Spatial variability of hydraulic conductivity of the Cretaceous aquifer in Belgium

Flanders (Belgium). The Cretaceous aquifer—consisting of chalk sediments and other forms of carbonates—is an important source of fresh water for drinking water and industry in Flanders. Therefore, maintaining optimal water quality and quantity in this aquifer is critical. However, uncertainty of the Cretaceous hydrogeological parameters is high due to its depth, confinement, scarce observation wells, and the complex lithostratigraphic formations and members, resulting in limited information on the aquifer hydrogeological properties. This work provides novel insights on the Cretaceous characterization, focused on the spatial distribution of hydraulic conductivity estimated through multiple pumping tests, geophysics, and flowmeter logs. A correlation between hydraulic conductivity and depth displays decreasing values as depth increases towards northern regions. The analysis indicates that the high heterogeneity of the Cretaceous and the spatial variability of hydraulic conductivity is led by lithological differences, including the presence of a hardground layer with variable thickness and permeability. This correlation also highlights the influence of fractures and karstification, enhancing hydraulic conductivity at shallower regions while decreasing it at deeper sections of the aquifer given the lower fracture density due to higher overburden pressures. Results demonstrate the influence of depth, lithology, and fracture development controlling the hydraulic conductivity variability within the Cretaceous, providing important insights for further research on water extraction and aquifer storage capacity, among others. • The Cretaceous aquifer is highly heterogeneous due to lithological differences, fractures, and karstification. • A strong correlation between hydraulic conductivity and the Cretaceous depth was found in the study area. • Hydraulic conductivity decreases with depth and models can explain this spatial variability. • Hardground layers and phosphatic gravels greatly control permeability and well yields in the Gulpen Formation.