§ 410-92.17
Technical standards
All applicants are required to develop and submit a stormwater management plan. All stormwater management plans must address stormwater management on a site-by-site basis and all requirements of this article. All stormwater management practices shall be consistent with the Rhode Island Stormwater 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 best management practices for water quality control, which in combination are demonstrated to reduce the average annual total suspended solids in post-development runoff by 80%. 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 detention basins and other stormwater 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 detention facility.
- 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 best management practices with appropriate maintenance design in accordance with the Rhode Island Stormwater Design and Installation Standards Manual, as amended; or the Rhode Island Soil Erosion and Sediment Control Handbook, 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 Stormwater Design and Installation Standards Manual, as amended, or a municipally approved regional stormwater management plan for the watershed in which the development site is located. Stormwater management plans shall demonstrate incorporation of the following standards into the proposed project:
- (1) Control and maintenance of post-development peak discharge rates from the two-year, ten-year, twenty-five-year, and one-hundred-year storm events and predevelopment levels.
- (2) Downstream analysis of the one-hundred-year storm event and control of the peak discharge rate for the one-hundred-year storm to mitigate significant 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 stormwater conveyance system consisting of open channels, pipes, and other conveyance devices shall at a minimum accommodate the runoff from a twenty-five-year storm event. The stormwater conveyance system must provide for nonerosive flows to receiving waters.
- E. Surface water and groundwater. Stormwater management plans shall demonstrate that during develop and post-development, 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 those prior to disturbance.