Thursday, Dec 03, UTC 02:00 to 02:55
Geohazard risk monitoring and mitigation approaches for increasing the Himalayan road network resiliency against climate change
Organizer: Michigan Technological University; KOKUSAI KOGYO CO; icem – International Centre for Environmental Management, INES Ingenieros, World Bank, JICA, BHUTAN DOR
|Climate change is leading to a more extreme environment and increasing the recurrence rate of natural hazards, making infrastructures subject to actions to which they had not necessarily been designed for. Risk estimation and mitigation measures deriving from climate change are creating new concepts that are being incorporated into the different infrastructure departments policies, resulting in new strategies based on prevention instead of on the existing reactive approach used to address detected damages or failure processes.|
In the case of the road networks, landslides become of great importance due to their recurrence as well as because of its impact. Particularly significant is the case of the South Asian region occupied by Nepal, Buthan and North of India, which have the combination of a young Geology with the highest mountains on Earth. This, together with a road network designed following the old transport paths (not following the bottom of the valleys but going along the half of the hill) and with the state of development of the countries; ends on a pore road network system subject to many landslides that cause accidents, road blocks and road failures that condition the economy and way of living of the people of the region.
This proposal presents four case studies undertaken in the region and funded by the World Bank or JICA, which summarizing, provide on one hand different possibilities of identifying the most vulnerable or hot spot locations, depending on the scope; and secondly, how to work towards mitigating strategies that look preventing the landslides from happening. The fact of being developing countries reinforces the need for these two aspects. Due to the lack of money available, prioritizing where to intervene is particularly critical. Additionally, there is no tradition of acting without an evidence of a problem. All interventions until now have been in reaction to a failure, so a change of mentality is required to get the most benefit of the investment.
The four case studies are:
1) Proactive Monitoring and Assessment of Critical Slopes Using Remote Sensing in the Transport Sector in South Asia
2) Road Slope Monitoring for Ex-ante Traffic Control of High Disaster Risk Road Slopes in Bhutan Selected by using PSIn-SAR
3) Landslide risk assessment, risk mapping and decision support system along primary highways in Nepal
4) Geohazard risk management and resilient asset management in Bhutan.
The first two case studies are focused on better understanding the landslide process and obtaining higher accuracy on the landslide prediction, while the second two case studies are proposing two different approaches on how to obtain a risk ratio having in consideration a vast region subject to different properties and external actions. In these two last ones, the goal was to develop an asset management tool that could help the Department of Roads to outcome with the best possible invesment strategy using the information currently available but that the future incorporation of information could also improve the accuracy of the system.
The following paragraphs include a brief summary of each of the Technical Assistances that will be presented.
1. Proactive Monitoring and Assessment of Critical Slopes Using Remote Sensing in the Transport Sector in South Asia.
Remote sensing using satellite and aerial platforms provide an alternative that can give a synoptic view and quantitative measurements of a vast region. In this project, we explore the application of satellite-based Interferometric Synthetic Aperture Radar (InSAR) particularly persistent scatterer interferometry (PS-InSAR) for landslide monitoring in parts of India, Nepal, and Bhutan. The study area in India, Nepal, and Bhutan where 268 km2, 370 km2, and 1404 km2 respectively. The Sentinel-1 satellite images were used for the study. The PS-InSAR analysis of the Sentinel-1 data provided a large number of persistent scatterers that could be used to measure ground deformation. Subsequent filtering was applied to the persistent scatterers using high velocity and high coherence as the filtering criteria. The filtering enabled to reduce the number of points to be analyzed and focus on the points of higher priority.
The study certainly proves the value of PS-InSAR based analysis for monitoring landslides and critical infrastructure. Several opportunities for PS-InSAR technique in the development sector have been identified. The use of this technique can provide value in mitigating hazards proactively as well as identifying better routes and sites that could potentially lead to a significant saving in infrastructure maintenance costs. The current and proposed radar satellite mission provides a consistent source for data to monitor landslide hazards. The historic archive of radar data provides a valuable resource for policy and planning in sparse data regions of the world.
