Skip

Channel Roughening Fact Sheet

What is Channel Roughening?

Channel Roughening is accomplished by constructing very low and frequently spaced "V" shaped weirs constructed from logs or rock across swales and drainage ways.

When is Channel Roughening Used?

Channel Roughening is used on small drainage ways in burned areas where the natural erosion protection from vegetation and woody debris has been lost. It is used where sufficient numbers of logs are available, or rock can be substituted for the logs. Channel Roughening increases infiltration, adds roughness, reduces erosion, and helps retain small amounts of sediment within the channel. Channel Roughening should be effective for a period of one to three years, providing short term protection in areas where permanent vegetation will eventually return to provide long term erosion control. Channel Roughening should not be used on channels with drainage areas greater than 50 acres. Straw wattles or similar light weight material should not be used for channel roughening where the area drained by the channel exceeds 1 acre. Channel roughening will have limited effectiveness for channels that were unstable and eroding prior to the wildfire event.

How is Channel Roughening Installed?

Using Logs.  6" to 12" diameter logs are cut to a length approximately equal to the channel width, up to about 30 feet. (longer logs are too hard to handle). Limbs are removed to the extent necessary for the log to lie flat on the ground. Beginning from each side of the channel, a shallow trench (about 3 to 5 inches deep) is dug at a 60 degree angle upstream towards the center of the channel, creating a "V" configuration as shown in Figure 1. A log is placed in each side of the trench with its butt end towards the side of the channel, and seated with tamped backfill such that water flowing down the channel will not run under it. Where the soil in the channel is deep enough, the logs should be braced with wooden stakes. 2" x 2" x 24" long wooden stakes spaced four feet apart should be driven on the downstream side of the logs, until the top of the stake is even with the top of the log. When complete, the upstream point of the "V" must be the lowest point along the constructed weir, the top of the weir should be no more than 6 to 9 inches above the channel at the center, and the weir must extend the full width of the channel on either side.

Using Rock Riprap. Graded angular rocks ranging in size from 4 inches to 16 inches can be substituted for logs. The trench is constructed in the same configuration as before, except that the trench must be at least 12 inches deep and twice as wide as the largest rock. The trench is filled with the rock such that the upstream point of the "V" is the lowest point along the constructed weir, the top of the weir should be no more than 6 to 9 inches above the channel at the center, and it must extend the full width of the channel on either side.

How Much Channel Roughening is Required?

The log or rock weirs used for channel roughening should be uniformly spaced along the channel beginning near the upper end of the drainage way. The maximum recommended spacing between "V" shaped weirs is shown below:

Channel Slope
(%)

"V" Weir Spacing
(feet)

< 2

200

2 - 5

100

5 - 10

50

10 - 20

25

>20

Not recommended

Log FIGURE 1 - Log "V" Weir for Channel Roughening

 

Rock FIGURE 2 - Rock "V" Weir for Channel Roughening