Desert winds can excavate tons of soil from exposed sites and smudge dazzling desert views.Alluvial fans and bajadas can be fabulous locations for desert development. Being above the desert floor, they offer sweeping views. They are likewise situated above the areas of the basin floor prone to conventional flooding. In their depths they can hold abundant water resources; water from countless brief storms that has coursed from the rocky uplands to infiltrate quickly in the deep alluvium of the mountain front. It is the ability to tap such vast aquifers that allows and sustains development in many desert regions. But the worst-case erosion hazards of infrequent and unpredictable gully washers must be factored into site planning in desert development. It is critical also to consider wind. In an ecosystem that supports only sparse vegetation with limited leaf surfaces, wind erosion has more significant impacts than in better-watered areas where natural vegetation acts as a windbreak and protects the soil. Regional winds funneled through passes in arid landscapes can achieve awesome forces capable of feeling out and stealing away every grain of sand, speck of soil, and mote of dust, leaving behind only a skeletal matrix of sand-blasted rock known as desert pavement. Swirling and shifting winds can play havoc with dust control on development sites. Once aloft, the finest materials can be transported long distances, sullying air quality, swimming pools, and air filters. Wind carries the sand-size materials away in storms of blowing grains close to the ground, abrading cars and everything else in their way. Where winds abate, shifting fields of sand might be left behind, capable of covering highways, railroads, and development in their path when the wind picks up again. Stocking a Different EC ToolboxWhen storms finally hit arid lands, runoff can move down the mountain fronts with tremendous force, transporting decades of weathered rock debris.Practitioners of erosion control in desert regions need to work with the dynamics of wind and the potential for water erosion processes that operate only episodically over long periods of time. For the most part, they must meet these challenges without the aid of one of the most effective tools in the erosion control toolbox: ground cover. To establish and maintain dense ground cover requires water for germination and for sustained growth. In desert settings where ground temperatures might be significantly higher than ambient air temperatures and where evaporation and plant transpiration rates are high, the cost of water to sustain dense ground cover can be prohibitive. For this reason, arid land erosion control tends to rely on measures that avoid and phase land disturbances, shorten running slopes, and use plant and rock materials to protect soils from wind erosion and to dissipate the energy and velocity of overland flow.Developing Sustainable LandscapesOne business, Native Resources (www.nativeresources.com), applies many of these principles by re-creating natural ecosystems as landscaping for a variety of development projects. The company operates from a core understanding that native plants are uniquely adapted to local conditions, says Vice President Doug Sheehan of Native Resources Nevada. The company salvages desert plants in the path of development and reinstalls them as carefully planned and sustainable landscaping.The salvage process begins with an inventory of site conditions, during which mature plants are located with a Global Positioning System and mapped in CADD (Computer-Aided Drafting and Design). Botanists assess the salvageability of each plant, based on its condition, structure, and likelihood of survival if moved. At this stage, the company works with the client’s site planners and engineers to evaluate the site infrastructure plan and to assess the potential for preserving unique site features such as large plants and rock. The company next salvages boulders, shrubs, organic litter, soil, gravel, dead branches, and native seed. Trees are partially dug, major roots are cut, and the specimens are side-boxed, watered and fed, and held for several weeks before boxing is completed and they are moved to an onsite nursery. Here, in order to prevent sunscald, the plants are oriented to the same aspect as they were growing in the field. The plants are drip irrigated while they remain in the temporary nursery.After the development landscape is contoured, the company reclaims it by reintroducing appropriate soil microorganisms and original soils; re-creating soil conditions, including the proper kind and amount of organic debris, sand, gravel, and rocks; and finally reinstalling the plants. The result is a sustainable landscape that is adapted to local conditions and does not require heroic measures or unnatural additions of water resources or nutrients to maintain.Rethinking Water UseAs gusts pluck sand from disturbed desert soils, wind-shifted dunes can march over downwind highways, railroads, and development.This is not cheap. In fact, Sheehan says most people don’t realize the expense of drought-tolerant vegetation in a master-planned community, golf course, business campus, or corporate park. “The cheapest landscaping for a developer to put in is grass,” he states, “but that’s not the cheapest to maintain for those who buy the property.” Rising concerns over water and energy costs are causing owners to be more interested in salvaging the plant and rock resources on their property for reinstallation as sustainable landscaping. “The market is definitely becoming more receptive,” he notes.Recognizing the powerful need to conserve desert water resources, Nevada’s leading dust control company, Soil-Tech (www.soil-tech.com), uses soil binders and stabilizers on a wide range of construction projects. In Las Vegas, where any graded lot that will sit vacant for 30 days or more must be stabilized, “The first instinct is to use water to control dust,” says Tony Brighi, manager of Soil-Tech’s Las Vegas office. “Yet in the desert, this can be an expensive solution.”Using Soil StabilizersFor short-term dust control on building pads, stockpiles, and disturbed vacant land, Soil-Tech uses Ecco-Tex, a spray-applied fiber product that forms a wind-resistant crust over unstable soils. Seed can be added. The fiber acts as a mulch, attracting moisture and providing heat for germination. An inert organic tackifier holds it together against wind and water erosion. For longer-term stabilization on disturbed soils that will not sustain traffic, the company applies Plas-Tex, a gypsum-based product it developed and now distributes throughout the West. Both products are biodegradable and allow evaporation, infiltration, and penetration by plants.Brighi compared the costs of keeping down the dust on a 2-mi.