Planting for erosion control isn’t like tending a garden. The scale of such projects-often covering acres or miles-makes it impossible to give each site the “tender loving care” one might lavish on a favorite flowerbed. Yet the required tasks are somewhat the same; one chooses the right seeds for the site and climate, uses mulch to keep the soil moist and combat weeds, and enriches the soil to make sure it provides the best growing medium.
Seeding for Erosion-and Aesthetics
When the Talley family decided to develop property adjacent to its Arroyo Grande, CA, ranch into a prestige development named Las Ventanas, combating erosion wasn’t the only concern. “Preserving the heritage and beauty of this amazing land is of utmost importance to my family,” says Brian Talley. “Long-term sustainability and a commitment to quality are hallmarks of our four-generation history in the Arroyo Grande Valley. Las Ventanas is the ultimate expression of these beliefs.”
Of course, building homes required a lot of construction. “First, new roads had to be built,” Talley explains, “requiring substantial grading and earthmoving. All areas had to be hydroseeded, per San Luis Obispo County’s guidelines. It also stipulated using a seed type specific to this area.” Talley purchased his seed from S&S Seeds in Carpinteria, CA; the mixture included native wildflowers: goldfields, tidy tips, lupine, and poppy.
The project began in April 2007. The roadsides were hydroseeded that August and required irrigation. “This is a very moderate climate, with about 20 inches of rain per year, and very little frost,” Talley says. “The rains come between November and May; between June and October, it’s almost completely dry. But, thankfully, it’s cooler here than in southern California, because of ocean currents. Since we have a farming operation, we know how to grow things. To get the wildflowers growing, we used standard irrigation piping, a Rainbird-type system, and also water trucks as needed.”
Stan Shahan, manager of construction services for RRM Design Group, worked on the Las Ventanas project. “Las Ventanas consists of 55 residential lots, situated on approximately 3,800 acres in what’s known locally as cluster housing. The lots range from one-and-a-half to two acres each, with the remainder of the property dedicated to open space,” he explains. “The Arroyo Grande Creek runs adjacent to the property and was a major concern during the project’s construction phase with respect to erosion control and runoff.
RRM Design Group provided oversight and project construction assistance to the owner during the construction phase. “The designers decided to use Profile Products’ Flexterra Flexible Growth Medium-hydraulically applied blankets, as opposed to rolled blankets,” says Shahan. “A native-seed-mix design, approved by the county and supplied by S&S Seeds, was chosen for the hydroseeding. The plants sown reseed themselves each year, providing beautiful spring blooms.”
Roadways were a particular problem. “One of the challenges was approximately five miles of residential roadways carved from the project’s scenic hillsides. This resulted in miles of cut-and-or-fill slopes-some 30 acres-and the existing soils varied extensively, from clays to sandy soils. Flexterra helped hold moisture and expedited the hydroseed mix’s germination. Talley Farms also helped by using sprinklers and other types of irrigation to hasten the establishment of vegetation.”
Overall, the revegetation went well. “The project was adequately stabilized to file for the Notice of Completion with the regional water board,” Shahan says. “During construction, the project required over five miles of silt fencing, thousands of feet of fiber rolls, hundreds of gravel bags, and other extensive measures to help in the control of erosion and runoff. Given the close proximity of the Arroyo Grande Creek and the natural topography that drained toward it, it was a challenge to keep sediments from entering the creek. Credit should be given to the Talleys for their commitment to spare no expense to meet this challenge and maintain the clear-water integrity of the Arroyo Grande Creek.”
Seeding for the Site-A “Natural” Look
Projects that cross property lines or extend for long stretches can present challenges. One person’s wildflower can be another’s weed, and “aesthetically acceptable” is a very personal preference.
Utah’s Questar Gas Co. faced such challenges when replacing its 25-mile-long Feederline No. 26 (FL 26), a high-pressure natural-gas pipeline. Buried beneath private, city, county, and US Forest Service property, FL 26 required removal, replacement, and remediation work completed in phases over several years.
