Erosion control helps to keep highways safe

The Debris Management Task Force has been working for more than a year to remove thousands of dead and dying trees left behind by the 2020 wildfires. These trees threaten the safety of our state highways, rural communities and homesites where wildfire survivors and families are trying to recover and rebuild. The burnt trees are an obvious visual reminder of the fires, but the soil beneath those trees has also been significantly altered.

Across the million-acre footprint of the fires, soils – once held together by vegetation and protected by ground cover – no longer have the ability to retain water and lack the root support to prevent erosion. The burnt grounds are now more susceptible to landslides, increased water runoff with flooding and debris flows, and the expansion of invasive plants and noxious weeds.

Almost immediately following the fire, the State of Oregon and federal partners formed the Erosion Threat Assessment and Reduction Team (ETART) to assess the potential for landslides and address the erosion threats in all of the fire areas. The ETART is an interagency team of experts tasked with collectively assessing the threats that exist in the burn areas: biologists, engineers, hydrologists, foresters, botanists, soil scientists, geologists, mapping experts, archeologists and support staff.

The ETART’s reports are massive – here is one just on water quality impacts and another on the Holiday Farm Fire – but they do an excellent job of explaining the types and levels of threats associated with the wildfires and the necessary steps to help mitigate those risks.

Working collaboratively with the ETART and via the Task Force’s Environmental Protection Plan, operations crews have built extensive erosion control tactics into both hazard tree removal work and private property ash and debris cleanup.

“Erosion control is a really important part of what we do because it not only protects the streams and the rivers and the tributaries that run along our highways, but it also helps keep our highways safe,” explained Joel Zeni Project Manager for Suulutaaq Inc, the prime contractor for hazard tree removal in the Beachie Creek/Lionshead, Riverside and Holiday Farm Fire areas.

While they are removing trees, crews use standard erosion control construction practices like laying down wattles (fiber filled mesh tubes) to prevent runoff. But in an operation with the complexity of removing over 70,000 trees along highways, some with extremely steep slopes, crews have also taken some more extreme measures. These measures sometimes include removing logs with helicopters so they don’t have to be dragged through the already disturbed soil. In some areas, crews are leaving and even strategically placing logs and woody debris to catch runoff and to serve as habitat to the natural areas.

As Zeni explains:

“Sometimes we leave the logs sideways, and that will allow for rocks or falling debris to be caught behind the log. As long as we and ODOT deem that log is safe to remain, we try to do so. We do that a lot on areas like Highway 224 where it is a scenic corridor. It’s a perfect way to leave material in the wildlife area and also protect the public.”

Other mitigation tactics include spreading wood chips created from the tree removal operations to cover bare soil, laying temporary log crossings to protect tributaries and spreading wood chips thicker in certain areas to form “tracks” to protect the soil from the heavy machinery as they work.

With hazard tree cutting operations almost complete, a few final steps of erosion control, like hydromulching and ditch cleanout, are underway statewide.

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Hydromulch – seeded with an organic, native mix and tackifier, which helps bind the seed and mulch to the soil surface – is applied to bare earth on slopes to further stabilize the soil.

Ditch cleanout helps ensure that debris that fell into roadside ditches during the fire, or subsequent cleanup, doesn’t create a back up and force water flows onto the roadways.