Contour wattling is a soil erosion control method that involves placing bundles of branches (wattles or fascines) in shallow trenches along the contour of a slope or streambank to break long slopes into shorter ones, thereby reducing surface erosion.
Here's a more detailed breakdown:
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Purpose: The primary goal of contour wattling is to control surface erosion. By shortening the slope length, it reduces the distance water can flow and gather momentum, thus minimizing the erosive force.
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Materials: The "wattles" or "fascines" are bundles of branches, typically secured tightly together. The specific types of branches used can vary depending on local availability and the project's requirements.
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Installation:
- Shallow trenches are dug along the contour of the slope. The trenches are typically excavated by hand.
- The trenches are sized to accommodate about half the diameter of the wattles.
- The wattles are placed snugly into the trenches.
- The wattles are often secured to the ground using stakes to ensure they remain in place.
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How it Works:
- Slowing Runoff: The wattles act as a physical barrier, slowing the flow of water down the slope.
- Trapping Sediment: As water slows, sediment is deposited behind the wattles, further reducing erosion and gradually building up terraces.
- Promoting Vegetation: The wattles create a favorable microclimate for plant growth. The trapped sediment provides a seedbed, and the wattles themselves can provide some protection from the elements. The eventual vegetation helps stabilize the soil long-term.
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Applications: Contour wattling is typically used for:
- Streambank stabilization: Preventing erosion along riverbanks.
- Slope stabilization: Preventing erosion on hillsides or embankments.
- Construction sites: Minimizing soil loss during construction activities.
- Restoration projects: Helping to re-establish vegetation in degraded areas.
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Advantages:
- Environmentally friendly, using natural materials.
- Relatively low-cost compared to some other erosion control methods.
- Effective in reducing surface erosion.
- Promotes vegetation establishment.
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Disadvantages:
- Labor-intensive to install.
- May require regular maintenance.
- Not suitable for areas with very steep slopes or high water flows.
