Take Erosion Control Requirements Seriously

We witnessed an installer’s poor job with silt fencing and we didn’t like it

Take Erosion Control Requirements Seriously

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Recently we had the opportunity to observe a site being prepared for installation of an onsite system in a wooded area on a lakeshore. What we saw was disappointing for several reasons. First, the topsoil was scraped off and stockpiled on the site. More disconcerting was the silt fence installed to supposedly keep sediment and runoff from reaching the lake was woefully inadequate.

The purpose of a silt fence is to retain the soil on the disturbed site until the installation is complete and the site is revegetated and stabilized. Keeping the soil on site rather than letting it be washed off into lakes or streams prevents the degradation of aquatic habitats. Controlling erosion and runoff is required in these sensitive environmental areas.

Environmental protection

As an installer, it is your responsibility to install and maintain any erosion control measures required by the permitting authority. Silt fences are the most common required element. A silt fence is a temporary sediment barrier made of porous fabric. It’s held up by wooden or metal posts driven into the ground, so it’s inexpensive and relatively easy to remove.

The fabric ponds sediment and water runoff, causing sediment to be retained by the settling processes. If water flows over or around the fence it is not installed properly. This happens when they are not well designed, installed or maintained.

The three principal aspects of silt fence design are proper placement of fencing, adequate amount of fencing and appropriate materials. Placement is important because where a fence starts, runs and ends is critical to its effectiveness. Improper placement can make the fence a waste of time. The fence should be installed on the contour with both ends of the fencing higher than the top of the middle of the fence. The fence is wrapped upward on the ends so the fencing is curved. This prevents water from running around the ends of the fencing, defeating its purpose.

In general, silt fence is effective for areas of about one-quarter acre in size. This is an area of 10,000 to 11,000 square feet. For most residential septic installations, the area disturbed is less than this, so silt fences make sense as an erosion control measure. Where larger areas are involved, multiple silt fences or other control measures such as earthen berms may be required.

Silt fence construction

The silt fence on this site was installed poorly and will not retain water and sediment as intended. It appears the installer did not follow any of the required installation steps to allow the fence to work as it should. We have discussed in a previous column the steps in a good silt fence installation but here they are again.

1. Dig a 4- to 8-inch-deep trench on the contour at the bottom of the slope. This can be done using a shovel, backhoe or trencher.

2. Hammer wooden or metal stakes on the downslope of the hill. The stakes (usually 2 x 2 inches) should be placed on the lower part of the trench. Use a hammer to drive the stakes 1 foot into the ground. Place stakes 3 to 5 feet apart and run the stakes across the entire length of the trench.

3. Place two stakes 1.5 feet (0.5 m) (45.72 cm) upslope on each end of the trench. These posts will be on the end of your fence and prevent the flow from bypassing the sides of the fence. Hammer these posts in like you did with the rest of the stakes. The fence should now look somewhat curved.

4. Wrap and staple the silt fence around the stakes. Unroll the silt fence fabric and wrap it across the stakes so that the bottom of the fabric rests in the trench. As you wrap the silt fence onto one side of the stakes, use a stapler to attach the fabric to the stakes.

5. Backfill the trench with the bottom edge of the fabric in the trench. Pack down the soil over the silt fence material so that the material runs underground. Continue along the length of the trench until the entire length is filled.

It may rain anytime for the duration of the project. After each rain event, the fence should be checked to make certain it is doing its job. After heavy rains it may be necessary to do some repair work on the fence and remove some of the accumulated sediment from behind the fence so it will continue to prevent sediment from washing into the nearby water body. If the fabric is ripped or torn, it should be replaced and any broken stakes replaced.

Don't cut corners

With proper placement and maintenance, silt fences provide a relatively inexpensive and easy way to prevent sediment from impacting the area being protected. It doesn’t take a lot more time or effort to do this right. Do not be the installer who does a slipshod job taking care of erosion control measures. As we look at this we must wonder if they didn’t do a good job with this, how well are they doing the system installation? In addition, not installing the silt fence correctly may bring additional regulatory scrutiny over the rest of the project.    


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