(Feature Image: Ganga river flowing in severe flood condition in Rishikesh on August 14, 2023. Image Credit: PTI/ Source: DH)
On August 14, 2023, there was flash flood in Alaknanda rivers in Uttarakhand causing sharp rise in water level at Center Water Commission (CWC) stations along Alaknanda upto Devprayag and then along Ganga in Rishikesh and Haridwar. The volume of water was so huge that it narrowly missed breaching the June 2013 peak flood level at Rishikesh and Haridwar site. This report tries to analyze hydrographs of 15 CWC flood monitoring sites on Alaknanda and Ganga rivers to assess the actual flood levels in these rivers during this flood spell in comparison with the previous peak flood levels attained on these sites.
Chhinka
The flood spell started from Chhinka site on Alaknanda in Chamoli district where the river witnessed a sharp rise of 6.83 meter in one hour (from 1004.17 meter at 24:00 hour on 13.08.2023 to 1011 meter at 01:00 hour) on 14.08.23. The sudden rise in water level was also 5.31 meter higher than the highest flood level (HFL) of 1005.69 meter dated 19.08.2019 at the Chhinka site.
There are three upstream sites on Alaknanda River namely Badrinath, Joshimath and Pipalkoti and one site Suraithota on Dhauliganga river where no significant rise in water level was observed during this period.
The sudden rise at Chhinka is possibly attributed to a ‘cloud burst’ incident in the area. However, there is no official information available about the event.
Birahi
The Birahi is a new site on Birahiganga close to its confluence with Alaknanda in Chamoli. The flood level increased by 1.35 meter in 36 hours at this site (between 01:00 hour on 14.08.2023 to 13:00 hour on 15.08.2023). The hydrograph of the site did not register the rise in water level at the site from 02:00 hour on 14.08.2023 to 12:00 hour on 15.08.2023 for unknown reasons.
The flash flood in Birahiganga appears to have affected the 7.2 Mw Birahi Ganga hydro power project in the early morning hours of 14.08.2023. As per this short local media report, two workers of Hydro Power Limited plant were trapped in a vehicle near the project site and were later rescued by police as the flash flood had washed away a bridge and approach road near Gaadi village there.
The HFL for the site 1042.24 dated 07.08.2020 was also breached by the event, setting up 1042.55 meter as new HFL on 15.08.2023. The new HFL has then been breached twice at the same site, first on 18.08.2023 (1042.72 meter) and second on 19.08.2023 (1042.88 meter).
Birahi site is located upstream Chhinka site on Birahiganga river and the flood level in Birahiganga must have added to the sudden increase in water level recorded at Chhinka on August 14, 2023. CWC has wrongly mentioned the Birahi site on Alaknanda River in place of Birahiganga River.
Nandprayag
The Nandprayag site is located on the Alaknanda River after its confluence with Nandakini river in Chamoli district. The site witnessed a rise of 1.78 meter in 7 hours (from 851.52 meter at 24:00 hour on 13.08.2023 to 853.3 meter) on August 14, 2023. The hydrograph for the site did not record the hourly rise in water level for 6 hours between the above-mentioned period. However, the peak flood level of 853.3 meter remained 0.40 below the warning level (WL) of 853.7 meter at the site.
Karanprayag (A)
After Chhinka the sharp rise of 5.72 meter crossing WL 758.5 meter and danger level (DL) 759.5 meter in three hours has been recorded at Karanprayag (A) site on Alaknanda river in Chamoli district. The water level rose from 754.88 meter at 01:00 hour to 760.6 m at 04:00 hr on 14.08.2023 at the site. However, it fell 0.75 meter short of the HFL 761.35 m attained on 19.06. 2021.
Karanprayag (P)
Karanprayag (P) site is located on Pinder River before its confluence with Alaknanda in Chamoli. A rise of 1.35 meter in one hour was recorded at this site when the flood level increased from 769.15 meter at 01:00 hour to 770.50 meter at 02:00 hour on 14.08.2023. But the flood level remained below the WL of 772 meter.
The Pindar valley had also witnessed excessive rainfall event in early morning hours of August 14, 2023, causing flash flood destruction along Pranmati river a tributary joining Pindar river near Tharali block in Chamoli district. The deluge in Pranmati washed away 5 homes, 2 bailey, 2 foot and 1 motor bridges apart from damaging farmlands in the area and subsequently added into the flood level of Alaknanda.
Rudraprayag (A)
The site is located on Alaknanda River before its confluence with Mandakini in Rudraprayag district. The flood level at the site went up by 5.7 meter in four hours (from 624 meter at 01:00 hour to 629.7 meter at 05:00 hour) on 14.08.2023. The flood level did cross the WL 626 meter and DL 627 meter in during these hours but fell 5.15 meter short of breaching the HFL 634.85 meter dated 17.06.2013 at the site.
