Environmental impact assessment on water quality deterioration caused by the decreased Ganges outflow and saline water intrusion in south-western Bangladesh

This paper deals with an environmental impact assessment of low water flow in the river Ganges during a dry period at the Khulna and Mongla port areas in south-western Bangladesh. Large-scale surface water withdrawal in India after commissioning the Farakka Barrage causes a drastic fall in the Gange s low-flow condition within the Bangladesh territory during every dry perio d. The average lowest discharge in the Ganges is 552 m(3)/s, which is about 73% less than that in the pre-Farakka time. This has caused the deteriorat ion of both surface and groundwater quality of the study area. Salinity is the principal cause of water quality degradation in the area, Present obser vation shows that the surface water of the area is sulphate-chloride domina ted, which signifies high salinity whereas the groundwater is categorized a s of medium to high salinity. To maintain the Rupsa River's maximum salinit y below 1000 muS/cm the discharge in Garai basin is similar to 10 m(3)/s. I f this present situation continues it will be a crippling blow to the envir onment of the area in the long term. An integrated multidisciplinary approa ch to hydrogeological refurther deterioration.