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Rhode Island's New Stormwater Manual

The Rhode Island Smart Development for a Cleaner Bay Act of 2007 required the state's Department of Environmental Management and the Coastal Resources Management Council to amend the 1993 Stormwater Manual.

The new Rhode Island Stormwater Design and Installation Standards Manual is the product of a two-year technical analysis and revision. The new manual was written, compiled, designed and illustrated by Horsley Witten Group, Inc. (HW) of, Sandwich, Mass., with technical services from the University of New Hampshire Stormwater Center, Durham, N.H., and Loon Environmental, LLC, Riverside, R.I.

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This graphic for structural stormwater treatment practices for meeting water quality criteria is among 33 illustrations and 28 tables in the Rhode Island Stormwater Design and Installation Standards Manual
Graphic: Adapted from UNHSC, 2009


HW is a consulting group specializing in low-impact development (LID) techniques, stormwater management, land use regulation, site design, coastal/watershed planning and protection, civil/environmental engineering, hydrology and hydrogeology.

The update provides enhanced stormwater practice performance criteria and mandates LID strategies for stormwater management in site planning and design, including: 1) maintaining pre-development groundwater recharge and infiltration on site to the maximum extent practicable; 2) Demonstrating that post-construction stormwater runoff is controlled, and that post-development peak discharge rates do not exceed pre-development peak discharge rates; and 3) Using low impact-design techniques as the primary method of stormwater control to the maximum extent practicable.”

How does the new manual affect landscape architects? LID often utilizes vegetative practices for enhanced stormwater treatment and infiltration. This presents opportunities for designers to play a significant role in the implementation of these techniques for residential, commercial and municipal clients. By choosing appropriate native plants for varying hydrologic conditions, landscape architects can help create LID projects that are not only in compliance with the new stormwater standards, but are beautiful functioning landscapes. 

Horsley Witten will be assisting the Rhode Island Department of Environmental Management and the Coastal Resources Management Council with a series of LID workshops in the Fall/Winter of 2010.  Visit for more information.

The 498-page final draft of the new manual is at


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June 16, 2019, 10:40 pm PDT

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