Sept. 19, 2011 04:42

After the Fire

For nearly a week this past June, residents and officials in northern New Mexico watched helplessly as the Las Conchas wildfire-the most severe in state history-engulfed more than five dozen homes, 50 outbuildings and ancient pueblos. As the fire carved it´s path of destruction across a vast landscape, it devastated more than 150,000 acres.

The fire also burned through thousands of acres of watershed in Frijoles Canyon, part of Bandelier National Monument, a popular tourist destination where ancient pueblos nestle against rock paintings, petroglyphs and dwellings carved into canyon walls. The fire was so intense that most of the area’s vegetation, particularly in the critical watershed area, was destroyed.

While New Mexico battled the fast-moving fire, neighboring Arizona, too, was contending with a record-breaking blaze. The Wallow fire burned more than a half-million acres and resulted in 6,000 evacuations, more than 70 destroyed buildings, and 16 injuries in the northeastern part of the state.

The fire itself is only the beginning. Damage to property, natural resources, and injury to people happen after the fire is out, when the rains come. Hillsides that have been denuded of their natural erosion protection lay bare. When the rains come there is nothing to hold the water, so it will just run down the hill.

Now, the threat of flash floods sending a cascade of ash, soil and debris into homes and communities looms large for residents in both affected areas. Figuring out how to prevent flooding and mudslides from inflicting further damage will be the responsibility of those in the soil erosion control profession.

The lasting effect of a blaze on the soil is determined by a number of factors, among them the severity and intensity of the fire, its temperature, vegetation type, and post-fire conditions. In general, the hotter the fire, and the longer it burns in one particular spot, the more devastating it will be.

Root of the problem

When severe wildfires, like the Las Conchas, rip through low-lying shrubs and vegetation, they can burn up even subterranean root systems, which grip the soil and help keep it in place, and are vital for soil stability. Erosion frequently occurs in areas affected by fire, although slope and the soil’s texture often contribute to its severity.

Damagingly, fire can decrease how much water the soil can absorb. When the heat is especially severe, it forms a gas, which can settle on the surface as a waxy coating that is resistant to water. S o m e - t i m e s known as h y d r o - phobicity, t h i s w a t e r repellency can l e a d t o increased w a t e r r u n o f f and soil e r o s i o n following rainfall. A s o i l t h a t rebuffs water, but is also loose from a lack of vegetation, can quickly lead to mudslides or flooding. To make matters worse, the soil is often still thick with ash and debris following a fire, which can be toxic to wildlife, especially fish, as the polluted water cuts off their oxygen intake.

Fortunately, native vegetation is resilient; even following a major fire it will eventually return on its own. But it won’t happen overnight. In fact, it can take years for the protective cover of vegetation and chaparral to re-grow, leaving the exposed soil vulnerable to erosion, should heavy rains occur.

Rains can lead to flooding and soil erosion that can damage property.

More pressingly, when residences and communities creep too close to scorched earth, human intervention will likely be necessary to help prevent rapid soil erosion from causing further damage.

Planting the seeds

To combat potential rapid soil erosion, the best defense is often a good offense. Working quickly, Burned Area Emergency Rehabilitation (BAER) teams, consisting of soil scientists, geologists and other specialists, can assess the situation and recommend corrective actions. Stabilizing the soil is a top priority before the rains fall. Laying down a bonded fiber matrix (BFM) or tackifier, along with new seed across the affected area, can help prevent soil from slipping, making it more resistant to damage from the rains.

Frequently, seeding the area is of paramount importance. “Vegetation is the best erosion control out there,” says Russell Chambless, director of business development for the Pro Turf Team at Pennington Seed, Inc., in Madison, Georgia.

“If the area is scorched or burned, you want to get that vegetation back. Putting seed down gets the vegetation down quicker, instead of relying on natural vegetation to come back on its own.” A thorough investigation of the area post-fire may determine the severity of the destruction, and can help decide when hydromulching should include seeds, and what seeds might be most appropriate.

When native vegetation survives, adding additional seed may be unnecessary. For instance, if a fire does not linger in an area for too long, natural roots and seeds may be left behind in abundance, and will come back on their own. In fact, careless seeding in these areas can delay germination if appropriate species are not used, or if existing seeds have to compete with those introduced after the fire.

When fires burn too hot and destroy organic material, reseeding with native vegetation may be ideal, although in some cases, cover crops can also be used. These can grow quickly to provide temporary cover when time is of the essence. In some climes, like those found in Western states, reseeding with native vegetation will produce the most optimal results. However, Chambless notes that in other regions, like the Southeast and along the Eastern seaboard, they may opt to seed with turfgrass, or something likely to root faster than the native species found in those areas.

Hot fires can also eliminate all traces of germination, leaving a blanket of open soil. Ground that has been scorched completely bare is usually most optimal for seeding, as it provides greater soil contact. “If it’s partially burned, or you still have a lot of existing dead grass or thatch, you may not get that seedto-soil contact,” Chambless says.

And although seed may be planted, there is no guarantee that it will grow. Factors like the nutrients in the soil, outside temperatures, and precipitation—rain, in moderation, can prove beneficial once seeds have been sowed—all play a role. “We just have to evaluate the conditions that determine the seeding to put our best option down, or the best available seeding for that time of year, and hope for the best as far as Mother Nature is concerned,” Chambless says.

