November 11, 2019

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Quantifying Snowmelt Recharge into Hillslope Soils and Rocks, and Solute Export to Rivers

Time- and depth-resolved hillslope subsurface measurements of flow and chemistry constrain exports to rivers.

Subsurface flow and transport. (a) Seasonal variation in subsurface flow. (b) Flow rates along soil, weathering zone, and bedrock. (c) Seasonality of subsurface flow and specific conductance (SC) of discharging water. (d) Concentration–discharge relation for SC.

[Reprinted under a Creative Commons Attribution 4.0 International License (CC BY 4.0) from Tokunaga, T.K., et al. “Depth- and Time-Resolved Distributions of Snowmelt-Driven Hillslope Subsurface Flow and Transport and Their Contributions to Surface Waters.” Water Resources Research 55, 9474-9499 (2019).]

The Science

Quantifying connections between snowmelt infiltration and seasonal variations in solute export to surface waters is frequently confounded by a lack of critical measurements.  This study introduces a novel approach whereby distributions of fluid flow paths are highly resolved through the use of critical subsurface measurements to reveal their strong temporal sensitivity to snowpack accumulation and melt timing.

The Impact

This study presents a novel methodological approach to quantify how hillslope subsurface flow and chemical transport contribute to stream flow and water quality.


Although most of the water entering watersheds permeates through soil and underlying bedrock before entering rivers, subsurface flow paths and their influence on river water chemistry are poorly understood. This study presents a new framework for quantifying depth- and time-dependent subsurface flow and solute transport along an intensively studied hillslope that utilizes in-situ hydrologic and geochemical measurements to constrain predictions. Results quantify the importance of abrupt groundwater excursions accompanying snowmelt for mobilizing dissolved chemicals in soil and weathered bedrock, with the latter responsible for the greatest contribution to solute export. The new concept of subsurface concentration-discharge relations was developed through this work that provides information needed to mechanistically explain solute concentrations and flow measured in rivers. With information on topography, meteorology, and subsurface hydraulic properties, this framework is broadly transferrable to other hillslope and watershed settings.

Principal Investigator

Susan Hubbard
Lawrence Berkeley National Laboratory

Program Manager

Jennifer Arrigo
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science


This work was conducted as part of the Watershed Function Scientific Focus Area at Lawrence Berkeley National Laboratory. It was supported by the Office of Biological and Environmental Research’s (BER) Environmental System Science (ESS) program (formerly Subsurface Biogeochemical Research) in the U. S. Department of Energy’s (DOE) Office of Science under DE‐AC02‐05CH11231.


Tokunaga, T.K., et al. "Depth- and Time-Resolved Distributions of Snowmelt-Driven Hillslope Subsurface Flow and Transport and Their Contributions to Surface Waters." Water Resources Research 55 (11), 9474-9499  (2019).