[Amended 7-141997 by Ord. No. 735]
A. General.
(1) The Storm Water Management Act, P. L. 1981, c. 32, which amends the supplements to the Municipal Land Use Law, N.J.S.A. 40:55D-1 et seq. at N.J.S.A. 40:55D-4, 40:55D-5, 40:55D-6, and 40:55D93 et seq., requires municipalities to prepare and adopt a stormwater management plan and implementing ordinance.
(2) It is hereby determined that waterbodies, roadways, structures, and other property within the borough are at times subjected to flooding; that such flooding is a danger to the lives and property of the public; that such flooding is also a danger to the natural resources of the borough; that development tends to exacerbate such flooding by increasing stormwater runoff, due to alteration of the hydrologic response of the watershed in changing from the undeveloped to the developed condition; that runoff produced by the development of real property may contribute increased quantities of water-borne pollutants, and may tend to increase channel erosion; that such increased runoff, increased erosion, and increased pollution constitutes deterioration of the water resources of the borough and that such increased runoff, increased erosion and increased pollution can be controlled to some extent by the regulation of stormwater runoff from such development. It is, therefore, determined that it is in the public interest to regulate the additional discharge of stormwater runoff from such developments as provided in this ordinance.
(3) In order to minimize the impact of development on the infrastructure and waterbodies of the borough, all new development shall incorporate on-site stormwater facilities and incorporate best management practices that will result in no increase in the rate stormwater leaves the site. It is the purpose of this section to establish a stormwater management system to:
(a) Reduce artificially induced flood damage to public health, life and property;
(b) Match the pre-development runoff rate and minimize the increased volume of stormwater runoff from any new land development;
(c) Confirm the adequacy of existing culverts, bridges, dams and other drainage infrastructure for the post development conditions;
(d) Prevent, to the greatest extent feasible, an increase in nonpoint source pollution;
(e) Maintain the integrity of the stream corridor for their biological functions, as well as -for drainage and other purposes;
(f) Reduce erosion impacts of development upon downstream properties by matching the post development stormwater velocity for the required design storms with the stormwater discharge velocity for the pre-development condition;
(g) Reduce the erosion from any development or construction project;
(h) Minimize the increase in pollutants in runoff due to land development, which otherwise would degrade the quality of water and may render it both unfit for human consumption and detrimental to biological life; by providing water quality within each proposed detention facility by storing ten percent (10%) of the one (1) year storm for a minimum of eighteen (18) hours;
(i) Preserve and protect water supply facilities and water resources by means of controlling increased flood discharges, stream erosion. and runoff pollution.
(4) All subdivisions and site plans shall be designed so as to take advantage of the natural drainage features of the land. In considering an application for development, the Board shall use the following criteria:
(a) The utilization of the natural drainage system to the fullest extent possible.
(b) The maintenance of the natural drainage system as much as possible in its unimproved state.
(c) When drainage channels are required, wide shallow swales with indigenous vegetation will be preferred over other types of channels, which shall be designed in accordance with the requirements of N.J.A.C. 4:24-42.
(d) The use of nonstructural flow-retarding devices, and perforated piping systems to minimize runoff.
(e) Maintenance of base flows in streams, reservoirs and ponds.
(f) The reinforcement, improvement and/or extension of the natural drainage system to such an extent as is necessary to eliminate flooding and reduce on-going maintenance requirements.
(g) All stormwater management systems shall be located so as to minimize disturbance of natural grading and drainage patterns so as to preserve existing on-site vegetation on the site.
(5) Best available technology shall be employed in all instances including measures such as porous or perforated piping, contour terraces and swales and other techniques designed to provide necessary control of stormwater runoff.
(6) The construction of any facility utilized to control runoff or drainage shall be designed to minimize maintenance and to create an aesthetic and' pleasing environment. The perimeter of all storm water detention basins shall be landscaped with plants native to the area and compatible with the proposed environment. Vegetation which stabilizes the soil in accordance with N.J.A.C. 4:24-42, retards erosion and runoff and promotes infiltration of surface waters shall be encouraged so as to increase the aesthetic values of the site for recreation and domestic life.
