Now showing 1 - 10 of 17
  • Publication
    Open Access
    The worst 2020 saline water intrusion disaster of the past century in the Mekong Delta: Impacts, causes, and management implications
    (2021) ;
    Ho, Huu Loc
    ;
    Doan, Van Binh
    ;
    Sameh Kantosh
    Vietnam Mekong Delta (VMD), the country's most important food basket, is constantly threatened by drought-infused salinity intrusion (SI). The SI disaster of 2020 is recognized as the worst in recent decades, hence inspiring this perspective article. The authors' viewpoints on the disaster's impacts and causes are presented. The arguments presented are mainly drawn from (i) up-to-date publications that report on the recent SI intensification in the VMD and (ii) the power spectral analysis results using water level data. We verified the intensifying SI in the VMD both in its frequency and magnitude and remarked on four of the key SI drivers: (i) upstream hydropower dams, (ii) land subsidence, (iii) the relative sea-level rise, and (iv) riverbed sand mining. Also, a non-exhaustive yet list of recommendable management implications to mitigate the negative effects of the SI is contributed. The mitigation measures must be realized at multiple scales, ranging from pursuing transboundary water diplomacy efforts to managing internal pressures via developing early warnings, restricting illegal sand mining activities, alleviating pressures on groundwater resources, and diversifying agriculture.
    WOS© Citations 39Scopus© Citations 39  74  303
  • Publication
    Metadata only
    The 2020 Hpakant jade mine disaster, Myanmar: A multi-sensor investigation for slope failure
    (2021)
    Lin, Nina Yunung
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    ;
    Wang, Yu
    ;
    Quek, Yu Pin
    ;
    Lim, Jana
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    Alcantara, Enner
    ;
    Ho, Huu Loc
    A quarry failure along the slopes of the Wai Khar open-pit jade mine in Hpakant, Myanmar has led to the deaths of at least 172 jade miners on 2 July 2020. This paper conducts a systematic investigation of the incident by integrating data from multiple sensors, including high-resolution optical imagery, Sentinel-1 synthetic aperture radar (SAR) images, unmanned aerial system (UAS) footage, SRTM and ALOS digital elevation models (DEMs), soil moisture product from multi-spectral Landsat-8 satellite and precipitation records from the Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS). Optical imagery, UAS footage and DEMs allow us to build a comprehensive mapping of tailing areas and quarry scarps from 2010 and reconstruct the 2D pit geometry prior to failure. Deformation signals from multi-temporal SAR interferometry (MTInSAR), soil moisture variations and precipitation trends further allow us to identify possible failure causes. To evaluate the quality of deformation obtained from different distributed-scatterer phase estimators, we develop an empirical mapping function based on areal fraction values to facilitate the comparison of temporal coherence values that are differently formulated in each phase estimator. The comparison shows that phase linking algorithm outperforms the small baseline subset method in terms of signal recovery and phase reliability. Our investigation points out that the mining site is under aggressive mining cycles that are exacerbated by frequent, uncontrolled landslides. Seepage failure, which involves the expulsion of water from rapidly compacting tailings, may be a critical factor in the 2020 incident. Instead of extreme weather, the failure had occurred under normal to drier conditions. This means that the sliding planes were already in a critical state, which is evident from the accelerated deformation around the collapse area since the beginning of 2020. Based on these findings, we provide recommendations to improve mining site regulations and management practices for safer open-pit mining in Myanmar and probably in similar contexts outside Myanmar.
    WOS© Citations 10Scopus© Citations 12  64
  • Publication
    Metadata only
    New systematically measured sand mining budget for the Mekong delta reveals rising trends and significant volume underestimations
    (2022)
    Gruel, Charles-Robin
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    ;
    Switzer, Adam D.
