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All applicants are required to develop and submit a stormwater management plan prepared by a professional engineer licensed in the State of Rhode Island. All stormwater management plans must address storm water management on a site-by-site basis and all requirements of this chapter. All storm water management practices shall be consistent with the Rhode Island Storm Water Design and Installation Standards Manual and the Rhode Island Soil Erosion and Sediment Control Handbook, as amended. (a)
Performance standards. Stormwater management plans shall incorporate structural and nonstructural best management practices (BMPs) for water quality control, in accordance with the Rhode Island Storm Water Design and Installation Standards Manual. Development in drinking water supply watersheds or watersheds where impaired waters as defined by the state's 303(d) list exist may be held to higher standards.
(b)
Disallowed stormwater best management practices. The placement of storm water structures within a floodplain shall be avoided. If there is no alternative, the applicant must show what effects, if any, the tailwaters created by the floodplain will have on the outflow and effective storage capacity of the storm water best management practice.
(c)
Facilitation of maintenance. Facilities that require maintenance shall be designed to minimize the need for regular maintenance, facilitate required maintenance, and ensure accessibility of components that require maintenance. At a minimum, all stormwater management plans must incorporate BMPs with appropriate maintenance design in accordance with the Rhode Island Storm Water Design and Installation Standards Manual, as amended.
(d)
Flood protection. Stormwater management plans shall demonstrate that a proposed project provides for protection of life and property from flooding and flood flows. Water quantities must be controlled in accordance with the Rhode Island Storm Water Design and Installation Standards Manual, as amended, or a municipally approved regional stormwater management plan for the watershed in which the project site is located. Stormwater management plans shall demonstrate incorporation of the following standards into the proposed project:
(1)
Control and maintenance of postdevelopment peak discharge rates from the two-year, ten-year, 25-year, and 100-year storm events to predevelopment levels.
(2)
Downstream analysis of the 100-year storm event and control of the peak discharge rate for the 100-year storm to mitigate downstream impacts.
(3)
Discharge from any stormwater facility must be conveyed through properly constructed conveyance system to provide for nonerosive flows during all storm events. The proposed storm water conveyance system consisting of open channels, pipes, and other conveyance devices shall at a minimum accommodate the runoff from a 25-year storm event. The storm water conveyance system must provide for nonerosive flows to receiving waters.
(e)
Surface water and groundwater. Stormwater management plans shall, in accordance with the Rhode Island Storm Water Design and Installation Standards Manual, as amended, demonstrate that during development and postdevelopment, all receiving waters will be recharged in a manner closely resembling predevelopment conditions and that the developed site will retain hydrological conditions that closely resemble of those prior to disturbance. The goal of the storm water design shall be that hydrologic conditions in each subwatershed match predevelopment conditions.
Where practicable, development and redevelopment projects should aim to reduce runoff volumes. This may include minimizing and eliminating impervious surface areas such as roads, parking, paving or other surfaces, encouraging infiltration of noncontaminated runoff, preventing channelization, encouraging sheet flow, and where appropriate, preserving, enhancing or establishing buffers along surface water bodies and tributaries.
(Ord. of 1-12-2010)