Flood hazards are common in Bhutan as a result of torrential rainfall. Historical flooding events also point to flooding during the main monsoon season of the year, which has had a huge impact in ...many parts of the country. To account for climate change patterns in flood hazards in Bhutan, 116 historical flood events between 1968 and 2020 for 20 districts were retrieved and reviewed. The preliminary review revealed that the frequency of flood occurrence has increased by three times in recent years. In this study, seven flood vulnerability (FV) indicators were considered. Five are the attributes of historical floods, classified into a number of incidents for flood events, fatalities, affected population, and infrastructure damages including economic losses. Additionally, the highest annual rainfall and existence of a flood map were other two indicators considered. Using historical data, flood hazard and impact zonation were performed. The analytic hierarchy process (AHP) method was employed to derive a multi-criteria decision model. This resulted in priority ranking of the seven FV indicators, broadly classified into social, physical/economic, and environmental. Thereafter, an indicator-based weighted method was used to develop the district flood vulnerability index (DFVI) map of Bhutan. The DFVI map should help researchers understand the flood vulnerability scenarios in Bhutan and use these to mediate flood hazard and risk management. According to the study, FVI is very high in Chhukha, Punakha, Sarpang, and Trashigang districts, and the index ranges between 0.75 to 1.0.
The study of land use land cover has become increasingly significant with the availability of remote sensing data. The main objective of this study is to delineate geohazard-prone areas using ...semi-automatic classification technique and Sentinel-2 satellite imagery in Bhutan. An open-source, semi-automatic classification plugin tools in QGIS software enabled efficient and rapid conduct of land cover classification. Band sets 2-8, 8A, and 11-12 are utilized and the virtual colour composites have been used for the clustering and creation of training samples or regions of interest. An iterative self-organizing data analysis technique is used for clustering and the image is classified by a minimum distance algorithm in the unsupervised classification. The Random Forest (RF) classifier is used for the supervised classification. The unsupervised classification shows an overall accuracy of 85.47% (Kappa coefficient = 0.71) and the RF classifier resulted in an accuracy of 92.62% (Kappa coefficient = 0.86). A comparison of the classification shows a higher overall accuracy of the RF classifier with an improvement of 7.15%. The study highlights 35.59% (512,100 m
2
) of the study area under the geohazard-prone area. The study also overlaid the major landslide polygons to roughly validate the landslide hazards.
Article highlights
Semi-automatic classification technique was applied to delineate the geohazard-prone area in the heterogeneous region of Bhutan Himalaya.
Unsupervised and supervised classification technique were used to perform land cover classification using the semi-automatic classification plugin (SCP).
The Random Forest classifier predicted higher accuracy and the application is rapid and efficient compared to the unsupervised classification.
Landslides, floods, fires, windstorms, hailstorms, and earthquakes are major dangers in Bhutan due to historical events and their potential damage. At present, systematic collection of data is scarce ...and no multi-hazard zoning is reported in the existing literature for Bhutan. In addition, for proper disaster management, recognizing the existence of the hazards and identifying the vulnerable areas are the first important tasks for any multi-hazard risk studies. To fill the gap, the main objective of this study is to prepare the multi-hazard zoning and assess the multi-hazard population risk for Bhutan on seven historical hazard events. To achieve this, we first collected data on the historical events of different periods based on the data availability and created a district-level database. A total of 1224 hazard events were retrieved. We then calculated the weighted score for individual hazards based on the number of occurrences and the degree of impact through a multi-criteria decision analysis model (MCDA) using the analytic hierarchy process (AHP). The district-wise individual hazard scores are then obtained using the weighted scores. The total hazard score (THS) was aggregated and normalized to obtain the district-wise multi-hazard scores. A multi-hazard zoning map was created in the open-source software QGIS, highlighting 70% of districts with moderate to severe multi-hazard vulnerability. Considering the population distribution in each district at the local levels, the multi-hazard score is integrated and the multi-hazard population risk is mapped.