Questar’s environmental safety services coordinator, Mark Maldonado, explains the project’s recently completed Phase 3: “This was a 7-mile section along the foothills of the Wasatch Front mountain range east of Provo. Five miles of this project were located on a steep hillside, much of it about 200 to 300 feet above residential areas. These slopes were so steep that it usually required excavating a bench into the hillside to provide a safe work area for employees, vehicles, pipe, and heavy equipment.”
Because of this traffic, Questar Gas had to reclaim more ground than what was needed for the pipeline trench, he explains. “For a 24-inch-diameter pipe, the excavated trench is typically at least 4 feet wide by 6 feet deep. To prepare for construction, Questar Gas graded the right of way 60 to 100 feet wide, which had to be reseeded when work was complete. After recontouring the right of way to preconstruction contours, track-hoes were driven across the disturbed area to leave tread pockets to hold water and seed on the site.”
To ensure that native species were sown on the land, Questar Gas contracted with Granite Seed Co. of Lehi, UT. “Granite visited the site prior to construction to identify the vegetation and develop the correct seed mix,” Maldonado explains. “For these foothills, Granite determined we needed Oakbrush sumac, a slow growing shrub; slender wheatgrass; western wheatgrass; bluebunch wheatgrass; prairie junegrass; needle and thread grass; annual sunflower; mules ear; low rabbitbrush; mountain big sagebrush; chokecherry; and quickguard sterile triticale. Since part of this project crossed Forest Service property, we had to meet their seed criteria, too, which included adding Utah serviceberry. Granite Seed was able to provide us with everything we needed.”
The seed application was performed by Salt Lake City’s WRR Industries. “After the seed was broadcast on the disturbed area, WRR used a turret-mounted tanker to apply hydromulch.” Maldonado says. “About 2,000 feet couldn’t be accessed by the tanker, so WRR installed Curlex erosion control blankets instead.”
Work on the FL 26 Phase 3 took an entire summer, so the site was seeded in the fall. “Since this area gets more moisture in fall and winter, we had very successful germination. Questar Gas received some complaints immediately following seeding, because the hydromulch was so green, but then we had incredible growth. We needed to reseed a couple small sections, in particular in an area where unapproved traffic prevents growth.”
Although it was important to re-create attractive hillsides, the reclamation project’s number-one priority was to prevent erosion. “We can’t afford to have mudslides,” Maldonado concludes. “Between the seeding and the hydromulch, I’m unaware of any erosion that was problematic. There was a rockslide about a mile above the right of way a year later due to a moist spring, but our right of way was intact. We’re very pleased that everything worked so well.”
Safety From Seed and Mulch
When soils contain harmful elements, it’s imperative to keep them onsite. In the Ochoco Mountains, near Prineville, WA, Cascade Earth Sciences, a wholly owned subsidiary of Valmont Industries, cleaned up abandoned mines and created repositories onsite. Cascade project engineer Diana Washington explains the challenges: “The Mayflower Ochoco Creek mine complex was a former gold mine. Gold itself isn’t harmful, but you liberate other things from the soil when you dig-heavy metals can come out, too. Once exposed, they weather and change, and this can pollute.
“Also, when refining the gold, which was also done on the site, the process leaves heavy metals in the pile-arsenic and lead, for example. Such practices, of course, can’t be done these days; this is a historic mine. This area receives recreational use-people hike and camp in the area-so we needed to keep contaminants on the site, making sure they didn’t wash out to other areas, while also keeping humans away from the contaminants.” How dangerous were these chemicals? “At times, our people had to be in protective suits, depending upon how much was in the area,” she says.
The removal project, which began in summer 2008, entailed about 8 acres at multiple locations within the complex. “We isolated the contaminants in locations removed from the floodplain, then the containment was capped with natural soils,” Washington says. “Then we mulched, seeded, and fertilized the area, to spur vegetative growth.”
