Estimating hydraulic parameters of a heterogeneous aquitard using long-term multi-extensometer and groundwater level data

Zhuang, Chao; Zhou, Zhifang; Illman, Walter A.; Guo, Qiaona; Wang, Jinguo

Estimating hydraulic parameters of a heterogeneous aquitard using long-term multi-extensometer and groundwater level data | Estimation des paramètres hydrauliques d’un aquitard hétérogène à partir des données piézométriques et de multi-extensomètre de longue durée Estimación de parámetros hidráulicos de un acuitardo heterogéneo utilizando datos a largo plazo de extensómetros múltiples y niveles de agua subterránea 利用长期多重分层标和地下水位资料估算非均质弱透水层的水力参数 Estimativa de parâmetros hidráulicos de um aquitarde heterogêneo usando séries de dados de multiextensômetros e de nível de água

2017

Zhuang, Chao | Zhou, Zhifang | Illman, Walter A. | Guo, Qiaona | Wang, Jinguo

The classical aquitard-drainage model COMPAC has been modified to simulate the compaction process of a heterogeneous aquitard consisting of multiple sub-units (Multi-COMPAC). By coupling Multi-COMPAC with the parameter estimation code PEST++, the vertical hydraulic conductivity (K ᵥ) and elastic (S ₛₖₑ) and inelastic (S ₛₖₚ) skeletal specific-storage values of each sub-unit can be estimated using observed long-term multi-extensometer and groundwater level data. The approach was first tested through a synthetic case with known parameters. Results of the synthetic case revealed that it was possible to accurately estimate the three parameters for each sub-unit. Next, the methodology was applied to a field site located in Changzhou city, China. Based on the detailed stratigraphic information and extensometer data, the aquitard of interest was subdivided into three sub-units. Parameters K ᵥ, S ₛₖₑ and S ₛₖₚ of each sub-unit were estimated simultaneously and then were compared with laboratory results and with bulk values and geologic data from previous studies, demonstrating the reliability of parameter estimates. Estimated S ₛₖₚ values ranged within the magnitude of 10⁻⁴ m⁻¹, while K ᵥ ranged over 10⁻¹⁰–10⁻⁸ m/s, suggesting moderately high heterogeneity of the aquitard. However, the elastic deformation of the third sub-unit, consisting of soft plastic silty clay, is masked by delayed drainage, and the inverse procedure leads to large uncertainty in the S ₛₖₑ estimate for this sub-unit.

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