N.J. Admin. Code § 19:4-8.6
Current through Register Vol. 56, No. 12, June 17, 2024
Section 19:4-8.6 - Drainage(a) General requirements for drainage are as follows: 1. Drainage plans shall be signed and sealed by a New Jersey-licensed professional engineer or other professional authorized to prepare drainage plans.2. All vehicular use areas shall be drained so as to direct surface water runoff to a stormwater drainage system for eventual subsurface or stream disposal. Conveyance via vegetated channels is acceptable but shall be supported with calculations verifying stability during peak flows.3. A watershed runoff hydrograph that displays and compares the peak discharge rate and volume shall be prepared for both pre-and post-development conditions. Runoff volume calculations shall be used to determine the sizing of detention facilities, if necessary.4. The receiving stormwater drainage system (pipe flow or open channel flow) shall be analyzed to ensure that it has the additional capacity necessary to handle any increase in stormwater flow during the 25-year design storm. The analysis shall include all upstream and downstream runoff peak contributions, estimated per N.J.A.C. 19:4-8.6(b)3, to a downstream point established by the NJMC. If the receiving stormwater drainage system is at or over capacity, or is not analyzed, detention and/or infiltration facilities shall be provided in order to maintain site runoff peak flow at pre-development levels.5. The size of the drainage area shall include on-site and off-site lands contributing stormwater to the discharge point. Additionally, the pre-development drainage patterns of any off-site contributions shall be maintained unless a compensatory system is provided, which, at a minimum, maintains the pre-development on-site capacity to carry neighboring stormwater runoff peak flow during the 25-year storm.6. An operation and maintenance manual for stormwater drainage systems, including stormwater quality measures, shall be provided to ensure proper function and operation of the system and in a manner consistent with N.J.A.C. 7:8, the Stormwater Management Rules. The operation and maintenance manual shall be updated as necessary. Updates shall be provided to the NJMC.(b) Design requirements for drainage are as follows:1. The applicant shall provide information sufficient for the NJMC to determine compliance with the applicable sections of N.J.A.C. 7:8, the Stormwater Management Rules. With regard to water quality, proposed development and redevelopment that may introduce petroleum hydrocarbons to runoff water shall install stormwater management measures that target and remove such pollutants.2. All drainage systems shall be designed for a 25-year storm event. The magnitude of the 25-year rainfall depth and/or rainfall intensity specific to each site shall be developed from the "Precipitation-Frequency Atlas of the United States," National Oceanic and Atmospheric Administration (NOAA) Atlas 14, Volume 2, Version 2, incorporated herein by reference, as amended and supplemented. This document is available from the NOAA National Weather Service, Office of Hydrologic Development, Hydro-meteorological Design Studies Center, Bldg. SSMC2 W/OHD13, 1325 East-West Highway, Silver Spring, MD 20910-3283, or online at http://hdsc.nws.noaa.gov/hdsc/pfds/orb/nj_pfds.html. An outline of the above document, specific to New Jersey, is available from the National Resources Conservation Service (NRCS) New Jersey State Office (NJSO). This outline, NJ Bulletin No. NJ210-4-1, dated September 8, 2004, incorporated herein by reference, as amended and supplemented, is available through the NRCS New Jersey State Office, 220 Davidson Avenue, 4th Floor, Somerset, New Jersey 08873, or online at http://www.state.nj.us/dep/damsafety/nrcs_24hour_rainfall.pdf. Per N.J.A.C. 7:8, the Stormwater Management Rules, properties within the District and outside the FEMA Special Flood Hazard Area (SFHA) may be required to meet water quality control requirements for events greater than the 25-year event. Additionally, the water quality design storm shall be developed pursuant to N.J.A.C. 7:8-5.5.3. Runoff estimation: i. The Rational Method, utilizing the rational formula listed in Figure 8-2 below, shall be used for the sizing of storm sewer systems only. The antecedent precipitation factor (Ca) shall be used with the Rational Method, as shown in the Standards for Soil Erosion and Sediment Control in New Jersey at N.J.A.C. 2:90-1.3, incorporated herein by reference, as amended and supplemented. For the sizing of volume-based stormwater systems and for comparing pre- and post-construction peak flows, the National Resources Conservation Service's (NRCS), Technical Release No. 55 (TR-55), "Urban Hydrology for Small Watersheds," incorporated herein by reference, as amended and supplemented, or equivalent approved by the NJMC, shall be used. A copy may obtained from the NRCS New Jersey State Office, 220 Davidson Avenue, 4th floor, Somerset, New Jersey 08873, or online at the NRCS website, http://www.wcc.nrcs.usda.gov/hydro/hydro-tools-models-tr55.html; and | GFigure 8-2 |
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| Rational Formula |
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| Q = ciA |
| where: |
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| Q = ciA |
