(Feature Image: NHPC’s Teesta VI hydro project at Sirwani, Sikkim affected by GLOF deluge on Oct. 04, 2023. Image Source: Weatherman Shubham.)
The Teesta River has witnessed unprecedented scale of floods following South Lohnak Glacial Lake Outburst Flood (GLOF) event in the intermittent night of October 03-04, 2023. The details and impact of the deluge can be seen here. The incident has once again underlined shortcomings in Central Water Commission’s (CWC) flood monitoring and forecasts work.
The CWC’s Flood Forecasts website shows 18 flood monitoring stations on Teesta River of which 12 are in Sikkim and 6 are in West Bengal. Out of 12 sites in Sikkim presently only 2 are functioning, 5 are non-functioning, 1 is inactive and 4 are wrongly listed on Teesta River while these are located on its tributaries. The issues observed at each of the sites and their current status is given in the table below.
| SN | Site/ District | HFL/ Date | Present status | Remark |
| 1 | Lachen/ North On upstream tributary of Teesta, Teesta gets from on confluence of Lachen and Lachung, about 400 m upstream of Chungthang | NA/ NA | Non-functioning since 22:00 hour 03.10.2023 | Despite being a base site has no information on Highest Flood Level (HFL) and date This site, if functioning, could have given fore warning of the flood traveling from South Lohnak lake to Chungthang and could have given 10-20 minutes lead time, that may have helped empty the Teesta 3 dam and open the spillway gates, in turn possibly helping save the dam. |
| 2 | Rangma Range/ North | NA/ NA | Non-functioning since 23:00 hour 03.10.2023 | The site has no information on HFL and date |
| 3 | Teesta III/ | NA/ NA | Non-functioning since 22:00 hour 03.10.2023 | This is first inflow forecast site for the 1200 Mw Teesta III dam. |
| 4 | Sankalang/ North | NA/ NA | Non-functioning since 22:00 hour 03.10.2023 | The site has no information on HFL and date |
| 5 | Teesta V/ East | NA/ NA | Non-functioning since 22:00 hour 03.10.2023 | This is inflow forecast site for the Teesta V Dam |
| 6 | Khanitar/ East | 297.7 m 18.09.1974 | This is first active site about 110 km downstream from Lachen site. Teesta river here breached HFL after 49 years and has set 298.4 meter as new HFL at 09:00 hour on 04.10.2023, 0.7 meter higher than the old HFL. | The water level increased here by 8.5 m in 9 hours from 289.9 meter at 24:00 hour (before flood level) on 03.10.2023 to 298.4 meter at 09:00 hour on 04.10.2023. The flood level remained above old HFL for 5 hours. |
| 7 | Melli/ South | 225.25 m/ NA | At Melli forecast site also the Teesta has breached old HFL, new HFL is at 225.5 m at 04:00 hr on 04.10.2023 which is 2.75 meter higher than the old HFL. | The flood level increased here by 13.07 meter in 03 hours from 214.93 meter (before flood) at 01:00 hour on 04.10.2023 to 228 meter at 04:00 hour on 04.10.2023. CWC did not have old HFL date for the site. Interestingly, the peak at the Melli site was attained at 04:00 hour while at upstream Khanitar site at 09:00 hour on 04.10.2023. The flood level remained above old HFL for 7 hours. |
Screenshot of Lachen, Rangma Range, Sankalang sites hydrographs with no updates on Teesta flood level.
Hydrographs of Non functional Teesta III & V inflow forecast sites of CWC’s during GLOF event.
The table below has details of 1 inactive and 4 sites wrongly listed on Teesta River.
| SN | Site/ District | HFL/ Date | Present status |
| 1 | Bakcha/ North | NA/ NA | The site is active but seems located on Dik Chu a tributary of Teesta River. |
| 2 | Sankalan/ North | NA/ NA | Inactive since 18:00 hour 12.11.2022 |
| 3 | Ranipool/ East | NA/ NA | The site is active but is located on Rongni Chhu a tributary of Teesta River. |
| 4 | Singtam/ East | 356.09 m/ NA | The level forecast site is active but located on Rongni Chhu a tributary of Teesta River. |
| 5 | Majitar/ South | 279.29 m/ 17.10.1985 | The site is active but is located on Rangit river a tributary of Teesta. |
There are 2 more sites found non-functioning and with no HFL details in Teesta basin during the Lhonak GLOF disaster, details of which is given in table below.
| SN | Site/ District | HFL/ Date | Present status |
| 1 | Bop/ North | NA/ NA | The site is on Lachung Chu upstream Teesta III dam and non-functioning since 24:00 hour on 03.10.2023. |
| 2 | Laven/ North | NA/ NA | The site is functioning and Talang Chu, a tributary of Teesta, but has no HFL and date. |
Table on status of 6 sites on Teesta River in West Bengal.
