Sierra Science Lecture Series to focus on connection between groundwater and surface-water |

Sierra Science Lecture Series to focus on connection between groundwater and surface-water

Submitted by Diane Wright

Dr. Gus Tolley will present the next Sierra Science lecture, “From Mountains to Valleys: The Connection between Groundwater and Surface-Water” from 6:30 to 7:30 p.m. on March 10 in the Multipurpose Center, building N12-103, at the Nevada County Campus of Sierra College. Those who arrive early are invited to enjoy a meet-and-greet and refreshments at 6 p.m.

While surface-water flow is relatively easy to understand since it can be physically observed, groundwater flow is much more obscure since it is practically invisible. Despite its mysterious nature, groundwater accounts for about 40 to 60% of our water supply. In California, groundwater aquifers can store more than 15 times the volume of all surface-water reservoirs in the state combined, making them a valuable asset during prolonged droughts. This presentation will demystify groundwater and explain how it is intimately connected to surface-water. Results from research conducted in mountainous watersheds in New Mexico and Colorado, and an alluvial groundwater basin in Northern California, are used to illustrate processes such as recharge, flow, discharge, and stream flow depletion.

Tolley received a bachelor of science degree in geology from the University of California, Santa Barbara, a master’s in hydrology from New Mexico Institute of Mining and Technology and a Ph.D. in hydrology from U.C. Davis. His doctoral research focused on groundwater-surface-water interactions in agricultural groundwater basins with groundwater dependent ecosystems. He has experience with development, sensitivity analysis, calibration, and uncertainty analysis of integrated hydrologic models. He was one of the lead developers of the Scott Valley Integrated Hydrologic Model (SVIHM), which is currently being used to formulate the groundwater sustainability plan for the basin. He recently returned to Daniel B. Stephens & Associates where he is working out of the Grass Valley Geo-Logic Associates office.

The Nevada County Campus is located at 250 Sierra College Drive in Grass Valley. Parking is $3. Permits can be purchased at the kiosk machine at the main entrance to the campus. For more information, email series coordinator Jason Giuliani at

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