The exponential decline in saturated hydraulic conductivity with depth: a novel method for exploring its effect on water flow paths and transit time distribution

A. A. Ameli*, J. J. McDonnell, K. Bishop

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

54 Citations (Scopus)


The strong vertical gradient in soil and subsoil saturated hydraulic conductivity is characteristic feature of the hydrology of catchments. Despite the potential importance of these strong gradients, they have proven difficult to model using robust physically based schemes. This has hampered the testing of hypotheses about the implications of such vertical gradients for subsurface flow paths, residence times and transit time distribution. Here we present a general semi-analytical solution for the simulation of 2D steady-state saturated-unsaturated flow in hillslopes with saturated hydraulic conductivity that declines exponentially with depth. The grid-free solution satisfies mass balance exactly over the entire saturated and unsaturated zones. The new method provides continuous solutions for head, flow and velocity in both saturated and unsaturated zones without any interpolation process as is common in discrete numerical schemes. This solution efficiently generates flow pathlines and transit time distributions in hillslopes with the assumption of depth-varying saturated hydraulic conductivity. The model outputs reveal the pronounced effect that changing the strength of the exponential decline in saturated hydraulic conductivity has on the flow pathlines, residence time and transit time distribution. This new steady-state model may be useful to others for posing hypotheses about how different depth functions for hydraulic conductivity influence catchment hydrological response. Copyright (c) 2016 John Wiley & Sons, Ltd.

Original languageEnglish
Pages (from-to)2438-2450
Number of pages13
JournalHydrological Processes
Issue number14
Early online date21 Dec 2015
Publication statusPublished - 1 Jul 2016

Bibliographical note

We thank Dr. James Craig at the University of Waterloo for his scientific support throughout the process. This research was funded by a 2014 NSERC Discovery Grant and NSERC Accelerator to JJM, and the FORMAS Strong Research Environment QWARTS.


  • exponential decline in saturated hydraulic conductivity with depth
  • semi analytical model
  • integrated flow and transport model
  • transit time distribution
  • subsurface flow pathline
  • saturated-unsaturated flow
  • groundwater dynamics
  • unsaturated flow
  • series solutions
  • drainage basins
  • runoff
  • infiltration
  • topography
  • catchments
  • storage
  • tracer


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