Using Geostatistical Approach to Assess the Hydrogeological Model Uncertainty on Groundwater Flow and Land Subsidence in Huwei Township, Taiwan

The distribution of hydrogeological materials is an important characteristic in a three-dimensional hydrogeological system. Simulations of groundwater flow and land subsidence in a heterogeneous aquifer system are challenging because the hydrogeological uncertainty embedded in the natural sedimentary sequences. How to quantify the hydrogeological model uncertainty to mitigate the danger in civil engineering is another challenge. Huwei Township is selected as the study area because it has sufficient geological borehole data, hydrological data, and sink and source data for a numerical model study. Forty-six boreholes are used to construct the three-dimensional heterogeneously hydrogeological models (HHMs). The transition probability/Markov-Chain model is one of the commonly used geostatistical approaches, which is capable of conducting simulations of the 3D heterogeneously hydrogeological aquifer system. The outcome of thirty-six realizations of HHM with Monte Carlo simulation reports how the heterogeneous system reflects the hydrogeological model uncertainty in groundwater flow and land subsidence simulations. To quantify the HHM uncertainty, the coefficient of variation (CV) is adopted, which is defined as the ratio of the standard deviation to the mean. The mean CV values are 0.8% and 25% for hydraulic head and subsidence simulations, respectively, which indicate that the estimated land subsidence has significant uncertainty due to the realizations of HHM. The results show that the CV values at 90th percentile (P₉₀) of the cumulative distribution function is 0.295 in subsidence simulation. The structure of HHM is shown to largely influence groundwater flow and land subsidence behaviors. The study results provide an important reference for groundwater resources and land subsidence investigations.

Keywords: Hydrogeological model uncertainty, Heterogeneous model realization, Groundwater flow, Land subsidence, Markov-Chain approach.