Rudraprayag (M)
The site is located on Mandakini River before its confluence with Alaknanda River in Rudraprayag district. The flood level at this site crossed the WL 625 meter and DL 626 meter by rising 5.6 meter and in two hours (from 623.4 meter at 03:00 hour to 629 meter at 05:00 hour) on 14.08.2023. But, the peak level 629 meter was 5 meter short of HFL 634 meter dated 17.06.2013 at the site.
Rudraprayag (Conf)
Rudraprayag (Conf) site is located after the confluence of Mandakini and Alaknanda rivers in Rudraprayag district. The site recorded a rise of 6.02 meter in flood level in ten hours (from 618.78 meter at 19:00 hour on 13.08.2023 to 624.8 meter at 05:00 hour) on 14.08.2023.
The hydrograph has not registered the hourly rise in water level at the site between 20:00 hour on 13.08.2023 and 04:00 hour on 14.08.2023. The flood progress is missed in the hydrograph for the same time period on 14 and 15.08.2023.
The flood level had crossed the WL 623.7 meter and the DL 624.7 meter but remained 8.2 meter lower than the HFL 633 meter attained at the site on 17.06.2013.
Srinagar
Alaknanda river witnessed a sharp rise of 3.02 meter in four hours (from 534.18 meter at 03:00 hour to 537.2 meter at 07:00 hour) on 14.08.2023 at Srinagar level forecast site in Pauri Garhwal. The flood level crossed the WL 535 meter and DL 536 meter but fell short by 0.7 meter from the HFL 537.9 meter dated 17.06.2013.
Devprayag (B)
Devprayag (B) site is located on Bhagirathi River before its confluence with Alaknanda in Tehri Garhwal. The flood level at this site increased by 8.3 meter in five hours (from 461.5 meter at 04:00 hour to 469.8 meter at 09:00 hour) on 14.08.2023.
The flood level did cross the WL 462 meter and DL 463 meter but fell 4.7 meter shorter than reaching the HFL 474.5 meter dated 17.06.2013 at the site. No significant rise in flood level was seen at upstream Koteshwar site on the river during this period indicating that the flood spell has mainly affected river course downstream of Koteshwar site.
Devprayag (A)
Devprayag (A) site was opened after 2013 on Alakananda River upstream of its confluence with Bhagirathi in Pauri Garhwal district. The river recorded a huge increase of 9.12 meter in five hours (from 460.85 meter at 04:00 hour to 469.97 meter at 09:00 hour) on 14.08.2023 in flood levels at the site before declining fast. The peak flood level 469.97 meter is 2.49 meter higher than the previous HFL 467.48 meter attained at this site on 19.10.2021.
Devprayag (G)
This is the first site on Ganga River after the confluence of Bhagirathi and Alaknanda in Pauri Garhwal district. The flood level here increased by 7.9 meter in five hours (from 459 meter at 04:00 hour to 466.9 meter at 09:00 hour) on 14.08.2023. The WL 462 meter and 463 meter were breached but the peak flood level fell 5.6 meter short of the HFL 472.5 m attained on 17.06.2013.
Rishikesh
The flood level in Ganga at Rishikesh level forecast site in Dehradun district increased gradually from 339.65 meter at 01:00 hour to reaching the peak of 341.3 meter at 12:00 hour on 14.08.2023 and stayed at this level for four hours before coming down.
The river crossed the WL 339.5 meter and DL 340.5 meter but the peak flood level fell 0.42 meter lower than reaching the HFL of 341.72 meter dated 05.09.1995 at the site. Interestingly, 341.45 meter was the peak flood level recorded for this site on 17.06.2013 and the peak flood level of 14.08.2023 missed reaching the 2013 peak flood level by only 0.15 meter.
Haridwar (Dudhia Band)
At Haridwar (Dudhia Band) site in Haridwar district, the HFL on Ganga River has been 296.3 meter dated 19.09.2010, attained after the river crossed the old HFL 296.23 meter of September 1978. The river has attained 295.75 meter as peak flood level at this site on 17.06.2013.
Notably, 295.7 meter has been the peak flood level at the site on 14.08.2023 which is just 0.05 meter lower than the June 2013 flood level and 0.6 meter & 0.53 meter lower than the HFL of September 2010 and peak flood level of September 1978.
Summary
River Ganga has indeed witnessed a high scale flood event during August 14-15, 2023. The deluge mainly started in Alaknanda basin downwards the Chhinka site. The flood level in Alaknanda River was possibly further increased by huge volume of water brought in by some of the tributaries like Birahiganga, Nandakini, Pinder & Mandakini rivers in sequence during this period.
The Chhinka, Birahi, Nandprayag, Alaknanda (A) and (P) are new flood monitoring sites functioning after 2018, hence there is no data of peak flood level rise at these sites in June 2013. The HFLs at three sites of Nandprayag, Alaknanda (A) and (P) attained in June 2021 remained uncrossed during August 14, 2023 flood spell. However, the Birahiganga at Birahi and Alaknanda river at Chhinka sites have attained new HFLs during August 14, 2023 flood spell.
