Rain Gardens

Rain garden constructed by Clean Annapolis River Project (www.annapolisriver.ca)

Rain gardens are small, landscaped areas that capture, filter and infiltrate rainwater.  Rain gardens can create an attractive detention area where runoff can slowly soak into the ground, be taken up by plants and return to the atmosphere through evapotranspiration. Planted with water-tolerant native plants, rain gardens can become a beautiful and functional feature on your property.

Rain gardens allow at least 30% more water to infiltrate into the ground, compared to a conventional lawn (source). They can help recharge groundwater resources, reduce stormwater volumes and create habitat. Rain gardens are relatively easy and inexpensive to design and build. Just keep in mind a few important considerations when deciding where and how to install a rain garden on your property:

-Observe how stormwater naturally runs in your yard. Place the rain garden at a low point or elsewhere along the natural flow path.

- Maintain at least a 1% slope from the impervious surface to the garden. 

- Rain gardens should be located approximately 3 m away from a building to avoid drainage problems on your property.

-Clay soils don’t allow for proper drainage, therefore look for a place with soil that is sandy, gravelly, loam or a mix. If your soil has a high clay percentage, you can add sand, fine gravel and/or organic matter to improve permeability.

- The surface area of a rain garden should be 20-30% of the roof/parking lot area it drains.

- A general guideline for rain garden depth is 7.5 cm in soils with relatively low infiltration rates (i.e., loam) and up to 15 cm in soils with high infiltration rates (i.e., sandy or gravelly soils).

-  A downspout can empty directly into a rain garden. Just add some stones or a splash pad to prevent erosion.

Rain garden (Photo CMCH: bit.ly/dCOkur)

Some really helpful tips on installing and maintaining rain gardens can be found from the Canadian Mortgage and Housing Corporation's factsheet 'Improving Stormwater Management in Your Yard'.  

More great information on rain gardens, including a list of native, water-loving plants, can be on the Clean Annapolis River Project website. 

Do you have a photo of a rain garden or maintenance tips that you'd like to share? We'd love to see them! 

Beautiful! (Photo: www.atlantic.sierraclub.ca)

Continuous Deflection Separation (CDS)

This week we wanted to find out more about stormwater quality treatment technologies, so we contacted The Shaw Group. They have installed over 150 Continuous Deflection Separation (CDS) systems across the Maritimes. CDS units improve water quality of stormwater runoff by removing sediment, floatables, oil and grease. 

CDS unit (image:www.shawpipe.com)

CDS units have a screen filter that removes all floatable materials and a separate treatment chamber which captures sediment and hydrocarbons. Due to potential high volumes of trapped pollutants, maintenance on these systems is very important. At a minimum they should be maintained twice per year, which includes sucking out the floatable debris and sediment with a vacuum truck.

We went to visit Portland Hills Estates, a large development surrounding Russell Lake, where several CDS units are installed at different stormwater outfalls around the Lake. We saw a ‘56/40 unit’, the largest CDS system which can filter up to 56 cubic feet of water per second.  This system is designed to capture the 1 in 25 year storm (as opposed the 1 in 100 year storm), and as a result it functions very effectively 80% of the time. The other 20% of the time surplus flows through a by-pass valve. 

Let's life the lid and see what is inside!

Wow! Tennis balls, water bottles and several other floatables from the development and neighbouring school are trapped by the CDS. These items would otherwise eventually end up in Russell Lake.

The stormwater outfall is virtually garbage-free!

The impetus for filtering stormwater came from the Russell Lake community group who were concerned about how the Portland Hills Estates development would impact lake water quality. This concern lead to the developer, Clayton Development, including the purchase and installation of these systems into the development agreement. Using these CDS systems is now common practice for Clayton Development.

Permeable Pavement

Permeable pavement allows precipitation to slowly soak into the ground, thereby reducing runoff from driveways, roads and parking lots. There are two main types of permeable pavement – permeable pavers (also known as interlocking concrete blocks) and porous pavement. These BMPs can be incorporated into designs for new developments, or used as a retrofit option for existing homes and buildings. 

Permeable Pavers consist of impervious concrete blocks or tiles that allow water to infiltrate between blocks in voids filled with gravel or grass.  

Permeable Paver (photo: bit.ly/be1x3a)

Parking space at the Ecology Action Centre

Porous Asphalt or Concrete consists of standard asphalt or concrete mixes with the finer aggregates removed resulting in pores within the pavement that allows water to permeate through the surface. 

