Analysis of post-fire sediment yield in a western Sierra Nevada watershed burned by the 2021 Caldor Fire

Watershed sediment yield commonly increases after wildfire and has the potential to affect downstream infrastructure and water resources. Direct measurements of post-fire sediment yield are needed to assess risk to water supply but such measurements are commonly lacking. We present field measurements of sediment yield for a 120-km2 watershed burned by the 2021 Caldor Fire in the western Sierra Nevada, California, over the first winter wet season following the fire. We collected data by repeat bathymetric mapping of a 260-ha reservoir, Jenkinson Lake, that drains the Sly Park Creek watershed, much of which experienced moderate to high soil burn severity in late summer 2021. Using swath interferometric sonar equipment to map the lake floor before and after the wet season, we analyze bathymetric surfaces to quantify sediment deposition that occurred between January and August 2022. These estimates of post-fire sediment yield are intended to be transferable to other, similar terrain in northern California, where direct field measurements are rare. We conclude that measurements of post-fire basin sediment export using reservoir depocenters have the benefit of integrating sediment-generating processes at a scale that offers practical value to water-resource managers.