By: Jim Tolstrup
The growth of cities in the American West has increased water consumption from the Colorado River and pushed this critical natural resource beyond its limits. Yet we could reduce some of this demand within the communities that we design and build by switching to a style of landscaping that is more appropriate for our region, thereby conserving water while restoring some of our state’s unique biodiversity.
Here in Colorado, where we typically get 12–15 inches of precipitation per year, the average person uses 150 gallons of water per day. Sixty percent of residential water usage goes to support landscaping. This amounts to approximately 90 gallons of water per person per day used to keep exotic landscapes on life support.
When we look at wild landscapes in the fall, the changing colors reveal patterns that may be imperceptible at other times of the year. These patterns in the landscape provide subtle clues to the ways that plants are arranged in nature, based on available soil moisture.
In planning restoration projects, ecologists look at the aspect (the direction the site faces and the amount of sunlight it receives) as well as the degree of slopes, variations in soil moisture, and other conditions of the site. This same information is also valuable when planning sustainable landscaping projects utilizing native plants with minimal watering or maintenance costs. The grounds that surround buildings receive different amounts of stormwater, sunlight, exposure to wind, and other influences than undeveloped open spaces. To create a low-water use garden, it is necessary to evaluate the site in these terms and put the right plant in the right place for our purposes.
In 2007–2008, McWhinney (the developer of Centerra, a master-planned community in Loveland, Colorado), High Plains Environmental Center (HPEC), Ark Ecological Services, and BHA Landscape Design created a document called the Centerra Stormwater Pond and Natural Areas Design Guidelines. The guidelines won a Land Stewardship Award from the American Society of Landscape Architects in 2009. Although this document is primarily about the design and construction of native open space, it has influenced our thinking on all aspects of landscape design.
In front of our visitor center at HPEC is a bioswale. It is a low channel that receives the stormwater runoff from our parking lot. The channel has a series of pools that are excavated to different depths. Each shallow pool contains plants with varying degrees of moisture requirements. The channel banks have plants that require increasingly less moisture up to the top of the bank, which receives virtually no moisture except our natural precipitation. This type of swale can also improve water quality by removing nutrients from fertilizer, pet waste, and other sources that may have been picked up in the water along the way.
The concept of passive rainwater harvesting has been implemented to a large extent in other regions of the country. In Colorado, our complicated water laws do not allow for the evaporative loss of rainwater trapped in ponds of any size unless the landowner has water rights to offset it. However, it is possible to create high and low spots that allow rainwater to flow through the landscape slow enough to provide irrigation to the plants before flowing on.
When we work with nature in this way, placing plants in the appropriate zone in the landscape, and literally “go with the flow”, we can create beautiful, sustainable landscapes, reduce costs, conserve resources, and preserve the natural beauty of Colorado.
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