CONTRIBUTIONS OF SHALLOW SUBSURFACE CHARACTERIZATION TO HYDROLOGY INVESTIGATIONS

Keith Turner contributed in many ways to furthering scientific endeavors from early in his career, both in his student advisory role and in his research. Early efforts to characterize the shallow subsurface and produce user-friendly data and information in state-of-the-art formats, employing digital techniques and GIS, informed hydrologic studies from arid land groundwater modeling and groundwater travel time estimates to infiltration and regional recharge estimates. Shallow geology (<10 meters) and its associated physical properties provide a regional characterization of below the root zone that can be used to inform numerical hydrological modeling important to evaluating regional water availability, drought, streamflow, forest health, and wildfire risk. We will present examples of how research to which Keith contributed enabled interdisciplinary contributions in the field of hydrology. Specifically, we will show early work in 2000 with Keith’s PhD students employing 3-D geologic products for the Death Valley regional flow system to estimate recharge and groundwater travel times for Yucca Mountain and the Death Valley region from estimates of the effective travel-path porosity and the thickness of the unsaturated zone. In the mid 2000s the geologic mapping was used to develop a regional water balance model that uniquely used shallow bedrock and estimates of bedrock permeability to calculate recharge, discriminating between recharge and runoff processes to identify where on the landscape these processes occur throughout the desert southwest. Most recently, in 2021 and 2022, Keith collaborated on evaluating and validating global estimates of bedrock permeability to inform water balance modeling for continental-scale estimates of recharge and runoff.