Slecting the Best Site for the Rain Garden: Slope and Soil

Before you get started on building your rain garden, you want to know the answer to two basic questions: "What's my slope?" and "What kind of soil do I have?".  This article will help you get to the bottom of these two questions.

What’s My Slope?

 To calculate the slope of the intended rain garden, pound one stake uphill of the site and the other at the downhill end approximately 5 m (15 feet) apart. Tie the string to the stakes and make sure it is horizontal with a carpenter’s levels. Once the string is properly secured and level, measure the length of the string between the two stakes and then the height of the string from the ground at the downhill stake.   The percent slope will be equal to:

Percent Slope = Height x 100

                         Length

Slope <4%, easiest to build 8-13 cm (3-5 inch) deep rain garden.

Slope 5-7%, try to build it 15-18 cm (6-7 inches) deep.

Slope 8-12%, build it 20 cm (8 inches) deep.

If the slope is greater than 12%, it would be easier to install a garden elsewhere.

How Do I Know What Kind of Soil I have?

Before you even think of putting a shovel in the ground, you also need to figure out what type of soil your rain garden site has. Sandy soils have the fastest infiltration; clay the slowest. Sandy soils are described as gritty and coarse, silty as smooth but not sticky, and Clay as sticky and clumpy. Clay garden must be bigger to handle infiltration and should have sandy pits installed in them to help infiltration. Here is an easy test to help you see if your rain garden will work well at your selected spot:

Soil test: Dig a hole 15 cm (6 inches) deep and fill with water and allow it to filter away. If it takes more than 24 hours to drain, the soil is more clay-based and is not good for a rain garden. You can mitigate the lack of drainage by adding sandy soil pockets during installation, but that takes time and money.

Planning the Rain Garden

The first thing you need to know is where the water goes. Where do the downspouts from your gutters point? Do you see small rivulets of water passing through the grass? Do they join the stream from the downspouts? Does the water pool anywhere? Where can you catch the most water?

This downspout allows stormwater to flow away from the property.

Once you have an idea of where the water flows, you can start eliminating areas around your house. Do not install a rain garden where the water naturally pools, that is where filtration is slowest; think about installing it where the rain garden can catch the water before it pools. You also want to avoid large tree roots. If there are branches overhead, there are roots beneath your feet.

Try to put the rain garden close to a downspout but it is important that you keep the rain garden at least 3 meters (or 10  feet) away from the building to protect the foundation of your house. It is also important to keep your rain garden at least 7.6 meters (or 25 feet) away from your septic system.

After that, it is more a matter of practicality. Installing a rain garden in a flatter portion of land will be easier to dig and level. Make it easier for yourself and do not decide to dig a rain garden where the slope is more than 12%, you will need retaining wall or a high berm to keep the water in and it will take a lot of earth to level out the garden.

In terms of design, crescent-, kidney-, or teardrop-shaped gardens work well. You will want the longer side of the garden to face upslope. Water will hit the berm at the back of that long line, and then flow back towards the garden like a receding wave at the beach. A larger surface will catch the most water possible.

Consider the height, bloom times, colours, and textures of the plants you are planning to use. By choosing plants that bloom at different times, your garden will have a longer flowering season. If you want a traditional, more formal look, try clumping individual species in groups of 3-6 plants and repeat the pattern throughout the garden. Try mixing sedges, rushes, and grasses with flowering species to keep the root network strong and keep some plants from overpowering each other. 

What is a Rain Garden and Why build one?

Rain gardens function as a stormwater absorption and filtration site.  They are beneficial to the local environment by improving water quality and absorbing excess runoff. Rain gardens function by directing stormwater into a plant-filled channel or shallow depression filled with a variety of native plants.  A berm or raised edge at the lower end of the rain garden prevents the water from spilling out.  This allows the water to slowly filter into the soil instead of running out into the streets and down storm drains.  Besides all these environmental benefits, they are beautiful and for the most part they water themselves!

What are the benefits of a rain garden?

• Absorbs 30% more water than a patch of grass.
• Helps reduce stormwater runoff.
• Enhances the aesthetic appeal of your property
• Provides habitat for birds and other critters.
• Recharges groundwater aquifers
• Improves the water quality of your community.
• The plants’ root networks will stabilize the soil on your property and reduce erosion.
• Plants provide a buffer to winds, acting as wind-break for your property.

These photos show the stages of construction of a rain garden.  This rain garden was built in September 2012 at the George Dixon Centre in the North End of Halifax.

For an overview of rain garden, please visit our previous article on rain gardens

Video from Demonstration Site Launch

Our volunteer videographer, Colin MacDonald, put together this video for us from the launch of the stormwater management demonstration site in November 2012.  Take a virtual tour of the demonstration site  by watching this short video.

You can have a look around the stormwater site any time, it is located at fire station #2, 5988 University Avenue, on the corner of Robie Street.  Guided tours will be available when the snow melts and the rain starts flowing, dates will be posted to this blog.

Download our Stormwater Brochure

Want to plant the seed for alternative stormwater management with your friends, co-workers or members?  Download our colour brochure here and spread the word!

For a higher resolution version, please contact the Ecology Action Centre.

Demonstration Site is OPEN!

The launch of Halifax's first Stormwater Retrofit Demonstration Site took place last week and we have lots of photos to share on the blog.  Click here to see the whole album (22 photos)!

Take a tour of the Stormwater Demonstration Site at 5988 Robie Street in Halifax!

Site Launch - Tuesday November 27th 2012

Stormwater Management 

Demonstration Site Launch

Join the Ecology Action Centre, and project partners, in launching Halifax’s first stormwater retrofit demonstration site.

With changing climate conditions and heavier rainfall predicted, it is more important than ever to understand how to manage stormwater effectively.

This event is for everyone interested in learning about alternative techniques for managing stormwater on site, in order to prevent damage to properties and municipal  infrastructure, to save money and improve ecosystem health.  We hope to see you there!

    When:            Tuesday November 27th, 2012          

                     10:30 am, site tour at 11:00 am.      

    Where:           Halifax Fire Station

                     5988 University Ave. (corner of Robie St.)

   Will there     

   be Coffee?   You bet!

    

This is a rain or shine event, so bring a

jacket and hope for… rain of course!