Flood characteristics and dynamics of sediment environment during Anthropocene: experience of the lower Damodar river, India

摘要

Flood is considered as a very common natural disaster associated with the Indian rivers, and the lower Damodar river has been experiencing it since the long past. Heavy monsoonal rainfall during the short time period enhances the river flood which devastates mainly the lower part of the lower Damodar basin. The present study aims to analyse the past and present floods in the lower Damodar river using the recorded data and fluvial deposits, and also the societal interaction with these river floods. The entire work was carried out on the basis of a detailed field survey and secondary database. The recorded discharge data used in flood frequency analysis reveals 2 years of recurrence interval of flood during pre-dam condition; while in the phase of the post-dam situation, it was shifted to 10 years and 20 years recurrence interval at Rhondia gauge station and at the Damodar junction bridge site respectively. The mean grain size (M-z) of sediment distributed downstream ranges from 3.32 phi to 1.19 phi with significant variation in the downstream sorting process. This anomaly is due to high discharge events during the monsoon period and extensive unscientific sand mining during the lean period. The coarse and mixed grain sediment layers in the sediment succession of the lower Damodar river provide evidences of past flood events. In 2017, the lower part of the lower Damodar basin has experienced floods for 3-5 days, and more than 330,000 people along with many socio-economic and socio-cultural structures were severely affected. This study may help the concerned authority to take scientific steps for the necessary upgradation of the existing flood management systems to minimize flood vulnerability of the riparian society.