Abstract
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.
Highlights
Subglacial basal hydrology is a potentially critical control on basal drag and ice streaming
We present a computationally fast physics-based subglacial hydrology model for continental-scale ice sheet systems modelling over glacial cycles, which is meant to capture the relevant features of basal water flow for the above three contexts
For the analyses presented the subglacial hydrology model is passively coupled to the glacial systems model (GSM)
Summary
Subglacial basal hydrology is a potentially critical control on basal drag and ice streaming. We present a computationally fast physics-based subglacial hydrology model for continental-scale ice sheet systems modelling over glacial cycles, which is meant to capture the relevant features of basal water flow for the above three contexts (including both distributed and channelized flow components). Similar to BraHMs, their hydrology model simulates the subglacial water flow using a Darcian flux and limits the basal pressure to the ice overburden pressure (due to long timescales) Their model consists of several basal components, including a water-filled till layer and an effective cavity-based water storage. Hoffman and Price (2014) developed a physically based model to be used as a part of the Community Ice Sheet Model (CISM) This model is rather detailed in combining cavity formation (providing water storage) and a method to form Röthlisberger channelized flow.
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