Impact of tropical cyclone storm surges on groundwater salinity in southwest regions of Bangladesh

Excess salinity in drinking water is a serious issue along the southwest coastal of Bangladesh, mainly in reclaimed lands where around 14 million people live and sustain in low-lying deltas. The low-lying deltas are particularly vulnerable to episodic tropical cyclones. The tropical cyclones induced storm surges cause severe floods and extensive damage and result in the salinity in surface water and subsurface water, which have serious impacts on human health such as hypertension and food security due to loss in agricultural yield. In 2011, two years after Cyclone Aila hit the southwest regions of Bangladesh (in 2009), many parts of these regions were still underwater which caused disruption of water supply and contamination of drinking water. The lands were unproductive due to excessive salt in soil and water. A fully coupled surface-subsurface model of a coastal low-lying land is used to investigate the role of tropical cyclonic storm on long-term salinity of water resources in Bangladesh. The hydrogeological parameters of the model were calibrated using data from fieldwork at the site of a pond in Dacope, Khulna. We used the observed water level data from a station at Mongla during Cyclone Aila hit southwest regions of Bangladesh (26 May 2009).The results show how groundwater salinity changes in response to storm surges and monsoon in the coastal low-lying areas. Near-surface groundwater salinity (below 1m-2.3m) takes 4-6 years to return the salinities to pre-surge levels by monsoonal rainfall.