Plastic Netting Used For Foothills Erosion Control Not Biodegradable

Hikers and bikers in the Boise Foothills may find tattered pieces of plastic netting years after the slopes of Hulls Gulch and Crane Creek have healed from the effects of the Eighth Street Fire.

More than 15 miles of plastic netting used to contain straw have been placed on slopes in the Boise Foothills to prevent erosion.

Officials of the Boise Interagency Logistics Center, which is coordinating the Foothills rehabilitation, initially said the plastic in the “wattles” was biodegradable.

“No, not the netting,” Rudy Dyke of R.H. Dyke Inc., which manufactures the wattles, said Friday. “You can’t make that stuff biodegradable.”

The netting may be unsightly for years to come, but it is unlikely to cause other problems.

The wattles are a relatively new technology. They have never been used in Idaho - part of the reason for the misunderstanding about its makeup, said John Thornton, a Boise National Forest hydrologist working on the rehabilitation project.

The rush to begin rehabilitation also kept the agencies from going through an exhaustive contracting process, he said.

The wattles are made in a device patented by Dyke, but copied by others. They replace straw bales, which often come apart, allowing erosion.

Quadel Industries of Coos Bay, Ore., which supplies the plastic netting to Dyke, said the tubular-shaped mesh netting is photo-degradable, meaning it breaks down in sunlight. That takes from five to seven years.

Quadel makes plastic netting that breaks down faster, but not the black-dyed mesh used in the Foothills.

“We add an ultraviolet inhibitor,” said Mary Ring, a Quadel saleswoman. “If we didn’t, it would break down in six months.”

But even then, it breaks down only under ultraviolet light.

“If it’s buried, it would certainly inhibit the process,” she said.

If large pieces of netting remain five to 10 years from now, Thornton said the agencies will send crews up to collect it, just as they plan to do with check dams and other short-term erosion prevention devices.

The wattles stabilize the slope by capturing soil carried downslope by rain and runoff. They also disperse the water flow so gullies do not form.