The article deals with unsteady ground water flow in an aquifer of limited horizontal extent. The changes in storage are taken to be dependent on a storage coefficient S, and flow rates are taken to be dependent on the coefficient of transmissibility T. Here the relation to Darcy's constant k is that T ≿ kD, where D is the aquifer thickness. The equilibrium ground water surface is found and further calculations are based on the departure of the ground water level from this equilibrium value.
An expression of the impulse response function (the instantaneous unit hydrograph or IUH) is found, and its use demonstrated.
Finally, it is shown how such calculations have been used to analyse the inflow into a water reservoir in Iceland, serving as guidelines in the planning of field investigations of a major ground water reservoir in a nearby lava field.