In the mountainous areas of India, landslides can cause extensive damage, loss of infrastructure, and hundreds of fatalities each year. When combined with the impact of extreme weather, the region’s fragile geological and geomorphological conditions can accelerate many landslides, with most occurring in the monsoon season from June to September when India receives 68% of its rainfall. In particular, the country’s North-Eastern Himalayan State of Sikkim experiences a large number on a yearly basis.
As Biwajit Bera recently discussed in Natural Hazards Research, the increasing number of landslide incidents, glacial lake outburst floods, and other climate change-related hazards ‘can raise a critical question about the sustainability of big dam projects in this kind of active tectonic belt of the Himalayan area’.
He gave the example of the Glacial Lake Outburst Flood which occurred at South Lhonak Lake in October 2023. It destroyed the Chungthang dam (part of the Teesta III hydropower project), washing away several structures and part of National Highway 10. Consequently, the author claims, it also affected part of the Teesta Stage V project too, as slope strength can be reduced as a result of toe erosion of the river.
In addition, Bera says, the region also experienced continuous rainfall in June and July 2024 which can increase pore water pressure over the slope and the slope steepness, with less vegetation cover and high anthropogenic imprints significantly accelerating slope instability processes too.
A massive landslide then occurred in August 2024 at Dipu-Dara near Singtam in Sikkim. Measuring over an area of 0.02km2, it was 175m long and 136mwide, bringing down a huge part of the slope over the National Hydroelectric Power Corporation’s Teesta V 510MW hydropower project. A large part of the powerhouse was destroyed, with the tailrace tunnel gate structure and gas insulated switchgear building also being affected. Teesta V is not expected to become operational again until 2026.
The Teesta V dam is an 88.6m high, 176.5m long concrete gravity structure impounding a regulating reservoir for daily power peaking. The head works divert flow into the desander and a 17km headrace tunnel which runs through fragile phyllite, schist, slate and quartzite rocks – decreasing rock strength, Bera claims. Numerous past earthquake epicentres are located between Dikchu and Signtam and its nearby areas, with the highest 5.45 magnitude earthquake recorded in the vicinity of the slide area in 2013.
‘The frequency and magnitude of landslides along the Singtam-Dikchu road are being increased due to fragile geology, cloudbursts and the execution of the Teesta Dam V power station and 17km underground head race tunnel. More research is required for hazard risk reduction, particularly in the populated Teesta River basin within the Eastern Himalayan terrain,’ Bera says.
He goes on to claim that the Teesta V landslide highlights how hydropower station construction in the steep slopes of the Himalayas can accelerate the pathways of big destructive landslides in the region. He urges the Central Government of India and State Government of Sikkim to review these projects with ‘a new direction’ because the economic impact after this kind of disaster can render them unfeasible in this region.
Ethiopian dams
Complex geological and structural conditions are posing challenges for the ongoing construction of the Gololcha dam on the Kurkura River, in Eastern Ethiopia. Located in the Main Ethiopian Rift volcanic terrain, this 48m high rock and earthfill dam will irrigate approximately 950 hectares of land upon completion. However, issues of leakage and slope instability are reportedly a cause for concern, according to research published in Scientific African.
In the late 1970s, Ethiopia began constructing micro dams to address drought relief and enhance food security, but the country’s history of such dam construction is said to have been coupled with significant geotechnical issues.
As Merdassa et al claim, over half of Ethiopian dams have encountered issues such as leakage, reservoir siltation, spillway damage, and dam body deterioration due to insufficient initial geological, hydrological, and geotechnical investigations. High leakage rates contribute to over 60% of hydraulic structure failures in Northern Ethiopia’s Tigray region, with several micro dams constructed in central, southern, and western parts of the country also at risk of failure due to a lack of comprehensive geological understanding, insufficient subsurface investigation, and inadequate implementations of ground improvement techniques.
To address abutment slope stability and leakage at the Gololcha dam, Merdassa et al employed kinematic analysis and the Limit Equilibrium Method (LEM) to assess slope stability. Additionally, engineering geological mapping, discontinuity surveys, seismic refraction tomography (SRT), and in-situ permeability testing were used to evaluate the leakage condition of the dam site.
Notably, the permeability and SRT survey results identified potential leakage zones to the depth of 35m, 30m, and 35m at the left, right, and central foundations of the dam, respectively. The kinematic method revealed one planar and two wedge modes of failure in the slope section covered by slightly weathered and fractured basalt rock at the right abutment. Further stability analysis of these two modes of failures via LEM analysis indicated slope instability under saturated conditions, emphasising the role of pore water pressure. Based on the study findings, this study recommended curtain grouting to address potential leakage, as well as slope flattening and removing unstable rock wedges and loose material to stabilise unstable slope sections.
Iranian dam
Built in 1992 the Jiroft Dam in Iran’s Kerman province is crucial for water management, flood control, and agricultural development in the region. However, the surrounding mountainous terrain, marked by fractured and weathered rock formations, presents considerable geotechnical challenges with landslides posing significant risks to the stability and safety of infrastructure projects.
Research by Soltaninejad et al was based on comprehensive field surveys and mapping, which revealed significant ground displacements and evidence of slope instabilities in the area. The investigation identified key factors, including soil composition, rock formations, groundwater flow, and seismic activity, that contribute to these shifts in the terrain. To ensure the accuracy of the elevation data, the study employed Monte Carlo simulation techniques to analyse the statistical distribution of the collected survey data. Additionally, the Overall Equipment Effectiveness (OEE) was utilised to evaluate the effectiveness of the current monitoring equipment and infrastructure, providing a clearer understanding of operational efficiency and areas for improvement.
The observed land displacement and the growing instability around the Jiroft Dam pose a serious and imminent threat to the integrity of this crucial infrastructure, the authors claim. Vertical displacements, some exceeding 45cm, indicate not only minor disruptions but also the potential for significant structural failure if not addressed. Such a disaster could result in irreparable damage to the dam, catastrophic flooding, and the loss of invaluable water resources—consequences that would be felt far beyond the immediate area.
The need for action is not only urgent but critical, Soltaninejad et al say. Failure to act now could lead to an irreversible disaster and to prevent this an essential combination of advanced technological solutions, innovative engineering, and proactive vigilance needs to be employed.
Equally important is the establishment of a continuous, real-time monitoring system that integrates cutting-edge remote sensing, GPS, and geophysical sensors, with ongoing geotechnical investigations helping to deepen understanding of the underlying causes of the instability.
In terms of stabilisation methods, considering the severe fragmentation and significant displacement observed, Soltaninejad et al say efforts should focus on more cohesive and robust engineering solutions. Approaches such as dry-stone walls, precast concrete walls, and combined mesh systems with shotcrete are recommended, as they are better suited to address the extensive ground movement and shifting soil and rock formations in the region. These methods provide a stable and adaptive foundation, reducing the risk of further degradation and displacement.
