Abstract:
Accumulation of excess salts in the root zone resulting in a partial or complete loss of soil
productivity, which hampers crop production and reduces the utility of lands. The extent of
salt-affected lands in Sri Lanka are about 223,000 hectares or about 3 percent of the land
cover of the island. Identification of salt-affected lands and estimation of their salinity levels
are very important for land use planning and restoration.
In this study, salt-affected lands in Hambantota district of Southern Sri Lanka are identified
and demarcated into different categories according to the salinity levels using GIS and
Remote Sensing technologies. An extensive soil survey was conducted to collect soil samples
throughout the district. The sampling was done with a manual soil auger. Electrical
Conductivity and pH of the samples were determined.
Field salinity data are mapped in a GIS environment of ArcView 3.2a and Ilwis 3.2 for
Windows. To create salinity distribution maps, surface interpolation Inverse Distance
Weighting (IDW) method developed by Environmental Systems Research Institute, Inc., was
used.
In the Hambantota district, salinity levels are high along the coastal belt. Highly salinized
areas were identified in Tangalle, Ambalantota, Hambantota, Lunugamwehera and
Thissamaharama where salinity is greater than 4 dSm*1. In Katuwana, Weeraketiya and
Okewela areas, saline levels were lower than 2 dSm'1 while in Beliatta, Angunakolapalassa
and Sooriyawewa, moderately saline areas were located with salinity levels of 2 - 4 dSm*1.
The study helps to produce a salinity map of the Hambantota District. From the total land
area (including inland water resources) of the Hambantota district (2120 square kilometers),
40% of in-lands have no threats from salinity (855 sq.km.). Thirty eight percent of the land
in the district (806 square kilometers) is of slightly or prone to salinity. There is 433 square
kilometers (20%) of land, which are moderately saline and needs improvement. It was
revealed that from the total area of 2120 sq km, there is an extent of 25 square kilometers
(1%) where salinity is severe.
The Remote Sensing analysis conducted using the digital satellite data (30x30 meter
resolutions) helped to locate saline areas. It was revealed that optical parameters of the
Acacia leucopholea as a reliable indicator to identify the salinity spots when Remote Sensing
techniques are used to locate saline patches in Hambantota District.
