Teton Mountain Range

Technical Resources

Contour Sandbags Fact Sheet

What are Contour Sandbags?

Biodegradable bags are filled with on site soil and bedded in a shallow trench forming a continuous barrier along the contour (across the slope) to intercept water running down the slope.

When are Contour Sandbags Used?

Contour Sandbags 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 6 inches. Contour Sandbags increase infiltration, add roughness, reduce erosion, and help retain eroded soil on the slope. Contour Sandbags should be effective for a period up to one year, providing short term protection on slopes where permanent vegetation will be established to provide long term erosion control. Contour Sandbags accomplish the same treatment as Log Terraces, but require less skilled labor to install and can be placed on the slope more effectively. Sandbags should not be placed across drainage swales and channels with more than 1 acre of contributing drainage area because they are not sturdy enough to resist the forces of concentrated flows.

What Materials are Needed?

Sandbags
Hand tools -shovels, polaskis

How are Contour Sandbags Installed?

Installation of Contour Sand Bags is straight forward and is an easy practice for untrained laborers, landowners and volunteer groups to complete.

Layout a contour line on the slope with a hand level and wire flags.
Dig a shallow depression, about 2 to 3 inches deep along the flag line
Use the soil from the trench excavation to fill bags ½ to ¾ full.
Fold the top over and lay the filled bags end to end in the trench.
Seat the bags with foot tamped backfill on the upstream side such that water flowing down the slope will not run under them.

How Many Sandbags Are Required?

The horizontal spacing of Contour Sandbags 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 of sandbags 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 Contour Sandbag Installation

Tables 1A, 2A, 3A - Recommended Spacing for Contour Sandbags based on Burn Severity - Hi Meadows Fire Area

**Table 1A, Burn Severity Low Intensity**
Land Slope (percent)	Spacing (feet)	Quantity (bags/acre)
< 5 %	250	135
5 - 10 %	200	164
10 - 20 %	120	272
20 - 50 %	60	544
> 50 %	40	818

**Table 2A, Burn Severity Moderate Intensity**
Land Slope (percent)	Spacing (feet)	Quantity (bags/acre)
< 5 %	160	204
5 - 10 %	120	272
10 - 20 %	60	544
20 - 50 %	30	1088
> 50 %	20	1634

**Table 3A, Burn Severity Severe Intensity**
Land Slope (percent)	Spacing (feet)	Quantity (bags/acre)
< 5 %	130	250
5 - 10 %	90	364
10 - 20 %	40	818
20 - 50 %	20	1634
> 50 %	20	1634

Tables 1B, 2B, 3B - Recommended Spacing for Contour Sandbags based on Burn Severity - Bobcat Fire Area

**Table 3B, Burn Severity Low Intensity**
Land Slope (percent)	Spacing (feet)	Quantity (bags/acre)
< 5 %	350	94
5 - 10 %	300	108
10 - 20 %	200	164
20 - 50 %	100	328
> 50 %	50	656

**Table 3B, Burn Severity Moderate Intensity**
Land Slope (percent)	Spacing (feet)	Quantity (bags/acre)
< 5 %	200	164
5 - 10 %	160	204
10 - 20 %	100	328
20 - 50 %	50	656
> 50 %	20	1634

**Table 3C, Burn Severity Severe Intensity**
Land Slope (percent)	Spacing (feet)	Quantity (bags/acre)
< 5 %	150	218
5 - 10 %	100	328
10 - 20 %	50	656
20 - 50 %	20	1634
> 50 %	20	1634

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.