Sept. 17, 2012 04:08

Sediment Control... Doing the Job Right

At every construction site, sediment control is an issue. Whether you’re working on an overpass or installing a housing pad, containing sediment from seeping off the project is always a concern.

Brandon Coppedge knows that concern firsthand—he’s a project manager for Selby’s Soil in Newcastle, California. He’s worked on a number of highway projects for Caltrans. On one particular project, they needed to cut a path into a mountain for a new highway.

The construction team removed vegetation and dug steep slopes on both sides of the project to level out the area for the road. All that digging left dirt, gravel, and other loose sediment sitting on the side of the hill. Coppedge knew that the next time it rained, the water flowing downhill was going to take that sediment with it.

This was a big issue for Coppedge. He explains that if the sediment wasn’t properly impeded then it could have blocked a service road, ended up in the construction site, or in a channel that fed back to an environmentally protected lake. All of these problems “would have cost the client hundreds of thousands of dollars” in clean-up and fines, Coppedge reports.

This situation isn’t unique. A lot of construction projects will have at least some aspect where sediment is a problem. Sometimes, plans call for a road to be laid down next to a farm, or an office building that is being constructed uphill from a major street. If proper controls are not put in place, when the rain comes, sediment could seep onto the farm land or down to the major street.

Government regulations require that any and all construction jobs manage their sediment. In some states, contractors say that for every inlet within 300 feet of a jobsite that you don’t protect from sediment, you can be fined $3,500 each day that it remains unprotected.

As a contractor, you want to do the job right. You want to ensure that nothing short of a tsunami will wash sediment from your jobsite into a channel, a bay or a busy street.

However, because these soil erosion controls are temporary—until the project is completed—clients prefer to keep their costs to a minimum while still conforming to the regulations. That puts the responsibility on you, the contractor, to figure out how to filter out the elements while staying cost-effective.

Nature can be unpredictable, though, and heavy rains may strike at any time. There are times of the year when a rain event can last for five days, sometimes even longer.

How do you build a system that can withstand all of that and still stay within a budget?

On more than one occasion, Vance McCullers, owner of Southerland Service of South West Florida, Inc., in Land O’ Lakes, Florida, had to fight against consecutive days of rain to keep nearby streets from being flooded. Usually, he was able to accomplish this while not exceeding his budget.

What’s his secret? McCullers says, “If you install the product right the first time, you and the client will save in the long run.” Properly installing and maintaining sediment control products means you won’t need to replace or fix them multiple times during a single project.

Armed with the right knowledge, you can extend the lifespan of your silt fence, increase the efficiency of your wattles, and find alternative methods designed for specific situations. Knowing how to get the most out of these will make you a valuable asset that any client will want.

All you have to know is what to look for before and while you dig.

Silt Fences

One of the advantages of silt fences is that they are less expensive than other products. The tradeoff is that they might not last quite as long as you may need them to. A disadvantage—what gives silt fencing a black eye—is when it is not installed properly. McCullers can attest to that. The Florida Department of Transporta- tion (FDOT) needed to widen a stretch of road five miles long. The project required installation of about 53,000 feet of silt fencing. His company lost the contract to a competitor who bid the job at five cents per foot less. 

Unfortunately, that competitor dug  shallow trenches and left exposed flaps, all of which are not things you want to do. McCullers was then called in to fix it.

Installation is critical in determining how effective and structurally sound a silt fence will be. Whether you dig the trench by hand or you use a machine, you want to make sure your fence is buried at least four to six inches deep. The water should hit the fence and filter through the fabric, not go underneath it, which is exactly what happened with the project mentioned above. Heavy Florida rains hit, and the fences failed to hold the sediment- filled water back. Runoff went from the road and onto nearby cat tle ranches and protected wetlands, causing a host of environmental issues. After a major disaster like that, FDOT hired McCullers’ company to install new fencing, properly. They were able to save the project; however, it ended up costing the department a lot more money because they didn’t hire someone to do the job right the first time. It’s exactly these kinds of situations that you want to avoid, and that can be done by taking the time to consider the various issues involved with silt fences. Installation is a big one, but by far not the only one. Spacing between a silt fence’s posts plays an important role as well. The closer the posts are, the stronger your fence will be. Roger Singleton, owner of Silt-Saver, Inc., Conyers, Georgia, warns that posts that have more than eight or 10 feet of space between them will probably fail if heavy rain falls. Coppedge advises that you shouldn’t place your fence at the bottom of a gully, channel or ditch. The water will build momentum as it travels downhill and it can topple the fence by its sheer force, unless there is something else in the way to slow it down.

