Unstable Slopes Find Protection through
State Law
Washington's foresters have taken important steps to include the protection of unstable slopes in their timber harvest designs. Certain forest practices have been found to accelerate the rate of slope failure by removing vegetation needed to absorb rainfall and hold the soil in place, increasing the chance for a landslide to occur. While landslides will always be a natural part of the ecosystem, the Forests & Fish Law has put into place guidelines that govern how steep slopes are managed to reduce the likelihood of these events.
Landslides Can Damage Salmon Habitat
The fallen trees, vegetation, and soil from a landslide can clog surface waterways, creating natural dams that cause flooding in upstream sites. Eventually, these dams break, and the pent-up water and debris moves downstream with damaging velocity, temporarily destroying streamside vegetation and scouring the bottom of stream channels. Small gravel particles which are essential for salmon spawning can be washed out.The Forests & Fish Law restricts forest practice permits in order to prevent the increase of landslide-related sediment into streams.
Landslide Hazard Zonation Project Identifies
Unstable Slopes
To identify and map the potential unstable slopes throughout Washington State, the Landslide Hazard Zonation (LHZ) Project was created in 2002. The LHZ project was developed to assist the Department of Natural Resources (DNR) with screening Forest Practices Applications for risks associated with unstable slopes, as required by the Forests & Fish Law. The mapping process uses a controlled methodology which creates and inventories landslides and the type of land on which they have occurred. The group then looks at these features to identify the possible landslide areas. Knowledge gained by the LHZ project will help private foresters plan timber harvests that keep fish habitat out of harm's way.
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