EGU21-8102, updated on 04 Mar 2021
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Controls on streamwater age in a saturation overland flow-dominated catchment

Dana Lapides1, David Dralle2, Daniella Rempe3, William Dietrich4, and W. Jesse Hahm5
Dana Lapides et al.
  • 1UW-Madison Aquatic Sciences Center/Wisconsin DNR, United States of America (
  • 2U.S. Forest Service, Pacific Southwest Research Station, United States of America
  • 3University of Texas, Austin, Jackson School of Geosciences, United States of America
  • 4University of California, Berkeley, Earth and Planetary Science, United States of America
  • 5Simon Fraser University, Department of Geography, Canada

Water age and flow pathways should be related; however, it is still generally unclear how integrated catchment runoff generation mechanisms result in streamflow age distributions at the outlet. Here, we combine field observations of runoff generation at the Dry Creek catchment with StorAge Selection (SAS) age models to explore the relationship between streamwater age and runoff pathways. Dry Creek is an intensively monitored catchment in the northern California Coast Ranges with a Mediterranean climate and thin subsurface critical zone. Due to limited storage capacity, runoff response is rapid (~1-2 hours), and total annual streamflow consists predominantly of saturation overland flow, based on field mapping of saturated extents and runoff thresholds. Even though SAS modeling reveals that streamflow is younger at higher wetness states, flow is still typically older than one day and thus older than event water. Because streamflow is mostly overland flow, this means that a significant portion of overland flow must derive from groundwater returning to the surface, consistent with field observations of exfiltrating head gradients, return flow through macropores, and extensive saturation days after storm events. We conclude that even in a landscape with widespread overland flow, runoff pathways may be longer than anticipated, with implications for contaminant delivery and biogeochemical reactions. Our findings have implications for the assumptions built into classic hydrograph separation inferences, namely, that overland flow is not all new water.

How to cite: Lapides, D., Dralle, D., Rempe, D., Dietrich, W., and Hahm, W. J.: Controls on streamwater age in a saturation overland flow-dominated catchment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8102,, 2021.

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