No abstract

An inductive method is presented for evaluating parameters in a two-dimensional linear equation describing groundwater flow. The approach employs finite difference approximations, which can be simply programed for calculation by computer. Before illustrating the method, which is applicable to both stationary and time-dependent problems, the various types of data required for evaluation in general are systematically enumerated. An assumption is introduced limiting the local variability of T, the transmissivity, and its relation to apparently similar assumptions used elsewhere is discussed. The particular aquifer chosen for illustration is the chalk of the South Downs between the rivers Adur and Ouse. The parameters are calculated on the basis of cyclic data in which annual abstraction is about 30% of the total infiltration for the year. The method gives a match to the minimum and maximum water levels during the year to within 7%.

The study of groundwater flow, given equations of motion and boundary conditions which are .mathematically linear, can be analyzed by using a normal mode approach. For the fully continuous case the simplest example is the familiar double Fourier analysis. Analogous results exist for the semidiscrete case, in which only time is treated as a continuous variable, and a method can be given for computing normal modes whose corresponding recession factors lie within prescribed ranges. One application of this approach suggests an empirical form for the base flow component of a stream hydrograph. The fully discrete case can also be treated and provides a convenient basis for the comparison of the more common approximations to the solution of the transient groundwater flow equation. In particular, it can be shown why the study of model problems does not provide a useful guide to the accuracy of the alternating direction implicit method applied to more general situations.

No abstract

No abstract