Gelephu, located in the Himalayan region, has undergone significant development activities due to its suitable topography and geographic location. This has led to rapid urbanization in recent years. ...Assessing land use land cover (LULC) dynamics and Normalized Difference Vegetation Index (NDVI) can provide important information about urbanization trends and changes in vegetation health, respectively. The use of Geographic Information Systems (GIS) and Remote Sensing (RS) techniques based on various satellite products offers a unique opportunity to analyze these changes at a local scale. Exploring Bhutan’s mandate to maintain 60% forest cover and analyzing LULC transitions and vegetation changes using Sentinel-2 satellite imagery at 10 m resolution can provide important insights into potential future impacts. To examine these, we first performed LULC mapping for Gelephu for 2016 and 2023 using a Random Forest (RF) classifier and identified LULC changes. Second, the study assessed the dynamics of vegetation change within the study area by analysing the NDVI for the same period. Furthermore, the study also characterized the resulting LULC change for Gelephu Thromde, a sub-administrative municipal entity, as a result of the notable intensity of the infrastructure development activities. The current study used a framework to collect Sentinel-2 satellite data, which was then used for pre-and post-processing to create LULC and NDVI maps. The classification model achieved high accuracy, with an area under the curve (AUC) of up to 0.89. The corresponding LULC and NDVI statistics were analysed to determine the current status of the LULC and vegetation indices, respectively. The LULC change analysis reveals urban growth of 5.65% and 15.05% for Gelephu and Gelephu Thromde, respectively. The NDVI assessment shows significant deterioration in vegetation health with a 75.11% loss of healthy vegetation in Gelephu between 2016 and 2023. The results serve as a basis for strategy adaption required to examine the environmental protection and sustainable development management, and the policy interventions to minimize and balance the ecosystem, taking into account urban landscape.
Flood hazards are common in Bhutan as a result of torrential rainfall. Historical flooding events also point to flooding during the main monsoon season of the year, which has had a huge impact in ...many parts of the country. To account for climate change patterns in flood hazards in Bhutan, 116 historical flood events between 1968 and 2020 for 20 districts were retrieved and reviewed. The preliminary review revealed that the frequency of flood occurrence has increased by three times in recent years. In this study, seven flood vulnerability (FV) indicators were considered. Five are the attributes of historical floods, classified into a number of incidents for flood events, fatalities, affected population, and infrastructure damages including economic losses. Additionally, the highest annual rainfall and existence of a flood map were other two indicators considered. Using historical data, flood hazard and impact zonation were performed. The analytic hierarchy process (AHP) method was employed to derive a multi-criteria decision model. This resulted in priority ranking of the seven FV indicators, broadly classified into social, physical/economic, and environmental. Thereafter, an indicator-based weighted method was used to develop the district flood vulnerability index (DFVI) map of Bhutan. The DFVI map should help researchers understand the flood vulnerability scenarios in Bhutan and use these to mediate flood hazard and risk management. According to the study, FVI is very high in Chhukha, Punakha, Sarpang, and Trashigang districts, and the index ranges between 0.75 to 1.0.
Transport networks are frequently exposed to geohazards, and losses can be observed frequently by notable disaster incidents such as landslides, earthquakes, and floods. Although losses due to ...natural disasters are frequently reported, limited attention is paid to assess the condition of strategic road networks in the Himalayas. Thus, to fulfill this gap, this study performs condition assessment of Asian Highway AH-48 in Bhutan and develops a system to rate the performance level of road assets. The assessment is conducted along a 157.6 km stretch of AH-48. The sum of findings highlights that about 55% of the road assets along the AH-48 are highly vulnerable to geohazards. Drains are observed to be the most vulnerable, with 52% drains lying below the standard rating among the considered assets followed by retaining walls and pavement. Landslide vulnerability function for highways that are situated in mountain regions is developed using the newly proposed landslide intensity scale. The sum of findings highlights that the Himalayan roads will be affected mostly by landslides and the drainage system is the most affected road asset showing the least serviceability among the common road assets.
Recycling of plastic waste (PW) is one alternate approach to reduce the adverse impact on environment despite many control measures adopted around the world. Current study introduces various types of ...PW as a binding material to completely substitute cement to produce cement-less paver blocks. The constituent of paver block comprises of mixture of different types of PW in different proportion mixed with natural fine aggregate. PW in varying proportions of 40%, 50%, 60% and 70% were used to replace cement and investigated to ascertain achieving satisfactory physical and mechanical properties considering temperature effects. The compressive strength increases with increase in the proportion of plastic content. However, when exposed to very high temperature, its strength is reduced by 31.17%. According to the test results, the plastic paver block has a low water absorption potential. The average initial and final setting time of the binder was 19 and 24 minutes respectively. Abrasion test indicated low surface wear, displaying high durability with maximum of 2.56% wear. A trial foot path pavement was constructed using cement-less paver blocks and evaluation of its performance are discussed. The production of one cement-less paver block utilizes 1.8 kg PW. As per the economic assessment, an average unit cost of cement-less block is evaluated to be 35.39% less than concrete paver block. The findings indicate cost benefit of 29.39 to 32.15% when PW is utilised in construction. To evaluate the sustainability, an “Environmental Suitability Index” (ESI) is developed based on three parameters: embodied energy, life-cycle costs (LCC) and re-usability based on literature review. Three additional parameters: fire resistance, social impact and labour efficiency are introduced to further enhance the ESI in the current study.
