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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

 

straw wattle installation

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.