International Journal of Geology, Earth and Environmental Sciences ISSN: 2277-2081 (Online) An Online International Journal Available at http://www.cibtech.org/jgee.htm 2012 Vol. 2 (3) September - December, pp.89-102/Mondal et al. Research Article 89 VULNERABILITY ANALYSIS OF EMBANKMENT BREACHING – A CASE STUDY OF MOYNA DRAINAGE BASIN IN PURBA MEDINIPUR WEST BENGAL INDIA Manojit Mondal 1 , Gouri Sankar Bhunia 2 and * Pravat Kumar Shit 3 1 Department of Geography, Ranchi University, Jharkhand, India 2 Rajendra Memorial Research Institutes of Medical Sciences (ICMR), Agamkuan, Patna-800007, Bihar, India 3 Department of Geography & Environment Management, Vidyasagar University, Medinipur-721102, West Bengal, India * Author for Correspondence ABSTRACT The breach of the Moyna drainage basin embankment in Purba Medinipur, West Bengal (India) marked the failure on conventional ways of controlling floods. Present study aimed to investigate the role of geotechnical, geometrical and hydraulic properties on embankment breaching of Moyna drainage basin area. A River Embankment Breaching Vulnerability Index (REBVI) was derived based on weightings of bank material to delineate the risk of vulnerability of the embankment. Amoeba diagram was used to represent the REBVI score. Cluster analysis was performed based on amoeba diagrams and vulnerability index for each indicator. Compaction tests results showed the average bulk densities of the embankment soil are 1.47g/cm 3 . The average plasticity index (PI) of Moyna drainage basin showed 28.26 per cent. The unconfined compressive strength (CS) of the bank materials varied from 0.43 kg/cm 3 – 4.69 kg/cm 3 , whereas, the mean safety factor (SF) of the drainage basin area was calculated as 0.67. The highest score REBVI values were recorded from Prajabard (Kasai River Right bank) and Gobradan (Keleghai Right bank), and the lowest score calculated at Bakcha (Moyna Drainage Basin Canal) and Dheubhanga (Kasai River Right bank). The result of the amoeba diagram analysis showed Kasai river right bank embankments occupied maximum area than other embankment of this drainage basin. Very high vulnerability points were delineated at Prajabard, Gobradan and Upalda, through cluster analysis, represented less potential to prevent embankment breaching. Key Words: Embankment, Bank Material, Geotechnical Analysis, Bank Geometry, Multi-Criteria Analysis INTRODUCTION Embankment breaching, an episodic process in fluvial dynamics, is affecting a wide range of physical, ecological and socio-economic issues in the fluvial environment, especially in developing countries. Because embankments are built of earth, usually that is presented locally, and are predisposed to breaches. These include the establishment and evolution of river and floodplain morphology and their associated habitats (Darby and Thorne, 1996a; Barker et al., 1997; Millar, 2000; Goodson et al., 2002), turbidity problems (Bull, 1997; Eaton et al., 2004), sediment, nutrient and contaminant dynamics (Reneau et al., 2004), loss of riparian lands (Amiri-Tokaldany et al., 2003), and associated threats to flood defense and transportation infrastructure (Simon, 1995). However, it can generate problems when rivers erode lands, wash away crops and demoralize the basis of local livelihoods. Moreover, floods increase the productivity of land, while fine sediment brought by river water; conversely, the deposition of large particles by sand casting harms agriculture. However, Moyna drainage basin area is located in Purba Medinipur district of West Bengal (India), where agriculture and fishing are the primary source of income of local people through out the historical past. However, earthen embankments in Moyna drainage basin (West Bengal) are beset with multi-facetted problems, such as erosion, breaching in every year. Historical records show that flooding and agricultural