For the mulch, Cascade Earth Sciences used Forest Concepts’ WoodStraw product. “We’ve been using WoodStraw for the last couple of years. It creates a microenvironment. The mulch gives seeds some shade while it also holds moisture. So WoodStraw serves a lot of purposes; it’s very good at what it does. Mulching keeps seed from being washed out and keeps sediment from being washed away. I have used other mulches, such as weed-free straw, and even though it’s “˜weed free,’ it still often contains seeds, and you’ll get unwanted growth. Regular straw can mat up; if it’s put on too thick, it will mold, and it doesn’t make a good growth environment. There are no seeds in the WoodStraw, and because the wood source has been cross-chopped for varied length, there’s much less matting.”
Depending upon which tree is the WoodStraw’s source, the product can have a varying pH, but that doesn’t seem to have much impact upon its effectiveness. On the Mayflower Ochoco Creek mine complex, with its many steep ravines, the main concern was holding the seed to the soil. “We broadcast seed,” Washington says. “These were very remote sites; we couldn’t take hydroseeding equipment there. Typically, we’ll seed in late fall and then reseed in spring, using seed varieties developed for the climate. Of course, since the US Forest Service was our client, it gives us the seed, so we avoided “˜bad seed’ issues.”
Food for Thought: Feed the Soil
When taking care of roadsides along US 97, a West Coast main thoroughfare that runs Oregon’s entire length, the US Forest Service concentrates on the most elemental ingredient for erosion control: the soil itself.
“In this area, the soils have originated from pumice, the airborne sands and gravels that blow out from an erupting volcano. It’s lightweight, with very high infiltration and permeability rates, but not after a bulldozer goes over it! Soil compaction is a huge issue for us,” explains David Steinfeld of the US Forest Service. “The challenge is that when you want a stable road system, you do want compaction and strong soil, but that’s just the opposite of what you need for plant growth. Healthy, uncompacted soil contains large pores, which are essential for water and air movement as well as root penetration.”
Reducing soil compaction starts with eliminating some “standard practices.” “We backed off track walking-a practice engineers use, in which they prepare a slope with a bulldozer. The vehicle’s cleat marks make reservoirs for the water, which is sometimes a better germination environment for the seeds. But, in the long term, this practice makes it tough for plants to get established, because the soil is too compacted. The newly germinated seedling can’t penetrate the soil, yet if it somehow manages to, it’s difficult for the roots to penetrate much further.”
Despite backing his arguments with a long career’s worth of soil science experience, Steinfeld decided visible proof would help his case. “We employed a portable rainfall simulator, operated by Dr. Mark Grismer, a scientist from University of California, Davis, and Michael Hogan of Integrated Environmental Restoration Services Inc.” The rainfall simulator consists of a plexiglass tank, which stands between 2 and 12 feet off the ground, from which protrude some 700 hypodermic needles. With applied pressure, the needles make drops of a known size and mass, so one can calculate the force with which each drop hits the ground. As different pressure produces different rainfall rates, a range of event types (from gentle rain to downpour) can be simulated.
“They simulated rainstorm events over soils that had been compacted, soils not compacted, and compacted soils that had an inch of mulch placed over the top, and then measured the amount of runoff,” Steinfeld explains. “The engineers building the road were surprised how track walking changed the water filtration rates. Water ran off the slopes very quickly-within several minutes. So we didn’t track walk very much on this project after that.” Although the demonstration proved his point, he admits, “We need a lot more study on other soils, slope gradients, higher rainfall, and so on before anyone else might follow our lead.”
In addition to eliminating track walking, Steinfeld’s crews added mulch when seeding. “We put a real mulch on the soil-a full inch. One of our former studies indicated this need. In the spring when seeds are germinating, the rainfall and humidity are too low for just applying seed to the surface. Hydromulch is only a very thin layer of material that covers the soil. Yes, one can use hydroseeding in this part of the world, if you irrigate afterwards-but we don’t have that luxury.”
