The 2016 flood of Bihar, India: an analysis of its causes

Abstract

Flood is common in the sub-Himalayan plains of the Indian state of Bihar. During the massive flood of the Ganga between 18 and 31 August 2016, 15 (out of 38) districts and 3459 villages of the state were affected. The flood inundated 6006 km2 of area, harmed 8.82 million people, and caused damages worth US$ 73.99 million. To investigate the factors behind the event, we utilised SRTM elevation data and Landsat-8 OLI images to extract drainage networks and reservoirs of the region. Inundated area was delineated using MNDWI on MODIS data of 25-Aug-2016. Different hydrometeorological parameters employed in the study include percentage departure of monthly rainfall, discharge data of selected dams and barrages, and gauge data from six stations along a 526 km stretch of the Ganga: Buxar, Gandhi Ghat (Patna), Hathidah, Munger, Kahalgaon, and Manikchak Ghat. It was found that the flood was mainly caused by rapid release of water from the Bansagar Dam on the Son from 18 to 20-Aug-2016, as a tropical storm traversed through its upper catchment. Contributions from the Ganga’s Himalayan tributaries and upstream of the flooded area were negligible. The flood peak (50.52 m), recorded at Gandhi Ghat on 21 August 2016, passed downstream, and reached Manikchak Ghat (25.78 m) on 27–28 August 2016. The upstream extension of flooding due to the highest recorded flood level of 26.66 m of the Ganga at Farakka can only reach up to 6 km above Kahalgaon. Therefore, impoundment of the Ganga by the Farakka Barrage cannot have any impact on inundation of the areas above that limit and did not cause the 2016 floods.