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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 8 | Copyright
Geosci. Model Dev., 11, 3497-3513, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Development and technical paper 30 Aug 2018

Development and technical paper | 30 Aug 2018

BrAHMs V1.0: a fast, physically based subglacial hydrology model for continental-scale application

Mark Kavanagh1 and Lev Tarasov2 Mark Kavanagh and Lev Tarasov
  • 1Faculty of Engineering and Applied Science, Memorial University of Newfoundland, St. John's, NL, Canada
  • 2Dept. of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John's, NL, Canada

Abstract. We present BrAHMs (BAsal Hydrology Model): a physically based basal hydrology model which represents water flow using Darcian flow in the distributed drainage regime and a fast down-gradient solver in the channelized regime. Switching from distributed to channelized drainage occurs when appropriate flow conditions are met. The model is designed for long-term integrations of continental ice sheets. The Darcian flow is simulated with a robust combination of the Heun and leapfrog–trapezoidal predictor–corrector schemes. These numerical schemes are applied to a set of flux-conserving equations cast over a staggered grid with water thickness at the centres and fluxes defined at the interface. Basal conditions (e.g., till thickness, hydraulic conductivity) are parameterized so the model is adaptable to a variety of ice sheets. Given the intended scales, basal water pressure is limited to ice overburden pressure, and dynamic time stepping is used to ensure that the Courant–Friedrichs–Lewy (CFL) condition is met for numerical stability.

The model is validated with a synthetic ice sheet geometry and different bed topographies to test basic water flow properties and mass conservation. Synthetic ice sheet tests show that the model behaves as expected with water flowing down gradient, forming lakes in a potential well or reaching a terminus and exiting the ice sheet. Channel formation occurs periodically over different sections of the ice sheet and, when extensive, displays the arborescent configuration expected of Röthlisberger channels. The model is also shown to be stable under high-frequency oscillatory meltwater inputs.

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Short summary
We present and validate BrAHMs (BAsal Hydrology Model): a new physically based basal hydrology model, which captures the two main types of subglacial drainage systems (high-pressure distributed systems and low-pressure channelized systems). BrAHMs is designed for continental glacial cycle scale contexts, for which computational speed is essential. This speed is accomplished, in part, by numerical methods novel to basal hydrology contexts.
We present and validate BrAHMs (BAsal Hydrology Model): a new physically based basal hydrology...