Preprints
https://doi.org/10.5194/hess-2022-431
https://doi.org/10.5194/hess-2022-431
 
13 Jan 2023
13 Jan 2023
Status: this preprint is currently under review for the journal HESS.

Prediction of the absolute hydraulic conductivity function from soil water retention data

Andre Peters1, Tobias L. Hohenbrink1, Sascha C. Iden1, Martinus Th. van Genuchten2,3, and Wolfgang Durner1 Andre Peters et al.
  • 1Division of Soil Science and Soil Physics, Institute of Geoecology, Technische Universität Braunschweig, Germany
  • 2Department of Earth Sciences, Utrecht University, Netherlands
  • 3Department of Nuclear Engineering, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil

Abstract. For modelling flow and transport processes in the soil-plant-atmosphere system, knowledge of the unsaturated hydraulic properties in functional form is mandatory. While much data is available for the water retention function, the hydraulic conductivity function often needs to be predicted. The classical approach is to predict the relative conductivity from the retention function and scale it with the measured saturated conductivity, Ks. In this paper we highlight the shortcomings of this approach, namely that measured Ks values are often highly uncertain and biased, resulting in poor predictions of the unsaturated conductivity function.

We propose to reformulate the unsaturated hydraulic conductivity function by replacing the soil-specific Ks as a scaling factor with a generally applicable effective saturated tortuosity parameter τs and predicting total conductivity using only the water retention curve. Using four different unimodal expressions for the water retention curve, a soil-independent general value for τs was derived by fitting the new formulation to 12 data sets containing the relevant information. τs was found to be approximately 0.1.

Testing of the new prediction scheme with independent data showed a mean error between the fully predicted conductivity functions and measured data of less than half an order of magnitude. The new scheme can be used when insufficient or no conductivity data are available. The model also helps to predict the saturated conductivity of the soil matrix alone, and thus to distinguish between the macropore conductivity and the soil matrix conductivity.

Andre Peters et al.

Status: open (until 10 Mar 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2022-431', Gerrit H. de Rooij, 16 Jan 2023 reply

Andre Peters et al.

Andre Peters et al.

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Short summary
The soil hydraulic conductivity function is usually predicted from the water retention curve (WRC) with the requirement of at least one measured conductivity data point for scaling the function. We propose a new scheme of absolute hydraulic conductivity prediction from the WRC without the need of measured conductivity data. Testing the new prediction with independent data shows good results. This scheme can be used when insufficient or no conductivity data are available.