Straw wattles (aka fiber rolls) are fiber filled mesh tubes used to interrupt and slow water descending a slope through sheet flow and/or minor rill/gully formations.
Straw wattles help slow, spread and sink water in addition to capturing sediment and other runoff.
Used extensively in transportation and construction as best management practice (BMP), straw wattles are useful tools for effective runoff and sediment control. Coupled with erosion control techniques like mulching, jute mats, soil pitting or fish scale straw mulch, wattles help keep runoff and sediment for moving further downslope on a site.
Cross section of proper wattle installation using five-stake method (for 25' wattles).
Our suggestion of overlapping wattle ends. You can also butt ends together, just monitor to ensure no water is channeling through the ends.
Resources abound covering various approaches towards wattle installation. Google "bmp straw wattle [YOUR STATE]" to begin exploring what's out there. But here are links to a few useful guides that have helped us in our training for using these:
Typical dimensions of wattles are 9" x 25'. Some styles are 12" in diameter and can be longer. The mesh tube or sock that holds the straw is usually sold with plastic netting, but we prefer jute, sisal or burlap nets due to their biodegradability.
Using a water level for finding level contour is essential to avoid concentrating water which could lead to more erosion.
Plastic or natural fiber mesh tubes of varying lengths filled with straw or fiber installed on contour for runoff and sediment control. When used as a diversion treatment to starve gully erosion, install at 1-2% grade away from the gully and spill at a spreading area or 2nd wattle section installed on contour Spacing of wattles or socks decreases as slopes increase in steepness.
Proper installation is crucial for wattles to work effectively, and when combined with mulch they improve moisture retention and reduce surface erosion which can lead to undercutting of the wattle.
Sloping eroded or bare soils, restoration project areas, recently disturbed construction sites, and revegetation work. Areas susceptible to runoff and sediment loss.
The site prior to any surveying or wattle installation. Note channeling and gully formation without treatment.
Marking slight off-contour line with a water level (bunyip) for straw wattle installation.
|Land Slope (%)||Spacing (ft)||# Wattles (ft/acre)|
Tamping down wattle into footer trench (5" is a good depth for 9" wattles, 7" of 12" wattles).
Without effective erosion controls, we don't really see how storms carry soil away. This sediment would be lost further downslope without this wattle.
When installed correctly, straw wattles perform well, but far too often, improper installation leads to premature failure. This is usually due to skimping on proper trenching and securing of the wattle, or not accounting for the volume of water impacting the wattle. At the Meadowview Training Day with the NCCC, finding the contour line for the wattle was easy using a water level (bunyip). We wanted to experiment with encouraging any overland flow to be shifted from the valley center towards the traditionally drier ridges. This was accomplished by adjusting our outer flags at a rate of 1/4" per 1', or 2% slope. Digging the 5" footer (for 9" wattles) was a challenge given the dry, compacted conditions of the site soil. We also only dug a 3-4" footer that we later agreed would be better served by extending it 1-2" deeper. The bottom of this footer also acts as a mini swale capturing and helping infiltrate water back into the soil. As for the stakes, knowing that our grounds were at the tail end of the dry season, we opted for #3 rebar. #4 (1/2") rebar would have been slightly easier to use due to the increased thickness. Another attempt at experimenting with securing the wattles was pre-bending a small "L" into one end so that it would crimp and pin the wattle better, alleviating the need for the orange rebar cap. But, given the thin #3 rebar we used and the awkward curved striking surface, we had horrible results, and advise to use 16-18" #4 rebar or 18" wooden stakes for future projects. Caltrans and other crews use a zig-zag wire tie method for securing the wattles in place. This is more effective, but also requires more hands to accomplish it and takes more time and materials, but does offer more peace and mind. For lower risk areas, the standard five-stake installation is sufficient if all other steps are followed correctly. Where installed appropriately, the straw wattles have worked wonderfully. Sediment accumulation on the upslope of the wattle is happening as well as seed recruitment and moisture retention. Gullying is reduced or eliminated downslope of the wattles in its entirety.
With effective native plant seeding, plants should be able to colonize the biodegradable wattle and reduce further erosion over time.
Gullying is all but eliminated in this section of the slope. They also benefited from a 1" compost layer.
In some areas, the sediment capture is quite impressive.
Where wattles are improperly installed, we see the same erosion and runoff conditions occurring that were present prior to the wattle installation. A couple of reasons for this failure are:
Poor installation of this wattle allowed water to bypass it and continue eroding soils and polluting our storm drains.
An example of improper leveling. Water concentrated in one area of the wattle until it overflowed it, undermining the soil downslope and carrying sediment to our streams, rivers and ocean.
When used appropriately and in the correct context, straw wattles (fiber rolls) are excellent and fast runoff and sediment control tools. They can look a bit ugly in a landscape, but when natural fiber meshes are used, they quickly return to the soil (3-5 years depending on rainfall and site conditions). Combined with seeding and inoculant for boosting soil biological diversity, plants benefit from the sediment and moisture capture that these wattles provide. Explore more straw wattles and fiber roll install photos on our Flickr album.
Learn the techniques we use on a daily basis to maximize your water budget.
Stay in touch with our Ecology Artisans team when new posts, courses and landscaping information is available!