Arunachal Pradesh and Assam need not spend sleepless nights even if the Chinese authorities release 9020 cumec of water on the Siang, which is known as the Yarlung Tsangpo or Yalungzangbu in China, due to heavy rainfall activities in Tibet.
A report published in the The Assam Tribune stated that at Pasighat in Arunachal Pradesh, the Siang is 756 metres wide and there the above added flow of the river will be able to raise its water level only by three metres. And, at Jonai, where the river enters Assam, the width of the river is around 7 km and hence the water level of the river will rise by only 30 cm there, said sources in the Water Resources Department (WRD) at Dhemaji.
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The report further stated that referring to the preliminary report issued by the Central Water Commission (CWC) on August 30, 2018 in this connection, sources said that though the Siang is in spate these days due to the rainfall activities in its upstream areas within the Chinese territory, “until and unless continuous rainfall occurs in the upper catchment between Tuting and Pasighat”, the high volume of discharge at Chinese stations alone would not create havoc in the downstream areas. Also, in the case of the main Brahmaputra, rise in the water levels of the major tributaries such as Lohit, Subansiri, etc., plays a vital role, said the sources, referring to the above CWC preliminary report.
WRD sources at Dibrugarh said the Siang was flowing at 414.79 metres at 9 am on Thursday at the Tuting gauge station of the CWC, 213 km upstream of Pasighat. It was found flowing at 415.04 metres at 7 am on Friday and 415.12 metres at 2 pm again on Friday, rising at the rate of 1 cm per hour at that gauge station. Thereafter, the river remained steady at 415.15 metres since 3p m, said the Dibrugarh WRD sources.
At Pasighat, the river was flowing at 153.40 metres at 11 pm on Thursday. The river was flowing at 153.27 metres at 12 am on Thursday night, at 153.30 metres at 5 am on Friday and at 153.28 metres at 2 pm again on Friday at Pasighat. There, the river was seen maintaining a rising trend at the rate of less than 1 cm per hour between 2 pm and 5 pm on Friday. At Pasighat, the danger level of the river is 153.96 metres.
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At Dibrugarh, 101 km downstream of Pasighat, the Brahmaputra is slowly rising. It was flowing at 105.30 metres at 9 am on Thursday and at 105.31 metres at 10 am on Friday and till 2 pm the river remained steady. The present level of the Siang at Tuting may raise the water level of the Brahmaputra by around 0.15 metres to around 0.20 metres at Dibrugarh, which will still keep the water level of the Brahmaputra below its danger level of 105.70 metres, lest no additional rainfall amount is added to the flow of the river in its upstream areas, said the Dibrugarh WRD sources.
The Tuting flow of the Siang water should require around 20 hours to reach Pasighat, while that of the river at Pasighat should require around 8 hours to reach Dibrugarh, WRD sources at Dibrugarh said.