A sprinkling experiment to quantify celerity–velocity differences at the hillslope scale

Verseveld, Willem van; Barnard, H. R.; Graham, C. B.; McDonnell, Jeffrey J.; Brooks, J. Renée; Weiler, Markus

doi:10.5194/hess-21-5891-2017

Cited by 16 publications

(11 citation statements)

References 62 publications

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“…Andrews Experimental Forest in western Oregon, USA. WS10 is a small 10.2-ha (0.1-km 2 ) catchment (Figure 2) that has been the subject of extensive research on hillslope hydrology (e.g., Brooks et al, 2006;Brooks et al, 2010;Gabrielli et al, 2012;Harr et al, 1972;Harr, 1977;McDonnell et al, 2010;McGuire et al, 2007;Sollins et al, 1981;van Verseveld et al, 2009;Van Verseveld et al, 2017). WS10 was chosen because it has less-developed riparian areas at the lower end of the stream reach and more prevalent riparian areas in the upper reach as a result of multiple debris flows that removed near-stream soils and riparian vegetation (Graham et al, 2013), as well as unique, existing infrastructure.…”

Section: Field Sitementioning

confidence: 99%

“…Gabrielli et al (2012) reported two distinct layers in the bedrock competency on hillslope A: a highly fractured and weathered layer that was approximately 1‐m thick and a less‐weathered layer with discrete fractures and occasional deep fractures. Near the stream, the depth to unweathered bedrock ranges from 0.1 to 0.6 m and gradually increases to 3 to 8 m up hillslope (Van Verseveld et al, 2017). At the base of hillslope A, there is a 10‐m long flume to capture lateral subsurface flow discharging to the stream channel ( McGuire et al, 2007).…”

Section: Field Sitementioning

confidence: 99%

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Water Table Depth and Bedrock Permeability Control Magnitude and Timing of Transpiration‐Induced Diel Fluctuations in Groundwater

Harmon

Barnard

Singha

2020

Water Resources Research

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The subsurface processes that mediate the connection between evapotranspiration and groundwater within forested hillslopes are poorly defined. Here, we investigate the origin of diel signals in unsaturated soil water, groundwater, and stream stage on three forested hillslopes in the H.J. Andrews Experimental Forest in western Oregon, USA, during the summer of 2017, and assess how the diurnal signal in evapotranspiration (ET) is transferred through the hillslope and into these stores. There was no evidence of diel fluctuations in upslope groundwater wells, suggesting that tree water uptake in upslope areas does not directly contribute to the diel signal observed in near-stream groundwater and streamflow. The water table in upslope areas resided within largely consolidated bedrock, which was overlain by highly fractured unsaturated bedrock. These subsurface characteristics inhibited formation of diel signals in groundwater and impeded the transfer of diel signals in soil moisture to groundwater because (1) the bedrock where the water table resides limited root penetration and (2) the low unsaturated hydraulic conductivity of the highly fractured rock weakened the hydraulic connection between groundwater and soil/rock moisture. Transpiration-driven diel fluctuations in groundwater were limited to near-stream areas but were not ubiquitous in space and time. The depth to the groundwater table and the geologic structure at that depth likely dictated rooting depth and thus controlled where and when the transpiration-driven diel fluctuations were apparent in riparian groundwater. This study outlines the role of hillslope hydrogeology and its influence on the translation of evapotranspiration and soil moisture fluctuations to groundwater and stream fluctuations.Plain Language Summary In many groundwater-fed streams, tree water uptake can create daily fluctuations in streamflow. The lowest value in these fluctuations, occurring during the afternoon or early evening, typically correspond to the maximum tree water uptake, while the peaks correspond to minimum tree water uptake during the night. The presence of these fluctuations in streamflow suggests that trees and streams are closely connected; however, because of limited access to the subsurface it is difficult to determine how these fluctuations propagate through the hillslope and into the stream. We found that trees in upslope areas rely on soil water that is hydraulically disconnected from groundwater, and thus fluctuations from transpiration are not transferred to groundwater and the stream from upslope. The creation of daily fluctuations in groundwater was limited to near-stream areas. By identifying the physical processes that control the expression of these transpiration signals, we can improve our ability to determine the water reservoirs that trees rely on.