(7) All new development shall follow a minimum disturbance and a minimum maintenance policy for landscaping where practical. Cleaning or site grading should only occur on land required for the structure and related utilities, drives, walls, roadways, and active recreational facilities. Following construction, disturbed areas not immediately adjacent to the structure drives, walks, or roadways shall be revegetated with carefully selected indigenous species requiring minimal or no maintenance. A landscaping plan identifying the revegetation methods and plant types must be submitted with each application for development utilizing any runoff or drainage control. This plan must include information on the size of the area to be cleared, soil conditions, a description of the existing vegetation (i.e.: tree caliper size, density, etc.) and a description of the proposed vegetation. Revegetation shall follow immediately after clearing and grading operations are complete. If the grading operations are completed outside of the ideal planting season, temporary vegetation shall be utilized to stabilize the area with permanent vegetation to be planted during the appropriate planting season.
(8) If the stormwater management area is to be used for active or passive recreational purposes, underdrains shall be required in order to aid in drying the surface. Applicant shall demonstrate that the soils will percolate sufficiently to allow for recreational use.
B. Applicability.
(1) The provisions of this section shall apply to all developments classified as Majors as defined in Section 94-2.3.
C. Compatibility with other permit and ordinance requirements. Development approvals issued pursuant to this section are to be considered an integral part of development approvals under the subdivision and site plan review process and do not relieve the applicant of the responsibility to secure required permits or approvals for activities regulated by any other applicable code, rule, act or ordinance. In their interpretation and application, the provisions of this section shall be held to be in the minimum requirements for the promotion of the public health, safety and general welfare. This section is not intended to interfere with, abrogate or annul any other ordinances, rule or regulation, statute or other provision of law. Where any provision of this section imposes restriction different from those imposed by any other ordinance, rule or regulation or other provision of law, which provisions are more restrictive or impose higher standards shall control.
D. General design considerations. Each proposed project not exempted from the implementation of this section shall meet the following stormwater management standards.
(1) General standards.
[1] Applicants for site plan and subdivision approval shall be responsible for establishment and submission of base data such as hydrograph and HEC II studies to determine the volume and quality of stormwater runoff for the proposed. development site prior to plan approval. The flood and erosion control standards for detention will require that rates be controlled so that the post-development runoff from the site will not increase the peak flow rate and velocity to any downstream discharge point or receiving body of water from the site than. experienced prior to development, for a 2-year, 10-year, 50-year and 100-year storm. The storms shall be considered individually, when comparing the existing and proposed runoff from drainage areas analyzed at the same discharge point.
(2) Each detention basin shall contain a water depth capacity which will accept all surface water directed to it as follows:
(a) Subdivision development.
[1] For a subdivision involving a tract of land which has a total contributing drainage area of five (5) acres or less, the stormwater management system shall be designed to accommodate a 50-year storm.
[2] For a subdivision involving a tract of land Of more than five (5) acres, the stormwater management system shall be designed to accommodate a 100-year storm.
(b) Site plan development.
[1] For a site plan proposing development on a tract of land which has a total drainage area of five (5) total acres or less, the stormwater management system shall be designed to accommodate a 50-year storm.
[2] For a site plan involving a tract of land which has a total contributing drainage area discharge at the downstream of more than five (5) total acres, the stormwater management system shall be designed to accommodate a 100-year storm.
(3) Stormwater detention systems which discharge directly to flood hazard areas shall conform to the requirements of N.J.A.C. 7:13-2.8.
(4) These design storms shall be defined as either a 24 hour storm using the rainfall distribution recommended by the U.S. Soil Conservation Service when using U.S. Soil Conservation Service procedures, (such as U.S. Soil Conservation Service, "Urban Hydrology for Small Watersheds", Technical Release. No. 55) or as the estimated total rainfall falling uniformly throughout the estimated storm duration (which may equal or exceed the estimated time of concentration) at the site when using a design method such as the Modified Rational Method.
(5) For purposes of computing runoff, all undeveloped or unpaved lands (e.g., cultivated. pasture, wooded or grassy) in the site shall be assumed, prior to development, to be in good hydrologic condition, regardless of conditions existing at the time of computation. For lands to be considered cultivated, they shall have been used for such purposes uninterruptedly for a period of the last ten (10) years prior to the time of computation. If such uninterrupted use has not occurred or cannot be satisfactorily documented, woods shall be assumed to be the predeveloped land condition of the undeveloped or unpaved lands.
