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Roads-Trigger Debris Flows
Step Wise Guide
· Which road segments have the greatest potential to trigger debris flows that scour headwater channels?
Debris flows are one of the most destructive types of mass wasting, but they can also be an important element of a productive and diverse ecosystem. Roads that trigger landslides can also trigger a debris flow that moves rapidly down steep headwater streams for hundreds to thousands of meters, impacting structures or aquatic habitats along the way, and including at the point of deposition. Debris flows that move down headwater streams may also impact roads at the road-stream crossing. NetMap contains a prediction for debris flows, and roads that cross channels are classified by debris flow potential.
Refer to the "Warning" button in the tool interface. Follow up any remote sensing work, including using NetMap, with field work to verify environmental conditions and landslide and debris flow risk. There is never zero risk, there is only degrees of risk, which often is best considered on a relative basis.
Step 1:Go to NetMap Eorsion Modue > Channelized Mass Wasting > Debris Flows. If you have not already imported the predictions into your NetMap dataset, do so know (e.g., use the "Import and Route" button). From the drop down list, select "Debris Flow Susceptibility - Reaches" to display the map of debris flow risk. If you are only interested in viewing debris flow impact potential in larger, fish bearing streams, select "Debris Flow Junctions".
Step 2: Go to NetMap Road Modue > Road Stream Crossings. This tool allows one to identify the intersections between road crossings and high debris flow potential. From the drop down list in the tool, select debris flow susceptibility - reaches. It would also be informative to examine the road instability predictions to identify areas within small headwater basins (that are predicted to have high road debris flow risk) to help understand if roads are at risk of triggering landslides, that then could trigger debris flows.