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    Sonu, Kumar
    ;
    Ho, Huu Loc
    ;
    Sameh, Kantoush
    ;
    Doan, Van Binh
    ;
    Feng, Lian
    The river beds of the Mekong Delta are some of the most intensively sand mined places in the world. However, sand mining budgets remain limited to rough and indirect estimates. Here, we provide a first systematic, field-based estimation of the Mekong Delta’s sand mining budget. This budget overcomes the limitations of relying on officially declared statistics and bathymetric surveys of short channel reaches. We applied Sentinel-1 radar imagery to monitor the distribution of sand mining activities using boat metrics-driven mining intensity maps correlated with a field-based bathymetry difference map which were derived from two extensive bathymetric surveys conducted in 2014 and 2017. The two surveys cover ∼ 100 km in the Tiền River, reaching approximately 15% of the Mekong Delta. We then extrapolated the Tiền River findings to the broader Vietnamese Mekong Delta from 2015 to 2020 and measured a continuous increase of the extraction budget by ∼ 25% between 2015 (38 Mm3/yr) and 2020 (47 Mm3/yr). We estimated a total sand mining budget of 254 Mm3 during the 6-year study period with an average annual rate of ∼ 42 Mm3. Our field-based annual rates are higher than both official declarations provided and estimates from previous studies which implies that a substantial portion of the sand mining budget remains unaccounted for. Riverbed sand mining remains a key threat to the Mekong Delta as it contributes to a multitude of other environmental threats including dam construction effects on sedimentation, ongoing subsidence, sea level rise and recurring saltwater intrusion. This study offers a new approach that can be implemented elsewhere to allow for systematic monitoring and quantification of sand mining activities that are vital for assessing future projections on environmental impacts.
    WOS© Citations 13Scopus© Citations 15  49
  • Publication
    Open Access
    Socio-geographical evaluation of ecosystem services in an ecotourism destination: PGIS application in Tram Chim National Park, Vietnam
    (2021)
    Yee, Jie Ying
    ;
    Ho, Huu Loc
    ;
    Poh, Yi Le
    ;
    Tan, Vo-Thanh
    ;
    Ecotourism in national parks of developing countries is increasingly recognised as a promising option to achieve sustainable development goals, regardless, might imply various paradoxical managerial challenges. This paper, therefore, seeks to contribute a methodological framework utilising ES-based social landscape metrics (SLM) to address the potential barriers in managing ecotourism-integrated multi-functional national parks. We present a mixed-method case study in Vietnam's Tram Chim National Park (TCNP), conducted via semi-structural interviews and PGIS with tourists and locals. Multiple key informants, i.e. TCNP's authorities were also interviewed to provide their managerial insights and assist in verifying the PGIS results obtained from the tourists and locals. Via the quantified and mapped SLMs, the study reveals the differences between tourists and locals in terms of how and where they perceive and appreciate the intangible values of TCNP. Through spatial statistics, we reported important spatial correlations (i) between different categories of Ecosystem Services (ES) and (ii) between ES richness and diversity on different TCNP's land covers. As a contribution to the decision-making outlook, we remarked potential areas to expand of ecotourism activities based on the spatial hot and cold spots. This study concludes by highlighting opportunities for future research in expanding on socio-geographical assessments of ES, especially in the fields of ecotourism.
    WOS© Citations 22Scopus© Citations 32  69  52
  • Publication
    Open Access
    Intensifying saline water intrusion and drought in the Mekong Delta: From physical evidence to policy outlooks
    (2021)
    Ho, Huu Loc
    ;
    Doan, Van Binh
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    ;
    Sangam Shrestha
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    Tran, Duc Dung
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    Vu, Hai Son
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    Nguyen, Hoang Thu Truc
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    Nguyen, Phuong Mai
    ;
    Seijger, Chris
    This paper assesses the recently intensified saline water intrusion (SI) and drought in the Vietnamese Mekong Delta (VMD). While the existing literature predominantly points the cause of drought to the hydropower dams in the upstream of the Mekong Basin, we contribute new physical evidence of the intensification of saline water intrusion (through backwater effect) in the VMD caused by three anthropogenic drivers: riverbed incision (due to both riverbed mining and dam construction), sea level rise and land subsidence. Thereupon, we highlight that it is critical to not underestimate the impacts from the localized factors, especially the riverbed-mining which can incise the channel by up to 15 cm/year and amplify the salinity intrusion. Our analysis is based on the extensive sets of hourly-to-daily hydrological time series from 11 gauge stations across the VMD. First, several signs of significantly increased tidal amplification (up to 66%) were revealed through the spectral analysis of the hourly water level data. This trend was further validated through the changes in slopes of the rating curves at the tidal zones, implying the relationships between the shift of the backwater effects on the rivers in VMD and the lowered water levels caused by the riverbed incision. Finally, we introduce a novel approach using the annual incision rates of the riverbed to compare four SI driving factors in terms of their relative contributions to the balance between fresh and saline water in the VMD.
    WOS© Citations 64Scopus© Citations 73  287  317
  • Publication
    Metadata only
    A deep learning framework to map riverbed sand mining budgets in large tropical deltas
    (Taylor & Francis, 2023)
    Suno Kumar
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    Tran, Dung Duc
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    Wang, Jinyu
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    Ho, Huu Loc
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    Feng, Lian
    ;
    Sameh, A. Kantoush
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    Van Binh, Doan
    ;
    Li, Dongfeng
    ;
    Switzer, Adam D.

