Preprints
https://doi.org/10.5194/hess-2021-15
https://doi.org/10.5194/hess-2021-15

  20 Jan 2021

20 Jan 2021

Review status: this preprint is currently under review for the journal HESS.

Coupling saturated and unsaturated flow: comparing the iterative and the non-iterative approach

Natascha Brandhorst1, Daniel Erdal2,3, and Insa Neuweiler1 Natascha Brandhorst et al.
  • 1Institute of Fluid Mechanics and Environmental Physics in Civil Engineering, University of Hannover, Germany
  • 2Center for Applied Geoscience, University of Tübingen, Germany
  • 3Tyréns AB, Lilla Badhusgatan 2, 411 21 Göteborg, Sweden

Abstract. Fully integrated three dimensional (3D) physically based hydrologic models usually require many computational resources. For many applications, simplified models can be a cost effective alternative. 3D models of subsurface flow are often simplified by coupling a 2D groundwater model with multiple 1D models for the unsaturated zone. The crucial part of such models is the coupling between the two model compartments. In this work we compare two approaches for the coupling. One is iterative and the 1D unsaturated zone models go down to the impervious bottom of the aquifer and the other one is non-iterative and uses a moving lower boundary for the unsaturated zone. In this context we also propose a new way of treating the specific yield, which plays a crucial role in linking the unsaturated and the groundwater model. Both models are applied to three test cases with increasing complexity and analyzed in terms of accuracy and speed compared to fully integrated model runs. The non-iterative approach is faster while the iterative approach is more accurate and robust. Besides, for the iterative coupling method a calibration of the specific yield is not needed.

Natascha Brandhorst et al.

Status: open (until 17 Mar 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2021-15', Gerrit H. de Rooij, 26 Jan 2021 reply
  • RC2: 'Comment on hess-2021-15', Orgogozo Laurent, 15 Feb 2021 reply
  • RC3: 'Comment on hess-2021-15', Anonymous Referee #3, 17 Feb 2021 reply

Natascha Brandhorst et al.

Model code and software

Coupled saturated and unsaturated flow model Natascha Brandhorst and Daniel Erdal https://doi.org/10.5281/zenodo.4422533

Natascha Brandhorst et al.

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Short summary
We compare two approaches for coupling a 2D groundwater model with multiple 1D models for the unsaturated zone. One is non-iterative and very fast. The other one is iterative and involves a new way of treating the specific yield, which is crucial for obtaining a consistent solution in both model compartments. Tested on different scenarios, this new method turns out to be slower than the non-iterative approach, but more accurate and still very efficient compared to fully integrated 3D model runs.