The next three sites of Rudraprayag (A), (M), (Conf) on Mandakini and Alaknanda rivers have HFLs attained on 17.06.2013. All these sites did see a sharp rise of more than 5 meters in few hours but the August 14, 2023 flood levels have been more than 5 meter shorter at these three sites in comparison with June 2013 HFLs.
The Devprayag (A) site further downstream is the only site where August 14, 2023 floods gained a maximum rise of 9.12 meter in five hours. This is the third site where August 14, 2023 floods have set a new HFL, after Birahi and Chhinka. The Devprayag (A) site is functional after 2018.
While, the peak flood level of August 14, 2023 at Devprayag (G) – the first site on Ganga – has been 5.6 meter lower than June 2013 HFL; the river missed breaching the June 2013 peak flood level only by 0.15 meter at Rishikesh and by 0.05 meter at Haridwar site.
One of the key reasons behind this significant rise in flood level at Rishikesh and Haridwar sites on August 14, 2023 could be the record-breaking rains of 419 mm in Rishikesh and heavy rainfall of 66.8 mm registered at Haridwar manual gauge sites in 24 hours between 13-14 August 2023.
Similarly, the manual rainfall gauges at Chamoli (81.6mm), Nandprayag (54.6 mm), Josimath (50.0 mm), New Birahi, (44.0 mm), Nandkesri, (41.2 mm) and Karanprayag (31.8 mm) witnessed heavy rainfalls this period raising the flood level in the Alaknanda river significantly. In fact, the Chamoli district as a whole received 40.5 mm rainfall against the normal range of 08.00 mm between 13-14 August 2023 which is in large excess category.
The summary table below provides the details of difference in water level between HFLs and peak flood level during august 14-15, 2023 flood spell as observed in the hydrographs of 15 sites along Alaknanda and Ganga in Uttarakhand state.
Summary Table
| SN | Site/ River/ District | HFL/ Date | Peak Flood Level on 14-15.08.2023 | Difference in Flood level & HFL |
| 1 | Pipalkoti/ Alaknanda/ Chamoli | 1052.82 meter 19.06.2021 | 1051.6 m 08:00 hour 14.08.2023 | -1.22 meter |
| 2 | Birahi/ Birahiganga/ Chamoli | 1042.24 meter 07.08.2020 | 1042.55 m 13:00 hour 15.08.2023 | +0.29 meter |
| 3 | Chhinka/ Alaknanda/ Chamoli | 1005.69 meter 19.08.2019 | 1011 m 01:00 hour 14.08.2023 | +5.31 meter |
| 4 | Nandprayag/ Alaknanda/ Chamoli | 854.19 meter 19.06.2021 | 853.3 m 07:00 hour 14.08.2023 | -0.89 meter |
| 5 | Karanprayag (A)/ Alaknanda/ Chamoli | 761.35 meter 19.06.2021 | 760.6 m 04:00 hour 14.08.2023 | -0.75 meter |
| 6 | Karanprayag (P)/ Pinder/ Chamoli | 774 meter 17.06.2015 | 770.5 m 02:00 hour 14.08.2023 | -3.50 meter |
| 7 | Rudraprayag (M)/ Mandakini/ Rudraprayag | 634 meter 16.06.2013 | 629 m 05:00 hour 14.08.2023 | -5.00 meter |
| 8 | Rudraprayag (A)/ Alaknanda/ Rudraprayag | 634.85 meter 17.06.2013 | 629.7 meter 05:00 hour 14.08.2023 | -5.15 meter |
| 9 | Rudraprayag (Conf)/ Alaknanda/ Rudraprayag | 633 meter 17.06.2013 | 624.8 meter 05:00 hour 14.08.2023 | -8.20 meter |
| 10 | Srinagar/ Alaknanda/ Pauri | 537.9 meter 17.06.2013 | 537.2 meter 07:00 hour 14.08.2023 | -0.70 meter |
| 11 | Devprayag (A)/ Alaknanda/ Pauri | 467.78 meter 19.10.2021 | 469.97 meter 09:00 hour 14.08.2023 | +2.49 meter |
| 12 | Devprayag (B)/ Bhagirathi-1/ Tehri | 474.5 meter 17.06.2013 | 469.8 meter 09:00 hour 14.08.2023 | -.4.70 meter |
| 13 | Devprayag (G)/ Ganga/ Pauri | 472.5 meter 17.06.2013 | 466.9 meter 09:00 hour 14.08.2023 | -5.60 meter |
| 14 | Rishikesh/ Ganga/ Dehradun | 341.72 meter 05.09.1995 | 341.3 meter 12:00 hour 14.08.2023 | -0.42 meter |
| 341.45 meter 17.06.2013 | -0.15 meter | |||
| 15 | Haridwar (Dudhia Band)/ Ganga/ Haridwar | 296.3 meter 19.09.2010 | 295.7 meter 14.00 hour 14.08.2023 | -0.60 meter |
| 295.75 meter 17.06.2013 | -0.05 meter |
Bhim Singh Rawat (bhim.sandrp@gmail.com)
SANDRP 