Brahmaputra basin faces unprecedented flood wave in Aug 2017

In the morning of Aug 11, 2017, while checking my daily morning routine sites, I saw the sudden appearance of purple patch (signifying rainfall in access of 175 mm rainfall in previous 24 hours) on NASA daily rainfall accumulation map for Indian subcontinent.[i] The purpose  patch covered parts of the West Bengal, North East Indian and Bangladesh. I was taken aback, but it was not very unusual to see in the peak of monsoon. So as we usually do, I took a screenshot and put up on SANDRP FB page with a warning that this could lead to floods. I did not realize that this was the beginning of an unprecedented wave of floods for these regions that may extend to Ganga basin as I write this. Such purple patches generally disappear in 24 hours, since the rains do not last to long. However, in the case of current phase, not only the purple patch has last now for 42 hours, it has extended  to the west, all along India Nepal region along the southern boundary of Nepal.  

By the time I write this, the CWC flood forecasting site[ii] has already shown at least seven flood forecasting sites in orange colour, signifying that at these sites the river water level was within less than half a meter of the Highest Ever Flood level achieved for that site. These included Torsa, Raidak-I, Sankosh, Gaurang, Beki rivers (all northern tributaries of Brahmaputra) and also Brahmaputra itself at three sites: Neamatighat, Dibrugarh and Tezpur. Closer scrutiny revealed that at many other sites, even though they were shown in pink dot (signifying that river water level is above the danger mark), they were likely to turn orange or red in over the next 24 hours.

Screen shots of CWC flood forecasting sites as on Aug 11 2017

In case of at least one site, namely Raidak-I river at Tufanganj site in Cooch Behar district of W Bengal, the site was already red as I write this, signifying that the river water level has already crossed the HIGHEST EVER FLOOD LEVEL for that site and had attained a new HFL. The river here has already crossed the earlier recorded highest ever flood level of 36.36 m, attained 24 years back on Sept 21, 1993. So the flood here was worst ever, worst in any case in a quarter century.

Assam and parts of W Bengal that had already experienced several waves of floods earlier this monsoon, were thus facing the prospects of even higher, unprecedented floods. Neither the state nor the centre is ready to face this new wave, from all available indications.

In the table below I have given an overview of these sites where water level has already come within half a meter of highest ever recorded flood levels, of the water level attained, water level forecast and HFL recorded on CWC’s flood forecasting site.

FLOOD MONITORING SITES WHERE RIVER WATER LEVEL REACHED CLOSE TO HIGHEST FLOOD LEVEL AT RESPECTIVE SITES

Site name River Dist/ state HFL attained / Date RWLevel attained / Time – Date RWLevel forecast / Time – Date
Golokganj Sankosh Dhubri/ Assam 30.95 /

08-09-2007

30.51-R / 10-1208[iii] 30.5-R / 18-1208
30.75-R / 19-1208 30.8-R / 06-1308
Tufanganj Raidak-I Cooch Behar/ WB 36.36 /

21-09-1993

36.22-R / 10-1208 36.36-R / 18-1208
36.46-R / 18-1208 36.56-R / 06-1308
Ghugumari Torsa Cooch Behar/ WB 41.46 / 03.08.2000 41.36-R / 10 – 1208 41.5-R / 14-1208
41.22 / 15/1208 41.3-R / 22-1208
41.25-R / 19-1208
Kokrajhar Gaurang Kokrajhar/ Assam 43.6 /

20-08-2015

43.16-F / 10-1208 43.1-F / 18-1208
Tezpur Brahmaputra Sontipur / Assam 66.59 / 27-08-1988 66.13-S / 15-1208 66.33-R / 09-1308
66.15-R / 18-1208
Neamatighat Brahmaputra Jorhat / Assam 87.37 / 11-07-1991 87.27-S / 0600-1208 87.36-R / 09-1208
87.17-F / 18-1208 87.00-F / 09-1308
Dibrugarh Brahmaputra Dibrugarh / Assam 106.48 / 03-09-1998 106.13-F / 06-1208 105.73-F / 18-1208

(unit: Meters)

Ganga Basin to face unprecedented floods next? That the Ganga basin could also face similar unprecedented flood situation in coming days is also apparent from the flood forecast at Basua site in Supaul dist in Bihar along Kosi river (Ganga Basin), already on Aug 12, 2017. The HFL for this site is 49.17 m (reached on Aug 25, 2010). Actual river water level here at 2300 hours on Aug 12 was 49 m, forecast to reach 49.23 m at 0700 hours on Aug 13. This means the river water level here is expected to achieve new HFL on Aug 13 morning already.

