Using the Continuumm Approach to Model Unsaturated Flow in Fractured Rock
Water Resources Research, 36(8), 2055-2066, 2000.
Lawrence Berkeley National Laboratory, Earth Sciences Division
University of California, Berkeley, CA 94720
Abstract. The appropriateness of using the continuum approach for simulations of unsaturated flow through fractured rock is examined in a numerical study of water seepage into an underground opening. A continuum model is calibrated against data generated with a high- resolution model that created discrete flow and seepage behavior. Probabilistic predictions of injection data and seepage rates are then compared to the values from the discrete model. The study shows that reasonable results can be obtained with a calibrated continuum model even for fractured systems in which the underlying flow processes are discrete. Calibration is a crucial step in this approach because it yields effective, model-related and process- specific parameters. The impact of discretization on the estimated parameters is discussed. Prediction uncertainty is evaluated by means of Monte Carlo simulations, including both the impact of parameter uncertainties and the effect of local heterogeneity. In this paper, the advantages and limitations of the continuum approach are discussed from a practical perspective, which includes a critical examination of project objectives, data needs, robustness of assumptions, and prediction uncertainty.