Hazard, vulnerability and risk on the Brahmaputra basin: a case study of river bank erosion.

The authors present an assessment of risk from river bank erosion in the Brahmaputra river basin. The concept of risk is conceptualised in the context of socio-economic vulnerability, and the potential for exposure to hazard. By addressing both the physical hazard and the variations across the socio-economic surface the approach presented attempts to spatially combine these parameters to provide a risk surface for use by policy makers and decision makers at a number of administrative levels. The concept of vulnerability and risk as a description of the status of a society with respect to an imposed hazard such as flooding or the associated bank erosion exacerbated by climate change is deep rooted in a very broad research effort and its associated publications. In part, this reflects the complex evolution of the underlying notion of hazard - which itself shows the concurrent evolution of a series of strands each representing one disciplinary tradition. The concept of vulnerability has been very widely treated in the literature, and For present purposes an acceptable approach to vulnerability may be to start with an influential (but still controversial) established model by IPCC (2001) who have developed working definition - and then explore its ramifications in order to develop a set of working definitions and operational indicators for the project. This provides a pragmatic route towards a realistic target. It also offers a possible buffer against the common experience that the more sophisticated indices of vulnerability are strongly sensitive to contingent local/historical circumstances. This approach is explored within this chapter. The hazard posed by unabated bank erosion has been analysed with the help of satellite imagery based data and through adoption of Plan Form Index along with its threshold values develop for the Brahmaputra. The land loss to erosion is depicting a significantly rising trend which has obviously contributed to the impoverishment of the riverine population. The attendant uncertainties of climate change of hydrological and hydraulic river behaviour may exacerbate the channel instability of the Brahmaputra.