Improvement of the soil drainage simulation based on observations from lysimeters
- 1Laboratoire de Géologie - CNRS UMR 8538 - École Normale Supérieure - PSL University, IPSL, Paris, France
- 2Centre National de Recherches Météorologiques, Université de Toulouse, Météo-France, CNRS UMR 3589, Toulouse, France
- 3Laboratoire Sols et Environnement-GISFI, Université de Lorraine (UMR 1120), Vandœuvre-lès-Nancy, France
- 4Andra, Direction RD, Centre de Meuse/Haute-Marne, 55290 Bure, France
- 5Université de Lorraine, CNRS, LIEC, F-54000 Nancy, France
- 1Laboratoire de Géologie - CNRS UMR 8538 - École Normale Supérieure - PSL University, IPSL, Paris, France
- 2Centre National de Recherches Météorologiques, Université de Toulouse, Météo-France, CNRS UMR 3589, Toulouse, France
- 3Laboratoire Sols et Environnement-GISFI, Université de Lorraine (UMR 1120), Vandœuvre-lès-Nancy, France
- 4Andra, Direction RD, Centre de Meuse/Haute-Marne, 55290 Bure, France
- 5Université de Lorraine, CNRS, LIEC, F-54000 Nancy, France
Abstract. Soil drainage is the main source of groundwater recharge and river flow. It is therefore a key process for water resource management. In this study, we evaluate the soil drainage simulated by the Interaction-Soil-Biosphere-Atmosphere (ISBA) land surface model currently used for hydrological applications from the watershed scale to the global scale. This validation is done using seven lysimeters from two long term experiment sites measuring hourly water dynamics between 2009 and 2019 in northeastern France. These 2-meter deep lysimeters are filled with different soil types and are either maintained bare soil or covered with vegetation. The commonly used closed-form equations describing soil-water retention and conductivity curves from Brooks and Corey (1966) and van Genuchten (1980) are tested. The results indicate a good performance by the different experiments in terms of soil volumetric water content and water mass. The drained flow at the bottom of the lysimeter is well modeled using Brooks and Corey (1966) while some weaknesses appears with van Genuchten (1980) due to the complexity of its hydraulic conductivity function. Combining the soil-water curve of van Genuchten (1980) with the hydraulic conductivity function of Brooks and Corey (1966) allow to solve this problem and even to improve the simulation of the drainage dynamic, especially for intense drainage events. The study highlights the importance of the vertical heterogeneity of the soil hydrodynamic parameters to correctly simulate the drainage dynamic, as well as the primary influence of the n and b parameters which characterize the shape of the soil-water retention curve.
Antoine Sobaga et al.
Status: open (until 13 Jul 2022)
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RC1: 'Comment on egusphere-2022-274', Anonymous Referee #1, 07 Jun 2022
reply
The manuscript focuses on the use of a Richards-based solver to reproduce hydrological observations from multiple lysimeters in France. The case study is also used to compare three soil hydraulic models (i.e., Brooks-Corey, van Genuchten-Mualem, a combination of both). The aim is relevant for HESS and somehow interesting, however the manuscript possesses multiple methodological weaknesses:
- The choice to use the ISBA LSM model, which was conceived to operate on larger scales, to investigate a process at the lysimeter level (and prove a soil physics point: Brooks vs van Genuchten) is questionable. The model solves the Richards equation using a Crank-Nicolson scheme but there are no details about the spatial discretization, boundary conditions, etc. By reading this (https://doi.org/10.1029/2018MS001545), the model seems to use a multi-layer approach based on the finite difference. Widely used vadose zone hydrological model such as HYDRUS or SWAP use schemes that comply with the mass conservative approach proposed by Celia et al. (1990). These models have been widely tested, and would be a more rational choice to investigate processes at the lysimeter level and compare multiple soil hydraulic models.
- The whole methodology on the comparison between model predictions and observations is cumbersome to read, not novel, and weak.
- No error metric is reported to compare multiple soil hydraulic models. Besides fitting (which should be quantified), other metrics should be used to compare also the complexity of the models (e.g., at least Akaike Information Criterion)
- The calibration procedure should compare time series of modeled and observed soil water quantities (e.g., water contents). An objective function or a likelihood (e.g., NSE, Gaussian, etc) should be selected, and a numerical algorithm should be used to perform the model calibration. Further, parameters uncertainty should be assessed to see how informative are data, and whether the choice of a more complex model is justified. Only after having performed a statistically robust analysis, it is possible to try to explain why BC+VG is better and when. As they are, methods don’t support enough the conclusions, and neither represent a novel contribution to the field.
Specific comments:
L15-20 Not really. Drainage is the amount of water that bypasses the root zone.
L47-50 Nonlinearity cannot be a source of criticism, otherwise an endless number of equations used in environmental modeling should be “criticized”. I would remove this part. Richards equation is not perfect, but we are still far from finding a viable, widely used, and extensively validated alternative.
L56 BC66 has that sharp singular point near the air-entry pressure that makes it not very stable. (https://doi.org/10.1029/93WR03238). Authors indeed discuss this point later. However, more specific references are needed to prove your point that BC66 is more numerically stable than VG80.
Data: Please add details about TDR sensors (e.g., type, accuracy, calibration type) and tipping bucket resolution
L124-125 Is the heat transport included in the numerical simulation of lysimeters? If yes, key equations should be provided. Otherwise, it should be removed from the text.
L130-140 This part should be moved after the Richards equation, and should describe how it is connected to the sink term S(z). Key equations should provided. Citing refs is good, but the manuscript should stand by itself.
L147-148 what is the discretization of the soil profile? What are the boundary conditions used?
Figure1. Very confusing. It is difficult to appreciate differences. What are the dashed lines? Figure+Caption should be self-explanatory
L176 There is not a single error metric to support the conclusion that one formulation is better than the other. It is really puzzling to see that.
L192 VG80 not stable for n<1.3?! Never experienced something like this. Indeed, I agree with the Authors that n>1.1 is a good constraint.
L197 Having a highly negative tortuosity is not recommended. Actually Schaap suggests a value of -1 (https://doi.org/10.2136/sssaj2000.643843x)
Antoine Sobaga et al.
Antoine Sobaga et al.
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