New Paradigm to Ensure Reliability of Dam Functioning in the Times of Climate Change

Subash Chander Mittal,
Chairman and Managing Director,
DMR Hydroengineering and Infrastructures Ltd 11th Oct 2023  

Dams are the structures built across the rivers to serve societies welfare. Societies repose great trust upon Engineers and Managers for Robustness , Reliability and Safety of Dams Functioning.

 

Climate change in 21^st Century is a reality. Recent Incidents indicate that current design , construction and operation practices of Dams are not sufficient to account for climate change.

 

Incidents of 2013, Kedarnath – Chorabari lake Burst , Severely impacted the functioning of Phata Byeung Dam in Mandakini Valley. High Intensity rains and cloud burst overwhelmed  Vishnuprayag Barrage in Alakhnanda Valley.

 

2021, (Flashflood in Rishi and Dhauli ganga rivers – severely affected Rishiganga Hydroelectric project and Tapovan Vishnugad Hydroelectric Project  Barrage and its appurtenant structures in Uttarakhand.

 

In Aug , 2023, several Hydropower projects in Kullu and Mandi Districts of Himachal Pradesh were overwhelmed raising concerns.

 

Recent, Oct 2023, incident of Lake Outburst in upper reaches of Teesta Valley resulted in Severely affecting the functioning of Teesta III and Teesta V Dams, which also resulted in washing out of several permanent bridges across Teesta River.

 

Gated Spillways in Dams are planned to successfully handle and mitigate the high floods of 1000 years or more return periods. An innovation in Gated Spillways in the form of low level gated spillways as an alternative to Crest type Gated Spillways , was introduced in Late 1990s for Himalayan Hydropower dams in India to provide for passing of sediment laden flows and high floods to preserve the Live Capacity/Pondage required for Peaking operation.

 

Both Crest Type gated Spillways as well as Low Level Gated Spillways have been found inadequate to handle sudden flashfloods coupled with movement of Boulders , Debris and Tree Logs.

 

With Spillways non functional , both concrete Dams and Earthen Dams have been found to be overtopped. Concrete Dams have withstood overtopping with limited damage. The Earthen Dams , Earth and Rockfill Dams , Rockfill dams , CFRDs and other embankment dams are presently not designed for overtopping as it is assumed that under the severe most condition, the available freeboard will ensure its safety. This assumption is found to be vitiated  with non- functioning/non-operation of Gated Spillways in critical hours and technical personnels at dam site are unable to control the situation.

 

Provision of Overtopping protection for all Existing Earthen Embankment Dams including Rockfill Dams and CFRD Dams in Himalayas Hydropower Projects is considered as the First Critical Intervention requiring immediate implementation to ensure their capacity to handle future Lake Bursts and Non-Functional/Non-Operative Gated Spillways Scenarios.

 

The provision of ungated Spillways to supplement the Gated Spillways in all Concrete and Rockfill Dams are considered to be next Requirement to face climate change induced floods.

 

Current Technical Literature and Standards on Dams do not address the Climate Change induced Scenarios, therefore there is a need to upgrade the Knowledge of Engineers, Managers and Planners regarding Coping the future situations in existing Dams.

 

Dam Safety protocols for Existing and New Dams should be based upon , new reality of 21^st Century as opposed to obsolete knowledge of 20^th Century.