Description
Brush mattresses are living branches placed close together on the slope surface to form a mattress (Morgan & Rickson, 1995) (Figure 1). The mattress is usually composed of 1-2 layers of branches laid in a crisscross pattern to homogeneously form a living ground cover. The mattress immediately protects the slope surface from runoff and soil erosion until the branches can sprout and native vegetation becomes established. As consequence the entire bank face is covered by native vegetation, encouraging natural infiltration and immediately acting as a sediment trap.
Advantages:
-
Immediate protection after installation;
-
Development of dense root system and thicket;
-
Flexibility in preparation and protection;
-
Material easily available as structures also serve as nursery for new plant material.
Disadvantages:
-
High demand on material;
-
Intensive labour;
-
Request of occasional thinning of thicket;
-
Not for steep slopes (Allen & Fischenic, 2001)
(Georgi & Stathakopoulos, 2006)
Design methods
(from Georgi & Stathakopoulos, 2006)
Living branches are placed along the bank face with the basal ends located toward the bottom of the slope. They are grouped in 15-20 or and 25-30 living branches each with length 60 cm and diameter 6-40 mm. The sprout buds of branches are bedded in the same direction and they tied up in fascines with 15-30 cm length in length fascines direction with touching between them. The mattress structure can be wide from few meters up to the entire width of the slope and it should be placed where the flood duration do not exceed plant tolerance (Allen & Fischenic, 2001), since these live branches can not tolerate permanent floodings. The mattress is fixed by using wedge-like dead stakes 1 m (or less) square spacing into the plant material (Figure 2). Biodegradable twine is used to link the dead stakes and secure the mattress (ernstseed.com). Multiple rows of brush mattresses can be used in slope direction depending on the stability conditions of the slope and its length (Allen & Fischenic, 2001). A thin layer of loose soil can be spread on the entire area to encourage rooting.
Period of installation: during plant dormant season.
Materials: Willow/Eleagnus/Platanus live branches; biodegradable twine; wedge-like dead stakes.
Operation and maintenance (based on Sotir & Fischenich, 2001 and Allen & Fischenich, 2001)
The stream and corresponding parameters like velocity, flood frequency, flood stage, timing, and future planned use governs the operation and maintenance program. As with any live plant, health, growth and form need to be evaluated periodically to ensure its continued function. Repair of the system may be required until the vegetation becomes well-established. Successful plants will grow vigorously and spread their roots into the surrounding substrate. If animal or human damage is evident, preventative measures, such as exclosures, may be required. Such exclosures, especially for woody plants, may only need to be used until the vegetation is well-established. Inspections are needed after high water events during the first year and once a year thereafter.
Figure 3. Profile view of bruch mattress with rock toe; note relationship to water level at basal flow and that live brush is not permanently flooded (Allen & Fischenich, 2001)
Functional suitability criteria
Type of movement |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Fall | 0 | Mostly applicable on slopes where shallow slides of flows can occur due to erosion processes. |
| Topple | 0 | |
| Slide | 7 | |
| Spread | 3 | |
| Flow | 6 | |
Material type |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Earth | 9 | Applicable irrespective for earth or debris slopes. Not suitable for rock slopes. |
| Debris | 8 | |
| Rock | 1 | |
Depth of movement |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Surficial (< 0.5 m) | 10 | This measure is only suitable for protecting surficial layers. If a good thicket is established, dense roots can also reach greater depths (shallow layers protection) |
| Shallow (0.5 to 3 m) | 6 | |
| Medium (3 to 8 m) | 0 | |
| Deep (8 to 15 m) | 0 | |
| Very deep (> 15 m) | 0 | |
Rate of movement |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Moderate to fast | 2 | Adequate for contrasting small volumes of slow or very slow-moving soil. Less suitable for contrasting higher volumes of fast moving soil. |
| Slow | 6 | |
| Very slow | 7 | |
| Extremely slow | 9 | |
Ground water conditions |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Artesian | 9 | Applicable irrespective of groundwater conditions. Indirect effects on groundwater levels due to root-water uptake from plants during evapotranspiration. |
| High | 9 | |
| Low | 7 | |
| Absent | 5 | |
Surface water |
||
| Descriptor | Rating | Notes |
|---|---|---|
| Rain | 8 | Typically used for reducing the rainsplash erosion, it can be suitable for contrasting the back erosion along a streambank. This technique is useful and effective when placed in riverbanks. |
| Snowmelt | 8 | |
| Localized | 6 | |
| Stream | 9 | |
| Torrent | 5 | |
| River | 8 | |
Reliability and feasibility criteria
| Criteria | Rating | Notes |
|---|---|---|
| Reliability | 8 | A well implemented measure can be reliable permanently. |
| Feasibility and Manageability | 8 | It requires intensive labour for the construction and occasional thinning of the thicket. |
Urgency and consequence suitability
| Criteria | Rating | Notes |
|---|---|---|
| Timeliness of implementation | 8 | Quick implementation with intensive labour demand. When realized it is immediately effective, even before vegetation establishment. |
| Environmental suitability | 10 | It involves only live or woody materials (indigenous plants are preferred) or, where no available, material from nursery. |
| Economic suitability (cost) | 8 | The cost mostly depends on the size of the slope to be covered. If the material is available on site, the cost could be very low. |
References
-
Allen H. H., Fischenich C. (2001). “Brush Mattresses for Streambank Erosion Control”. ERDC TN-EMRRP-SR-32, http://el.erdc.usace.army.mil/emrrp/pdf/sr23.pdf.
-
Ernst Seeds Bioengineering Materials. https://www.ernstseed.com/products/bioengineering-materials/
-
Georgi, J., & Stathakopoulos, I. (2006). Bioengineering techniques for soil erosion protection and slope stabilization.
-
Morgan R.P.C., Rickson R.J. (1995). “Slope Stabilization and Erosion Control: A Bioengineering Approach”. E & F Spon, London, England
-
Sotir R. B., Fischenich C. (2001). “Live and Inert Fascine Streambank Erosion Control”, ERDC TN-EMRRP-SR-31, http://el.erdc.usace.army.mil/emrrp/pdf/sr31.pdf
-
USDA NRCS Engineering Field Handbook, Part 650, Chapter 16, Streambank and Shoreline Protection. December 1996