Natural hazards such as landslides impose very high risks to the community and infrastructures. To mitigate such risk, proper long-term engineering solutions are must. Several studies conducted in ...the past proposed countermeasures on many occasions. Despite such interventions, the Rinchending Goenpa area still suffers high vulnerability to landslide hazard which continues every monsoon. To assess landslide characteristics in detail, we performed landslide susceptibility mapping using the unmanned aerial vehicle (UAV) technique and conducted a site investigation. High-resolution digital elevation model (DEM) was generated with the site-specific aerial photographs and processed in Agisoft PhotoScan to developed thematic layers in geographical information system (GIS) software. We implemented a multi-influencing factor (MIF) for deriving the influence of landslide conditioning factors and developed a landslide susceptibility map (LSM) using the weighted overlay method (WOM). The landslide conditioning factors include slope, elevation, aspect, topographical wetness index (TWI), and normalized difference vegetation index (NDVI). According to LSM, the areal coverage of landslide susceptibility of study area reveals 2.41% in very low susceptibility, 37.14% in low susceptibility, with highest in moderate susceptibility zone of 49.55% followed by 10.60% in high susceptibility zone, and 0.30% in the very high susceptible zone. Based on the zonal distribution of LSM, and considering findings from several other site investigation such as geophysical survey, the performance of existing countermeasures, soil characteristics, and footprint of last landslide occurrences, we proposed mitigation measures under each zone to provide long-term solutions.
The research area falls at the downstream level of Bhalujhora landslide area in Alay which is located in Pasakha, Bhutan. Local Government authority proposed for construction of custom station ...between the commercial town Phuentsholing and Pasakha Industrial estate. However, downstream region which connects the core town to industrial estate are severely affected by the flash floods every year and the runoff causes huge sediment deposits leading risk for community and substantial damages to the infrastructures. The site is seasonally eroded and subsequently deposited by the sediments from upstream. Although, the formation level for infrastructure are proposed on the deposit layer, the assessment of soil parameters is necessary for design and planning to ensure the overall safety and long-term economic benefits. Through this study, the subsurface soil parameters are assessed by in-situ open pit investigation, geophysical survey and Standard Penetration Test (SPT), while the engineering properties of the sediment deposits were determined from laboratory tests. The field investigation was important to decide the suitability of foundation type and depth. Further, soil parameters were determined to classify the soil type, understand permeability characteristics, and predict shear strength parameters and compaction behaviour. The result shows that the sediments consist of mixture of natural aggregates and sand mixed with silt and clay. An estimate of sediment accumulation was carried out to determine the volume of the sediment deposited. The outcome will allow the relevant stakeholders to decide the management of the risk from this future disaster and propose alternative use of the sediment materials in road works.
A moderate earthquake of local magnitude 6.4 occurred in Sonitpur Assam, India on April 28, 2021. Although the earthquake occurred in India, Bhutan suffered considerable damage to structures and ...infrastructures, especially in the eastern districts. Due to inherent vulnerabilities of Bhutanese residential buildings, encapsulated in rural stone masonry and rammed earth construction, widespread damages were reported in many districts although the shaking was moderate only. We report the damage mechanisms observed in buildings and infrastructures and juxtapose the mechanisms with seismic vulnerability of Bhutanese residential buildings using analytical and empirical approaches. Finite element analysis is performed to validate the failure mechanisms. Intensity map for the earthquake is constructed based on the damage description and vulnerability curve is derived for rural stone masonry building class using the damage data of 2009, 2011, and 2021 earthquakes. The sum of observations and analyses highlights that the Bhutanese residential buildings are likely to be damaged considerably even by moderate shaking, and their capacities are expected to be far exceeded by strong shaking.
•Seismic vulnerability of Bhutanese vernacular stone masonry is reported.•Seismic vulnerability is presented using observed damage mechanisms.•Empirical seismic vulnerability curve is derived using damage data.•Analytical fragility functions for Bhutanese vernacular stone masonry are created.
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