Integrating aerial geophysical data in multiple-point statistics simulations to assist groundwater flow models

Abstract

The process of accounting for heterogeneity has made significant advances in statistical research, primarily in the framework of stochastic analysis and the development of multiple-point statistics (MPS). Among MPS techniques, the direct sampling (DS) method is tested to determine its ability to delineate heterogeneity from aerial magnetics data in a regional sandstone aquifer intruded by low-permeability volcanic dykes in Northern Ireland, UK. The use of two two-dimensional bivariate training images aids in creating spatial probability distributions of heterogeneities of hydrogeological interest, despite relatively 'noisy' magnetics data (i.e. including hydrogeologically irrelevant urban noise and regional geologic effects). These distributions are incorporated into a hierarchy system where previously published density function and upscaling methods are applied to derive regional distributions of equivalent hydraulic conductivity tensor K. Several K models, as determined by several stochastic realisations of MPS dyke locations, are computed within groundwater flow models and evaluated by comparing modelled heads with field observations. Results show a significant improvement in model calibration when compared to a simplistic homogeneous and isotropic aquifer model that does not account for the dyke occurrence evidenced by airborne magnetic data. The best model is obtained when normal and reverse polarity dykes are computed separately within MPS simulations and when a probability threshold of 0.7 is applied. The presented stochastic approach also provides improvement when compared to a previously published deterministic anisotropic model based on the unprocessed (i.e. noisy) airborne magnetics. This demonstrates the potential of coupling MPS to airborne geophysical data for regional groundwater modelling.

Effect of volcanic dykes on coastal groundwater flow and saltwater intrusion: A field‐scale multiphysics approach and parameter evaluation

“…The model covered an area much larger than the field study area, including the tidal flat and the mapped geological boundary of the unconfined Sherwood sandstone (Figure ). The confined sandstone under the overlying Mercia mudstone was not included in the domain but a lateral entering flux was applied from results of previous regional modeling studies [ Dickson et al ., ]. The model contained 236,820 triangular prismatic elements and 129,649 nodes.…”

“…Despite an abundance of studies having mapped dykes occurrence in aquifers using methods such as field observations, remote sensing techniques or geophysical investigations [e.g., Sultan et al ., ; Dickson et al ., ], to our knowledge few studies have provided estimates of hydraulic properties of dykes, such as hydraulic conductivity and storativity. Moreover, their properties with respect to solute transport in groundwater such as saltwater intrusion are poorly documented despite their importance in many coastal settings, particularly volcanic islands.…”

“…This is uncommon in practice due to the relatively small thickness of dykes (few meters) and their dipping angle which is rarely perfectly vertical. Instead, other numerous studies [ Williams and Soroos , ; Takasaki and Mink , ; Dickson et al ., ; Izquierdo , ] have given equivalent (upscaled) properties for dyke‐intruded reservoirs or qualitative estimates of dyke role have been given by indirect observations such as evidence of barriers recorded on long‐term pumping tests, spring lines, etc. and these studies did not consider solute transport.…”

“…[]. This data set has provided the opportunity to revise existing regional groundwater models incorporating the mapped dykes [ Dickson et al ., ].…”

“…Airborne geophysical techniques are also increasingly used for hydrogeological investigations and modeling, including in heterogeneous volcanic environments [e.g., Kirkegaard et al , ; Dickson et al . ; Vittecoq et al . ].…”