Inverse analysis of stochastic moment equations for transient flow in randomly heterogeneous media

Monica Riva, Alberto Guadagnini, Shlomo P Neuman, Emanuela Bianchi Janetti, Bwalya Malama

Research output: Contribution to journalArticle

27 Citations (Scopus)

Abstract

We present a nonlinear stochastic inverse algorithm that allows conditioning estimates of transient hydraulic heads, fluxes and their associated uncertainty on information about hydraulic conductivity (K) and hydraulic head (h) data collected in a randomly heterogeneous confined aquifer. Our algorithm is based on Laplace-transformed recursive finite-element approximations of exact nonlocal first and second conditional stochastic moment equations of transient flow. It makes it possible to estimate jointly spatial variations in natural log-conductivity (Y = ln K), the parameters of its underlying variogram, and the variance-covariance of these estimates. Log-conductivity is parameterized geostatistically based on measured values at discrete locations and unknown values at discrete "pilot points". Whereas prior values of Y at pilot point are obtained by generalized kriging, posterior estimates at pilot points are obtained through a maximum likelihood fit of computed and measured transient heads. These posterior estimates are then projected onto the computational grid by kriging. Optionally, the maximum likelihood function may include a regularization term reflecting prior information about Y. The relative weight assigned to this term is evaluated separately from other model parameters to avoid bias and instability. We illustrate and explore our algorithm by means of a synthetic example involving a pumping well. We find that whereas Y and h can be reproduced quite well with parameters estimated on the basis of zero-order mean flow equations, all model quality criteria identify the second-order results as being superior to zero-order results. Identifying the weight of the regularization term and variogram parameters can be done with much lesser ambiguity based on second- than on zero-order results. A second-order model is required to compute predictive error variances of hydraulic head (and flux) a posteriori. Conditioning the inversion jointly on conductivity and hydraulic head data results in lesser predictive uncertainty than conditioning on conductivity or head data alone.

Original languageEnglish (US)
Pages (from-to)1495-1507
Number of pages13
JournalAdvances in Water Resources
Volume32
Issue number10
DOIs
StatePublished - Oct 2009

Fingerprint

inverse analysis
heterogeneous medium
transient flow
hydraulic head
conductivity
conditioning
variogram
kriging
confined aquifer
hydraulic conductivity
pumping
spatial variation
well
parameter

Keywords

  • Geostatistics
  • Moment equations
  • Stochastic inversion
  • Transient flow

ASJC Scopus subject areas

  • Water Science and Technology

Cite this

Inverse analysis of stochastic moment equations for transient flow in randomly heterogeneous media. / Riva, Monica; Guadagnini, Alberto; Neuman, Shlomo P; Janetti, Emanuela Bianchi; Malama, Bwalya.

In: Advances in Water Resources, Vol. 32, No. 10, 10.2009, p. 1495-1507.

Research output: Contribution to journalArticle

Riva, Monica ; Guadagnini, Alberto ; Neuman, Shlomo P ; Janetti, Emanuela Bianchi ; Malama, Bwalya. / Inverse analysis of stochastic moment equations for transient flow in randomly heterogeneous media. In: Advances in Water Resources. 2009 ; Vol. 32, No. 10. pp. 1495-1507.
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