Thursday, September 19, 2013

Flood Risk Assessment Of River Kosi And Disaster Management

From Geology  Pre-Issue Publication

Exploring the channel connectivity structure of the August 2008 avulsion belt of the Kosi River, India: Application to flood risk assessment- R. Sinha, K. Gaurav, S. Chandra and S.K. Tandon

The August 2008 avulsion of the Kosi River, northern India, resulted in a maximum eastward shift of >100 km and created an avulsion belt of 2722 km2. Based on A.D. 2000 Shuttle Radar Topography Mission data and on 2005 Landsat Thematic Mapper satellite image–derived channel network (pre-avulsion), we use a topography-driven connectivity model to simulate the avulsion pathway, which corresponds, to a large extent, to that observed in the post-avulsion period. We then use this model to postulate the avulsive course of the river from another upstream point based on avulsion threshold analysis. Our results demonstrate that this model has the potential for postulating the path of an avulsive channel, and can provide a priori information on the areas likely to be flooded following an embankment breach. 

The Kosi flood and channel shifting in 2008 absolutely devastated large extents of Bihar, so this kind of research is urgently needed. The problem is that it may sit within the confines of a small number of geomorphology experts and not make its way to people who draw up disaster management plans. As geologist K.S. Valdiya not so far back lamented, geology and geologists have not found their way or have not been invited to sit in position that can influence policy.

Sometime despite explicit warnings from geologists, government apathy is to blame. Take the recent flash floods and destruction of Kedarnath town in the High Himalayas. Its not that geologists were unaware of the danger. A recent documentary on National Geographic interviewed many geologists who expressed little surprise at the extent of damage done by the floods. The combination of steep Himalayan slopes made up of foliated fractured rocks, glacial debris, moraine blocked lakes that could breach and overflow and narrow valleys where precipitation and stream waters get focused and funneled into raging torrents makes for an elevated risk of landslides, debris flows and floods during heavy rains.

Ignoring all advice government authorities turned a blind eye as the town of Kedarnath made up of often flimsy substandard construction mushroomed unplanned unregulated in the narrow river bed and floodplain of the Mandakini river. That is inviting catastrophe and nature at some point will oblige.


  1. It's all of a pattern- specialists will not be consulted. All matters will be decided by the civil servants who have TWO WHOLE MONTHS' experience in the area- having been posted just then to the Department of Irrigation and Flood control from the Department of Handlooms and Handicrafts.

  2. Ha Ha... how right you are L.. :)