Swales & Berms vs Concrete: Low Tech Solutions for Stormwater Runoff
Here's a sample of email questions I've been getting lately:
- What can I do with all this rainwater? I have rain barrels, but they overflow. How can I deal with the overflow?
- I don't have time or money to install rain barrels or gutters, but I still would like to save rain water, what can I do?
Swales or berms could be your answer. They are literally as old as the hills and have been used to control water flow for centuries. Today they are still used around the world but have been all but forgotten here in the United States as a way to conserve water. (This is getting to be a familiar refrain!)
What's a Swale?
Swales are simply shallow, low depressions in the ground designed to encourage the accumulation of rain during storms and hold it for a few hours or days to let it infiltrate into the soil. Swales ideally are tree-lined and store water for the immediate landscape as well as help cleanse the water as it percolates down. Swales can be installed separately or as part of a larger water rain catchment system with rain gardens, cisterns and other water conservation measures.
Swales are one of the cheapest and easiest water storage methods and can be installed almost anywhere. If properly built they greatly reduce storm runoff; thereby reducing the impact of storms on local storm runoff systems. But more importantly they catch and preserve fresh rain where it can be used by your shrubs and trees. Swales are an easy solution that can be effective in homes, commercial buildings and along street mediums in place of curbs.
What's a Berm?
Berms are raised beds that can be used to direct water to swales. They are the equivalent of the slope in road used to push water off the middle of the road toward the curbs.
Ideally, berms and swales should be designed into the landscape where there is any noticeable slope to slow and capture runoff. They can be part of the site plan for an individual home or integrated into the design of an entire multi-unit complex or subdivision development.
Research Reveals Ancient Truths: Real Benefits
Recent research in Spokane, Washington, as well as Florida has documented the storm water quality benefits from swales and low-lying areas by reducing the flow and allowing slower infiltration into the groundwater system.
This is a finding which past generations were aware of. In our hurry to pave the world wit concrete, we threw our knowledge of swales and berms out with the stormwater (how's that for a mixed metaphor?).
It is best when designing the home landscape to preserve low-lying areas such as wetlands and swales. These low-lying areas retain storm water, provide water quality filtration and may allow for some infiltration to replenish groundwater supplies.
Swales can either be grassed, gravel or rocked. All designed to slow and retain the flow of runoff. They can also be used instead of costly curbs and gutters found in most neighborhoods and communities today.
As an example, at Prairie Crossing, a 678-acre residential development 40 miles northwest of Chicago in Grayslake, Ill. adopted conservation designs to reduce runoff rates and volumes and to reduce pollutant loads.
Storm water is routed into swales, rather than storm sewers. The swales provide initial storm water treatment, primarily infiltration and control sedimentation. The prairies diffuse the water and soils retain contaminants, slowing storm water velocity.
The development expects about 60 percent of the land to be devoted to open spaces. Residents also employ rain gardens and expect to retain 65 percent of its storm water onsite and reduce nutrient loads and reduce heavy metal pollutants by 85 to 100 percent.
Maintenance costs for storm water controls are expected to drop, downstream conditions have improved and there's less flooding. A sign of success has been thriving populations of native fish in the 22-acre lake.
Key elements to consider when building a swale include:
· Swales are not intended to move water but to hold water for soil absorption.
· The width of the swale should be covered by the crown of the mature surrounding trees.
· Soil in the swale should not be compacted or sealed but should be loose to encourage absorption.
Surprisingly one tree can reduce stormwater runoff by 4,000 gallons a year thus greatly reducing the need to build costly water treatment plants. So swales lined with native trees are an extremely-cost effective, and often overlooked low-tech, water conservation technique.
Swales with the proper plants and trees help manage runoff and make water healthy for people, nature and fish.
Swales are a low-cost win-win solution. Isn't it time we tried them?
Related Book: A Swale Guide: Permaculture: A Practical Guide for a Sustainable Future by Bill Mollison
Related Book: Rainwater Harvesting for Drylands (Vol. 1): Guiding Principles to Welcome Rain into Your Life And Landscape by Brad Lancaster
Truly wonderful books!