Linking Test to reduce the number of hydraulic parameters necessary to simulate groundwater recharge in unsaturated soils

In environmental studies, numerical simulation models are valuable tools for testing hypothesis about systems functioning and to perform sensitivity studies under scenarios of land use or climate changes. The simulations depend upon parameters which are not always measurable quantities and must be c...

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Bibliographic Details
Published in:	Advances in water resources Vol. 31; no. 2; pp. 355 - 369
Main Authors:	Pollacco, J.A.P, Ugalde, J.M.S, Angulo-Jaramillo, R, Braud, I, Saugier, B
Format:	Journal Article
Language:	English
Published:	Oxford Elsevier Science 01-02-2008 Elsevier
Subjects:	Earth Sciences Earth, ocean, space Environmental Sciences Exact sciences and technology Global Changes groundwater recharge Hydrogeology Hydrology Hydrology. Hydrogeology Linking Test mathematical models mathematics and statistics Mualem-van Genuchten parameters Richards' equation Sciences of the Universe simulation models unsaturated conditions unsaturated flow Equifinality Groundwater recharge sensitivity analysis simulation van Genuchten ground-water recharge vegetation Unsaturated flow Inverse modelling Richards equation matching saturation hydraulics water resources land use soils Hydraulic parameters flow climate change Linking Test models soil moisture testing climate infiltration Richards' equation
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Summary:	In environmental studies, numerical simulation models are valuable tools for testing hypothesis about systems functioning and to perform sensitivity studies under scenarios of land use or climate changes. The simulations depend upon parameters which are not always measurable quantities and must be calibrated against observations, using for instance inverse modelling. Due to the scarcity of these observations, it has been found that parameter sets allowing a good matching between simulated and measured quantities are often non-unique, leading to the problem of equifinality. This can lead to non-physical values, erroneous fluxes and misleading sensitivity analysis. Therefore, a simple but robust inverse method coined the Linking Test is presented to determine if the parameters are linked. Linked parameters are then sub-divided into classes according to their impact on water fluxes. The Linking Test establishes the causes of non-uniqueness of parameter sets and the feasibility of the inverse modelling. The Linking Test is applied to a one-dimensional soil-vegetation water flow model to predict groundwater recharge from the Richards' equation. Under the tested climates and by assuming the vegetation parameters constant, the Linking Test showed that only 2 parameters out of 6 Mualem-van Genuchten parameters are required to determine an accurate recharge for soils not reaching saturation. For a reference soil, the Linking Test enables to determine, all the different combinations of the parameters that give similar recharge. The parameter sets are obtained by optimising the parameters against time series of soil moisture profiles. The Linking Equations established for the reference soil have important implications for sensitivity analysis, upscaling and infiltration tests.
Bibliography:	http://dx.doi.org/10.1016/j.advwatres.2007.09.002 ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0309-1708 1872-9657
DOI:	10.1016/j.advwatres.2007.09.002