Rain Gardens


The GMU Grounds Shop is using biomediation techniques to improve the  water quality of storm runoff through the use of filtration, sedimentation and  biological processes.  The first of the biomediation  techniques in use on campus are rain gardens; low lying areas where water can  be allowed to accumulate during heavy rains.   Each rain garden consists of one or more excavated depression(s),  where the soil has been amended by tilling in sand (for improved infiltration)  and organic material (for improved absorption).   As part of the design, most rain gardens have a one or two tier rip-rap  stone wall, (with the excavated soil used to form shallow berms behind the  stones) to help stabilize the sides of the depression, yet allow water to  infiltrate between the stone into the banks. Rain gardens protect drainage  systems by slowing down the flow of runoff, allowing sedimentation to occur,  and increasing infiltration into the surrounding soil. At present ten rain  gardens have been retrofitted into the existing landscapes around campus, with  more planned.




The basic goal was to demonstrate the viability of  retrofitting existing landscapes with biomediation techniques in an effort to improve  water quality on.  Hopefully the success  of these demonstration areas will justify including biomediation techniques  into the design of new buildings, parking lots and roadways.

Accomplishments  / Outcomes

Although  there are no statistics available to quantify the success of the rain gardens,  observation has shown that, during a normal  rainfall event, water initially accumulates in the depressions and begins to  infiltrate before flowing into nearby storm drains.  During short duration rainfalls, storm water  may not even flow into the nearby drains, but be intercepted, retained for two  or three days and absorbed by the rain gardens.   Typically, the native mosquito life cycle requires two weeks of standing  water; after rainfalls, infiltration areas are monitored and amended as  necessary with sand and organic material, to ensure collected water infiltrates  within three days.  This is long enough  for the ponding water to also be available to beneficial insects, birds, and  other small wildlife, but not long enough to act as a viable breeding area for  mosquitoes.

Challenges and Responses

The  labor spent on installing the rain gardens was the major challenge; time spent  on biomediation projects was time not spent on standard grounds  maintenance operations, such as turf maintenance and horticultural activities.  But the increased interest and acceptance of  environmental and sustainability issues has increased the acceptance of time  spent employing biomediation techniques.   The program has also demonstrated to the Virginia Soil Conservation  Service, that the University is a responsible partner in mediating storm water  runoff issues.

Campus  Climate Action: Your School’s Carbon Footprint

No  effect on global climate change was evident or intended.


Installing rain gardens into  existing landscapes shows the viability of using simple biomediation techniques  to improve water quality, and control storm water runoff from flowing directly  into the Chesapeake Bay watershed.  Projects do not have to be large in scale,  and can become….
features in the landscape.  Rain gardens are just the first technique the  GMU Grounds shop is considering to improve water quality.  Other biomediation and retention techniques  under consideration, dependent on the situation where the techniques may be  employed, include but are not limited, to bioretention islands in parking lots,  bioretention benches, and drip line plantings along buildings.


Leaders and  Supporters

The projects were not done in conjunction with any  academic program on campus, but as an in-house initiative of the Grounds Shop.  However, the projects do serve to educate the  University community of the value in using small scale biomediation and  retention techniques as a part of landscape maintenance programs.

Funding and  Resources

The materials for the rain gardens were taken from  the normal stockpiles of stone and organic amendments used in normal  landscaping operations.  Note, most of  the organic material was created by shredding leaves collected during the  previous fall.  The cost of each rain  garden installation, sans labor, was minimal, and was not recorded.

Education and  Community Outreach

Mention  of the rain gardens on campus was included in the most recent University Earth  Day program, and the rain gardens are examples of small scale  biomediation and retention techniques that property owners within the  University community can consider using as a part of their landscape  maintenance activities.


Archie  T. Nesbitt
Grounds Shop Supervisor
Facilities Management-1E4
4400    University Drive
Fairfax, Virginia 22030
Phone: 703-993-3731
Nexxtel: 571-274-2532

 Rain Garden Backup 2008-2009
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