Advanced Simulation Capabilities to Explore Pre-and-Post Fire Surface water-Groundwater Interactions after the 2017 California Wine-Country Fires

In October 2017, an unprecedented set of fires devastated many forested and urban areas within Sonoma, Mendocino and Napa counties, impacting the Russian River Watershed. The Pocket, Tubbs, Nuns, and Redwood Valley burn areas provide a significant source of fine particulate ash-leachate runoff flowing to the Russian River, Lake Mendocino, and nearby tributaries during subsequent storms, as well as infiltration into local groundwater basins that support groundwater discharge to the Russian River during the dry season. Major water quality changes that may result from burned areas of the watershed include increased loading of sediments, nutrients, and dissolved organic carbon (DOC) which are hypothesized to potentially impact filtration efficacy of Riverbank Filtration Systems (RBF). Changing water quality dynamics, such as availability of labile DOC, could have consequences for important microbial processes that provide filtration benefits. Our present work assesses three main goals: 1) determine how the recent fires have impacted the hydrological, and chemical conditions of Russian River water quality, 2) evaluate how post-fire storm events will impact the hydrological and chemical connectivity across the Watershed including the tributaries, main stem, hyporheic zone, and groundwater, 3) continue to evaluate potential effects of ash-based DOC on infiltration and filtration efficacy. Our work will present pre-and-post fire water quality results from the Sonoma County Water Quality Monitoring Program and will present a statistical analysis of storm-based discharge-concentration relationships across the watershed network. Additionally, we will present initial results from a series of conceptual numerical modeling experiments using the MIN3P flow and reactive transport code to assess how changes in DOC could impact the abundance and distribution of microbial functional groups and pathogen transport.