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With climate-driven disasters on the rise, urgent action is needed to modernise flood resilience strategies worldwide.
Canada has a long history of recurrent flooding. Seven of the ten most costly flood events occurred between 1980 and 2019, and after 2010. This upward trend in flood risk is posing significant threats to critical structure such as dams and levees. However, as Islam et al suggest in recent research published by Discover Applied Sciences, national-level guidance on integrating resilience-based frameworks, and addressing climate risks and uncertainties in existing design flood estimation methodologies for dams and levees, are lacking.
The changes in the frequency and intensity of floods anticipated with climate change will be a challenge for conventional design flood estimation methods. As the authors explain, ageing dams in Canada also create an increasing risk. With approximately half of the country’s dams over 50 years of age, many were designed and well-maintained to withstand extreme events but weren’t designed with climate change in mind. In addition, it is claimed that some have deteriorated beyond repair and are vulnerable to failure even during moderate rainstorms and associated overland flows. Such vulnerability is now being exacerbated by the increasing occurrence of massive deluges, often following severe drought, which is a trend projected to intensify over time under climate change.
However, as Islam et al state, there currently is a lack of comprehensive and unambiguous guidance on climate-resilience-based frameworks, leading to confusion among engineers and policymakers. The authors wanted to address this gap by reviewing design flood estimation procedures, the potential impact of climatic trends and regional vulnerabilities to climate change, and the barriers and opportunities for advancing a climate-resilience framework. By studying the vulnerability of Canadian dams and levees to flooding in light of changing regional climatic patterns and associated hydrologic design criteria, the authors have tried to identify areas where interventions are necessary to enhance the climate-resilience of such assets.
The increasing trend of destructive floods across different parts of Canada and the projections of rising frequencies of higher return period floods in a changing climate, have highlighted the need for new regional and national initiatives to update design flood estimates. The authors say the conventional approaches which utilise stationary climatic assumptions are no longer adequate for calculating design values, and therefore new strategies must be developed to not only account for the dynamic behaviour of the climate system, but also alleviate undesirable consequences of future climate change. It is imperative, they add, to continuously update estimates of various risk components, including hydrologic loads, and monitor system response in order to enhance climate-resilience and inform the decision-making process.
Islam et al highlighted the various challenges for estimating climate-informed design floods for dams and levees. These include:
Design flood estimation for dams relies heavily on historical records of peak discharge and extreme precipitation events. A shorter record and incomplete information about storm characteristics introduce uncertainties. To overcome this, regional approaches are preferred for estimating frequency-based flood magnitudes and transposition of climatic variables and storm characteristics for estimating PMP-based floods.
Integrating copula-based multi-variate frequency analysis with the current design flood estimation guidance is crucial to address dependency between various flood characteristics (eg, flood peak, volume, and duration) and compound flooding (eg, joint occurrence of fluvial, pluvial, and coastal foods) in a realistic way.
Global warming is likely to augment the amount of water vapour in the atmosphere and consequently, changes in precipitation characteristics and extreme weather patterns are expected. This makes it important to explore non-stationary techniques for estimating design floods for both small and large dams, levees, and embankments and to develop associated design guidance.
The conventional design flood estimation approaches fall short in addressing the full extent of deep uncertainty. It is imperative to take steps to identify underlying those present at various stages of the design flood estimation process. This can be achieved by leveraging new understandings and statistical methods, such as by employing the Bayesian approaches to quantitatively capture the uncertainty, or performing sensitivity experiments across a plausible range of perception
Infrastructure designed by considering the impacts of climate change can offer increased service delivery and reliability, longer productive lifespan, and prolonged investment returns. Climate-resilience is a continuous process that must extend throughout the asset’s lifespan. There is documented evidence that investing in climate-resilience can result in benefits that can outpace costs by several folds.
In their work, Islam et al introduce a climate-resilience framework tailored for dams and levees. In this, the essence of resilience is encapsulated by threshold capacity, coping capacity, recovery capacity, and adaptive capacity of flood control structures.
Research in the US has also indicated an increased risk of dam failure due to a changing climate. Analysis of rainfall sequences and events associated with recent hydrologic failures of 552 dams across the country, suggests intensifying precipitation may contribute to increasing failures of dams by overtopping.
The decadal rate of dam failures has been increasing since the 1970s, and with over 90,000 ageing dams still in service, the increasing likelihood of intense rainfall is leading to increased concern about future dam failures.
As Hwang and Lall explain in Natural Hazards, conventional dam design criteria requires the spillway to be designed to handle the PMF using the PMP. Most large dams were designed to withstand extreme floods with an implied return period ranging from 104 to 107 years, as estimated by the PMF approach.
However dam failures in the last 20 years, and many near failures, suggest more modest return periods for failure. For example, climate conditions during the 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 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.
Studies in Iran have reached similar conclusions to 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 hydraulic structures under the impact of climate change need to be re-assessed.
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. bodies These include 477 glacial lakes and water bodies having water over an area greater than 50ha, and 425 glacial lakes 10-50 ha 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.
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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