A comparison of current and design operational efficiencies of scavenger wells in lower Indus Basin of Pakistan and possibility of upconing problem

Abstract

Groundwater resources in lower Indus Basin, Pakistan are limited and mostly available in thin layers. Upconging of underlying saline groundwater will occur if overlying fresh groundwater is abstracted extensively. Once quality of fresh water is deteriorated because of upconing of saline groundwater, it is very hard to make it again fit for irrigation usage. Therefore, it is always advised to abstract groundwater without bringing saline groundwater into the fresh water layer. In the early 1990s, the Government of Pakistan installed about 378 scavenger wells in three districts of Sindh Province (Nawabshah, Sanghar, and Mirpur Khas). Out of 378 scavenger wells, 79 were installed on the right side of Jamrao canal to intercept canal seepage and recover fresh water for irrigation and other uses. In this study, we have investigated the performance efficiency of 79 scavenger wells to check whether these wells were performing with the design operational efficiency. We found that a large number of scavenger wells were operating with a maximum of 30 % of the design operational efficiency. The low operational efficiency can cause rise in water table and result in waterlogging in the study area. We also performed a 26-h pumping test on one of the scavenger wells to check whether any chances of upconing were happening and if both pumps (fresh water and saline water) of the selected scavenger well were operational. The pumping test results reveal that chances of upconing were negligible if the pumps are run within the permitted operational factor 0.6 (i.e., 14.4 h/day).