PERFORMANCE EVALUATION OF A COLLECTOR WELL USING MODFLOW

Abstract

Conventionally, water supplies for drinking purpose have been drawn from sub-surface and/or surface sources. The system of tapping sub-surface water have been tube wells (vertical well), infiltration galleries, and radial collector wells. Nowadays, radial collector wells have become quite popular as the ground water supply wells. A radial collector well consists of a number of horizontal perforated pipes laid in an aquifer and connected to a vertical cylindrical caisson, plugged at the bottom end. In case of multiple laterals in a radial collector well, the laterals interfere with each other, and hence it is important to provide non-perforated portion of pipes near the caisson. Performance of such collector wells is assessed by estimating the safe yield which depends on several factors like: location of the radial collector well, length, diameter, direction, number, and percentage perforation of laterals, aquifer parameters, and permissible drawdown, etc. In this study, performance of a radial collector well located under riverbed, near a straight reach of a river, and near meandering river has been studied through numerical modelling using MODFLOW. While modelling the geometry, opening slots, and percentage perforation, etc. a concept of equivalent conductivity is used. Various possible lay outs with different number of laterals are analysed and safe yield is estimated in terms of dimension less parameters. Relationship between the safe yield and ranges of various parameters is proposed on the basis of regression analysis.