GUWAHATI, July 11 – The possible reason for the recent floods in Assam is the changes taking place in climate, observes Prof Nayan Sarma of the IIT, Roorkee, who is involved in an Indo-German project BRAHMATWINN, with its focus on the impact of climate change on the Brahmaputra.
He also warned, while talking to this correspondent, against any naïve attempt at tackling the State’s problems of flood and erosion. The solution has to be a very well-considered package of measures integrated on strong scientific analyses supported by prudent pilot studies with desired fine-tuning for long-term sustainability.
He underscored the need for massive soil conservation campaign to effectively reduce the sediment volume of the Brahmaputra along with creation of flood detention reservoirs, river training for erosion control, land reclamation and channelization, which may be supplemented by corrective dredging operations on selective basis.
Globally, the Brahmaputra river system has perhaps occupied one of the highest places for its loss of about 100 sq km of land per year to bank erosion. These eroded bank materials, coupled with the huge sediment volume contributed by the catchment area of about 5,40,000 sq. km, are much more than the sediment-carrying capacity of the Brahmaputra.
The around 800 million tonnes of sediment annually carried by the Brahmaputra is one of the highest in the world.
The annual specific yield of 3 cubic metres per second (cusecs) per square mile of the Brahmaputra is the highest in the world and as against that the average valley width is hardly 40 to 50 km only, while Brahmaputra itself occupies about 10 km of it.
Out of the annual runoff of 537.2 km3 for the Brahmaputra system, 429.76 km 3 volume of water flows during the four monsoon months. Due to constant silt deposition over the years on the main stem Brahmaputra and its tributaries, the rivers are becoming insufficient to safely carry this huge flow volume.
Even the over 4000 wetlands in the Brahmaputra valley, the rivers are fast degrading due to wanton encroachments and siltation, losing their flood absorption capacities.
The reasonably effective river management achieved by China for the Yangtze and the Yellow rivers may provide some direction in this case, Prof Sarma said.
He said the study done under the BRAHMATWINN indicated the likely impact of climate change with the temperature projected to increase in the Brahmaputra basin in the coming decades, the higher values being in the Tibetan Plateau.
Parameters directly dependent on temperature, like potential evapotranspiration, are also assumed to show clear trends of rise. This will have a severe impact on the hydrology of the Brahmaputra river basin. Different climate change indicators point to more frequent and prolonged droughts, said Prof Sarma.
