Sustainable Building Technical Manual - Etn-presco.net

Irrigation Equipment★ S I G N I F I CA N C E .In dry regions of the United States, landscape irrigation can constitute half a city’s waterusage; up to half of that is wasted. 12 Facing such statistics, municipalities are enforcingwater-efficiency laws and strictly monitoring commercial landscape irrigation.Automatic irrigation systems can save water when compared to hand-watering or floodirrigation. However, by definition, any form of irrigation involves addition of surfacewater beyond what is naturally found on-site. The baseline for evaluating irrigationstrategies should be natural precipitation and practices that rely on it. Even efficient irrigationshould not be a s s u m e d to be environmentally responsible without comparisonagainst this baseline.. ☛ SUGGESTED PRACTICES AND CHECKLISTI❑ Base irrigation design on Xeriscape principles.See “Plant Materials and Management” section of this chapter concerning thisapproach to water-efficient irrigation and planting design. 13 Always coordinate designof planting and irrigation system.❑ Employ water-harvesting techniques.Using processed city water for irrigation is wasteful, since plants do not require potablewater, and are often vulnerable to chlorine. For landscape purposes, use cisterns orponds to collect run off from roofs and pavement. Check dams trap runoff in pocketsto support plants, as do swales. Diversion of water along key contour lines, or “keylines,”efficiently spreads runoff along topographic planes for gradual release 1 4 ( s e eChapter 6, “Water Issues”).❑ Use graywater in irrigation.Graywater plumbing (separated from sewage pipes, either by retrofit or in newconstruction) can save money and reduce water consumption (see Chapter 6,“Water Issues”).❑ Install drip irrigation systems.Drip irrigation systems direct water accurately onto the base of each plant. Drip systemsmay use less than half the water of conventional systems, which lose water toevaporation and soak areas of soil that may not need water. Uniform drip wateringoften produces faster, healthier plant growth. Surface drip systems usually use“spaghetti tubing” while underground systems use “leaky” pipe (permeable-walledpipe specific to underground drip irrigation).❑ Increase efficiency of irrigation with controllers and sensors.Timers and computers provide measured amounts of water at regular intervals. Sensorsoverride the timer in response to rainy or windy conditions, reducing waste. Such controlsand the electrical valves they operate require power, either from a transformer or,in some systems, solar electricity. 15❑ Be sure design and layout of the irrigation system are site-specific.Topography, structures, and drainage affect the direction, height, and coverage ofspray-heads. The site’s lowest sprinkler often leaks wastefully after the system is turnedoff, as water further uphill drains to the low point. Overspray can result either frombad design or from wind. Drip systems avoid these problems, but share the problem ofpressure drop: the farther water flows through a pipe, the lower its pressure.