But even when areas requiring seeding have been mapped out, finding the right seeds may be a challenge in itself. Chambless says that while a variety of useful seeds—both native variety and cover crops—are typically available, attempting to obtain seeds outside of their correct seeding w i n d o w m a y p r o v e tough.

Another concern for l a n d - s c a p e s ravaged by severe fire is the loss of its b e n e f i - c i a l microbial systems, including m y c o r - r h i z a l fungi, an important part of soil life. The fungi attach to plant roots and help them absorb water and nutrients, encouraging growth. To refurnish the population following a fire, mycorrhizal inoculants can be added, which can effectively accelerate colonization.

The right solution

For broad slopes prone to mudslides, and other areas that directly threaten civilization, seeding alone will not be enough to stave off disaster from the rains. Hydroseeding is ideal in accessible areas. It is one of the least expensive methods to get seed, nutrients, and mulch or a BFM down. The mulch, tackifier or BFM will often be laid on the vulnerable ground to keep the soil in place and prevent erosion.

For areas where organic matter has been completely devastated, adding a legume, such as clover, may also be beneficial. The good news is that, when properly applied, a BFM can effectively blanket the soil and stay in place for months, buying valuable time for freshly planted seedlings.

You may also choose to lay seed down dry first, before hydromulching. While seeds can, of course, be incorporated into the hydromulch solution, this could cause them to get bound up in the upper layers of mulch, which can hamper seed-to-soil contact. Dry seeding first can help alleviate this problem.

Depending on accessibility, you can also apply a mulching solution mixed with seed and fertilizer aerially. Whether via airplane, helicopter, or on the ground from trucks, the logistics of how to apply the hydromulch solution is typically one of the biggest challenges for teams tasked with post-fire erosion control. Since fires can burn through acres of inaccessible, wild land, setting up equipment, trucks and hoses can be difficult.

Fortunately, only those areas that pose a direct threat to manmade structures or residences are generally seeded, which is typically only a small percentage of total area burned. For those less accessible areas that still require erosion control, airplanes can be used to drop the material directly onto the burned landscape. For rugged, remote terrain, impossible to traverse by other means, helicopters can also be used.

Determining which method to use often involves weighing some costs.

“When an aerial contract comes out from the forestry service, you have to look at a few things, and one of them is what the distance from the burn area is to either the nearest airport or the nearest helicopter pad,” says Jay Selby, president of Selby’s Soil Erosion Control Company, Inc., Loomis, California. “You’re guaranteed to always have a water source at an airport, but you’re not guaranteed to always have a water source at a helicopter pad.”

Ultimately, the distance from the airport or helicopter pad will determine which method is most cost and time effective. “When you have the guys mixing the mulch and the fertilizer standing half a day waiting for aircraft to come back, everything starts costing more,” Selby says. “You need a good, efficient ground crew and you need to have a five- to seven-minute turnaround time on aircraft.”

Selby generally looks for an airport no more than 10 miles from the burn area, and will consider another option if one is not available. If, for example, he finds a suitable place for helicopters to take off within three miles or so of the burn area, he might choose to use them instead. “The big expense with these jobs is airplane fuel,” he says. Adding that to the longer flight time, and the more expenses will rise.

Control efforts

Aside from hydromulching, a variety of other remedies can be found to prevent flooding and soil erosion.

In places where there is danger of falling rock or debris, concrete K-rails can be placed to keep debris from reaching roadways. Straw wattles and contour felled logs can also be used to slow water down. Wattles can be used on slopes of 50 to 70 degrees, where contour felled logs may not be safe. The wattles help control erosion by impeding the flow of sediment and slowing down the run of the water, helping to keep the soil in place, to encourage revegetation. When secured to the ground, typically via wood stakes, water and debris cannot pass underneath, slowing soil creep.

Hydrophobic soil may need to be broken up, or scarified, to help make the land more resistant to erosion and encourage new vegetation to take root. Tractors and other equipment can be fitted with soil-loosening equipment that can break up soil down to a few inches below the surface. To help save time and reduce costs, the process, called contour scarification, can also be performed in strips across the land’s surface, alternating treated land with untreated land.

The best bid

Assessing which methods will be best suited for the post-fire erosion control job will, above all, need to be conducted quickly, as rain can fall at any time.

“When we put our proposals together they’re huge—easily 80- to 90-page proposals,” Selby says. “Usually, we have about a four-day window from when the job becomes available to when it bids.” This means that contractors must have all their ducks in a row to get a comprehensive, well-compiled bid out on deadline. Above all, contractors must be willing to work quickly, both when estimating their costs and then when putting bids together.

Doing research on the subject beforehand, thoroughly evaluating means of access to the site and knowing what to expect before placing a bid can make a big difference when it comes to writing—and winning—the proposal. “There’s a lot of prep involved in putting out a fire contract bid,” Selby says. “It’s like, drop everything you’re doing and this is all you do for the next week.”

Also in Soil Erosion News

In many ways, we are fortunate that, in our chosen profession, we are able to help people when certain disasters occur: the tornadoes in Missouri, Oklahoma, Louisiana and Georgia, the flooding in Louisiana, the snows in the northeastern part of the country, the rain in California, and the snow in Colorado....

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