Preferential flow through shallow fractured bedrock and a 3D fill-and-spill model of hillslope subsurface hydrology

Li Guo, Hangsheng Lin, Bihang Fan, Jonathan Nyquist, Laura Toran, Gregory J. Mount

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

The role of preferential flow through unsaturated saprock (fractured bedrock with weathering restricted to fracture margins) in hillslope hydrology remains inadequately described. To address this issue, ground-penetrating radar (GPR), controlled infiltration, and high-frequency subsurface moisture monitoring were integrated to characterize saprock preferential flow (SPF) in the Susquehanna Shale Hills Critical Zone Observatory in Pennsylvania, U.S.A. In a planar hillslope with shallow fractured shale bedrock (starting at 0.1–0.3 m below ground), two pulses of water (79.5 L in total) were released followed by time-lapse GPR surveys. Differentiating GPR images collected before and after infiltration revealed lateral SPF in the direction of bedding plane fractures near the infiltration trench but with limited development of SPF down gradient along the hillslope. This was confirmed by soil and saprock moisture monitoring at a soil pit (0.2 m downslope of the GPR grid) where only one out of fifteen probes responded to the controlled infiltration. Lateral SPF frequently occurred at the GPR grid during a 24-day period with ten rainfall events, especially under the wet initial conditions. Additional infiltration experiments in a convex hillslope and a nearby bare slope with exposed saprock demonstrated the impact of fracture patterns on the routing of SPF. Three types of SPF in hillslope hydrology were identified, including (1) vertical percolation, (2) exfiltration from saprock to soil, and (3) stormwater transported downslope from planar and convex hillslopes to concave hillslopes. A 3D fill-and-spill model is proposed for the study site and similar areas that recognizes the importance of subsurface flow networks, with shallow saprock and concave hillslopes as essential controls of hillslope subsurface flow.

Original languageEnglish (US)
Pages (from-to)430-442
Number of pages13
JournalJournal of Hydrology
Volume576
DOIs
StatePublished - Sep 1 2019

Fingerprint

preferential flow
hillslope
bedrock
hydrology
fill
ground penetrating radar
infiltration
subsurface flow
shale
moisture
soil
bedding plane
monitoring
routing
stormwater
trench
weathering
observatory
probe
rainfall

All Science Journal Classification (ASJC) codes

  • Water Science and Technology

Cite this

Guo, Li ; Lin, Hangsheng ; Fan, Bihang ; Nyquist, Jonathan ; Toran, Laura ; Mount, Gregory J. / Preferential flow through shallow fractured bedrock and a 3D fill-and-spill model of hillslope subsurface hydrology. In: Journal of Hydrology. 2019 ; Vol. 576. pp. 430-442.
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abstract = "The role of preferential flow through unsaturated saprock (fractured bedrock with weathering restricted to fracture margins) in hillslope hydrology remains inadequately described. To address this issue, ground-penetrating radar (GPR), controlled infiltration, and high-frequency subsurface moisture monitoring were integrated to characterize saprock preferential flow (SPF) in the Susquehanna Shale Hills Critical Zone Observatory in Pennsylvania, U.S.A. In a planar hillslope with shallow fractured shale bedrock (starting at 0.1–0.3 m below ground), two pulses of water (79.5 L in total) were released followed by time-lapse GPR surveys. Differentiating GPR images collected before and after infiltration revealed lateral SPF in the direction of bedding plane fractures near the infiltration trench but with limited development of SPF down gradient along the hillslope. This was confirmed by soil and saprock moisture monitoring at a soil pit (0.2 m downslope of the GPR grid) where only one out of fifteen probes responded to the controlled infiltration. Lateral SPF frequently occurred at the GPR grid during a 24-day period with ten rainfall events, especially under the wet initial conditions. Additional infiltration experiments in a convex hillslope and a nearby bare slope with exposed saprock demonstrated the impact of fracture patterns on the routing of SPF. Three types of SPF in hillslope hydrology were identified, including (1) vertical percolation, (2) exfiltration from saprock to soil, and (3) stormwater transported downslope from planar and convex hillslopes to concave hillslopes. A 3D fill-and-spill model is proposed for the study site and similar areas that recognizes the importance of subsurface flow networks, with shallow saprock and concave hillslopes as essential controls of hillslope subsurface flow.",
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Preferential flow through shallow fractured bedrock and a 3D fill-and-spill model of hillslope subsurface hydrology. / Guo, Li; Lin, Hangsheng; Fan, Bihang; Nyquist, Jonathan; Toran, Laura; Mount, Gregory J.

In: Journal of Hydrology, Vol. 576, 01.09.2019, p. 430-442.

Research output: Contribution to journalArticle

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