(6) Any new agricultural development of five (5) acres or more shall be submitted to the local Soil Conservation District for review and comment in accordance with this section and any Soil Conservation District guidelines. An agency may condition approval of such stormwater control measures upon a positive approval of the appropriate Soil Conservation District.
(7) Soil erosion and sediment control shall be provided in accordance with Standards for Soil Erosion and Sediment Control promulgated by the State Soil Conservation Committee pursuant to N.J.A.C. 4:24-42 administered by the local Soil Conservation District, as required under Section 94-8.36.
(a) Water quality control. In order to prevent sediment transport and particulate contaminant pollution control from stormwater runoff, all site development stormwater management plans must provide for the control of a water quality design storm. The water quality design storm shall be defined as either the one-year frequency, 24-hour storm using the rainfall distribution recommended for New Jersey by the U. S. Soil Conservation Service or a storm of 1.25 inches of rainfall falling uniformly in two (2) hours.
(b) The water quality design storm shall be controlled by one of the following practices:
[1] The water quality requirement for detention will require prolonged detention of the runoff from the 1-year water quality design storm. Provisions shall be made for stormwater runoff to be retained and released so as to evacuate ninety percent (90%) of the design storm stormwater runoff from the basin within eighteen (18) hours. The detention time shall be considered a drawdown time of the elected water quality design storm and, therefore, shall begin at the time of peak storage of that storm. Drawdown time means that the time for detention basin to translate from a peak storage condition for the water quality design storm (maximum detention basin stage for that storm) to a time at which ninety percent (90%) of the volume of design storm runoff stored has evacuated through the basin. Evacuation shall be a gradual translation. If the above requirement would result in flow outlet smaller than three (3) inches in diameter, the period of detention shall be waived so that three (3) inches will be the minimum outlet size used. In the case of wet detention basins, the permanent storage water shall not be included in the analysis.
(2) In all cases, multiple level outlets or other fully automatic outlets shall be designed so that peak discharge rates from the development for the design storms will not be increased from what would occur if the development were not constructed. Outlet waters shall be discharged from the development at such locations and velocities as not to cause additional erosion or additional channels downstream of the development and shall be in accordance with Standards for Soil Erosion and Sediment Control administered by the local Soil Conservation District.
(3) Where the project consists of two (2) phases or more;
(I) new construction which requires provisions of storm drainage under the terms of this section; and
(II), repair or rehabilitation of existing structures and surfaces which do not result in increasing the extent of impervious areas or in rendering existing surfaces less pervious, the detention requirements may be computed on the basis of phase (I) exclusively.
(4) If detention basins or other detention facilities are provided through which water passes at times other than following rainfall, the Borough Engineer shall be consulted concerning design criteria. It will become necessary for detention requirements to be met, despite the necessity of passing certain low flows. This applies to all on stream or online detention basins.
(5) Detention basins located in freshwater wetlands may be allowed only in accordance with the Freshwater Wetlands Protection Act, N.J.S.A. 13-9B-1 et seq., and any rules adopted pursuant thereto.
(6) Any detention facility that impounds water through the use of an artificial dike, levee or other barrier and raises the water level five (5) feet or in ore above the usual mean low water height when .measured from the downstream toe-of-dam to the emergency spillway crest is classified as a dam and subject to the New Jersey Dam Safety Standards, N.J.A.C. 7:20. All such dams must be designed, constructed, operated and maintained in compliance with the rules of N.J.A.C. 7:20.
(7) Vegetated swales may be constructed; however in no case shall they be allowed without an outlet facility. The minimum gradient of swales shall be two percent (2.0%). The minimum side slopes shall be designed at a ratio of 3:1, with a hydraulic depth of one (1) foot or less and a 4:1 for depths greater than one (1) foot.
(8) All stormwater detention systems which discharge directly to a flood hazard area shall conform to the requirements of N.J.A.C. 7:13-2.8.
E. Design specifications.
(1) Basin slopes to the water's edge shall not exceed 4:1.
(2) The bottom of the basin shall contain a concrete low flow channel, unless the basin will retain water on a permanent basis.
(3) The bottom of the basin shall be sloped toward the low flow channel at a minimum slope of two percent (2%) in any direction.
(4) The basin shall be designed with an indigenous grass line emergency spillway (refer to Section 948.39A(4)(c).
(5) The basin shall be designed with a minimum of one (1.0) foot of freeboard above the outfall structure grate elevation.
