Barry’s early research was based on modelling of complex flow processes in natural systems. He focused on analytical solutions for important flow problems and developed new analytical solutions for unsaturated flow (Richards’ equation) that incorporate realistic nonlinearity in the hydraulic functions. By using mappings of Richards’ equation into itself, he demonstrated a class of soils that exhibited hydraulic similarity. This theoretical framework revealed all known solutions for constant flux infiltration and redistribution during unsaturated flow, and showed that available mathematical methods cannot produce new solutions for unsaturated flow.

Alongside this fundamental research on flow, Barry worked on solute transport, first using analytical methods, then increasingly using numerical modelling approaches to reactive transport in porous medium systems. He was an early leader in reactive biogeochemical modelling of groundwater systems, a research has grown from infancy to maturity during his career. Motivated by important practical problems, he tackled the major problem of remediation of chlorinated solvents, and created a comprehesive approach for modeling the fate of this highly recalcitrant contaminant.

Barry has also investigated mechanisms for surface-groundwater interaction in, e.g., coastal aquifers and marshes. Through multiple collaborations, he thoroughly elucidated the mechanisms controlling the response of coastal aquifers to forcings, as affected by capillarity and beach morphology. This work has important practical applications such as determination of aquifer properties and in design of beach dewatering schemes for erosion control.