Abstract:
Anuradhapura which is situated in dry zone area, is one of the major agricultural areas of the
country with wide range of agricultural crops being cultivated. There are many tanks, which
were built by ancient kings still in use for agricultural purposes. Area extent of surface water
of these water bodies vary with time as a result of both natural processes and human practices.
Therefore, it is essential to monitor them for agricultural management and other planning activities of the area. Remote Sensing technology can play a significant role in modeling spatiotemporal changes of surface water resources. In this study, the surface area changes of some important water features of Anuradhapura district during the period of 2000–2016 were investigated
using the multi-temporal Landsat 5-TM, 7-ETM+ and 8-OLI images. Different satellite-derived
indices including Automated Water Extraction Index (AWEI), Normalized Difference Moisture
Index (NDMI), Normalized Difference Water Index (NDWI), Modified NDWI (MNDWI) and
Normalized Difference Vegetation Index (NDVI) were calculated from Landsat data to evaluate
their performances for the extraction of surface water. The images were classified in to two
classes, land and water by applying a land-water threshold manually. Through trial and error
method and comparison to reference maps, proper land-water thresholds for each index were
determined. Absolute error and overall accuracy were calculated to assess the accuracy of the
results. Best index for water feature extraction from Landsat data was selected after analyzing
accuracy assessment. The best performances was observed in AWEI in comparison with other
indices. Therefore, the spatiotemporal changes of the selected water features were modelled
using the AWEI. During the study, changes in the surface area of water bodies were observed
in three different time periods; from year 2000 to 2007, from year 2007 to 2010 and from year
2010 to 2016. It could be identified that the fluctuation of surface area changes of water features
does not indicate a specific pattern during these three periods in almost all the selected water
features