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Section: Field Sitementioning

confidence: 99%

Section: Field Sitementioning

confidence: 99%

Water Table Depth and Bedrock Permeability Control Magnitude and Timing of Transpiration‐Induced Diel Fluctuations in Groundwater

Harmon

Barnard

Singha

2020

Water Resources Research

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“…In contrast, the outer and lower pairs, which are farther from the tree trunk, could be sensitive to flow occurring downward (infiltration) and away from the tree stem (downslope) at these locations. A lateral component of unsaturated hillslope flow after rainfall has been previous observed in this watershed (Harr, 1977;van Verseveld et al, 2017). These interpretations will be addressed more in the discussion of the measured and modelled data (Section 6.3).…”

Section: Measured Sp Datamentioning

confidence: 64%

Transpiration‐ and precipitation‐induced subsurface water flow observed using the self‐potential method

Voytek

Barnard

Jougnot

et al. 2019

Hydrological Processes

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Movement of soil moisture associated with tree root‐water uptake is ecologically important but technically challenging to measure. Here, the self‐potential (SP) method, a passive electrical geophysical method, is used to characterize water flow in situ. Unlike tensiometers, which use a measurement of state (i.e., matric pressure) at two locations to infer fluid flow, the SP method directly measures signals generated by water movement. We collected SP measurements in a two‐dimensional array at the base of a Douglas‐fir tree (Pseudotsuga menziesii) in the H.J. Andrews Experimental Forest in western Oregon over 5 months to provide insight on the propagation of transpiration signals into the subsurface under variable soil moisture. During dry conditions, SP data appear to show downward unsaturated flow, whereas nearby tensiometer data appear to suggest upward flow during this period. After the trees enter dormancy in the fall, precipitation‐induced vertical flow dominates in the SP and tensiometer data. Diel variations in SP data correspond to periods of tree transpiration. Changes in volumetric water content occurring from soil moisture movement during transpiration are not large enough to appear in volumetric water content data. Fluid flow and electrokinetic coupling (i.e., electrical potential distribution) were simulated using COMSOL Multiphysics to explore the system controls on field data. The coupled model, which included a root‐water uptake term, reproduced components of both the long‐term and diel variations in SP measurements, thus indicating that SP has potential to provide spatially and temporally dense measurements of transpiration‐induced changes in water flow. This manuscript presents the first SP measurements focusing on the movement of soil moisture in response to tree transpiration.

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“…Second, the presence of a non-linearity due to the water table intersection with the land surface creates a responsive zone (the variable saturated areas) for flows, while the transport response is still predominantly controlled by the transit times of the particles traveling in the groundwater compartment. Third, it is the total amount of groundwater stored that effectively conditions the particle velocity by modifying the Darcy velocity with the ratio 𝐴𝐴 𝜙𝜙 𝑑𝑑 𝜙𝜙 𝑡𝑡𝑡𝑡𝑡𝑡 (van Verseveld et al, 2017). In this model, these three effects contribute to dissociate celerity from velocity (McDonnell, 2017;McDonnell & Beven, 2014).…”

Section: A 2d Stratified Advective Transportmentioning

confidence: 99%

Dynamic Contributions of Stratified Groundwater to Streams Controls Seasonal Variations of Streamwater Transit Times

Marçais

Derry

Guillaumot

et al. 2022

Water Resources Research

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Streamwater transit time distributions display a variable proportion of old waters (≥1 year). We hypothesize that the corresponding long transit times result from groundwater contributions to the stream and that seasonal streamwater transit time variations result from (a) the variable contributions of different flowpaths (overland flow, seepage flow and baseflow) and (b) the stratification of groundwater residence times. We develop a parsimonious model to capture the groundwater contribution to the stream discharge and its effect on transient transit times. Infiltration is partitioned according to the aquifer saturation between Boussinesq groundwater flow and overland flow. Time‐variable transit time distributions are obtained with a new 2D particle tracking algorithm. Hydraulic conductivity, total and drainable porosities are calibrated by using discharge and CFC tracer data on a crystalline catchment located in Brittany (France). The calibrated models succeed in reproducing CFCs concentrations and discharge dynamics. The groundwater flow contribution to the stream is controlled by the aquifer hydraulic conductivity, while its age is controlled by the drainable and total porosities. Old groundwater (≥1 year) is the source for approximately 75% of the streamflow with strong seasonal variations (between 40% and 95%). Mean transit times are approximately 13 years, varying between 6 and 20 years, proportional to the groundwater contribution. These seasonal variations are driven by the groundwater versus overland flow partitioning. The stratification of groundwater residence times in the aquifer plays a minor role in the streamwater transit times but is key for the transit time dynamics of the groundwater contribution to the stream.

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A sprinkling experiment to quantify celerity–velocity differences at the hillslope scale

Cited by 16 publications

References 62 publications

Water Table Depth and Bedrock Permeability Control Magnitude and Timing of Transpiration‐Induced Diel Fluctuations in Groundwater

Water Table Depth and Bedrock Permeability Control Magnitude and Timing of Transpiration‐Induced Diel Fluctuations in Groundwater

Transpiration‐ and precipitation‐induced subsurface water flow observed using the self‐potential method

Dynamic Contributions of Stratified Groundwater to Streams Controls Seasonal Variations of Streamwater Transit Times

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