Spatial correlation analysis between hydraulic conductivity and specific storage in a heterogeneous sandbox by hydraulic tomography

Hydraulic conductivity (K) and specific storage (Ss) are closely related to porosity, the compressibility of aquifer skeleton, connectivity of pores, sorting of the grains, and many others. These well-known relationships promote the investigation of the correlation between spatially varying K and Ss values and their sensitivity to the overlying materials stresses in heterogeneous aquifers. However, the costs of the field experiments for this investigation limit us to a laboratory heterogeneous sandbox aquifer. Before the laboratory experiments, we conducted numerical experiments to verify our tools and approaches. Specifically, we tested the ability of the recently developed hydraulic tomography (HT) for mapping K and Ss fields in two cases. One case in which Ss field was correlated with the K field, and the other was uncorrelated. With the assurance of the ability of our approaches, the laboratory experiments mimicking the numerical ones followed. Accurate drawdown predictions of different flow events in the laboratory experiments further guarantee the reliability of the estimated detailed K and Ss fields. The estimated K and Ss fields reveal that the Ss field's variability is much less significant than K and has much longer correlation scales. Further, the K distribution is closely related to the distribution of sand grain sizes in the sandbox, while Ss is not. Moreover, Ss estimates show a decreasing trend with depth. This trend does not exist in K estimates, indicating that Ss is highly sensitive to overburden stresses and K is not. Lastly, there is no clear spatial correlation between K and Ss, and the variability of Ss is critical in predicting the transient behavior of groundwater flow.

Automated summary

Hydraulic conductivity (K) and specific storage (Ss) are closely related to factors such as porosity, connectivity of pores, and sorting of grains. Laboratory and numerical experiments were conducted to investigate the correlation between spatially varying K and Ss values and their sensitivity to overlying material stresses. The experiments confirmed the reliability of the tools and approaches used for estimating detailed K and Ss fields. The results showed that Ss is highly sensitive to overburden stresses, while K is not, and there is no clear spatial correlation between K and Ss. The variability of Ss is critical in predicting groundwater flow behavior.