Devastation of Ganga Basin in Uttarakhand in June 2013; Precautionary Management Measures Dr. B.P Das Expert Consultant FAO, UN Former Engineer In Chief & Chief Advisor Department of Water Resources, Odisha Former Vice Chairman, EAC for River Valley & HE Projects, MoEF Chairman, Expert Body for studying Uttarakhand Disaster, MoEF

Flood Risk assessment: lessons learnt from recent disasters in india Case Study (CS)-5 Flood Risk assessment: lessons learnt from recent disasters in india Devastation of Ganga Basin in Uttarakhand, June 2013 Precautionary Management Measures Dr. B. P. Das Former Chief Advisor & Engineer-in-Chief, WR, Odisha Former Vice Chairman, EAC for River Valley & HE Projects, MoEF Chairman, Expert Body for studying Uttarakhand Disaster, MoEF Chairman, Monitoring Committee, Indira Sagar & Omkareswar Command Area in Narmada Basin, MoEF Expert Consultant to FAO April 7, 2016

Introductory Remark Alakananda total catchment ~ 11787 Km2 Uttarakhand experienced unprecedented rainfall during June 15-17 (over 30,000 Km2 area) and catastrophic flood in Bhagirathi-Alakananda-upper Ganga Basin causing massive devastation with colossal, loss of life and property. Massive landslides originating in GLOF of Chorabari lake above Kedarnath exacerbated the disaster. Cloud bursts probably triggered by monsoon trough getting dragged north wards by the strong advancing westerly trough, precipitated 250-400 mm in a 24 hour spell around Kedarnath, Gangotri and Badrinath a rare phenomenon at + 3000 m elevation, extending to lower elevation. Dehradun experienced a massive 590 mm in two days. Alakananda total catchment ~ 11787 Km2 As a consequence of GLOF, the flood discharge at Kedarnath was around 2000 m3/sec, increasing to 6000 m3/sec at Rudraprayag from Mandakini (a mere 1664 Km2).

Introductory Remark Bhagirathi, total catchment ~ 7813 Km2. Upper Alakananda contributed almost 5000 m3/sec, a major contribution coming from the main arm upto Joshimath. Flood at Srinagar HE Project (CA-11,332 Km2) attained an unprecedented figure of 12,000 m3/sec, which the dam safety disposed, however causing serious bank scour, deposition downstream . Bhagirathi, total catchment ~ 7813 Km2. Major flood contribution of 7000 m3/sec from basin upstream of Tehri dam (CA-7,208 Km2). Outflow from Tehri dam limited to 400 m3/sec, saving the downstream. Peak flood at Hardwar (Assessed by THDC – 14,459 m3/sec) The fragile geology of the over bank, highways hugging the steep river edge and pore water pressure induced sliding phenomenon upon receding flood led to massive landslides.

Bhagirathi-Alakananda River System

Advance in South-West Monsoon-2013

Advance of South-West Monsoon-2013

Catastrophic Hydro Meteorology Details Unique episode of two weather systems converging & remaining stationary for several hours resulted in huge accumulated rainfall over most of North India, one month before normal monsoon onset. River Location Peak flood (m3/sec) Mandakini Rudraprayag 6000 Alakananda 8740 Srinagar 12000 Bhagirathi Tehri Dam 7535 Ganga Devprayag 10647 Haridwar 14457 Ganga at Haridwar would have received 21,400 m3/sec in the absence of Tehri Dam, which would have wiped away large urban stretches of Rishikesh and Haridwar.

Inflow & Outflow at Tehri

Situation at Haridwar

Isohyetal Map of Alakananda-Bhagirathi Basin

Depth-Area-Duration (DAD)Curves

Landslide Landslides are the geomorphic expression of slope instability that occurs when shear stress in a part of the slope/whole exceeds the shear strength. Major landslides located in the transitional zone between the lesser and higher Himalaya. The entire stretch from Kedarnath to Soneprayag highly vulnerable to landslides (Ref. Landslide Inventory released by NRSC/ISRO). Heavy rains accompanied by cloud bursts and change of moderate debris laden slopes into near vertical slopes during road widening and building construction triggered slope failure/landslide. These slides aggravated high flash flood along Mandakini basin. In Alakananda basin majority of landslides along NH-58 occurred in areas where road widening work was in progress, just completed. 300 slides were already there in 2010, which were further activated.

Deluge of 16th & 17th June 2013 at Kedarnath & other areas along Mandakini valley was the result of heavy & incessant downpour during the period & the breach or GLOF of Chorabri Lake (moraine dammed glacial lake). Intensity, devastation gauged by the fact that the downstream townships up to Sonprayag have been almost completely wiped out. Kedarnath township area & the valley are located geologically/ meteorologically high hazard terrain. The mobilization of giant boulders forming part of the morainic dump in Kedarnath area became source material for the destruction & razed almost every civil structure to ground that came their way.

Flood Spilling on 17th June

Deposition Upstream of Barrage Vishnu Prayag (400 MW)

Pertinent Points Of the 70 HEP’s planned (including commissioned and under construction) about 23 major projects are above 50 MW capacity. Only 5 projects are operational with capacity of about 4000 MW. Almost 60% of the riverine reach in the main rivers will be having head race tunnels in the flank in the relatively younger Himalayan geological formation, also seismically active. Will they impact, activate under earthquake condition. The problem of heavy sediment flow, attacking the head works in the upper reaches in 3000 to 1500 m elevational range is a distinct possibility. Land slides add to the sediment load not considered in the formulation of dead storage capacity. Significant aggradation of the river bed upto 5 m depth has occurred in Alakananda basin, which will cause the HFL to rise significantly above design assumption.

Lessons Learnt & Precautionary Measures The 2013 was marginally influenced by the hydro projects which have been commissioned / under construction but is a wake up call to Engineers, Geologist and the Civil Society. Absence of Installation of Real Time Telemetry Network and Flow Forecasting Mechanism at every project, which in a way did cause unpreparedness need very urgent attention. The IMD warning and the Meteorological scenario of the rapidly advancing monsoon did not receive due importance from the State authorities, the linkage of meteorological forecast with the possible devastation from such large precipitation (about 200 mm) on the first day and consequential flood risk was not duly analyzed. Influence of the regional geology on the vertically cut slopes of moraine and conglomerates was not critically assessed to prevent wide spread river bank cutting for development. The natural morainic dams at glacial lakes & volume of lake must be constantly monitored to avoid such devastations. Strengthen the morainic dams at the mouth of lakes, constant draining out of the lake is to be ensured so that they do not reach the breaking point.

THANK YOU bishnupdas@hotmail.com