdrain shall be installed in all cases where the groundwater table is closer than twenty-four (24) inches below the lowest finished bottom elevation of road base coarse for any roadway. The "iron-oxide" lens in the soil may be used as an indicator of the usual high pre-development groundwater elevation. Should underdrain quantities be adjusted in the field during construction the developer's engineer shall revise the construction plans accordingly and submit revised signed and sealed plans to the city. The size of the underdrain required shall be determined using accepted engineering practices. The minimum size acceptable is six (6) inches in diameter, and the minimum slope shall be 0.004 ft/ft.

(u)

As-built or record drawings: "As-built" or record drawings signed and sealed by a Florida registered professional must be submitted and approved for all stormwater management and collection systems intended for dedication.

(v)

Additional criteria may be added by the city as deemed appropriate on a site by site bases by the city manager, city engineer, city council or designee.

(Ord. No. 91-1-5, § 2, 5-6-91; Ord. No. 1998-31, § 1, 12-7-98; Ord. No. 2013-02, § 7, 6-10-13)