Sometimes you won’t be able to avoid steep slopes. In one situation, McCullers was hired to help manage sediment for the construction of a hospital next to a major road. The site was on a hill, so he had to ensure that rain didn’t wash out any sediment that would have blocked the road or caused damage to passing cars. These fences can slow down and filter water, but they aren’t the Hoover Dam. They need to be maintained—cleaned out from time to time. If there is too much sediment on the fence, then the fabric will clog and the water won’t be able to get through. Water will just build up until there is a break in the fabric or the entire fence falls over.

To avoid this, you should inspect the fence after each rain event. Check to see if you need to clear out the sediment. Coppedge’s rule of thumb is that “if you find sediment above the bottom third of the fence’s height, then you need to clean it out.”

Another potential problem to check for is tears in the material. McCullers would take note of areas in the fence that were damaged. Even if you fix the tears, the problem is that the water is hitting these sections too fast for the fabric to filter, so they give way under the pressure. Water always follows the path of least resistance, so he says, “If the water breaks through a particular section of your wall once, you can be sure that the water will go there every time.”

McCullers’ solution was to place ditch blocks and hay bails in front of the problem areas. This helps to slow the water down, so that it can be properly filtered with fewer issues.

When facing a challenging project like this, where rain could hit hard and heavy for days at a time, maintenance is the key to winning the battle. Coppedge, Singleton, and McCullers all agree that regular inspection and maintenance will keep your fence standing for a long time, even in extreme situations.

McCullers likes silt fences. He has found them to be a good way to control sediment. “You just need to take the time and effort to use them the right way,” he says.

Wattles

Wattles are a favored product for high-end projects, like highway construction. Contractors usually install multiple rows of them along the side of a hill, to act like a series of speed bumps for water and sediment.

If you’re cutting into the side of a mountain, wattles prove to be a useful product. Made up of straw, mulch, wood excelsior, coir, or a number of other materials, these slope interruption devices are tubes that catch sediment and slow the flow of water as it runs down a hillside and through it.

Before building a series of wattle rows, it’s important to determine how much space is required. If the spacing is close together, you’ll end up using more products than you need and your client’s expenses will swell. Too much space between rows and the wattles won’t be able to control and properly filter the water. Generally speaking, “The steeper the slope, the closer the spacing,” says Doug Bailey, owner of Earth Savers Erosion Control Products in Woodland, California. Just like with silt fencing, proper installation of wattles can make or break a project.

Coppedge knows that if it’s done wrong, you get a situation like the one he encountered at a wind farm in Northern California. A construction firm was hired to install 200foot windmills, but the site was 15 to 20 miles away from any paved roads. The company had to tear down a few hills to build a service road to the site.

The construction and lack of natural vegetation in this desert-like region meant that tons of sediment needed to be managed. Without any management one quick rain event would have dumped that sediment on to the service road or into nearby channels that led to the San Francisco Bay. If the roads were blocked by sediment, construction would have considerably slowed down if not stopped altogether. If it ended up in the bay, the company would be looking at huge fines from multiple environmental agencies.

Another contractor originally did the the job, but they didn’t dig small trenches to embed the wattles into it the side of the hill. The trenches are dug so that water will hit the wattles and filter through. If you don’t, water flows underneath the product and isn’t filtered.

In addition to the lack of trenches, Coppedge noticed that the previous contractors hadn’t made rows level. When a wattle is not level, the water doesn’t pass over evenly, causing water to gather in certain areas of your system. The water then digs gullies and channels into the slope and degrades its overall integrity.

Luckily for the construction company, no serious rain events had occurred by the time Coppedge and his team were brought in to finish the project. His workers dug proper shallow trenches to reinstall the wattles, using a laser level. The slope was secured and construction was finished on time with no sediment issues to worry about.

Alternative Products

Silt fences and wattles are popular products in this market, but they are not the only ones available. Depending on the kind of project you are working on, alternative products might actually better suit your needs.

If you are working near a busy street or a parking lot, you have inlets along the curbs to worry about. While working these types of jobs, you not only have to keep sediment out of the inlets, but you need to keep the streets from flooding. Augie Brayzs, national sales manager of Blocksom & Co., Michigan City, Indiana, says that maintaining a good flow rate is just as important as good filtration in these kinds of projects.

The biggest issue here is keeping these products from clogging. Products like filtration mats and gutter eels are installed directly on top of inlets, allowing you to check them with a glance. You can see if sediment is starting to back up, and you can fix it by sweeping it away.

There are many ways to effectively control sediment. Many times, contractors will use multiple products. They will line the side of the slope with rows of wattles and then place a silt fence at the bottom of the hill to filter any dirt that might have gotten through.

Staying within budget, avoiding fines, and keeping sediment from seeping offsite will help you cement better relations with your clients and expand your credibility.

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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