Evaluating the environmental impacts of hard coastal engineering structures on groundwater salinity and salinity intrusion: Insights from the Marawila Coastal Zone, Sri Lanka

Coastal erosion and groundwater salinity intrusion pose significant threats to beaches and their socio-economic values. Hard coastal engineering structures are commonly implemented to mitigate erosion but can inadvertently exacerbate the groundwater salinization. This study investigates the severity and drivers of groundwater salinity intrusion, focusing on the impact of hard coastal engineering structures on groundwater salinity in the Marawila coastal area, Sri Lanka. Marawila coastal area has been managed using hard coastal engineering structures since 2010 and is currently experiencing groundwater salinity issues. Groundwater electric conductivity (EC) was measured in 100 shallow wells during monsoon and non-monsoon periods and spatially analyzed using ArcGIS. Twenty-three borehole tests were conducted perpendicular to coastal protection measures to assess the landward variation of groundwater EC. Additionally, sea level, tide level, rainfall, significant wave height and soil particle size distribution data were analyzed. Semi-structured interviews were conducted to capture coastal users’ perceptions on salinity intrusion. The findings reveal that rainfall has a significant impact on groundwater salinity intrusion. The minimal rainfall, coupled with higher wave activity, significantly increased the groundwater EC. Hard coastal engineering structures were found to elevate groundwater salinity by enhancing wave setup, while sea level and tide levels have a minimal impact. Rising groundwater salinity has affected household water security, increasing dependence on purchased drinking water and leading to financial burdens. The findings highlight the need for integrated coastal management strategies that address salinity intrusion alongside erosion control. Beach nourishment emerges as a potentially sustainable alternative, provided its cost and durability are manageable.