Inherent Limitations of Hydraulic Tomography

Abstract

We offer a cautionary note in response to an increasing level of enthusiasm regarding high-resolution aquifer characterization with hydraulic tomography. We use synthetic examples based on two recent field experiments to demonstrate that a high degree of nonuniqueness remains in estimates of hydraulic parameter fields even when those estimates are based on simultaneous analysis of a number of carefully controlled hydraulic tests. We must, therefore, be careful not to oversell the technique to the community of practicing hydrogeologists, promising a degree of accuracy and resolution that, in many settings, will remain unattainable, regardless of the amount of effort invested in the field investigation. No practically feasible amount of hydraulic tomography data will ever remove the need to regularize or bias the inverse problem in some fashion in order to obtain a unique solution. Thus, along with improving the resolution of hydraulic tomography techniques, we must also strive to couple those techniques with procedures for experimental design and uncertainty assessment and with other more cost-effective field methods, such as geophysical surveying and, in unconsolidated formations, direct-push profiling, in order to develop methods for subsurface characterization with the resolution and accuracy needed for practical field applications.

Towards a better estimate of storage properties of aquifer with magnetic resonance sounding

“…The hydraulic tomography involves the simultaneous analysis of groundwater head responses recorded at numerous locations and produced by a sequence of pumping stressing different portions of the aquifer. Although hydraulic tomography created a high level of enthusiasm among the hydrogeological community, it has an inherent physic-imposed nonunique solution (Bohing and Butler, 2010). Moreover, both conventional pumping test and hydraulic tomography require the drilling of numerous boreholes for providing a spatial density of aquifer properties appropriate to most of the groundwater studies.…”

Joint interpretation of sequential pumping tests in unconfined aquifers

“…[39] Bohling and Butler [2010] advocated that some drawdown data obtained from a sequential pumping test in confined aquifers may contain redundant information and should be excluded from HT analysis due to the principle of reciprocity [Bruggeman, 1972]. However, as pointed out by Huang et al [2011], using ''redundant'' field data in the SimSLE improved the estimates due to issues related to measurement errors.…”

Estimation of heterogeneous aquifer parameters using centralized and decentralized fusion of hydraulic tomography data

“…With respect to the latter, Bohling and Butler (2010) caution practicing hydrologists against "overselling" the reliability of HT estimates based on their pilot point inverse method, and argue that some form of regularization is typically necessary to reduce uncertainties associated with the nonuniqueness effect. In this work, HT data are inverted using the EnKF.…”

“…A possible effective approach to improving parameter estimations for ill-posed problems is by integrating data from independent sources, which may be related to different physical processes, such as hydraulic, geophysical, geomechanical, and chemical processes (Bohling and Butler, 2010). In this situation, different physical processes (models) are utilized to relate measured responses to aquifer properties.…”