Design |


Above: India is prompting a design review of all existing dams and those under construction vulnerable to Glacial Lake Outburst Floods (GLOFs)


Oroville spillway failure in 2017, as well as during the Michigan dam failures in 2020, were shown to be relatively moderate. Notably, of the 630 recorded failures, 18 were primarily induced by snowmelt during moderate rainfall events. The authors say many of the recent dam failures, including Oroville, the Michigan dams, and the Libyan dam failures in 2023, highlight two main factors: The overtopping failure was associated with multiple prior rainfall events that led to “watershed memory” or high “antecedent soil moisture”, and to a full reservoir at the time of the last rainfall event that led to overtopping. Reservoir operators invariably kept the reservoir relatively full due to operational requirements anticipating future water demands, or to meet regulatory requirements, and hence there was low flood storage capacity when the overtopping storm occurred.


The authors say these conditions fall well below the assumed design criteria that are designed using extreme storm scenarios of some duration, under extreme antecedent moisture conditions as the causal factor. They conclude the current hydrologic infrastructure design standards are insufficient, given the substantial increase in the frequency of extreme meteorological events. Therefore traditional design criteria needs to be revisited to consider a broader set of conditions that may actually lead to failure.


Iranian research Studies in Iran have reached similar conclusions to


References


Climate resilience of dams and levees in Canada: a review by M.R.Islam, M. Fereshtehpour, M.R.Najaf, M. N. Khaliq, A.A.Khan, L.Sushama, V.T.V Nguyen, A.Elshorbagy, R.Roy, A.Wilson,· J. Perdikaris, M B.Masud, M.S.Khan. Discover Applied Sciences (2024) 6:174 https://doi.org/10.1007/ s42452-024-05814-4


Increasing dam failure risk in the USA due to compound rainfall clusters as climate changes Check for updates by Jeongwoo Hwang & Upmanu Lall, npj Natural


Hazards (2024) 1:27 https://doi. org/10.1038/s44304-024- 00027-6


Why structural solutions for flood control should be adapted to climate change? by Hosseinipoor, M, Mollaei Rudsary, A, Danesh- Yazdi, M.et al. Nat Hazards (2024). https://doi.org/10.1007/ s11069-024-06969-4


those carried out across North America. Despite utilising hydraulic structures for decades to control floods, their expected performance under the varied frequency or intensity of extreme precipitation due to climate change may be now less certain. This study used remote sensing and field data in the Imamzadeh Davood watershed in Central Northern Iran, which experienced a devastating flash flood in July 2022. Data was collected on river morphology, the structural characteristics of 18 check dams, and sedimentation patterns By using recorded data from synoptic stations, the distinct role of extreme precipitation in intensifying the flood incident was also investigated. The findings revealed an unprecedented > 100-year


return period precipitation event in the catchment, with devastating consequences that underscore the escalating impact of heavy rainfall due to climate change in many regions. In-situ observations revealed that all 18 check dams were destroyed between 17% and 100% during the flood event, while upstream check dams showed a higher degree of destruction. The external stability analysis demonstrated that under static forces, 100% and 62% of the check dams were potentially resistant against sliding and overturning, respectively. However, given the observed destruction of all check dams and high deposition depth of sediment in the river corridor, further analysis by considering dynamic forces and rock impact indicated the shock imposed by the unprecedented debris flow, was responsible for the cascade failure of check dams from upstream to downstream. These findings by Hosseinipoor et al in Natural


Hazards highlight that to increase the resiliency of flood control systems, the design principles of


20 | December 2024 | www.waterpowermagazine.com


hydraulic structures under the impact of climate change need to be re-assessed.


GLOF design review The Central Water Commission (CWC) in India has


decided to review the design flood of all existing dams and those under construction that are vulnerable to Glacial Lake Outburst Floods (GLOFs). This is to ensure their adequate spillway capacity for a combination of Probable Maximum Flood/Standard Probable Flood and GLOF. The decision was made following the collapse of the


Teesta-III hydroelectric dam in October 2023. A GLOF from Lhonak Lake washed away the 60m high dam that was a part of Sikkim’s largest hydropower project. Furthermore, GLOF studies have now been made mandatory for all new planned dams with glacial lakes in their catchments. CWC monitors 902 glacial lakes and water during the period from June to October every year. These include 477 glacial lakes and water bodies having water over an area greater than 50ha, and 425 glacial lakes 10-50ha in size. Such mandatory inspections will enable the detection of any changes, identifying those which have expanded substantially during the monitoring month from a disaster perspective. The Committee on Disaster Risk Reduction, with


representatives from six Himalayan States and other stakeholders, has identified a set of high risk glacial lakes. Expeditions will visit these to directly assess the lakes and prepare comprehensive mitigation strategies in terms of setting up early warning systems and other structural and non-structural measures. Forty-seven dams (38 commissioned and nine under construction dams) have been identified as likely to be affected by GLOF in the Indian territory. GLOF studies have been completed for 31 projects. The Ministry of Earth Science through its autonomous institute, the National Centre of Polar and Ocean Research, has been monitoring and carrying out scientific research on two pro-glacial lakes in the Chandra Basin, since 2013.


Safeguarding tailings NewRange Copper Nickel is embarking on four key


studies to assess whether new mining technology and sustainability developments can further enhance environmental safeguards and mining performance for its NorthMet project in the US state of Minnesota. The company is studying a variety of tailings


storage options that will minimise impact by reusing the former LTV iron ore tailings facility and cleaning up impacts from previous iron mining operations. Options include keeping the current design detailed in permits, potentially refining the current design to use a centreline dam design, or possibly relocating tailings storage to nearby unused mining pits. “Our NorthMet project already represents the


largest private investment in the cleanup of former mine sites in Minnesota’s history. We are evaluating if we can make this project even better. Regardless of which option is identified as the best solution, our objective is to ensure that tailings storage is safe and stable, and that we take advantage of any reasonable opportunities to clean up old contamination,” said Tannice McCoy, President and General Manager of NewRange.


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