GH23B-1243 - Impact of storm surge inundation and monsoonal flushing on drinking pond salinity in coastal Bangladesh

Salinity in surface water and groundwater is a major problem along the southwest coastal region of Bangladesh where over 14 million people are living. Comprised a reclaimed land from a network of low-lying polders, the area is particularly vulnerable to flooding from tropical cyclone storm surges. These episodic events (such as tropical cyclones Sidr (2007) and Aila (2009)) result in the salinization of drinking water (and other) ponds and near surface groundwater, causing disruption to water supplies and impacts on human health. Managing recovery from such events is crucial in order to mitigate these effects. It is, therefore, important to identify the controls surface water and groundwater salinity in these low-lying coastal areas. HydroGeosphere, a fully coupled surface-subsurface model of a coastal polder, is used to investigate the impact of storm surge inundation on a drinking water pond. The model was calibrated using data from a field experiment at the site of a drinking water pond outside Polder 31. The results show how the salinization of the drinking water pond and near-surface groundwater changes in response to inundation events and monsoonal flushing. In addition, episodic salt fluxes from inundation events can cause high pond salinities and subsequent infiltration into underlying sediments and groundwater. Flushing by monsoonal rainfall of the near surface groundwater salinity takes around 6-8 years to return concentrations to pre-surge levels.