A parking lot on the Dalhousie University campus uses porous pavement  to reduce stormwater runoff. The lot was graded allowing runoff to flow towards the strip porous pavement area at one end of the lot. There is a clear stone base under the permeable area with a perforated PVC pipe leading to catch basin in the corner of the lot.  Water that infiltrates through the pavement has a chance to soak into the ground before being picked up by the perforated pipe. A strip of permeable pavement on a graded lot works well, therefore repaving the entire parking lot is not necessary. Some concern exists about how porous pavements can withstand Nova Scotia's harsh winter conditions, however this was put in during the Fall of 2010, and there has been no damage reported to date.

Strip on porous pavement on a Dalhousie University parking lot (width of the car)

Regular asphalt on the left, porous pavement on the right

The City of Vancouver is using an alternative approach to reduce imperviousness on residential side streets called ‘Country Lane Treatment’. This design incorporates a soil and grass covered plastic mat between two parallel concrete driving strips. Permeable pavers were used to connect driveways to the driving strips. Click here to see more examples of road treatments from Vancouver. 

'Country Lane' in Vancouver (Photos: http://bit.ly/A4s9Os)

More information on permeable pavements and other stormwater management technologies can be found on the Sustainable Technologies Evaluation Program (STEP) website, an initiative led by the Toronto and Region Conservation Authority.

Stormwater workshop

We are excited to announce that registration is now open for our ‘Applied Stormwater Management’ workshops. Interactive presentations will be given by local and national experts with extensive knowledge and practical experience with stormwater management. 

The workshops will provide information, resources and opportunities to discuss topics such as:

• Impacts of stormwater including flooding, infrastructure damage and reduction of water quality
• Stormwater policy, regulations and initiatives in Nova Scotia and elsewhere in Canada
• Innovative stormwater BMPs for existing and new developments
• Site assessment methodology to guide on-site BMP implementation

 The workshop dates and locations are as follows. Please click on the location to register online.

  

-       February 20^th-21^st - Dalhousie University, Halifax, NS. Includes a half day field trip.

-       February 22^nd - Isaiah W. WilsonPublic Library, Digby, NS

-       February 23^rd – Rockwood ParkInterpretive Centre, Saint John, NB

These workshops are hosted by the Ecology Action Centre, Halifax Regional Municipality (HRM) Environment and Energy Office, Halifax Water, Insurance Bureau of Canada (IBC) and the Bay of Fundy Ecosystem Partnership (BoFEP).  Enrollment is limited, so sign up quickly!

Retention Basins (Wet Ponds)

In a recent blog post we talked about dry detention basins which hold water temporarily and release it slowly into the environment.  A retention basin works in a similar way but retention basins can store water for longer periods of time, mimicking a real lake or pond.  Retention basins are effective in storing and slowing runoff, thereby improving water quality by allowing pollutants to filter out of the water column. 

To find some examples of retention basins, we visited Dartmouth Crossing to see how stormwater runoff was collected from the large roofs and parking lots at the shopping centre.

Retention pond behind Walmart

We were pleasantly surprised to see and hear a gurgling stream in this landscape with so much pavement and hard surface cover.  The stream, Grassy Brook, is largely fed by runoff collected off parking lots and rooftops. A drop of water that lands on Walmart’s roof or parking lot is collected underground then released into Grassy Brook which flows behind the building. Marsh vegetation and willow trees were planted to enhance habitat and slow the flow of water, thereby helping to remove pollutants. Since white surfaces absorb less heat and stay cooler on sunny days, Walmart's roof is painted white to keep water temperature cool, as warm water entering a natural system can harm fish and other species. The increased flow of water into the retention basin and into Grassy Brook has created an active spawning site for trout.

White roof

 The wet pond shown below has both aesthetic and functional purposes. The pond is surrounded by a walking path, and an amphitheatre, so people can listen to concerts and enjoy the scenery. Trout also use this pond as a spawning area.

Pondside amphitheatre retention basin.The pipes in the background (left)
collect overflow during extreme precipitation events.

Runoff is slowly released into the pond through this small opening
to avoid a high peak flow.

Stormwater Quiz

Stormwater Quiz » create e-learning

Kunsthofpassage Funnel Wall

This building in Dresden, Germany, plays music when it rains. Not only does the design look beautiful, but it sounds great, too! We will try to incorporate some fun ideas like this when we retrofit a building in Halifax this summer!

Source: bit.ly/rFHh0K