-long, 25-ft.-wide haul road with a magnesium chlorideÐbased product, Chlor-Tex, and by means of repeated applications of water over one-month, six-month, and one-year periods. Although water was needed to precondition the soil before applying Chlor-Tex and to rejuvenate the product on a weekly basis, the cost of using water alone as a dust palliative over a yearlong period was more than three times the cost of the Chlor-Tex treatment.Developing Design StandardsDuring the thousands of years that desert rock is exposed to wind, moisture, and weathering, it acquires a dark surface “varnish” composed of mineral precipitates. Active channels on alluvial fans might be signaled by brighter surfaces on rocks that recently have been transported and tumbled by water. When Native Resources inventories a native landscape, field staff are on the lookout for these dynamic areas so that site planners can account for them in site design. Setbacks might be left for such drainageways in the development. Alternatively, planners might promote construction standards, such as limited structure footprints, tuck-under garages, sparse plantings, and open fencing (e.g., split rails), that allow the development to remain permeable to alluvial-fan flood events. In other areas, vast networks of concrete-lined channels have been constructed to direct alluvial-fan drainage to regional detention basins so that development does not need to be as accommodating to alluvial-fan dynamics.Protecting such basins from construction sediments has become a primary objective of Soil-Tech in the rapidly growing Las Vegas region. As development ascends the alluvial-fan systems ringing the valley, stabilization of disturbed sites is essential to protect both the region’s dazzling views and the taxpayers’ investment in the regional drainage infrastructure. Erosion control is important to public health as well, according to Brighi, EC expert at Soil-Tech. He notes that good air quality is essential for people who have asthma or allergies. It is also an important element of quality of life for those who choose to live in the desert.Soil-Tech aims to stabilize construction sites so that impaired-visibility alerts and outdoor-exercise alerts will become things of the past. This is a challenge because the wind that stirs up dust in the valley is spotty and multidirectional. As a result, Brighi’s staff are keen weather watchers, ready to shift to “Plan B” when wind conditions affect their plans for hydroseeding and soil stabilization. He laughs about his staff’s early morning cell phone communications always being about wind speeds and directions. A weather vane and an anemometer are installed outside the office.On an August afternoon of 2002, a visitor to the Las Vegas basin might not be aware that the valley floor, with average annual rainfall of only 4 in., was in the grips of an extreme drought. Yet only about a half inch of rain had fallen in the water year, there had been no winter precipitation, and the monsoonal rains of July and August had failed. Seeds of the native flora had not germinated in spring, points out Sheehan of Native Resources, so there were no seasonal seed resources for wildlife. Parched hydroseeded areas waited under the blaring sun for moisture. The delicate desert crust of precipitates, lignins, and cryptogams had become so desiccated that the dust devils touching down on the dry earth lifted spirals of fine soil into the dry air.Using Rock and Gravel MulchesExtensive talus slopes are typical upland features in many arid settings, where weathering and gravity are important agents of erosion.With water at a premium in such environments, many site managers and landowners look for alternatives to vegetation for wind and water erosion control. For this reason, rock and gravel mulches are common landscaping elements in residential, commercial, and industrial settings and on road shoulders and fill slopes in arid areas. Yet many developers of master-planned communities, golf courses, and office campuses in these settings seek climate-adapted water-conserving landscaping that will blend with local native ecosystems. Personnel at Native Resources and Soil-Tech work together to re-create such landscapes, where the nterspersed plants and native rock work in tandem as windbreaks, as desert armor, and as roughness elements capable of diffusing sheetwash and limiting its velocities. Finally, Soil-Tech applies a color mitigation system, ACT, to blend the disturbed soils into the surrounding environment. This product completely coats and stabilizes the soil, resulting in a dust-free environment.Rehabilitating Scenic ResourcesWhen a site is disturbed for development, the bright, unweathered surfaces of rock materials are exposed, creating a raw look. Soil-Tech blends the restored landscape into the adjacent, undisturbed ecosystem using the product Permeon, which speeds up weathering of rock surfaces and subdues the bright faces of freshly exposed rock in cut and fill slopes, mines, road edges, quarries, and graded areas. Thus, such sites blend in with their surroundings and do not detract from prized visual resources.In a landscape where 25- and 50-mi. vistas are a part of everyone’s everyday quality of life, Soil-Tech and Native Resources take pride in doing their part to maintain scenic quality. Vincent Robert, Permeon expert at Soil-Tech, puts it this way: “Living in the desert, you learn to love how difficult it is for one plant to survive in this environment. You learn what the earth had to go through to get all its rocks, crevices, and cracks.” We are touring a completed project at a golf course where the luminous green grass is framed by a restored desert landscape and Permeon-treated rocks. “You’ve gotta love it!” he remarks, indicating the entire desert basin with one sweep of his arm. “This is why we work with the desert, not against it.”