2. Road Slope Monitoring for Ex-ante Traffic Control of High Disaster Risk Road Slopes in Bhutan Selected by using PSIn-SAR
The Japan International Cooperation Agency (JICA) is implementing “The Project for Capacity Development on Countermeasures of Slope Disaster on Roads in Bhutan (from December 2018 to January 2023)” aimed at developing road disaster prevention capacity in Bhutan. In this project, an early warning system was built and the monitoring of rainfall and slope tilt data on road slopes for ex-ante traffic control is being implemented on the Primary National Highway (PNH) in Bhutan. The monitoring sites were selected by the following procedures: 1) selection of the high velocity surface displacement areas on the PNH, taking into account the result of the WB project (mentioned above); 2) field investigations conducted on the selected areas; 3) selection of the target slopes based on field investigation data such as the width and height of slopes and hazard risks on roads. Thus, the Dzongkalom and Reotala areas on PNH 4 in Bhutan were selected as the target slopes for this project, and rain gauges and slope tilt sensors were installed in those areas in May 2019. Through this study and by using the monitoring data on rainfall and tilts on road slopes measured every 10 minutes, we aim to understand the timing of slope failures to implement the ex-ante traffic control.
During the monitoring, a slope failure was observed in part of the Reotala area at 19:10 on 28 May 2019. The 24-hour and 1-hour rainfall at that time were 72.5 mm for the previous 24 hours and 14.5 mm for the previous hour, respectively. Moreover, similar data on slope failures were observed in areas of Dzongkalom and other areas of Reotala. These results succeeded in showing the high correlation between rainfall and slope failures based on the monitoring data, and contributed to understanding the timing of slope failures. In this project, the monitoring results are used for ex-ante traffic control and are expected to contribute to disaster risk reduction of road slope disasters in Bhutan.
3. Landslide risk assessment, risk mapping and decision support system along primary highways in Nepal
From May 2018 to August 2019, the Department of Roads, with technical support from ICEM and GEOCE and funding from the World Bank, have implemented the project: “Improving the Resilience of Nepal’s Strategic Roads Network”. The key objective of the project was to document and analyze past experience and identify future vulnerability of eight national road corridors for a number of natural hazards, which have the potential to influence the integrity, condition, and/or function of the road.
A total of four risk indices have been developed capturing risk from physical hazards and climate change. Each of the indices is composed of multiple, often interrelated parameters selected based on risk assessment good practice and data availability. Climate change is integrated into landslide, flood, and drainage risk through anticipated changes in rainfall. The four risk indices have been combined into one multi-hazard risk index. Risk values have been assigned for each 1km of road section for a total of 700km roads in Western and Central Nepal. The risk assessment results have then been visualized through maps and integrated into a dynamic user-friendly Decision-Support System for risk-informed road development and management.
4. Geohazard risk management and resilient asset management in Bhutan.
This project developed from May 2018 until August 2019 has as outcome a full risk assessment tool for the Road network of Bhutan. The tool, which uses ArcGIS as base, materializes a theoretical approach based on assets’ risk of failure, internationally estimated as the likelihood of failure times the consequences derived from such failure
Involving climate change in the risk assessment implied, on the one hand, considering the susceptibility of the region to the different hazard events, and on the second hand, looking on how the intrinsic properties of the assets (geometry, design parameters, materials, protection elements, etc.) enhance their response against the natural hazards to which they are exposed. In other words, the likelihood of failure of an asset against the occurrence of natural hazards necessarily needs to consider the probability of occurrence of such events in order to determine potential design drawbacks that may influence the assets capacity to withstand such actions and to assess how the condition or state of conservation of assets may increase the probability of failure in such situations. In the aforementioned project, this issue was addressed by developing susceptibility and hazards maps of natural events for the country and assessing the vulnerability of assets against such events.
The consequences of failure, which completes the risk calculation, were estimated by means of a criticality factor that considers the importance of each asset within the road network, taking into account the impact that a failure would have on the main economic sectors, the user safety and the country’s connectivity and communications.
Finally, the project involved the development of a Risk Mitigation Guide, which includes a description of possible damages that the road assets can present and possible interventions linked to them, to be undertaken to improve their resiliency.