The following sequence of photographs document the installation of silt fencing as a tool to trap sediment and estimate erosion rates. This silt fence is being installed in an undisturbed swale in a forest of ponderosa pine trees on the Pike National Forest in Colorado. The trees in this area will be harvested as a part of the watershed study.

Photo credits: Mr. Kevin Bayer.
The silt fence installation team includes Mr. Zamir Libohova and Mr. Richard Anderson.

Carefully spaced steel rods are driven into the ground to support the mesh, or silt fence. After the series of rods are installed, the litter and debris is cleared away from the base of the rods and the area immediately up slope. The rods create an arc across the swale.

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The length of the arc is measured and the mesh material is then cut to length. Small pieces of wire are cut and shaped to attach the mesh to the steel rods. The rods are of uniform length and approximately one-half of the width of the material is suspended from the rods while the other half of the material is spread out on the ground to function as an apron upon which the sediment is trapped.

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This sequence of photographs depicts the way in which the mesh is attached to the rods and how the apron is attached to the ground uphill of the rods. Heavy wire is used to make staples which are driven into the ground to hold the apron in place.

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31	32	33	34	35	36

This sequence of photographs depicts an operational silt fence being cleaned out after a storm. As water and sediment moves down hill, it collects in the silt fence. The water either infiltrates or passes through the fence and the sediment is filtered out and held in place. The trapped sediment is shoveled into pails and weighed. If the contributing area (acres or hectares) of the land above the fence is known, the erosion rate can be estimated. In this case, a double fence is present. The purpose for the second fence, is to determine trap efficiency of the first fence. An additional length of fabric is also added, on the uphill side, to increase the efficiency of sediment collection and the accuracy of sediment weighing.

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Silt fences can be used in many situations to trap sediment and estimate erosion rates. In the US study, they are cleaned out after each rainfall event. Like any technique to measure sediment that requires storage, care should be taken that they do not overfill and fail.

For more information on the Upper Platte Watershed Study or silt fencing, contact Charles Troendle at ctroendle@fs.fed.us.