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Rain Gardens & Bioswales

Rain gardens and bioswales are special gardens designed to capture and reduce stormwater runoff. Though they are similar in function, they differ in design and application.


Rain gardens are shallow, planted depressions in the landscape that reduce runoff by allowing it to soak into the ground as opposed to flowing into storm drains or surface waters. Rain gardens are widely used by homeowners and other property owners to capture runoff from roof tops, sidewalks, and driveways. The foot print of a rain garden may range from about 1/6th to 1/12th the size of the area that drains into it. 


Bioswales, which look similar to rain gardens on the surface, also include a reservoir below the surface of the garden that can store a large volume of water. As a result, the surface footprint of a bioswale is generally much smaller than a rain garden. Because of their small size and large storage capacity, bioswales are widely seen in urban areas where space is limited but where reducing runoff is imperative for reducing pollution to waterways downstream. 

Rain Garden 101

Smaller rain gardens can be dug by hand with a shovel. Larger gardens may require additional equipment, such as a bobcat or excavator. Once the shallow depression is dug, it won't take any more time or expense to plant your garden than it would to plant other landscaped areas in your yard. 


Our rain garden section--inlcuding the link to the Rain Garden Design Guide, below--is a collaboration between Save the Sound and the University of Connecticut Department of Extension's NEMO program, funded by The Fairfield County Community Foundation, the Greater New Haven Green Fund, and the Quinnipiac River Groundwater Natural Resources Damages Fund adminstered by the Connecticut Department of Energy and Environmental Protection (CT DEEP).


As a part of this collaboration, the UCONN NEMO program created a Rain Garden Design Guide and Rain Garden App for your smartphone or Android. Peruse the site in the link below to learn more about how to:


  • Pick the ideal site for your rain garden

  • Check the soils to see how quickly it will soak up the rain

  • Size your rain garden and choose the layout

  • Choose your plants

  • Dig your rain garden

  • Plant

UCONN Rain Garden Design Guide for Connecticut & New England Homeowners

You can also access the link directly:

Save the Sound worked with the City of New Haven and the Urban Resources Initiative to design and build a bioswale in New Haven. This bioswale, pictured during its first growing season in summer 2015, helped to disconnect the last section of combined sewer along Yale Avenue in the West River Watershed. Source: Kendall Barbery


Bioswales improve water quality by capturing and filtering polluted runoff from roadways and other sources. Bioswales are starting to appear in urban areas throughout the United States and abroad as cities attempt to reduce runoff and prevent pollution from stormwater and combined sewer overflows. 


While bioswale design--like any other green infrastructure--must be site-specific and take into account the underlying geology, soils, and depth to the water table on the site, there are numerous templates available from municipalities who have already started building and monitoring their bioswale projects.  


The City of New Haven, for example, adapted the New York City Bioswale Design Standards (found here) to the specific needs of the city's soils and geology. The pilot bioswale project, pictured above, was a collaboration of Save the Sound, the City of New Haven, and the Urban Resources Iniative. 


See the Resources section below for additional bioswale information and materials. 


The City of New Haven adapted the New York City Bioswale Design Standards to meet local needs. This image depicts the engineered cross section of the bioswale and shows layers of plants, mulch and engineered soils over a reservoir of open-graded stone. Source: City of New Haven


Grant for private property owners in Combined Sewer Areas of New York City:


Natural Resources Conservation Service Bioswale Fact Sheet:


NYC Department of Environmental Protection Bioswale Standard Designs:


NYC Green Infrastructure Program:


Performance of Engineered Soil and Trees in a Parking Lot Bioswale:


Philadelphia Water Department Green Infrastructure Design Guide:


University of Florida Field Guide to Low Impact Development, Fact Sheet:


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