EGU21-8074
https://doi.org/10.5194/egusphere-egu21-8074
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Bedrock outcrops: A window for enhanced midwinter recharge

Stephanie Wright1 and Kent Novakowski2
Stephanie Wright and Kent Novakowski
  • 1Queen's University, Civil Engineering, Kingston, Canada (stephanie.wright@queensu.ca)
  • 2Queen's University, Civil Engineering, Kingston, Canada (kent.novakowski@queensu.ca)

As midwinter melt and rain-on-snow events become more common occurrences in the northern hemisphere under climate change, incorporating frozen processes when simulating winter-time recharge is increasingly necessary. The activation of infiltration pathways and recharge dynamics of shallow bedrock environments under frozen conditions has received relatively little attention. Over the 2019-2020 winter, hydrogeologic and cryospheric conditions of the surface, unsaturated, and saturated zones were monitored around a low-lying granitic outcrop in eastern Ontario, Canada. Interpretation of the data indicated that the soil-rock contact around outcrop margins was the key pathway enabling midwinter infiltration and recharge. To support this conceptual model and further explore the role of outcrops in enhancing midwinter bedrock recharge, a numerical investigation was undertaken. Measured climate data (hourly time step) was used to govern the surface energy and water balances of a 1D finite difference model that incorporates frozen processes. Measured snow depth, soil moisture content, and soil temperature profiles were simulated. Simulations with vertical infiltration alone could not account for observed increases in moisture content in the deepest soil horizons. This is attributed to additional lateral flow along the unfrozen soil-rock contact that bypasses the frozen soil layers. Preliminary results support the concept that bedrock outcrops provide a window for midwinter infiltration since repeated winter melts reduce frozen soil permeability and inhibits vertical infiltration until the ground thaws. Results from the surface/near-surface simulations are used to guide the development of a 2D finite element model that includes heat and flow transport and ground freeze-thaw. The impacts to bedrock recharge under different rainfall and snowmelt scenarios as well as various outcrop geometries are explored. Results from these numerical experiments help provide greater insight into the processes driving enhanced midwinter bedrock recharge under conditions of warmer winters.

How to cite: Wright, S. and Novakowski, K.: Bedrock outcrops: A window for enhanced midwinter recharge, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8074, https://doi.org/10.5194/egusphere-egu21-8074, 2021.

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