How To Install A Silt Fence To Protect Nearby Water From Soil Migration At Your Construction Site

If you are going to be doing a significant amount of digging or earth-moving adjacent to a body of water, it is important to take measures to protect the water from uncontrolled soil influx.  The erosion of soil can upset the natural ecological balance found in a stream or pond and result in the destruction of plant and animal life. Fortunately, erecting a barrier to keep soil on-site and away from the water is not difficult and can be accomplished at a reasonable cost. Below is a list of materials needed, as well as instructions on how to build a silt fence:

What you will need

  • 3-foot wide roll of wire-backed polypropylene fabric
  • Steel u-channel fence posts in 48-inch lengths
  • 12-inch cable ties
  • 12-inch walk-behind trencher
  • Trenching shovel or spade
  • 3-pound or 5-pound sledge hammer
  • Measuring tape
  • Torpedo level

Step-by-step guide to building a silt fence

1. Lay out the fence location and purchase your materials - Before you buy materials, you will need to lay out the right-of-way for the silt fence to determine exactly how much you need to purchase. When choosing a location, look for a flat site, if available, in dry, stable soil. Avoid placing your silt fence in sandy or boggy soils, as these will not provide a firm foundation for the fence and may contribute to a possible collapse. In addition, determine the run of the fence based on the prevailing flow of soil toward the body of water. The fence should be erected at a 90-degree angle to this flow to provide the most effective barrier.

After you chosen a right-of-way for the silt fence, measure its total length, and use this calculation to determine how many feet of polypropylene fabric you need to purchase. Next, divide the total length of the fence by six to determine how many steel fence posts to purchase. For example, if your fence will measure 78 feet long, divide by 6 to find you will need to buy 13 fence posts. Round up any fractional amounts to the nearest whole number.

2. Dig the trench line - Once you have laid out the right-of-way for the silt fence, use a walk-behind trencher to dig a 12-inch deep trench along the designated right-of-way. The trench should be approximately 6-inches wide. After using the trencher, scoop out loose soil inside the trench with a shovel or spade, but don't dispose of the soil.

3. Install fence posts - After the trench has been dug, you will need to install fence posts along the backside of the trench closest to the water. Steel u-channel fence posts work best, since they can be driven into the ground easily and also contain small "hooks" that provide convenient fastening spots for the wire mesh. The fence posts need to be no further than six feet apart to provide the strongest protection.

Locate the end of the fence line, then drive the first post using a 3-pound or 5-pound sledge hammer into the ground about 1 foot deep. Keep the fence posts as level as possible, and use a small torpedo level if you have difficulty assessing the incline, if any exists. Position the posts so they are on the side of the fence facing the body of water.

4. Install the fence fabric - Once the fence posts are placed, have a helper assist you in unrolling the fence fabric with wire backer. Don't attempt to unroll more than a few feet at a time, as the fabric will become unwieldy.

Align the fabric with the fence right-of-way, and position it so the bottom 8-to-10 inches of the fabric and wire backer are inside the trench you dug in step 2. Be sure to align the fabric so the wire backer is facing the body of water. Next, attach the end of the fence fabric to the first post in the fence line. Hold the fabric in place and use cable ties to fasten it securely to the post. Continue to unroll a few feet of fence fabric at a time and attach it to the fence posts as you proceed; keep the fabric level and aligned as you continue forward.

5. Bury the fence bottom - After you have attached the fence fabric to the posts with cable ties, backfill the trench with soil you removed earlier, and bury the bottom of the fence fabric in the trench. This will prevent any gaps from appearing that might otherwise permit topsoil and water to flow underneath the fence.