In an effective and cost-saving move, mulch was created from materials at hand. “We ground up roadside right-of-way material instead of burning the slash, which is what’s usually done. We ground up the brush and blew it out on the site. We didn’t create “˜chips,’ but long strands of woody material, which hold on the slopes better, while also being better for seed germination. Since we don’t get much rainfall, things dry out quickly-but we got good plant establishment with the mulch, and this process is really working on our projects in central Oregon.”
The mulch will eventually work its way into the soil, adding organic matter and creating better soil structure, which is desperately needed, as many roadside sites the US Forest Service reclaims have little or no topsoil. “I put mycorrhiza in when we have no “˜native’ topsoil,” Steinfeld explains. “I’ve done some testing with Dr. Mike [Mike Amaranthus of Grants Pass, OR’s Mycorrhizal Applications Inc.] on effects with mycorrhizae on trees and grasses on disturbed sites and seen positive responses.”
But Steinfeld makes an effort to salvage native topsoil from any project and return it to the site. “You need to restore the soil,” he stresses. “If you do, plants will start coming in on their own. We need to get carbon back onsite-that’s the energy source that gets soil organisms, including mycorrhiza, going. When you improve the soil, the plants stay greener longer into the year, which just might make them less of a fire hazard. We’re trying to restore soil function for the long term, greater than 10 years out, so that they begin to function like the natural soils surrounding our projects. But we have a lot of practical experience and research left to do to understand how to do this.”
What’s planted on restoration sites can also have an impact. “We’re moving the system to perennials. Annuals and weeds don’t really do much to restore the soil in arid and semi-arid environments. We plant native grasses, forbs, and shrubs; bunchgrasses; lupines; and, where we can, trees. We use our native nitrogen-fixing plants to reduce the need for fertilizer.
“When we get involved with a road project, we’re usually called in one to three years before they break ground,” he adds. “That’s part of the plan-we want to locate reference sites, look for natural models to guide us in our planning. If Bitterbrush grows well in rocky soil, that’s what we’ll use. We collect the seeds ourselves, then have local or regional seed growers mass produce seed from the seed we collect. We don’t buy on the open market very often. Are we being too conservative? Some plants have adapted, but we don’t want to move the seed source too far. We’re not trying to cram these guidelines down anyone else’s throat; these are Forest Service guidelines, but we believe they make sense for other lands and projects, too.”
The Best Foundation
Michael Hogan, president of Integrated Environmental Restoration Services in Tahoe City, CA, agrees with Steinfeld’s soil solutions. “Yes, tracks from heavy machinery make a physical spot for seeds and water-but, just as when you squeeze a sponge, it doesn’t hold water, which is what happens to compacted soil. If you “˜fluff the soil up’ it holds more water, and plant roots can more easily get into the soil. When you’re talking erosion control, it’s the plant roots that hold the soil together, giving it strength.”
While admitting that taking the time to revitalize soil can be costly, Hogan counters, “What are you trying to achieve? If “˜kinda good’ is enough, sure, do it the cheap way. But how many times do you want to re-treat before you retreat? In the arid West especially, simple and cheap often doesn’t work over the long haul. You have to invest if you want it to last. A site can absorb 10 times the amount of water when you have a loose soil that contains organic matter. And you don’t have to do the work by hand; we’ve used a range of tools to achieve these goals. A big excavator with a specialized bucket, or a Cat like you’d use on a farm, can do the job.”
As a coauthor (with Mark Grismer of the University of California, Davis) of papers on how the rainfall simulator works, Hogan knows what it can teach. “It helps us understand how treatments work, compared with one another. For example, a hydroseeded site can make four to six times more sediment per year over a site that’s received full soil restoration. Many people believe that if you have plants, you have erosion control. That’s not always true; we’ve tested and showed that a lushly vegetative slope can allow the same erosion as a bare slope. The plants aren’t making the rain go into the soil, it’s the soil itself; a fully functional soil will allow more water to infiltrate, roots to penetrate, microbes to flourish, and the site to sustain itself while it’s controlling erosion for the long term. You can force plants to grow, but they’re not necessarily doing all the job.”
