This paper describes a study of the Chalk aquifer of the Berkshire Downs. Extensive fieldwork provided sufficient information for the development of a mathematical model of the aquifer system. Particular emphasis was placed on the representation of the variation of changing transmissivity with saturated depth and the simulation of streams and rivers; flows from the Chalk to the Upper Greensand were also found to be important in certain locations. Comparisons between field and modelled values of both groundwater flow and groundwater head showed good agreement. The model was then used for predictive purposes with particular emphasis on the use of groundwater for river augmentation.