Geophysical Investigations of Surface Water and Groundwater Exchanges at a Riverbank Filtration Facility

The Sonoma County Water Agency (Water Agency) operates one of the largest riverbank filtration facilities in the world along the Russian River in Sonoma County, California.  The Water Agency has been involved in a series of studies to better understand the surface water and groundwater flow characteristics as they relate to water production and water quality and to develop both insights and tools that can be used to develop optimized operational schedules.  Studies conducted by researchers from Lawrence Berkeley National Laboratory (LBNL) have focused on the collection of geophysical data, including spontaneous potential and electrical resistivity monitoring and the integration of that data with hydrological computer models to simulate surface water infiltration and groundwater flow characteristics. 

The findings of these studies suggest that riverbed permeability is a key control on surface water infiltration characteristics, which is particularly affected by seasonal clogging of the riverbed by fine particles associated with the seasonal operation of an inflatable dam located downstream of the study area.  These studies also suggest that riverbed and aquifer permeability both influence the development of an unsaturated zone below the riverbed.  Ongoing studies are focusing on utilizing a suite of investigation methods to better characterize temporal changes in streambed permeability and seepage as a function of river stage and inflatable dam operation, including seepage meters, sediment traps, cryogenic coring, ground penetrating radar, electrical resistance tomography, focused spontaneous potential surveys, riverbed topography, piezometers, and thermistors.  Initial findings from these studies will be presented.