Supplementary drainage requirements
No land alteration, construction, or development in the Town of Narragansett may result in an increase in the rate or volume of stormwater runoff, erosion, or sedimentation off-site or downstream. All proposed construction and development which will increase the impervious surface on any lot or tract by more than ten percent of the lot area shall include systems to manage stormwater and to control erosion and sediment.
(1) Stormwater management. The stormwater management system for any site shall be designed to offset the increase in the rate of stormwater resulting from the proposed development. It shall implement the techniques and measures recommended in the most current revision of or supplement to "Urban Hydrology for Small Watersheds, Technical Release No. 55," prepared by the United States Department of Agriculture, Soil Conservation Service or the Rational Method as may be deemed appropriate by the town engineer based on the size and characteristics of the property under review.
The system shall incorporate, to the maximum extent practicable, the natural drainage features of the site, including natural drainageways and permanent and periodic ponding areas. It also shall include stormwater control facilities such as pipes, ditches, culverts, swales, and, if necessary, water retention areas and structures.
The system shall prevent the discharge of stormwater runoff onto adjoining property in a manner which causes flooding or impairs the use or development of the property. Temporary stormwater and erosion control facilities adequate to protect adjoining property shall be installed at the commencement of construction, excavation, grading, or removal of vegetation. For purposes of this section, any property which faces a construction site across any street or highway shall be deemed adjoining property.
(2) Erosion and sediment control. In order to minimize erosion and sedimentation, all development shall preserve salient natural features, limit cut and fill operations, and ensure conformity with topography to the maximum extent practicable. The erosion and sediment control system shall include the following techniques and measures, as necessary:
a. Disturbed soils shall be stabilized as soon as practicable;
b. Temporary vegetation and/or mulching shall be used to protect exposed land areas during development;
c. Permanent (final) vegetation shall be planted and supplemental erosion control measures shall be installed as soon as practicable;
d. Until a disturbed area is stabilized, sediment in the runoff water shall be trapped by the use of debris basins, sediment basins, silt traps or similar measures;
e. Provisions shall be made to prevent surface water from damaging the cut face of excavations or the loping surface of fills;
f. All fills shall be compacted to stabilize material and to prevent undesirable settlement;
g. Fills shall not encroach on natural watercourses or constructed channels;
h. Fills placed adjacent to or having an impact upon natural watercourses, constructed channels or floodplains shall have suitable protection against erosion during periods of flooding;
i. During grading operations, appropriate measures for dust control shall be exercised;
j. Grading equipment shall not be allowed to enter into or cross any watercourse, unless absolutely necessary.
Preservation of vegetation, including but not limited to trees, ground cover, and aquatic vegetation, is important for soil retention. Natural vegetation, particularly trees, shall be retained, protected, and supplemented to the maximum extent practicable. Removal of vegetation and regrading shall be done in such a way as to minimize erosion. Disturbed areas shall be replanted as soon as practicable.
(3) Content of stormwater management and erosion control plans. All applicants for site plan approval or, if site plan approval is not required, for a building permit, shall submit plans and specifications for the construction and maintenance of systems for stormwater management and erosion and sediment control. The plans shall include the following:
a. A narrative description of the development;
b. A construction schedule showing when, in the sequence of grading and construction activities, the installation of stormwater, erosion, and sediment control facilities will occur;
c. Base flood elevation data;
d. Stormwater runoff calculations analyzing the peak discharge rates of flow and volume from ten year and 25-year storms of 24-hour duration, using a type III distribution. Calculations shall be based on the methodology contained in "Urban Hydrology for Small Watersheds, Technical Release No. 55," as revised or supplemented;
e. Design criteria and construction details for proposed stormwater, erosion, and sediment control facilities;
f. A narrative description of the procedures to be used to install, operate, and maintain proposed stormwater, erosion, and sediment control facilities;
g. A narrative description of the plans for preserving trees and other vegetation.
The plans also shall include a site plan showing the following:
a. The proposed site layout;
b. A schematic layout of the proposed methods of controlling stormwater runoff, erosion, and sedimentation;
c. Existing and proposed contours, grades, and critical spot elevations;
d. Existing tree lines, grassy areas, or unique vegetation;
e. Boundaries of the different soil types existing on the site;
f. The dividing lines and direction of flow for different drainage areas;
g. Areas with potentially significant erosion problems;
h. Areas which are to be cleared and graded.
(4) Compliance and enforcement. No application for site plan approval shall be granted nor building permit issued unless the town engineer certifies that the proposed development complies with the requirements of this section. The zoning board of review may require an applicant to provide surety covering the estimated costs of completing the necessary stormwater, erosion, and sediment control systems.
The failure of an applicant or property owner to install, maintain, repair, and replace all required stormwater, erosion, and sediment control facilities shall be a violation of this ordinance. The town engineer may enter any land or water in order to conduct any investigation, inspection, examination, or survey necessary to effect the purpose and intent of this section. If the owner of the property does not consent to such inspection entry, the town engineer is empowered to apply for an administrative search warrant permitting the inspection entry.
(Ch. 1016, § 6, 5-2-2016)