(6) If the basin is designed to retain water on a permanent basis (wet basin), adequate aeration shall be provided to prevent stagnation.
(7) Where the Board deems necessary, the detention basin shall be enclosed by a six (6) foot high fence, and if necessary, a guardrail to be in accordance with NJDOT specifications. In such event, a fourteen (14) foot wide gate shall be provided to gain access to the basin for maintenance purposes and for emergency vehicles.
(8) Every detention basin shall be thoroughly landscaped around the perimeter. However, the street side of the basin shall be landscaped with low lying vegetation as required for sight triangle easements as set forth in Section 85-67 of this chapter. It is intended that the street side of the basin shall be visible for security purposes.
(9) No consideration shall be given to groundwater recharge for sizing of the basins and total recharge basins shall not be allowed.
(10) The lowest point on the bottom of the basin shall not be located any closer than one (1) foot to the seasonal high water table. Where the seasonal high water table is less than two (2) feet from the lowest point, an under drain system below the low flow channel shall be provided with a positive outlet into the outfall control structure.
(11) In the event that the design requires that the basin either entirely or partially be constructed by berming above the surrounding ground elevation, a suitable, impermeable core shall be provided.
(12) Basins shall have tapered bottoms. No flat bottomed basins will be permitted.
(13) AD outfall control structures shall meet the following requirements:
(a) Compliance with the Water Quality Management Standards, as specified in Section 948.39D(7)(a), (b).
(b) A grate shall be set on the outfall control structure at the elevation of the 50- or 100-year storm, as applicable.
(c) AR orifices, weirs and spillways which are part of the outfall. structure shall be fitted with a trash rack. The maximum opening (spacing) for the trash rack shall be three (3) inches.
(d) All detention basin drainage calculations shall include a calculation to prove a vortex at the outfall structure will not occur. In the event a vortex is created, an anti-vortex device and other necessary devices to assure safety of the facility shall be required.
(14) All detention basins shall provide access for vehicular equipment for maintenance and for emergency purposes. The accessway shall be a minimum of twelve (12) feet in width and constructed of pervious pavers, crushed stone or the material capable of supporting maintenance equipment which is acceptable to the Borough Engineer.
(15) In the event the detention basin outlet is connected directly to the existing storm sewer infrastructure system, the applicant's Engineer can either review or purchase the Borough of Shrewsbury's infrastructure maps. These maps indicate the location and sizes of the existing sanitary and storm piping system in the borough.
F. Detention basin location.
(1) Residential developments.
(a) Detention basins may either be constructed on a lot solely utilized for the purpose of the basin or on a lot dedicated for the purpose of open space or on a lot on which a dwelling is to be erected. If the basin is to be constructed on its own lot, the lot may vary from the bulk requirements of the zone in which it is located, however, a minimum of twenty (20) feet of lot frontage on an improved street shall be provided. The lot shall be of sufficient size to contain the basin and all outfall. structures entirely with a minimum twenty-five (25) foot distance from the top of the slope to any property line in any direction.
(b) If the basin is to be constructed on a lot on which a residential structure is to be erected, the basin and all associated drainage structures shall be constructed a minimum of twenty-five (25) feet from the top of the slope to any property line in any direction. In addition a minimum of forty (40) feet shall be maintained from the top of the slope to any residential structure or accessory structure. Final plats shall provide for a twenty-five (25) foot wide minimum drainage easement from the top of the slope around the basin and shall provide for a twenty (20) foot wide minimum access to an improved street. The maintenance of the basins and associated structures shall be clearly identified within the homeowners association documents submitted to the Board's Attorney for review.
(c) Single family homeowners association. Where a detention basin is constructed within common areas or single family residential developments, the maintenance of the basin and that of all drainage structures and collection systems outside of rights-of-way dedicated and accepted by the borough shall be the sole responsibility of the single-family homeowners association. Where a detention basin(s) is constructed on a separate lot or on a lot on which a single family residence is also constructed, the developer shall deposit with the borough a sum of money for the maintenance of the basin as calculated by the Borough Engineer. The amount of the deposit shall be based on the approved schedule of maintenance and costs approved by the Board. The Borough Engineer shall apply a time value analysis to the present day costs to estimate future costs to be incurred by the borough for the maintenance of the basin for one hundred (100) years into the future. The developer shall deposit this amount with the borough at the time of final subdivision approval. The borough's responsibility for the maintenance of the basin shall commence upon release of the performance guarantee posted with the borough to insure that the basin has been completed according to the approved preliminary subdivision drawings. Prior to the release of the performance guarantee, the basin shall be cleaned of all silt and debris which may have accumulated during construction.