Damage in Assam The full dimensions of the impact of this particular wave of flood is not known as yet it will take at least a couple of days to get clear picture. However, the extent and intensity of the impact is only likely to be greater than the earlier wave. As per the latest available Flood report from Assam Disaster Management Authority[iv] the damage in this round of flood assessed so far is given below. These numbers are so far lower than earlier rounds of floods, but these numbers are likely to go up rapidly in next few days.

  • Districts affected: 19 (66 circles, 1752 villages)
  • Crop area affected 1 lakh ha
  • Population affected 99 lakh
  • No of people in relief camps 63800 In 268 camps
  • No of people dead 5
  • No of houses damaged 56 (fully) + 13 partially
  • No of people rescued 2615

This flood wave, when it reaches Bangladesh, along with all the heavy rains in that country, the flood situation in Bangladesh could also worsen in days to come.

Questions about dams and other interventions in North East During the earlier rounds of floods in Assam & rest of North East India, the role of dams, hydropower projects and embankment breaches had come into focus and questions were raised about efficacy of these structures. Similarly, the govt attempt at dredging the river, creating waterways, building roads cum embankments on both sides of Brahmaputra were also questioned in the context of floods. There is already demand for decommissioning of Ranganadi Hydro in Arunachal Pradesh and Loktak Hydro Project in Manipur, in addition to Dumbur Dam in Tripura earlier and also demand for scrapping of Lower Subansiri Hydro in Arunachal Pradesh Assam border. The role of CWC had also come into sharp focus with questions about how useful its flood forecasting is since many areas where floods occur, there is no flood forecasting by CWC and at other locations, their flood forecasting is too late, erroneous or just not available to right people at right time.

SANDRP (ht.sandrp@gmail.com)

END NOTES:

[i] https://trmm.gsfc.nasa.gov/publications_dir/instant_2.html

[ii] http://www.india-water.gov.in/ffs/current-flood-forecast/

[iii] Explanation: 30.51-R / 10-1208: 30.51 is in meters, as all levels are. R stands for Rising, similarly S stands for steady and F stands for Falling. This shows that trend of this site at this location, both in terms of actual level and forecast level. 10 means 10 hours, 1208 means 12 Aug.

[iv] http://www.asdma.gov.in/pdf/flood_report/2017/Daily_Flood_Report_12.08.2017.pdf

5 Comments on “Brahmaputra basin faces unprecedented flood wave in Aug 2017

  1. This is the problem of flood in North East region.One of the solution is flood moderation by construction of dams on rivers Subhansiri, lohit ,Siang etc.

    But environment al loby may opose such proposal s .
    Sandrp should give constructive suggestions
    On such problems..

    Like

    • how could you ensure that the dams in Subansiri, Lohit and Siang wil able to control the floods in its downstream.

      Like

      • I do not think it is possible to ensure that. The Dams are being proposed with basic objective of hydropower generation, which requires high storage level, contrary to the requirement of low storage if the dams are to provide flood cushion. Moreover, the dams are supposed to generate peaking power, which means floods everyday, twice a day in morning and evening, with no or very low flows rest of the hours. Thirdly, the character of the floods changes in the downstream area, including water and silt flow pattern. This is the experience of most dams.
        Himanshu

        Like

  2. Very good and timely narration of the situation. We are using as a story in GreenWatch Dhaka.

    Like

  3. Pingback: Brahmaputra basin faces unprecedented flood wave in August 2017

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