Geomorphology and the controls of geohydrology on waterlogging in Gangetic Plains, North Bihar, India

Waterlogging is a complex phenomenon, the severity of which depends on a number of natural as well as anthropogenic factors. The present study pertains to the evaluation of control exerted by various factors, viz geomorphology, relief, groundwater fluctuation, rainfall, catchment area and canal-road network density, on waterlogging in the north Bihar region of Gangetic Plains. Satellite images IRS P6 LISS III acquired in the years 2005 and 2006 were used to map temporal variability in surface waterlogging which revealed a reduction of 52 % in the waterlogging area during the pre-monsoon. The seasonal groundwater fluctuation was examined using 2005-2006 pre- and post-monsoon water level data. It clearly indicated that a large portion of the area was also under highly critical groundwater level occurring at a depth of less than 1 m belowground surface during the post-monsoon periods. The percentage of waterlogged area per square kilometer in each geomorphological unit clearly depicts that the Kosi megafan (Lower), because of a high density of paleochannels, comprises the highest post-monsoon waterlogged area. The Tropical Rainfall Measuring Mission (TRMM) data were analyzed for the period 1998-2009 to examine the spatial variability of rainfall over the entire catchment during the monsoon period. The high incidence of post-monsoon surface waterlogging delineated through satellite data and high average rainfall (> 1,100 mm) in the same area indicates a positive relationship between rainfall and surface waterlogging. Waterlogging is more prominent in the lower relief zones, but anomalous relative rise in waterlogging within 40-50 m of relief zone was attributed to anthropogenic factors primarily related to the development of canal network.