Estimation of regional groundwater system in a granitic body by 3D permeable zone modeling and flow simulation

Abstract

Because clarifying a regional groundwater system is required for development and management of groundwater resources, it is important to evaluate the hydraulic property of a fracture system and alteration zones which act as the pass of groundwater flow in a rock body. For a case study of such hydraulic characterization, we selected an area in which the basement rock is composed of Cretaceous granite. We first constructed a 3D fracture model by a geostatistical method to simulate the regional fracture distribution by incorporating the orientation of the sampled fracture data obtained from the borehole investigations, and this model revealed the features of this fracture system in that area. We then incorporated a dataset of hydraulic conductivity obtained from single borehole hydraulic tests and rock-core tests using a N2 gas permeameter and found a positive correlation with the size of simulated fractures. Finally, a numerical simulation using MODFLOW was applied to this hydraulic conductivity model for estimating the regional groundwater flow system. Anisotropic behavior of flows near the fault was revealed by this simulation.