Analysis of pumping test results of North West aquifer using numerical techniques

Abstract

This report is intended to analyze the pumping test results of North west aquifer using nu1nerical techniqu-2s. The pumping test results were taken from Water Resources Board , Sri Lanka. These pump tests were carried out during the period March l980- m arch l98l. in analyzing the flow to a pumped well, the radial flow can be represented by a differential equation, which is derived from Darcy's law. There are various approaches to solve this differential equation of radial flov1 to an aquifer. These methods are dependent on the type of aquifer and the condition of flow. Therefore suitable method should be selected for particular problem. Most of these approaches are graphical methods. A numerical method was introduced by K.!{. Ruston (Ruston, K.R. & Chan, Y.K. ~976). In graphical methods, the differential equation of radial flov1 are solved using analytical expressions. Generally these analytical expressions contain-~ infinite integrals and summations of higher transcendental functions. Therefore the evaluation of these analytical expressions is sometimes difficult. But the values of aquifer parameters can be obtai;1ed by matching the theoretical curves derived from analytical expressions with the field data. The same differential equation can be solved by using numerical techniques. In one such technique a discrete space -discrete time model is introduced to represent the radial flovJ in an aquifer. Thus, the saoe differential equation for radial flow can be replaced by the discrete space- discrete time numerical mode1 • The number of assumptions can be reduced in using numerical technique compared to the graphical methods. In addition to that, most of the actual field conditions can be included in to a single numerical solution. These field conditions are leakage, variable saturated depth