Simultaneous inversion of hydrogeologic and thermal data: 2. Incorporation of thermal data

Abstract

Introduction of a data set for a second potential field provides an approach to deal with data limitations in the inverse problem. We examine how temperature measurements can be used to improve the resolution of model parameters in constructing a model of a steady state groundwater flow system. The approach is applicable to cross‐sectional models with vertical components of fluid flow. In media with low hydraulic conductivity, the thermal regime is conductive and temperature measurements do not carry direct information on the hydrogeologic regime. In more permeable systems however, fluid velocities are sufficient to redistribute heat within the basin, perturbing the conductive regime. Parameter estimates developed in the inverse simulation are required to satisfy a weighted measure of both the hydrogeologic and thermal data. The effectiveness of this joint inverse depends upon the extent of the advective disturbance, which, in turn, is controlled by the magnitude of hydraulic conductivity, the length scale and location of hydraulic conductivity variations, the depth of active flow, and the regional configuration of the groundwater flow system. A series of hypothetical examples are presented to demonstrate how model misfit can be reduced when noisy hydraulic head data are augmented with thermal data. Because the extent of an advective disturbance depends upon the absolute value of hydraulic conductivity, addition of temperature measurements in an inverse simulation is particularly helpful in cases where there is uncertainty in boundary conditions, such as recharge rates. The approach is used to construct a model of the groundwater flow system at Downie Slide, north of Revelstoke, British Columbia. Results presented in part one suggest that the slide behaves as a homogeneous, isotropic medium (Woodbury et al., 1987). With a homogeneous hydraulic conductivity, only the ratio of fluid flux to hydraulic conductivity could be determined. By including thermal data, the value of hydraulic conductivity can be estimated.