(d) Single-family residential lots without a homeowner association where a detention basin is constructed without common open areas or within a single family residential development, the maintenance of the basin and that of all drainage structures outside the rights-of-way dedicated and accepted by the borough shall be the sole responsibility of the homeowner on which the facility is located.
(2) Nonresidential developments. Detention basins shall be constructed so as to take advantage of natural feature as to the greatest extent possible. Maintenance access shall be provided to the basin from either the surrounding right-of-way or from within the site driveway or parking areas. Basins shall not be screened from view from the developed portions of the site.
G. Detention basin maintenance responsibility.
(1) Maintenance schedule. Where detention basins are to be constructed as shown on the approved subdivision site plan drawings, the applicant's engineer shall provide on the preliminary subdivision or preliminary site plan drawings, an anticipated schedule of maintenance of the basin over a one hundred (100) year period. This schedule shall include items such as, but not limited to, removal of siltation at an interval of a minimum of once every ten (10) years; annual inspection, cleaning and repairs to inflow and outfall structures; periodic routine maintenance such as grass cutting, maintenance of the low flow channel; fence repairs and cleaning of trash racks and small outfall orifices, and be approved by the Borough Engineer. Also included, shall be the itemization of any permits from the New Jersey Department of Environmental Protection which will be required (under the current legislation) to perform the maintenance. In the case of wet detention basins, a cost associated with the lowering or emptying of the basin shall be included. The applicant's engineer shall estimate the present day costs associated with each item of maintenance and submit that to the borough for review by the Borough Engineer. Upon approval of the annual maintenance fee, the applicant shall post a lump sum fee to maintain the basins for the one hundred (100) year period, which should be determined by the Borough Engineer and approved by Mayor and Council.
(2) Detention basins within residential developments.
(a) Multi-family association. Where detention basins are constructed within common areas of multi-family residential developments, the maintenance of the basin and that of all drainage structures and collection systems outside of rights-of-way dedicated and accepted by the borough, shall be the sole responsibility of the multi-family association.
(3) Nonresidential detention basins. All nonresidential detention basins shall be maintained by the property owner. In the event that the basin also controls stormwater from off-site runoff from borough owned property rights-of-way and/or easements, the owner of the property may request that the borough maintain the basin only if a prorated cash contribution has been deposited with the borough as calculated in Section 94- 8.39G(2)(b).
H. Detention basin fund and deposit calculations. A detention basin fund is hereby established. The detention basin fund shall be utilized for the maintenance of detention basins approved and accepted by the borough including structural inspection and repair, lawn and structure maintenance, siltation removal, and landscape maintenance. The methodology for calculating the amount of the detention basin maintenance deposit are included in Exhibit K - Detention Basin Fund Calculation Methodology. [Adopted 7-7-1998 by Ord. No. 736; amended 11-2-1998 by Ord. No. 755]
A. All major and minor arterial, collector, local collector, local and marginal access streets shall be designed in accordance with the proposals contained in the Master Plan of the borough and in accordance with this subsection.
(1) Upon receipt by the municipal agency of any subdivisions or site plans calling for the installation of new streets or the extension of old streets, the plats shall be referred to the Borough Engineer, Police Department, Fire Department and the first aid squad for review.
(a) They shall make recommendations as to the acceptable minimum widths of each street and shall base the recommendations upon such factors as the location, proposed use and intensity of traffic, with an emphasis upon safety considerations of a fire, first aid and police nature.
(b) These recommendations shall be submitted to the Borough Engineer to be considered in conjunction with such studies and statistics and other data which the Engineer shall have assembled as a basis for determining minimum street widths within the borough.
(2) The enumerated standards are to be construed as minimum standards and may be increased where, because of high traffic volumes, steep grades or other such reasons, the municipal agency determines that such action is necessary.
(3) In residential subdivisions, the minimum street width required by the attached Schedule of Street Design Standards shall only be the minimum of thirty (30) feet for certain minor streets designed solely to allow access by residents to their homes. Under no circumstances is the minimum width of any street in the Borough of Shrewsbury to be less than thirty (30) feet.
