Borough of Hampton, NJ Article VII Stormwater Control [1]

[1] Editor's Note: See also Ch. 207, Stormwater Management.

§ 157-88 General requirements.

A. The applicant shall provide the Engineer with sufficient information to determine whether or not the proposed development will conform to Borough runoff control details and stormwater detention facility design criteria.

B. In the judgment of the Borough Engineer, the proposed development shall substantially conform to the standards and design criteria set forth in this article.

§ 157-89 Runoff standards.

No site in the Borough shall be developed so that:

A. The rate of stormwater runoff occurring at the site is increased over what occurs there under existing conditions.

B. The drainage of adjacent areas is adversely affected.

C. Soil erosion during and after development is increased over what naturally occurs there.

D. Soil absorption and groundwater recharge capacity of the site is decreased below what occurs under existing conditions.

E. The natural drainage pattern of the area is significantly altered.

§ 157-90 Runoff control details.

In order to duplicate as nearly as possible natural drainage conditions, the regulation and control of stormwater runoff and erosion for any land area to be developed shall be through on-site water detention and/or ground absorption systems, which include but are not limited to the following:

A. Detention areas, which may be depressions or lots of areas, excavated basins, basins created through use of curbs, stabilized earth berms or dikes or any other form of grading which serves to temporarily impound and store water.

B. Rooftop storage, through temporary impoundment and storage of stormwater or slightly pitched building rooftops by use of drain outlets which restrict the stormwater runoff from the roof surface.

C. Dry wells or leaching basins, which control stormwater runoff through ground absorption and temporary storage.

D. Porous asphaltic pavement, which preserves the natural ground absorption capacity of a site and provides a subsurface reservoir for temporary storage of stormwater.

E. Any system of porous media, such as gravel trenches drained by porous walls or perforated pipes, which temporarily stores and dissipates stormwater through ground absorption.

F. Any combination of the above-mentioned techniques which serves to limit stormwater runoff from a given site to what presently occurs there.

G. Preservation of natural vegetation.

§ 157-91 Stormwater detention facilities; sediment and erosion control.

A. Stormwater detention facilities shall be designed to contain an amount equal to the increase in volume of runoff which would result from development of any site. The volume of runoff shall be computed on the basis of the total rainfall which produced the flood of record for the area involved and shall be equivalent to the rainfall excess, as previously defined. The total rainfall which produced the flood of record shall be determined from accurate local records of the United States Department of Commerce, Natural Weather Service, or by calculations using accepted engineering techniques.

B. The rainfall excess shall be computed for each site using accepted, published runoff coefficients, such as found in Urban Hydrology for Small Watersheds, Technical Release No. 55, Engineering Division, Soil Conservation Service, United States Department of Agriculture, January 1955, and may be modified by the Borough Engineer. The range of coefficients for each land use and surface type reflects differences in land slope, intensity of development, amount of impervious surface and degree of ground saturation due to antecedent precipitation.

C. The runoff coefficients shall be determined for each site for both existing and proposed conditions, and the differences in the two shall be used to compute the volume of rainfall excess for design of stormwater detention facilities. The volume for design is equal to the depth of the rainfall excess multiplied by the area of the site. If any such facility will contain water under normal conditions, the amount so contained shall not be counted in calculating the capacity required for the detention of water for the design storm. Rainfall intensity shall be as recommended by the Borough Engineer.

D. In the case of detention facilities utilizing porous media for ground absorption, such as dry wells, porous pavement or the like, the volume of the porous media shall be large enough to contain the total volume of rainfall excess within the voids. Ground absorption systems shall be used only where the infiltration rate of the receiving soil is acceptable as determined by percolation tests and soil borings or as determined by the Borough Engineer. Provisions shall be made to contain overflow of such systems on site or to surface-drain the overflow of such systems on site or to surface-drain the overflow in such a way as not to adversely affect any other property.

E. If detention facilities utilizing surface impoundment, such as detention basins or rooftop storage, are used, sufficient volume to fully contain the total volume of rainfall excess shall be provided. The outlets of such facilities shall be designed to limit the maximum discharge rate of stormwater runoff to what occurs at the site under existing conditions and shall discharge in such a way as not to adversely affect any other property. If rooftop storage is proposed, the weight of the impounded water on the roof shall be accounted for in the structural design of the building, and the roof shall be designed to provide maximum protection against leakage. If berms or dikes are used to create the impounding area, they shall be adequately stabilized and the slopes protected with vegetative cover, paving or riprap to protect against failure or breaching.

F. If a combination of different stormwater detention techniques is used, the combined volume of the systems shall be large enough to fully contain the total volume of rainfall excess.

G. Stormwater detention facilities shall be constantly maintained by the owner to ensure continual functioning of the systems at design capacity and to prevent the health hazards associated with building debris and stagnant water. In no case shall water be allowed to remain in any facility long enough to constitute a mosquito-breeding, disease or any other type of health problem, unless approved as a multifunction facility to include water, such as a pond. If the land or stormwater detention facility or facilities are proposed to be dedicated to the Borough and said dedication is accepted by the Borough Council, the procedures for the construction, dedication and acceptance and maintenance of such facilities set forth in Article III, Subdivision Review and Approval, including but not limited to performance and maintenance bonds, inspections, etc., shall govern.

H. Detention and sediment and erosion control facilities shall be designed in conformance with the Standards for Soil Erosion and Sediment Control in New Jersey of the New Jersey State Soil Conservation Commission, as approved by the Borough Engineer or the Hunterdon Soil Conservation District under agreement, except where the Borough Engineer has determined that conditions peculiar to a certain site warrant exception.

I. Sediment and erosion control measures shall be installed prior to any other site development, shall apply to all aspects of the proposed development and shall be in operation during all stages of development. Increased runoff and sediment resulting from modified soil and surface conditions caused by the proposed development shall be minimized and, where possible, retained on site.

§ 157-92 Maintenance agreements.

Prior to the granting of any site development approval, the applicant may be required to enter into an agreement with the Borough, in a form satisfactory to the Borough Attorney, requiring the installation and maintenance by the applicant and the applicant's successors in interest of such improvements on or to the site or imposing such limitations upon the development thereof as are deemed necessary by the Planning Board for implementing the standards and criteria set forth in this article. Improvements installed or maintained in violation of such limitations shall be corrected at the expense of the applicant or the applicant's successors in interest. The agreement shall also provide for inspection annually and after each major flood by the Borough Engineer or his agent at the expense of the applicant and the applicant's successors in interest and for the undertaking, by the applicant and successors, of such corrective measures as are shown by such inspection to be required for the proper functioning of the facilities.

§ 157-93 Inspections; stop-work orders.

Improvements on the site related to stormwater control, during and upon completion of their construction, shall be subject to inspection and approval by the Borough Engineer or his agent, who shall be notified by the applicant at least 24 hours prior to the start of construction. No underground installation of such improvements shall be covered until inspected and approved. Approval or reasons for withholding approval shall be given promptly. If work proceeds without such approval or not in compliance therewith, the Borough Engineer, in addition to any other remedies available to the Borough, may issue an order requiring immediate cessation of the affected work and prohibiting resumption thereof until approval is obtained or noncompliance corrected.

§ 157-94 As-built certification required.

Prior to the acceptance by the Borough of any stormwater facilities, the developer's engineer shall certify that said facilities were constructed in accordance with the approved plan.