Influence of spatial borehole density on estimation of geostatistical properties and construction of heterogeneous hydrogeological models

Abstract

The distribution of hydrogeological materials affects geotechnical engineering, groundwater flow and transport, and geomechanics. The number and spatial distribution of boreholes influence the construction of hydrogeological models. This study examined the impact of spatial borehole density on the geostatistical properties and construction of three-dimensional heterogeneous hydrogeological models (HHMs). A dataset of 437 boreholes was analyzed, where a true case and three scenarios with varying borehole densities were used. To maintain data consistency, a uniform random selection method is proposed to reduce the borehole density. Spatial characteristics were assessed using a one-dimensional continuous-lag Markov chain and the spMC package. Conditional realizations of HHMs (generated using 40 simulations) revealed that volumetric proportions of a material remained stable across densities, indicating that the proposed selection strategy is effective. Geological continuity in the alluvial fan was estimated to be longer in the strike direction than the dip direction, which is inconsistent with traditional assumptions. Higher borehole density produced more heterogeneous models, whereas lower borehole density produced a more continuous pattern. Deep boreholes were found to be important for HHM construction. An uncertainty analysis using the coefficient of variation (CV) shows that increasing borehole density reduces model uncertainty, with the 90^th percentile CV for clay thickness reaching 0.309. This highlights the importance of spatial borehole density (two-dimensional density and volumetric density) in influencing material distribution and reducing uncertainty in stochastic HHMs. These findings provide insights for enhancing the reliability of HHMs and have implications for groundwater management, land subsidence mitigation, engineering geology, and environmental assessments.