TN-4 : Unsteady flow to a large-diameter well influence by a river and a no flow boundary

Abstract

Large-diameter wells are extensively used in many parts of the world. The cheapness and simplicity of construction and operation of these wells are often the main reasons for their use. Besides, large diameter wells are suitable for shallow aquifers with low transmissivity. In many situations an impervious boundary or a recharge boundary is encountered in the vicinity of the well. In the present report a general but simple mathematical tool has been developed to analyse unsteady flow to a large-diameter well located near a river and an impervious boundary. The analysis has been done using image well theory and discrete kernel approach.

Variations of drawdown at the well point with time have been presented in non-dimensional form for various durations of pumping and for different values of storage coefficient for specific positions of the hydrologic boundaries. The influence of the hydrologic boundaries on drawdown at well point has been analyzed. The recovery of the well storage when the well has been pumped for different durations have been determined for different values of storage coefficient. Making use of the graphs, the time required for 90 percent recovery of the well storage can be known. It is seen that as the value of storage coefficient decreases the time span for 90 percent recovery increases.