FLOOD HOT SPOT IDENTIFICATION AND MITIGATION - A CASE STUDY OF BIHAR

Abstract

Floods are frequent and most common phenomena among all natural disasters. Impact of flood is devastating in tropical or temperate regions, as they inundate large areas causing threat to life, damage to property and disruption in services. Approximately 68 percent of the global population vulnerable to flood falls within South and East Asian countries, out of which India alone accounts for nearly 23 percent of total affected population. Bihar is among the most flood prone state in India having 6.88 million hectares area liable to flood. The Kosi river basin is the major contributor in flood prone area in North Bihar presenting a challenge in terms of long and recurring flood risk. Kosi river basin extend up to 8000 m above mean sea level (MSL) in the Himalayas. After flowing in numerous hilly channels it converges to form main rivers namely Sun Kosi, Indravati, Tamba Kosi, Bhote Kosi, Dudh Kosi, Arun and Tamur in Nepal. All these important river converges at Tribenighat, Nepal and form source point of Kosi river at 1294 m MSL, coordinate 26°54′47″N 87°09′25″E. It enters Bihar at Bhimnagar, Birpur and drains into the Ganga river in Kursela, Bihar at an elevation of 40 m MSL, coordinate 25°24′43″N 87°15′32″E. Its total catchment is 74,500 km2 of which China – 35567 km2, Nepal – 27863 km2 and Bihar – 11070 km2. The catchment has an annual average rainfall of 1456 mm and total discharge of 52219 million m3. Its principal tributaries in Bihar are Bagmati, Kamala Balan, Bhutahi Balan. Flood risk analysis of Kosi river in Bihar based on flood mapping & analysis in HEC-RAS and ArcGIS has been done in present work. Ideally, the flood map should include information regarding all consequences of floods i.e. social, economic and environmental. Mostly the scope of flood maps is limited to the vulnerability aspects and ignores intangible and indirect losses. The study employs inundation mapping to identify flood hotspot in Kosi river basin of Bihar, India and its prioritization for effective flood management by multiple criteria decision analysis (MCDA). iii The method adopted for MCDA is choosing by advantage (CBA) with some modifications keeping it as choosing by Disadvantage (CBD) using social, economic and environmental impact as attribute and vulnerability index. Whereas, severity of flood corresponding to depth and velocity as severity index. The attribute considered in this study for social impact are human causalities, loss of shelter and livelihood, public inconvenience, health impact by water borne diseases, effect on education & administrative work. For environmental impact it is erosion, water pollution, ecosystem degradation and sewer outflows whereas productivity loss in terms of working hours, impact on agriculture and industries, property loss and expenditure on evacuation & rehabilitation are considered as attributes to the economic impact of flood for CBD analysis. Flood mitigation method by integrated flood risk management (IFRM) has been suggested in this study. Seven components of IFRM and its expediency in context of flood hotspot has been explained in the study.