Abstract:
Coastal groundwater systems are at risk of saltwater intrusion caused by excessive
pumping and rising of sea levels. To address this, vulnerability assessments of
coastal aquifers is crucial. This study aimed to use a model with Geographic
Information System (GIS) to assess groundwater vulnerability of seawater
intrusion in coastal line from Negombo to Galle, observe salinity distribution
patterns, predict salinity intrusion, and examine the influence of geology and
population. The GALDIT model considered factors influencing vulnerability to
seawater intrusion, including groundwater occurrence, aquifer hydraulic
conductivity, depth of groundwater level above the sea, distance from the shore,
impact of existing seawater intrusion, and aquifer thickness. For the purpose of this
study groundwater data from 2016 to 2019 in both during and off monsoons for
above factors were measured in addition to the data on population and geology.
The used model demonstrated high explanatory power and showed that the
existing status of seawater intrusion was the most influential factor. The study
found lower salinity intrusion during monsoon seasons compared to off-monsoon
periods. No significant relationship was observed between salinity data and
population. Vulnerability maps categorized divisional secretariats, identifying
Beruwala, Colombo, Ambalangoda, Hikkaduwa, Bentota, and Balapitiya as the
most vulnerable areas. Leucocratic rock type majorly affects, and Alluvial
Lagoonal Clay formations have minimal impact on salinity intrusion. The
findings offer valuable insights for sustainable management of coastal
groundwater resource. Future implications suggest including transient population
in assessments for a more accurate understanding of water demand.
