Jun. 23rd 2010
Written by Leland Walmsley
Within the context of sustainable landscape architecture, water efficiency serves a pivotal role. Many of these water efficiency ideas are not new, merely recycled from an earlier era – a time before satellite irrigation controllers, a time before PVC irrigation and a time before the irrigation we know today. Once upon a time, professionals practiced a holistic approach to landscape, architecture and horticulture. Those “ancient” approaches can still be found in the third world and in esoteric books and periodicals that are themselves recycling ideas for a new generation of thinkers – sustainably-minded thinkers. Together, these age-old sustainable methodologies and new emerging technologies result in life-cycle cost savings, a better and healthier environment, and enhance the very social fabric of those places where they are utilized.
We have all become familiar with the bucolic American suburb, but there is an ugly side to our notion of civilization. Even the most basic of civilized trappings – water, has a dark side. Our society pays a heavy price for potable drinking water. 3% of U.S. public energy demand is used to move water. In California, that number jumps to 20% with 8% occurring at the end user site (heating water, reverse osmosis, pool pumps, etc)[1]. Therefore, to save water is to save energy. Half of the potable drinking water is used for non-potable applications, landscaping and agriculture. Due to the unnecessary cost associated with safe, potable water, a sustainable site might best limit or eliminate the use of potable water for non-potable purposes (i.e. irrigation and toilets). Actually, the last thing plants want is potable (chlorinated) drinking water.
Better yet, use plants with little or no water needs. In order, to minimize water requirements, use regional native plants based on your site location. Once established, these plants need little to no supplemental water, depending instead on naturally occurring rainfall. Additionally, these native plants may provide much-needed food for migratory birds making up for habitat loss, and sustain local insects and pollinators that help sustain wildlife populations up the food chain.
Harvest rainwater. Rainwater is perhaps the most valuable, clean, nutrient rich water we can hope for. Rainwater leeches salts and minerals that accumulate in soil overtime and ultimately prove toxic to plants. Rainwater has balanced pH and is the best thing we can put on our plants. Prevailing thought is to get rid of rainwater runoff for fear that it will result in flooding. That is changing.
In much of the world cisterns capture rainwater and store it for everyday uses. In the US, cisterned rainwater also reduces the chances of urban flooding caused by stormwater. Once captured, we may use rainwater for irrigation or to flush toilets. During the dry months, even air conditioner condensate (moisture) may be cisterned as well.
Use non-potable municipal water. Plants have no need for potable drinking water. Non-potable treated waste water will do. Check with the local water agency to see if there is a non-potable source near the site in question. If there is a public park or golf course nearby, then there may be a non-potable water supply for purposes of irrigation, available at a much reduced rate.
Spread mulch. In addition to preserving topsoil and reducing erosion, mulch keeps soil cool in summer and warm in winter, and will facilitate greater and deeper root growth. Mulch helps maintain soil moisture longer, further minimizing irrigation needs and thwarting the weeds that compete with the desirable plants for water. Mulch can easily reduce your water needs in half.
Add a weather-based irrigation controller. Landscape plants can drink up half of the domestic water use. Weather-based irrigation controllers create a site-specific irrigation schedule for any landscape. Menu choices include: sprinkler type, slope angle, sun exposure, soil type, geographic location and plant material types. Minute by minute, weather stations measure wind, rain, temperature, relative humidity, and solar radiation and compute the amount of water vapor given off by plants (evapotranspiration) to the .01 inch. In real time, sensors recalculate water needs, adjusting to deliver irrigation with exacting precision to save water and money. Weather stations can be wireless, solar powered and easy to install.
Sites with vast landscaping, i.e. theme parks, parks, R&D campuses, golf courses, etc, are saving hundreds of thousands of dollars per year by irrigating exactly what the plants require. There is no guess work and with the correct amount of water, plants are healthier, resulting in less maintenance.
Hydrozone plant areas. Plants should be zoned into areas with similar water requirements, similar growing conditions (sun, shade, hillside, etc.) Lawn irrigation should be separated from plant beds as they have vastly different water requirements. Different sprinkler types (i.e. drip and pop-up sprays) should not be mixed as they put out different volumes of water. The idea is that every square foot of soil receives the same amount of water.
Maintain irrigation regularly. It is critical that irrigation systems are inspected monthly for clogs, proper sprinkler/drip function and broken pipes. The delivery time of day should be set for morning to minimize evaporation and potential fungal growth. The controller schedule should be changed to accommodate seasonal changes, and to adjust for the maturation of new plants.
Use efficient irrigation. Drip irrigation has come a long way, primarily perfected in Israel where water has always been scarce. Drip irrigation will substantially reduce water requirements as very little evaporation will occur, water is placed directly on plants, and little water is wasted on non-planted areas.
Replace your lawn. Considering water and maintenance costs over-time, the traditional lawn is the most time-consuming, energy-consuming and expensive plant per square foot in the garden. Consider low/no water use grass alternatives. In California, alternatives include Bouteloua gracilis (Buffalo grass), Dymondia margaretae (no common name), Juniperus conferta (Shoreline juniper) and Carex cultivars (Sedge, native to all 50 states). Once established, these alternatives do not need mowing, irrigation, chemical fertilizers, herbicides or pesticides.
Many cities are offering rebates for lawn removal. The Southern Nevada Water Authority (Las Vegas) offers a $2 rebate per square foot for lawn removal up to 1,500 square feet, and a $1 rebate for additional removal thereafter. Through 2006, nearly 80 million square feet of thirsty lawn had been removed. In Las Vegas, a typical 1,500 square foot lawn conversion saves more than 80,000 gallons of water per year. Furthermore less lawn means less water, less chemicals, and less maintenance. The absence of mowing, edging and blowing means less fossil fuel use. By replacing the traditional lawn substantial costs savings are realized.
Use Greywater. Clothes washers are the second highest water usage device behind toilets. Front loading washers use up to 18,000 gallons per year for an average American family. With the right detergent, wastewater from a washing machine is just fine for the purposes of irrigation. Except for toilet and kitchen disposal/dishwasher wastewater (blackwater), all other washwater (greywater) can be used a second time – on the landscape. Greywater reduces the need for potable water on plants. It’s perfect for bioswales, native plants and trees. And in fact, most of the world’s greywater is used in that way. Here in the US, the Uniform Building Code requires greywater be treated and managed similar to wastewater in the interest of public health. Most safety officers frown on greywater altogether, but greywater can be legally treated and dispersed much like a wastewater in a septic tank. California (and some other states) allows residential greywater without a permit.
Another form of greywater that helps recharge ground water includes outdoor drinking fountain runoff. Outdoor drinking fountains should be built atop a gravel sump. Rather than piping the relatively clean runoff to the sewer, the gravel sump allows for excess water to percolate down and recharge groundwater without puddling at the surface.
About the Author
Leland Walmsley, founder of everGREEN landscape architects, inc., was born into a family of professionally renowned designers practicing Architecture, Landscape Architecture, Construction, and City Planning in California since 1918. Leland’s personal passion is seamlessly blending great garden design, sustainable science, and environmental stewardship, whatever the design theme. He is on the Board of Directors of the US Green Building Council’s California Central Coast Chapter, is the 1st LEED AP Landscape Architect in Santa Barbara and Ventura Counties, is a LEED Trainer and recently co-authored Green Facilities Handbook. In 2006, everGREEN received the Santa Barbara County “Green Award” for its cutting-edge innovation, and recently completed work on one of the most energy-efficient and environmentally-sensitive commercial buildings in California that received the highest rating, LEED Platinum.
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