Assessment of surface and sub-surface waterlogged areas in irrigation command areas of Bihar state using remote sensing and GIS

Satellite remote sensing coupled with Geographical Information Systems (GIS) offers an excellent alternative to conventional mapping techniques in monitoring and mapping of surface and sub-surface waterlogged areas. In the present study, pre-monsoon and post-monsoon surface waterlogged areas were delineated in all the 132 irrigation command areas of the Bihar State, India using Indian Remote Sensing (IRS-1D) Linear Imaging Self Scanning Sensor (LISS-III) data acquired during the period 2002-2003. Normalized Difference Water Index (NDWI) was used primarily to delineate surface waterlogged areas. Perennial waterlogged and seasonal waterlogged areas were identified for the study area by integrating the waterlogged areas derived for both the pre- and post-monsoon seasons under GIS environment. Results show that the total surface waterlogged area in Bihar is 628x10³ ha, which is 10.57% of command area (5939x10³ ha) and spread over 132 command areas. Perennial surface inundation covers 2.95% of the waterlogged area in all the command areas. Maximum waterlogged area is observed in Gandak command (212x10³ ha) followed by Eastern Kosi irrigation scheme (116x10³ ha) and Sone modernization scheme (82x10³ ha), respectively. Further, waterlogged areas induced by rise in groundwater level were also assessed spatially under GIS environment using the ground water level data pertaining to pre- and post-monsoon seasons of the year 2002-2003 which were spread all over the study area. The analysis of pre- and post-monsoon groundwater levels indicates that the area under non-critical category during pre-monsoon period was reduced from 4287x10³ ha (72.72% of command) to 1391x10³ ha (23.42%) in the post-monsoon. Area under most critical category during post-monsoon period increased from 0.083x10³ ha of command area in pre-monsoon period to 50x10³ ha. The study demonstrates utility of integration of remote sensing and GIS techniques for assessment of waterlogged areas particularly in regions where waterlogging conditions occur both due to excessive irrigation and accumulation of rain and floodwaters.