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| Q = |
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| Peak flow in cubic |
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| feet per second (cfs) |
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| c = |
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| Runoff coefficient |
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| (weighted) x the |
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| antecedent |
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| precipitation factor |
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| i = |
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| Rainfall intensity |
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| in inches per hour |
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| (in/hr) |
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| A = |
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| Drainage area in |
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| acres (ac) |
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ii. The runoff coefficients (c) listed in Table 8-2 below shall be used in the rational formula: | Table 8-2 |
| Coefficient of Runoff Values |
| Land Use | Description | Hydrologic Soils |
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| Group |
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| A | B | C | D |
| Cultivated Land: | Without conservation treatment | 0.49 | 0.67 | 0.81 | 0.88 |
| With conservation treatment | 0.27 | 0.43 | 0.61 | 0.67 |
| Pasture: | Poor condition | 0.38 | 0.63 | 0.78 | 0.84 |
| Grassland or Range Land | Fair condition | ------- | 0.25 | 0.51 | 0.65 |
| Meadow | Good condition | ------- | ------- | 0.41 | 0.61 |
| Wood or Forest Land: | Poor cover; thin stand, no mulch | ------- | 0.34 | 0.59 | 0.70 |
| Good cover | ------- | ------- | 0.45 | 0.59 |
| Open Space: | Poor Condition (grass cover < |
| 50 percent) | ------- | 0.65 | 0.70 | 0.85 |
| Lawns, Parks, Golf Courses, etc.) | Fair Condition (grass cover 50 |
| percent to 75 percent) | ------- | 0.45 | 0.63 | 0.74 |
| Good Condition |
| (grass cover |
| 75 percent) | ------- | 0.25 | 0.51 | 0.65 |
| Commercial and Business Areas: | 85 percent impervious | 0.84 | 0.90 | 0.93 | 0.96 |
| Industrial Districts: | 72 percent impervious | 0.67 | 0.81 | 0.88 | 0.92 |
| Residential: |
| Average Lot Size (acres): | Average percent impervious: |
| 1/8 | 65 | 0.59 | 0.76 | 0.86 | 0.90 |
| 1/4 | 38 | 0.29 | 0.55 | 0.70 | 0.80 |
| 1/3 | 30 | ------- | 0.49 | 0.67 | 0.78 |
| 1/2 | 25 | ------- | 0.45 | 0.65 | 0.76 |
| 1 | 20 | ------- | 0.41 | 0.63 | 0.74 |
| Impervious Areas: | Parking lots, roofs, driveways, etc. | 0.99 | 0.99 | 0.99 | 0.99 |
| Paved | Streets and roads | 0.99 | 0.99 | 0.99 | 0.99 |
| Gravel | Streets and roads | 0.57 | 0.76 | 0.84 | 0.88 |
| Dirt | Streets and roads | 0.49 | 0.69 | 0.80 | 0.84 |
| Note: Hydrologic Soil Groups texture descriptions are the following: |
| A | Sand, loamy sand, or Sandy loam. |
| B | Silt loam or loam |
| C | Sandy clay loam |
| D | Clay loam, silty loam, sandy clay, silty clay or clay |
iii. The time of concentration (Tc) used shall be calculated using the NRCS TR-55 methodology or other method approved on a case-by-case basis by the NJMC. The time of concentration shall have a sheet flow component of no greater than 150 feet on paved surfaces. Vegetated surfaces shall have a sheet flow component no greater than 100 feet. The minimum time of concentration shall be six minutes.4. Stormwater drainage collection system design requirements are as follows: i. The design of pipes and conduits shall use Manning's equation, listed in Figure 8-3 below, to determine capacity. | Figure 8-3 |
| Manning's Equation |
Data in image
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ii. Pipe sizes shall be determined using the design runoff, conduit entrance conditions and hydraulic capacity. No stormwater systems may be designed to function under a pressure condition unless justified by the design professional and approved by the NJMC.iii. Design velocities in pipes shall be a minimum of two feet per second, or as otherwise approved on a case-by-case basis by the NJMC, to allow for self-cleaning and a maximum of 15 feet per second to prevent scouring of pipes, manholes, and inlets and erosion at points of discharge.iv. The materials used in the construction of storm sewers shall be reinforced concrete, ductile iron, corrugated polyethylene, or other as approved by NJMC. Corrugated metal and steel shall not be permitted. Should existing corrugated metal or steel pipes be incorporated into a proposed system, their condition shall be verified.v. The Manning's roughness coefficient "n" for circular cross section, nonporous concrete pipe shall be 0.013. Other cross sections or pipe materials shall have commensurate friction factors.vi. All transitions in pipe slopes, junctions and changes in pipe sizes shall be confined to manholes, catch basins, or other accessible structures designed for one or more of these purposes. Additionally, all manhole, catch basin, and other pipe connections to structures shall be equipped with flexible, water-tight joints.vii. Where a drainage system discharges to a tidal waterway, tide