Leveraging post-fire soil loss: Can we use fire-derived sediment to fill incised channels and restore degraded meadows in the southern Sierra Nevada?

Practices such as over-grazing have caused soil compaction and stream incision in many Sierra Nevada meadows, rendering them unable to provide the services of a functioning riparian meadow, which includes groundwater and sediment storage, flood attenuation, carbon sequestration and refuge for aquatic organisms. Due to low sediment transport rates in the southern Sierra Nevada, current restoration practices often rely on heavy machinery to manipulate and fill incised channels, limiting the scale of restoration. Within the same mountain range, sediment loads from high severity wildfires pose significant threat to ecosystems and infrastructure. To increase the rate of meadow restoration to address widespread degradation, our study pairs wildfire with beaver dam analogues (BDAs) and post-assisted log structures (PALS) to capture post-fire sediment loads in incised meadow channels. Our goal is to cause rapid channel aggradation that leads to reconnecting channels with their meadow floodplains. To test the potential of post-fire meadow restoration in the southern Sierra, we selected three study meadows: two with catchments severely burned in the 2020 Creek Fire and one that was unburned. We will install BDAs and PALS in one unburned (Ahart Meadow) and one burned (Lower Grouse Meadow) meadow in summer 2022. McCreary Meadow will serve as a burned reference meadow. During the summer and fall of 2021, we collected baseline hydrologic, ecological, and geomorphic data, as well as LiDAR and thermal imagery using unmanned aerial vehicles (UAVs). Using a real-time kinematic position (RTK) GPS system and a total station, we also completed topographic surveys of incised channels at each meadow. We combined the survey data with LiDAR-derived DEMs to generate DEMs that include bathymetric data. We explored the results of several potential restoration designs on channel complexity by manipulating the DEMs and using ProcessSpace, a publicly-available analysis toolkit that was developed to assess meadow degradation and restoration designs and written in the R programming language. We will use these potential designs to inform the planned meadow restoration.