Technical note: Novel analytical solution for groundwater response to atmospheric tides

Abstract. Subsurface hydraulic and geomechanical properties can be estimated from well water level responses to Earth and atmospheric tides. However, the limited availability of analytical solutions restricts the applicability of this approach to realistic field conditions. We present a new and rigorous analytical solution for modelling flow between a subsurface-well system caused by harmonic atmospheric loading. We integrate this into a comprehensive workflow that also estimates subsurface properties using a well-established Earth tide method. When applied to groundwater monitoring datasets obtained from two boreholes screened in a sand aquifer in the Mary-Wildman Rivers region (Northern Territory, Australia), estimated hydraulic conductivity and specific storage agree. Results also indicate that small vertical leakage occurs in the vicinity of both boreholes. Furthermore, the estimated geomechanical properties were within the values reported in literature for similar lithological settings. Our new solution extends the capabilities of existing approaches, and our results demonstrate that analysing the groundwater response to natural tidal forces is a low-cost and readily available solution for unconsolidated, hydraulically confined, and undrained subsurface conditions. This approach can support well-established characterisation methods, increasing the amount of subsurface information.