Wildfires have a direct/immediate impact on physical and chemical processes in watersheds including acute loss of vegetation and soil organic matter, decreased soil cohesion, enhanced soil water repellency, ash layer deposition, decreased infiltration and increased runoff. These changes greatly impact the magnitude and timing of post-fire peak flows. Water quality is also impacted by fires often resulting in increases in nutrients and suspended sediment. The goal of this RAPID proposal is to collect immediate and essential field observations of hydro-geochemical behavior within pristine mountain reservoir systems following a catastrophic wildfire. The proposed work will address a significant gap in our knowledge of the coupling of hydrologic flux and water quality in sub-alpine, snow-dominated post-fire systems, especially with regards to trace metal behavior after a catastrophic wildfire.
The Rim Fire, which has burned 255,858 acres, is the third largest fire in California?s history and is one of the largest in the Sierra Nevada. Post-fire processes threaten water supplies to the city of San Francisco as well as 29 other wholesale buyers. Water supply from the Hetch Hetchy reservoir system (three lakes in total) is unfiltered and therefore especially vulnerable to increased turbidity and sediment loads as a consequence of the Rim Fire. Collected data will ultimately be used to develop models and predictive tools to quantify short and long-term impacts on water quantity, sediment flux and contaminant loads into Hetch Hetchy and other regional lakes which encompass a nearly singular input to the SF water supply system.
