The paper presents an account of the Kusaha breach of the Kosi river which has been widely perceived as a flood event in the media and scientific circles. It is true that a large area was inundated after this event but it is important to appreciate that this inundation was different from a regular flooding event. It is argued that this event marked a mega-avulsion of the Kosi river. While the basic mechanism of this avulsion needs a detailed study, this paper aims to document the avulsion event and speculates the causative factors of the dynamics of the Kosi in general based on limited field evidence and available maps.

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