Surface parameters and bedrock properties covary across a mountainous watershed: Insights from machine learning and geophysics

Abstract

Bedrock property quantification is critical for predicting the hydrological response of watersheds to climate disturbances. Estimating bedrock hydraulic properties over watershed scales is inherently difficult, particularly in fracture-dominated regions. Our analysis tests the covariability of above- and belowground features on a watershed scale, by linking borehole geophysical data, near-surface geophysics, and remote sensing data. We use machine learning to quantify the relationships between bedrock geophysical/hydrological properties and geomorphological/vegetation indices and show that machine learning relationships can estimate most of their covariability. Although we can predict the electrical resistivity variation across the watershed, regions of lower variability in the input parameters are shown to provide better estimates, indicating a limitation of commonly applied geomorphological models. Our results emphasize that such an integrated approach can be used to derive detailed bedrock characteristics, allowing for identification of small-scale variations across an entire watershed that may be critical to assess the impact of disturbances on hydrological systems.

Variability of Snow and Rainfall Partitioning Into Evapotranspiration and Summer Runoff Across Nine Mountainous Catchments

“…The lithology of the main stem East River Watershed is dominated by Cretaceous Mancos shale bedrock with Oligocene quartz monzonite and granodiorite laccoliths comprising many of the higher elevation peaks. At Coal Creek, the underlying bedrock is mainly composed of Cretaceous and Eocene sandstones, mudstones, and quartz monzonite and granodiorite intrusive rocks (Gaskill et al., 1991; Uhlemann et al., 2022). The climate in the region is defined as continental subarctic with long, cold winters and short, cool summers (Dfc, according to Koeppen‐Geiger, Peel et al., 2007).…”

Variability of snow and rainfall partitioning into evapotranspiration and summer runoff across nine mountainous catchments

“…The lithology of the main stem East River Watershed is dominated by Cretaceous Mancos shale bedrock with Oligocene quartz monzonite and granodiorite laccoliths comprising many of the higher elevation peaks. At Coal Creek, the underlying bedrock is mainly composed of Cretaceous and Eocene sandstones, mudstones, and quartz monzonite and granodiorite intrusive rocks (Gaskill et al, 1991;Uhlemann et al, 2022).…”

Variations in Bedrock and Vegetation Cover Modulate Subsurface Water Flow Dynamics of a Mountainous Hillslope

“…Previous studies within the East River watershed (Hubbard et al., 2018), which is representative of many headwater catchments of the Rocky Mountains, have shown that watershed functioning is controlled by hillslope‐scale processes that are expressed in terms of their vegetation cover, and their geomorphological and subsurface characteristics (Wainwright et al., 2022). Large‐scale fracture zones have been identified that are expected to pose a strong control on the watersheds hydrological response (Miltenberger et al., 2021; Uhlemann et al., 2022). Following a system‐of‐systems approach and going to smaller granularity, here we focus on hillslope‐scale hydrological processes, with a particular emphasis on the differences induced by varying bedrock type and vegetation cover.…”

“…The shown size of the tree indicates their maximum canopy height. Borehole logs are shown on the right, showing fluid electrical conductivity (blue) and temperature (black) (b), nuclear magnetic resonance (NMR) derived hydraulic conductivity (K est ) (c), and NMR derived water content (d).Note that the K est was calibrated using pumping tests from nearby boreholes(Uhlemann et al, 2022).…”