Rain Gardens 4 Resilience
Landscapes of the future will need to handle extremes in rainfall and temperature. Our food and water supply will depend on it. Fortunately, you can take small actions at home to increase landscape resiliency, and this program aims to build a library of possibilities about one kind of helpful practice: rain gardens.
WHAT IS THE RAIN GARDENS 4 RESILIENCE PROGRAM ABOUT?
Beginning in 2017, with support from Alberta Environment and Parks, the Alberta Low Impact Development Partnership built rain gardens in the Bow, Battle, North Saskatchewan and Oldman watersheds.
The project has a longer-term goal to educate property owners and landscaping trades about the importance of managing runoff at home, and address barriers to implementation and provide inspiration and resources for future installations. We built ten rain gardens in 2017, two in 2018, and one in 2019. We'll be following them and developing resources from our learnings in 2020, including rain garden designer and rain garden installer certifications. We'll also be using our learnings to design and construct community hubs in Calgary and Edmonton in 2020.
Three of these rain gardens in Calgary are also being monitored for water quantity in the form of soil moisture and spill events. One of these has a weir. A fourth site is being monitored in a 'before' condition with shallow soil and was our final garden constructed in the fall of 2019, with 'after' monitoring starting in 2020.
BACKGROUND ABOUT CONTROLLING RUNOFF
WHY DO WE NEED TO CONTROL RUNOFF?
When land is converted from its natural or agricultural past use into urban uses, the roads, roofs, and land disturbance greatly exceed the capacity of what is left of the natural landscape to buffer floods and droughts, and to keep water quality at acceptable levels.
WHERE DOES RUNOFF COME FROM IN THE BUILT ENVIRONMENT?
We know that about one-half of runoff is generated by roads, and the remainder by the rest of the landscape. Roads contribute tremendous pollutant loads, and remedial solutions for quality-improvement, such as roadside and open-area bioretention, oil-grit separators, sacrificial ponds with sediment-removing forebays, and other more engineered interventions are needed to protect our wetlands, riparian areas, and receiving bodies from the burden of pollutants found on and transported by these hardened surfaces.
On the other hand, runoff generated on the rest of the landscape is relatively clean, and the primary objective for this rainwater is to keep it from becoming runoff at all, at the property level. At the same time, there is a significant quality payoff to keeping rainfall on lots, since atmospheric deposition on roofs routinely contains orthophosphate and other sediment-bound pollutants (primarily generated by certain agricultural land uses and by open construction sites). Holding these compounds at the lot-level means they will not concentrate to impair and shorten the life of other measures designed for treatment and flood control, or reach receiving bodies where they will contribute to eutrophication (algae blooms), for example.
I'VE NEVER HEARD OF LOW IMPACT DEVELOPMENT, WHAT IS THAT?
Low impact development is a comprehensive approach to managing runoff that harnesses natural landscape features and processes to restore the absorptive and assimilative capacity of the landscape and to recreate more natural rainfall recharge pathways, while still allowing land development to occur, but with reduced impact. Rain gardens are one part of the low impact development toolbox.
WHY RAIN GARDENS?
Rain gardens are one type of practice that is really useful for newer existing lots that have compacted, shallow soil depths (10-15 cm or less) and immature trees.
In suburbia, a single rain garden can hold back, on average about 20 to 25 percent of the runoff that an entire lot with a typical home generates. Put four of these on an average lot, and you can reduce your lot to not contribute any runoff at all during most storms.
In a very wet year, it is possible to have some runoff, but there would still be a dramatic reduction in flows, attenuating the worst nuisance overland flooding and protecting properties. In a dry year, precious water is held in place and is available to sustain the landscape and slowly recharge groundwater and water-body baseflow.
On top of this, rain gardens offer the opportunity to expand the planting palette beyond typical dry-sunny xeriscaping, and, widely implemented, could dramatically improve habitat and habitat connectivity, particularly for pollinators. Maintenance is no different than regular gardening.
Adding a rain garden is one of the best things landowners with an existing lot can do to contribute to resiliency at home. With all this to offer, shouldn’t every property with a building have at least one?
WHAT IS A RAIN GARDEN?
Holding back and soaking in runoff in small depressed planting beds is like gardening the rain, hence the name. Rain gardens allow you to passively water plants without touching a tap. They are meant to both absorb and cleanse runoff. They deliver a similar range of environmental benefits as ponds and wetlands, while avoiding the challenges of standing water.
Rain gardens have deep, spongy soil. They have a surface that is depressed 10 cm to create a small ponding area. After it rains they may stay wet for a day or two. In our relatively dry climate they are a great way to keep plants healthier and happier without extra watering. Download the Rain Gardens flyer excerpt to learn more about design considerations, sizing, and plants that do well. The flyer is part of a larger series on low-impact practices, called the Clean Runoff Action Guide, which has been finalized and getting ready for its debut in 2021. We have used the lessons from this Rain Gardens 4 Resilience Program to inform and improve the Rain Gardens flyer.
The Watershed Resiliency and Restoration Program is our primary funding partner.