Hillslope erosion and hydrologic response in two small watersheds in Yosemite National Park following the 2013 Rim Fire, CA
Abstract
The 2013 Rim Fire burned 1036 km2 in the Sierra Nevada, including 312 km2 within Yosemite National Park, and generated concern about post-fire effects in the Tuolumne River watershed. We evaluated hillslope erosion and water quality during the winter storm seasons of 2013-2015, in two small watersheds (3.0 and 3.6 km2) in Yosemite located within the rain-snow transition zone. Within a month of fire containment, we installed equipment to monitor streamflow, rainfall, turbidity, and total suspended solids during storms. On moderate and high severity burn areas (based on initial dNBR data), we established 21 plots (100-150 m2) to trap all sediment (≥ silt size) eroded from moderate to steep (11°-26°) slopes. Soil temperature sensors were installed at 14 plots to measure the presence of snow cover. Lastly, we conducted seven terrestrial lidar surveys to measure vegetation recovery and topographic change. In the three study years, precipitation intensity events were generally low and lacked more typical higher intensity storms (I-30 in mm: Min = 1.5; Max = 34.0; Median = 6.1). Preliminary results suggest that despite revegetation, a lack of intense storms during the 1st and 2nd years following the fire produced less suspended solids in streams than the 3rd year. Hillslope erosion in plots was controlled by burn severity, with moderate severity plots having significantly more transport of coarse material (>2mm, mainly litterfall) and high severity plots having significantly more fine material (<2mm). Notably, sediment yields contrast with results from adjacent USFS lands with similar burn severity and slope but with differences in glaciation, burn history, and geologic parent material; a topic of current analyses. The dominant surface processes revealed by lidar were sheetflow and minor rill formation in the plots, and rilling and gully erosion on slopes near the plots. Analyses of sediment produced from snow storms, or those with pre-existing snow cover, indicate sediment export is dampened by these conditions, and allow for partitioning of within-channel and hillslope sediment sources. Overall, initial analyses suggest that precipitation and burn intensity were the two dominant factors that determined hillslope erosion and in-stream water quality following the Rim Fire.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.H42A..02K
- Keywords:
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- 1803 Anthropogenic effects;
- HYDROLOGYDE: 1804 Catchment;
- HYDROLOGYDE: 1860 Streamflow;
- HYDROLOGYDE: 1871 Surface water quality;
- HYDROLOGY