Delineating suitable aquifers for agricultural and drinking water supply in Southwest coastal area

Abstract

Fresh water scarcity is one of the major problems in the southern region of Bangladesh. Khulna and Satkhira were selected as the study area since these two districts are widely recognized as areas affected by the most severe groundwater salinity problem. The main objective of the study was to delineate suitable aquifers for agricultural and drinking water supply in these two districts and the outcome of the study was a database for groundwater salinity distribution at different depths, which could be potentially useful for planning of southwest coastal groundwater resources as well as for any future research requiring salinity data. The study was conducted mainly based on secondary data and information. Secondary data included borehole electrical resistivity logs from Department of Public Health and Engineering (DPHE), electrical conductivity (EC) measurements by Bangladesh Atomic Energy Commission (BAEC), Bangladesh Agricultural Development Corporation (BADC) and Bangladesh Water Development Board (BWDB). Resistivity data were interpreted and verified for groundwater salinity (in terms of electrical conductivity), and together with other direct EC measurements were used to map groundwater salinity across the study area for different depths. A large number of lithological logs available in the study area were analyzed and treated in two-dimensional environment to produce stratigraphic units and determine vertical distributions of subsurface formations. These data together with salinity maps were used to identify suitable aquifer areas with acceptable limits of salinity for agricultural (i.e. irrigation water use for paddy) and drinking water uses. In Satkhira district, most of the suitable aquifers in terms of drinking and irrigation purposes are found in the shallow zone, while in few cases they are found in the main aquifer. Shallow aquifers at Chandanpur union in Kalaroa upazila contain fresh water zone i.e. EC is below 1000 μS/cm which is suitable both for irrigation and drinking water purposes. Banshdaha and Labsa unions in Satkhira sadar also have the fresh water in shallow aquifers. On the other hand, Brahmarajpur and Dhulihar unions of Satkhira Sadar do not have suitable aquifers either for drinking or irrigation purpose due to EC range above 3000 μS/cm. Shallow aquifers in Nagarhata union of Tala, Parulia union of Debhata, Assauni union of Assasuni, and Shyamnagar union of Shymnagar contain the fresh water which is suitable for both drinking and irrigation purposes. The shallow aquifers in Kulia union of Debhata, Nalta and Sreeula unions of Kaliganj and Shyamnagar and Ranjannagar unions of Shyamnagar are not suitable for drinking but are suitable for irrigation purpose. In Khulna district, the shallow aquifer zone in most unions (except Chalna and Koyra) of Koyra upazila belong the high EC that is not suitable for either drinking or irrigation purpose. In Chalna union of Koyra, water is suitable for both drinking and irrigation, and in Koyra union water is suitable for only irrigation. The shallow aquifers in Dacope upazila in general have high EC contents (greater than 4000 μS/cm) except Batiaghata union, where water is suitable for irrigation. The water quality in Batiaghata upazila is better, with most shallow aquifers suitable for both drinking and irrigation except Dighalia where water is suitable for only irrigation. Rupsha, Phultala, Terokhada, Khulna metro upazilas have fresh shallow aquifers suitable for both drinking and irrigation, while shallow aquifer of Dighalia upazila is suitable for irrigation only.