Integrated Environmental Restoration Services offers a broad range of services to its clients, from overseeing onsite best management practices to monitoring and construction. “We continually test erosion control practices to see if they work well and improve procedures based on those findings,” says Hogan. Some of these findings, including reports he has co-authored with Vic Claassen of the University of California, Davis, are available for download from the company’s Web site. Although the items are specific to the Tahoe basin area, they provide concepts that can be applied to other soils and climates.
“I’ve seen a lot of things that don’t work-what can we do to make it better?” Hogan wonders. “Everyone’s looking for that “˜single thing’ that will fix our worries-but on very disturbed sites, one thing won’t do it. Soil is a system, and we need to address it as such.”
TO LEARN MORE
“Generation of Water-Stable Soil Aggregates for Improved Erosion Control and Revegetation Success” and “Soil Nitrogen Pools Associated with Revegetation of Disturbed Sites in the Lake Tahoe Area” are available for download from www.ierstahoe.com.
Not all soils are created equal, and you’re pretty much stuck with the type your site contains. Knowing the soil, and what you can do to improve it, can increase your odds of reclamation success.Soil type or texture is a determining factor for fertilizer absorption and plant establishment. A larger soil particle, such as sand, allows water to flow quickly through—often taking the fertilizer with it and wicking the moisture away from seeds or seedling roots. On the opposite end of the scale, clay, with its tiny, negatively charged particles, can bond with water and, after drying, create an impervious soil surface, making it nearly impossible for roots to establish.
Of course, few sites exhibit only one type of soil; visual inspection and/or testing will tell you the composition of your soil. As the figure below illustrates, the near-optimal mix of 40% sand, 40% silt, and 20% clay creates another designation, “loam,” which combines the best characteristics of all three soils.
Soil structure describes how soil particles bind together as aggregates. Sand, for example, is a simple soil, and since its particles are so large, it doesn’t clump and allows water to pass through it easily. When water is not present, the spaces between the particles, or pores, fill with oxygen, which is crucial for plant health.
At the opposite end of the spectrum, clay soils are dense, with very little pore space; when taking in water, clay soils easily clump up into clods, becoming impervious. However, difficult structure can be adapted by mixing organic materials into the soil. In sandy soils, organic matter will hold moisture; in clay soils, it “bulks” the soil, allowing for more pore spaces. Organic matter also adds to soil structure because it attracts insects and earthworms that will work themselves through the soil, mixing particles and creating pore spaces as they go. (In turn, the earthworms’ waste also enhances the soil.)
Soil types vary in water retention capabilities, as well—will the soil hold enough water to induce plant germination, or will it “drown” the plants, by holding too much? Is the soil impervious, causing water to simply run off? Table 2 shows water-retention levels of various soil types.
Again, adding organic matter to the soil increases water retention in sandy soils, while allowing deeper infiltration in clay soils.
No matter what type, topsoil is the most important facet of any site. As this layer of soil usually contains the most organic material and available nutritional elements, it’s the area where most plants set their roots.
Most soils have three major horizons: the surface (A), where bacteria, fungi, and small animals (such as earthworms) exist with plant roots; the subsoil (B), which has less living matter and more clay; and the substratum (C), mostly weathered rock material. Some soils contain an organic horizon (O) on the surface. Below the C layer is bedrock, which is not soil and allows no growth.
Unfortunately, most reclamation sites are bereft of topsoil; that’s why spurring plant growth can be so difficult. However, topsoil can be created: breaking up a few inches of the B horizon and incorporating organic matter will start the soil on its way to becoming “topsoil.” Organic matter will not only give the soil more nutrients and pore space but also attract those beneficial earthworms. And, as David Steinfeld proved in Oregon, finding organic matter isn’t that difficult; grinding and incorporating brush that is usually burned allowed him to add “free” organic matter that was already onsite. In more urban areas, residential yard waste (especially fall leaves, which will not contain the fertilizers and herbicides grass clippings might) could easily become part of a topsoil “recipe” instead of landfill fodder.
