title: Estimating River Conductance from Prior Information to Improve Surface-Subsurface Model Calibration.
abstract: Most groundwater models simulate stream-aquifer interactions with a head-dependent flux boundary condition based on a river conductance (CRIV). CRIV is usually calibrated with other parameters by history matching. However, the inverse problem of groundwater models is often ill-posed and individual model parameters are likely to be poorly constrained. Ill-posedness can be addressed by Tikhonov regularization with prior knowledge on parameter values. The difficulty with a lumped parameter like CRIV, which cannot be measured in the field, is to find suitable initial and regularization values. Several formulations have been proposed for the estimation of CRIV from physical parameters. However, these methods are either too simple to provide a reliable estimate of CRIV, or too complex to be easily implemented by groundwater modelers. This paper addresses the issue with a flexible and operational tool based on a 2D numerical model in a local vertical cross section, where the river conductance is computed from selected geometric and hydrodynamic parameters. Contrary to other approaches, the grid size of the regional model and the anisotropy of the aquifer hydraulic conductivity are also taken into account. A global sensitivity analysis indicates the strong sensitivity of CRIV to these parameters. This enhancement for the prior estimation of CRIV is a step forward for the calibration and uncertainty analysis of surface-subsurface models. It is especially useful for modeling objectives that require CRIV to be well known such as conjunctive surface water-groundwater use.
authors.affiliation: Le LyRE, SUEZ Environnement, Domaine du Haut-Carré 43, rue Pierre Noailles, 33400 Talence, France.
authors.forename: Yohann
authors.initials: Y
authors.lastname: Cousquer
authors.affiliation: EA 4592 Georessources & Environment, Bordeaux INP and Univ. Bordeaux Montaigne, ENSEGID, 1 allée F. Daguin, 33607 Pessac cedex, France.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Pryet
authors.affiliation: Geosciences Department, MINES ParisTech, PSL Research University, 35 rue Saint-Honoré, 77305 Fontainebleau, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Flipo
authors.affiliation: Le LyRE, SUEZ Environnement, Domaine du Haut-Carré 43, rue Pierre Noailles, 33400 Talence, France.|EA 4592 Georessources & Environment, Bordeaux INP and Univ. Bordeaux Montaigne, ENSEGID, 1 allée F. Daguin, 33607 Pessac cedex, France.|Université François Rabelais de Tours, EA 6293 GéHCO, Parc de Grandmont, 37200 Tours, France.
authors.forename: Célestine
authors.initials: C
authors.lastname: Delbart
authors.affiliation: EA 4592 Georessources & Environment, Bordeaux INP and Univ. Bordeaux Montaigne, ENSEGID, 1 allée F. Daguin, 33607 Pessac cedex, France.
authors.forename: Alain
authors.initials: A
authors.lastname: Dupuy
mesh_terms: D002138:Calibration; D060587:Groundwater; D008962:Models, Theoretical; D045483:Rivers; D014872:Water Movements