gates, constructed of cast iron or other corrosion-proof material, shall be provided at every discharge point. Additionally, the backwater condition generated by the mean high water (MHW) tide shall be considered in the drainage calculations associated with tidally influenced areas. Data on the tide elevations throughout the District is available from the NJMC.viii. Where a drainage system discharges to grade or into a stream, ditch or other body of water, a concrete headwall with wing-walls and a rip-rap apron pad, or other as approved by the NJMC, shall be constructed. The apron pad and/or scour hole design shall consider the tailwater elevation to be equal to the mean low water (MLW) elevation if tidally influenced. Additionally, where maximum velocities exceed the allowable velocities for soil stability, as determined in the Standards for Soil Erosion and Sediment Control in New Jersey, N.J.A.C. 2:90, scour control shall be provided.ix. Roof runoff shall be conveyed via roof leaders to a stormwater collection system, where feasible. Should direct connection to a stormwater collection system be impractical, roof leaders shall first discharge to stable, vegetated areas, where feasible, and then be directed to a stormwater collection system.x. Roof leaders and their respective receiving systems shall be sized to pass a minimum rainfall intensity per N.J.A.C. 5:23-3.1 5(b)12ii of the Uniform Construction Code (UCC), or the design storm intensity, whichever is greater.xi. All concrete pipes shall be minimum ASTM Class III unless loading conditions require stronger pipe.xii. The minimum depth of cover over the concrete pipe shall be in accordance with Table 8-3 below: | Table 8-3 |
| Minimum Depth of Coverage over Concrete Pipe |
| Minimum Cover |
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| Pipe Diameter | (surface to top |
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| (in inches) | ASTM Class Pipe | of pipe in inches) |
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| 12 | III IV V | 17 12 7 |
| 15 | III IV V | 16 11 7 |
| 18 | III IV V | 16 10 6 |
| 24 | III IV V | 15 6 6 |
| 30 | III IV V | 10 6 6 |
| 36 and above | III IV | 6 6 |
xiii. The minimum depth of cover for ductile iron, polyvinyl chloride (PVC), and high-density polyethylene (HDPE) pipe shall conform to the manufacturer's standards.5. Surface and subsurface detention basins shall be designed in accordance with N.J.A.C. 7:8, the Stormwater Management Rules, and the NJDEP "New Jersey Stormwater BMP Manual," each incorporated herein by reference, as amended and supplemented. The New Jersey Stormwater BMP Manual is available online at http://www.state.nj.us/dep/stormwater/bmp_manual2.htm. The following are exceptions to the above requirements: i. The design storm shall be reduced to the 25-year storm unless constructed outside of the FEMA Special Flood Hazard Area (SFHA). The NJDEP stormwater quantity requirements, which include larger storm events, shall apply to areas outside of the SFHA.ii. Backwater calculations shall be included in the design, per (b)4vii, above.iii. Subsurface detention systems that rely on infiltration for discharge shall only be designed in locations without known soil contamination or other issues which may threaten the quality of groundwater.iv. Detention basins shall be maintained to prevent clogging and/or siltation.6. Stormwater pollutant removal shall be performed in compliance with N.J.A.C. 7:8, the Stormwater Management Rules. In addition:i. Stormwater quality control devices shall be installed off-line unless it is demonstrated that resuspension of collected soils will not occur during storm intensities or depths greater than the NJDEP Water Quality Storm as defined in N.J.A.C. 7:8-5.5.ii. Similar structural stormwater management measures may not be used in series to achieve the required 80-percent TSS removal unless approved by the Chief Engineer.iii. Stormwater management measures, such as detention basins, swales and sand filters, shall not receive stormwater runoff until the site has been stabilized per the Standards for Soil Erosion and Sediment Control in New Jersey at N.J.A.C. 2:90-1.3.iv. All subsurface stormwater management measures shall have a clearly identified method of clean-out.N.J. Admin. Code § 19:4-8.6
Administrative correction.
See: 36 N.J.R. 1955(a).
Amended by R.2006 d.163, effective 5/1/2006.
See: 37 N.J.R. 4198(a), 38 N.J.R. 1860(a).
In (a), rewrote 2, 4, and 5, deleted 6, recodified former (7) as (6) and rewrote present (6); and rewrote (b).
Amended by R.2009 d.40, effective 1/20/2009.
See: 40 N.J.R. 4696(a), 41 N.J.R. 624(b).
In (b)3i, substituted "the sizing of storm sewer systems only" for "computing the runoff from any drainage area up to 20 acres" and "the sizing of volume-based stormwater systems and for comparing pre- and post-construction peak flows" for "areas larger than 20 acres" and deleted "and Modified Rational" following "with the Rational"; in (b)3ii, rewrote Table 8-2; in (b)4viii, substituted "discharges to grade or" for "starts at or discharges" and inserted the last sentence; in (b)4x, inserted ", or the design storm intensity, whichever is greater."; added (b)4xi through (b)4xiii; in (b)5iv, deleted the former last sentence; and in (b)6ii, substituted "Chief Engineer" for "NJMC".