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Contour Straw Wattle Fact Sheet
What are Contour Straw Wattles?
Straw Wattles, also known as straw worms, bio-logs, straw noodles, or straw
tubes are man made cylinders of compressed, weed free straw (wheat or rice), 8
to 12 inches in diameter and 20 to 25 feet long. They are encased in jute,
nylon, or other photo degradable materials, and have an average weight of 35
pounds. They are installed in a shallow trench forming a continuous barrier
along the contour (across the slope) to intercept water running down a slope.
When are Contour Straw Wattles Used?
Straw Wattles are used on burned slopes that have less than 30% of the
original ground cover remaining and are at risk for increased erosion. They
can be installed on slopes up to 70 percent, however their effect diminishes
greatly on slopes steeper than 50 percent. Soils can be shallow, but not less
than about 8 inches. Straw Wattles increase infiltration, add roughness,
reduce erosion, and help retain eroded soil on the slope. Straw Wattles should
be effective for a period of one to two years, providing short term protection
on slopes where permanent vegetation will be established to provide long term
erosion control. Contour Straw Wattles accomplish the same treatment as Log
Terraces, but require less skilled labor to install and can be placed on the
slope more effectively. Straw wattles should not be placed across drainage
swales and channels with more than 2 acres of contributing drainage area
because they are not sturdy enough to resist the forces of concentrated flows.
What Materials are Needed?
- 9 -12 inch diameter tubes, 10-30 feet long
- 5 - 1x2 or 2x2 wooden stakes, 18 - 24 inches long per wattle
- Hand tools -shovels, polaskis, & stake hammer
- Small machines may be used for plowing trenches on 30% or flatter slopes
How are Contour Straw Wattles Installed?
- Layout a contour line on the slope with a hand level and wire flags.
- Dig a shallow depression (about 3 to 5 inches deep) and lay the wattleinto it.
- Drive a 1x2 or 2x2 wooden stake through the center of the wattle at least6 inches into the ground, stopping about two inches above the wattle.
- Put 5 stakes in each wattle, installing them end to end in the trench.
- Seat the wattle with foot tamped backfill on the upstream side such thatwater flowing down the slope will not run under it.
How Many Straw Wattles Are Required?
The horizontal spacing of straw wattles on the slope is determined with
consideration for normal rainfall intensity, slope steepness, soil
characteristics, and the extent of surface cover remaining after the fire.
Figures 1 depicts the placement straw wattles on the slope. Table 1A and 1B show
recommended spacings for treating burn areas within the June 2000 HI MEADOWS and
BOBCAT Fires in Colorado
FIGURE 1 - Typical Straw Wattle Installation
Tables 1A, 2A, 3A - Recommended Spacing for Contour Straw Wattles based on
Burn Severity - Hi Meadows Fire Area
Table 1A, Burn Severity Low Intensity
Land Slope
(percent) |
Spacing
(feet) |
# Wattles
(feet/acre) |
< 5 % |
250 |
180 |
5 - 10 % |
200 |
218 |
10 - 20 % |
120 |
363 |
20 - 50 % |
60 |
726 |
> 50 % |
40 |
1089 |
Table 2A, Burn Severity Moderate Intensity
Land Slope
(percent) |
Spacing
(feet) |
# Wattles
(feet/acre) |
< 5 % |
160 |
272 |
5 - 10 % |
120 |
363 |
10 - 20 % |
60 |
726 |
20 - 50 % |
30 |
1452 |
> 50 % |
20 |
2178 |
Table 3A, Burn Severity Severe Intensity
Land Slope
(percent) |
Spacing
(feet) |
# Wattles
(feet/acre) |
< 5 % |
130 |
335 |
5 - 10 % |
90 |
484 |
10 - 20 % |
40 |
1089 |
20 - 50 % |
20 |
2178 |
> 50 % |
20 |
2178 |
Tables 1B, 2B, 3B - Recommended Spacing for Contour Straw Wattles based on
Burn Severity - Bobcat Fire Area
Table 1B, Burn Severity Low Intensity
Land Slope
(percent) |
Spacing
(feet) |
Number of
Wattles/Acre |
< 5 % |
350 |
125 |
5 - 10 % |
300 |
145 |
10 - 20 % |
200 |
218 |
20 - 50 % |
100 |
436 |
> 50 % |
50 |
872 |
Table 2B, Burn Severity Moderate Intensity
Land Slope
(percent) |
Spacing
(feet) |
Number of
Wattles/Acre |
< 5 % |
200 |
218 |
5 - 10 % |
160 |
272 |
10 - 20 % |
100 |
436 |
20 - 50 % |
50 |
872 |
> 50 % |
20 |
2178 |
Table 3B, Burn Severity Severe Intensity
Land Slope
(percent) |
Spacing
(feet) |
Number of Wattles/Acre |
< 5 % |
150 |
290 |
5 - 10 % |
100 |
436 |
10 - 20 % |
50 |
872 |
20 - 50 % |
20 |
2178 |
> 50 % |
20 |
2178 |
NOTE: After a fire many trees are weakened from burning
around the base of the trunk. The trees can fall over or blow down
without warning. Shallow rooted trees can also fall. Therefore be
extremely alert when working around burned trees.
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