Thursday August 29, 2024
USGS via Maven’s Notebook —
In a first-of-its-kind study, scientists compiled one year’s worth of soil and sediment erosion quantities occurring after large California wildfires between 1984 and 2021. Scientists found that postfire erosion has accelerated over time, particularly in northern California, likely reflecting both the increase in wildfire in the state and the frequency of wet water years. In addition, scientists found that 57% of postfire erosion by mass occurred upstream of reservoirs. This research helps planners understand the degree to which postfire erosion has impacted watersheds and can inform management actions to minimize the effects of runoff on clean water storage.
Using the Water Erosion Prediction Project model developed by the USDA Forest Service, in combination with field-based debris-flow volume measurements and modeled debris-flow volumes, scientists from the USGS and California Geological Survey evaluated postfire erosion throughout California for 196 large wildfires, which includes fires over 100 km2,~25,000 acres, in California between 1984 to 2021.
Researchers estimated the magnitude of erosion contributed by postfire debris flows and hillslope erosion in the first water year following wildfire. Results show that postfire debris flows can mobilize vastly more sediment than hillslope erosion processes. As climate change exacerbates hillside erosion, it has become more common and could create more of a downstream hazard for water resources. Examples of this include the filling of storage space in reservoirs and damaging infrastructure as ‘nuisance’ sediment that blocks roads and culverts.