| SN | Site/ District | HFL/ Date | Present status |
| 1 | Singla Bazar/ Darjeeling | 311 m/ 05.09.1980 | The site is on Rangit river and inactive since 31.10.2021. |
| 2 | Coronation/ Darjeeling | 156 m/ 12.10.1973 | The site is partially functioning. Water level in hydrograph is missing for hours between 21:00 to 06:00 for the past 3 days. The peak level attained at this site during the relevant period is 149.2 meter at 08:00 hour on 04.10.2023, 5.7 m above the level before this flood, but 6.8 m lower than the HFL. |
| 3 | Sevoke/ Darjeeling | 147.3 m/ 12.10.1973 | The site is functioning and attained peak of 145 m during the relevant period at 08:00 hour on 04.10.2023 which is about 5.6 meter higher than the water level before the flood, but 2.3 meter lower than the HFL. |
| 4 | Gazoldoba/ Jabpaiguri | This is inflow forecast site. The peak water level 110.3 meter and discharges of 8252.4 cumecs were recorded at the site at 10:00 hour on 04.10.2023. Before the deluge water level and discharges at the sites were 107.5 meter and 1066.93 cumecs at 02:00 hour on 04.10.2023. | |
| 5 | Domohani/ Jalpaiguri | 89.3 m/ 04.10.1968 | The GLOF has caused rise in water level by 1.12 meter from 84.83 meter at 06:00 hour to 85.95 meter at 10:00 hour on 04.10.2023 at this level forecast site. The flood level crossed the warning level of 85.65 meter and touched the danger level of 85.95 meter but remained below the HFL by 3.35 meter. |
| 6 | Mekhliganj/ Cooch Behar | 66.62 m/ 20.10.2021 | The flood level at this level forecast site increased by 1.01 meter from 65.27 meter at 10:00 hour to 66.28 meter at 14:00 hour on 04.10.2023 and missed reaching the HFL by 0.34 meter. |
Screenshots of CWC’s sites on Teesta river in West Bengal during GLOF event on Oct. 04-05, 2023.
The CWC has listed 6 sites on Teesta River in West Bengal. Of these Gazoldoba is inflow forecast site while Domohani and Mekhliganj are level forecast site. The site of Singla Bazar is wrongly listed on Teesta River while it is located on Rangit river in Darjeeling and is inactive since October 2021. Interestingly, the GLOF event has not caused HFL breach at any of the 5 sites on Teesta River in W Bengal.
Summary CWC is supposed to monitor floods in Brahmaputra basin from May 1 to October 31 annually as per its Standard Operating Procedure (SOP) for flood monitoring. The analysis of CWC’s website and hydrographs reveal that there are only 7 flood monitoring sites on Teesta River in Sikkim and presently only 2 sites Khanitar and Melli are functioning. The GLOF events has caused HFL breach at both of these sites. The remaining 5 sites along the Teesta River are non-functioning since the GLOF occurred.
Hydrographs of Khanitar and Melli sites where GLOF has led to breach in HFLs.
The CWC has been able to issue no inflow (from Teesta III & Teesta V) or level forecast (from Melli) before, during or after the flood disaster in Teesta valley. Apart from sites located on Teesta River, there are no flood level updates for Lachen site along Lachen river and Bop site on Lachung Chu since 22:00 hour on 03.10.2023. The site is located upstream Teesta III dam in Chungthang.
The Lachen site, if functioning, could have given forewarning of the flood traveling from South Lohnak lake to Chungthang and could have given about 10-20 minutes lead time, that may have helped empty the Teesta 3 dam and open the spillway gates, in turn possibly helping save the dam and also reduce the downstream disaster proportions. But this site provided no readings after 10 pm on Oct 3 and no explanation is forthcoming why this is so.
Referring to CWC’s sites, the press release by National Disaster Management Authority (NDMA) issued on 04.10.2023 mentions that first surge of water was 19 meters above the maximum water level at Sankalang site and 04 meters above the maximum water level at Melli site.
The Sankalang site hydrograph has not been updated since 22:00 hour 03.10.2023. If it was able to record the levels at these sites why same have not been reflected on the hydrographs for the respective sites.
So far, there is no official statement or report from CWC about the impact of GLOF event on its flood monitoring stations. The CWC’s Daily Flood Bulletin (Oct. 04 & Oct. 05) and Daily Flood Situation Cum Advisory (Oct. 04 & Oct. 05) in past two days have not mentioned or revealed anything about the GLOF incident and its impact on CWC flood monitoring network.
Sharad Chandra, Director, Flood Forecast and Monitoring Division, CWC on twitter (now X) just shared a very general information about the GLOF incident at 06.37 hour on 04.10.2023 which reads, “There is a lake outburst around midnight at #Chungthang, #NorthSikkim causing concern in catchment of River #Teesta. Low lying areas such as #Gazoldoba, #Domohani, Bangladesh area may be affected.” Contrary to statement, the Sikkim state has been impacted severely by the GLOF disaster and not W Bengal. The statement makes no reference to situation of flood monitoring or flood forecasting sites of CWC not about the washing away of the Teesta III dam or about the flow rates of the unprecedented GLOF aftermath.
It is worth mentioning that only in March 2023, a Parliamentary Committee report had raised serious concerns on severe shortage of meteorological and monitoring stations in Himalayan regions.
Moreover, in recent past there have been many such occasions, when CWC flood monitoring and forecast has been found absent at crucial moments asking for a lot of independent review and improvement. The GLOF disaster is latest example of this where CWC has once again totally failed.
It is high time we, particularly our governments, but also civil society, media and judiciary take the flood forecasting much more seriously, note CWC’s repeated failures and the conflict of interest involved in its work. The first thing that must happen is an independent assessment of flood forecasting during this disaster, this monsoon and in general.
Bhim Singh Rawat (bhim.sandrp@gamil.com)
SANDRP 
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