Effects of structure and volcanic stratigraphy on groundwater and surface water flow: Hat Creek basin, California, USA

Abstract

Hydrogeologic systems in the southern Cascade Range in California (USA) develop in volcanic rocks where morphology, stratigraphy, extensional structures, and attendant basin geometry play a central role in groundwater flow paths, groundwater/surface-water interactions, and spring discharge locations. High-volume springs (greater than 3 m3/s) flow from basin-filling (<800 ka) volcanic rocks in the Hat Creek and Fall River tributaries and contribute approximately half of the average annual flow of the Pit River, the largest tributary to Shasta Lake. A hydrogeologic conceptual framework is constructed for the Hat Creek basin combining new geologic mapping, water-well lithologic logs, a database of active faults, LiDAR mapping of faults and volcanic landforms, streamflow measurements and airborne thermal infrared remote sensing of stream temperature. These data are used to integrate the geologic structure and the volcanic and volcaniclastic stratigraphy to create a three-dimensional interpretation of the hydrogeology in the basin. Two large streamflow gains from focused groundwater discharge near Big Spring and north of Sugarloaf Peak result from geologic barriers that restrict lateral groundwater flow and force water into Hat Creek. The inferred groundwater-flow barriers divide the aquifer system into at least three leaky compartments. The two downstream compartments lose streamflow in the upstream reaches (immediately downstream of the groundwater-flow barriers) and gain in downstream reaches with the greatest inflows immediately upstream of the barriers.

Shallow and local or deep and regional? Inferring source groundwater characteristics across mainstem riverbank discharge faces

“…There has been rapidly growing use of TIR imagery to efficiently locate groundwater discharge for the inference of subsurface flowpath characteristics (e.g., Marcelli et al, 2022). Groundwater discharge faces in this study were selected based on TIR surveys along a 26.5 km stretch of the mainstem of the Farmington River (Moore, Jackson, et al, 2023) via the process described by Briggs et al (2022).…”

“…Approximately half of streamflow across the continental United States is supplied by discharge from groundwater (Scanlon et al, 2023), often focused to discrete high flow springs and seeps that arise from permeable geologic features (Marcelli et al, 2022). The water quality of groundwater discharging along riverbanks is influenced by source flowpath characteristics that can vary widely in spatial scale and average depth from the land surface (Barclay et al, 2020, Figure 1).…”