Description
Live stakes or live poles are live, woody vegetation cuttings inserted directly into the soil. This technique can be a primary solution for contrasting erosion or it can be combined with other techniques including live fascines, brush mattresses etc. The main goals of this live stakes planting are to protect from surface erosion and to give a reinforcement to the soil. However, the effectiveness of the action depends on the depth at which cuttings can be placed and the depth to which the roots are able to penetrate. The growth rate of roots is related to the volume of the cuttings, and some guides on how to choose and prepare cuttings are provided by Gray & Leiser (1982) and Schiechtl (1980). Usually the type of woody vegetation suitable for this technique includes willow, dogwood, cottonwood and alder, even if an indigenous plant to that site is preferred. The cuttings are placed in rows across the slope with the double function of controlling shallow mass movements and retaining sediments along the slope face (Figure 1).
Advantages
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Plant roots reinforce the soil and reduce water availability through evapotranspiration;
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No need for benches excavation;
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Simple installation
Disadvantages
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Not immediately effective in controlling erosion (plants need to establish);
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Not suitable for steep slopes;
Design methods
(From NY State Department of Environmental Conservation)
The live stakes are cuttings of woody vegetation, without many leaf buds on the tips initiating their growth, of dimension tipically varying from from 2.5 to 5 cm in diameter and from 60 cm up to 1.8 m in length depending on site application. The live stakes are placed in rows perpendicularly to the slope face with a distance between two rows of 60-100 cm (Figure 2). A pilot hole is first made with a dibble, iron bar or similar tool to facilitate the stake insertion into the ground and then the live cutting is inserted manually into the pilot hole, by tamping the surrounding soil. The live stake should be well embedded into the soil for a good and quick root growth and its upper part should be sufficiently exposed above the slope surface for the leaves and buds growth.
Period of installation: materials harvested on site should be installed after short time (the same day they are cut, to prevent plant decaying), while materials grown into a nursery can be maintained in a moist conditions before installed.
Materials: willows, dogwood, cottonwood, alder, american sycamore, viburnum.
Functional suitability criteria
Type of movement |
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| Descriptor | Rating | Notes |
|---|---|---|
| Fall | 1 | Live stakes are used for both controlling flowing prone slopes and for reinforcing potential slide surfaces. |
| Topple | 1 | |
| Slide | 8 | |
| Spread | 7 | |
| Flow | 7 | |
Material type |
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| Descriptor | Rating | Notes |
|---|---|---|
| Earth | 10 | This measure can be applied on an earth slope or for contrasting debris erosion. Not suitable for rock slopes, because the stakes cannot be fixed properly, and vegetation cannot be established. |
| Debris | 8 | |
| Rock | 1 | |
Depth of movement |
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| Descriptor | Rating | Notes |
|---|---|---|
| Surficial (< 0.5 m) | 10 | Live stakes are mostly used for controlling erosion, but the roots can permeate deeper layers acting as a reinforce. Live stakes` are typically from 60 cm to 1.8 meters long. The species choice is very relevant. |
| Shallow (0.5 to 3 m) | 8 | |
| Medium (3 to 8 m) | 2 | |
| Deep (8 to 15 m) | 1 | |
| Very deep (> 15 m) | 0 | |
Rate of movement |
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| Descriptor | Rating | Notes |
|---|---|---|
| Moderate to fast | 4 | Adequate for contrasting small volumes of extremely slow or very slow-moving soil. Less suitable for contrasting higher volumes of fast moving soil. |
| Slow | 6 | |
| Very slow | 9 | |
| Extremely slow | 9 | |
Ground water conditions |
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| Descriptor | Rating | Notes |
|---|---|---|
| Artesian | 8 | Applicable irrespective of groundwater conditions. Indirect effects on groundwater levels due to root-water uptake from plants during evapotranspiration. The species choice is very relevant. |
| High | 9 | |
| Low | 6 | |
| Absent | 3 | |
Surface water |
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| Descriptor | Rating | Notes |
|---|---|---|
| Rain | 8 | Typically used for reducing the rainsplash erosion and runoff along slopes or stream/river banks. This technique is effective when placed in riverbanks. |
| Snowmelt | 8 | |
| Localized | 6 | |
| Stream | 7 | |
| Torrent | 4 | |
| River | 7 | |
Reliability and feasibility criteria
| Criteria | Rating | Notes |
|---|---|---|
| Reliability | 8 | A well implemented measure can be reliable permanently |
| Feasibility and Manageability | 10 | Highly feasible and easy to install. It does not require much maintenance. |
Urgency and consequence suitability
| Criteria | Rating | Notes |
|---|---|---|
| Timeliness of implementation | 8 | Not immediately effective because plants need to establish. However, it is a quick and simple measure to install. |
| Environmental suitability | 10 | It involves only live or woody materials (indigenous plants are preferred), suitable with the surrounding environment. |
| Economic suitability (cost) | 10 | The cost can be low if the material is provided directly on site and the labour costs are not high (no need for equipment) |
References
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Gray, D.H., Sotir, R., 1996. Biotechnical and Soil Bioengineering Slope Stabilization. A Practical Guide for Erosion Control. John Wiley & Sons, New York.
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Li, X., Zhang, L., & Zhang, Z. (2006). Soil bioengineering and the ecological restoration of riverbanks at the Airport Town, Shanghai, China. Ecological engineering, 26(3), 304-314.
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Schiechtl, H.M., 1980. Bioengineering for Land Reclamation and Conservation. University of Alberta Press, Edmonton, Canada
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USDA NRCS Engineering Field Handbook, Part 650, Chapter 16, Streambank and Shoreline Protection. December 1996