    Rapid urbanization has dramatically increased the demand for river sand, leading to soaring sand extraction rates that often exceed natural replenishment in many rivers globally. However, our understanding of the geomorphic and social-ecological impacts arising from Sand Mining (SM) remains limited, primarily due to insufficient data on sand extraction rates. Conventionally, bathymetry surveys and compilation of declared amounts have been used to quantify SM budgets, but they are often costly and laborious, or result in inaccurate quantification. Here, for the first time, we developed a Remote Sensing (RS)-based Deep Learning (DL) framework to map SM activities and budgets in the Vietnamese Mekong Delta (VMD), a global SM hotspot. We trained a near real-time object detection system to identify three boat classes in Sentinel-1 imagery: Barge with Crane (BC), Sand Transport Boat (STB), and other boats. Our DL model achieved a 96.1% Mean Average Precision (mAP) across all classes and 98.4% for the BC class, used in creating an SM boat density map at an Intersection over Union (IoU) threshold of 0.50. Applying this model to Sentinel-1, 256,647 boats were detected in the VMD between 2014–2022, of which 17.4% were BC. Subsequently, the annual SM budget was estimated by correlating it with a recent riverbed incision map. Our results showed that, between 2015–2022, about 366 Mm3 of sand has been extracted across the VMD. The annual budget has progressively increased from 34.92 Mm3 in 2015 to 53.25 Mm3 in 2022 (by 52%), with an annual increment of around 2.79 Mm3. At the provincial-scale, Dong Thap, An Giang, Vinh Long, Tien Giang, and Can Tho were the locations of intensive mining, accounting for 89.20% of the total extracted volume in the VMD. Finally, our estimated budgets were validated with previous research that yielded a correlation coefficient of 0.99% (with bias of 2.65%). The automatic DL framework developed in this study to quantify SM budgets has a high potential to be applied to other deltas worldwide also facing intensive SM.

    Scopus© Citations 2  3
  • Publication
    Metadata only
    Impacts of agricultural expansion on floodplain water and sedimentbudgets in the Mekong River
    (2022) ;
    Ho, Huu Loc
    ;
    Doan, Van Binh
    ;
    Sameh Kantosh
    ;
    Poh, Danielle
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    Alcantara, Enner
    ;
    Try, Sophal
    ;
    Lin, Nina Yunung
    In this paper, we address the impact of agricultural expansion on hydrological patterns of water and sediment budget in one of the largest floodplains along the Cambodian Mekong since the 1980s, using field (water level, discharge, sediment, rainfall, and groundwater level) and remote sensing (land use, surface suspended sediment) data, and numerical simulations. Specifically, while both the surface suspended sediment concentration and water level in the Mekong River around Kampong Cham and Neak Luong decreased, the floodplain seasonal water storage increased. In addition, the rate of sediment input from the river to the floodplain was almost constant throughout the studied period. The investigation of the floodplain’s annual sediment budget, however, reveals a significant drop during the analyzed period, mainly due to the decreased sediment trapping rate (66% in the 1980s to 46% in the 2010s). Currently, a good amount of sediment bypass the floodplain and return back to the river. The observed hydrological patterns in the floodplain could have been triggered by the agricultural expansion that has increased surface erodibility (due to removals of primary vegetation) and lowered the land surface elevation (due to groundwater extraction). Despite the well-known impacts of the hydropower dams on the Mekong Delta hydrological conditions, particularly the reduction of sediment reaching the delta due to sediment trapping by dam reservoirs, our observations point to new and more localized driving factors of sediment deficit in floodplain: agricultural expansion. Finally, we used 2D hydrodynamic simulation (Telemac-2D) to visualize the processes of water routing and sedimentation in the floodplain accounting for land cover change since the 1980s. The floodplain hydrology reported in this paper is an unexplored environmental consequence of agricultural expansion in the lower Mekong. Geomorphologically, this study presents a peculiar case of floodplain showing how agricultural expansion can diminish the role of a floodplain as a sediment sink through decreasing the trapping rate.
    WOS© Citations 9Scopus© Citations 14  69
  • Publication
    Open Access
    Inferring floodplain bathymetry using inundation frequency
    (2020) ;
    Emadzadeh, Adel
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    Enner, Alcantara
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    Yang, Xiangyu
    ;
    Ho, Huu Loc
    This study proposes a new method to retrieve the bathymetry of turbid-water floodplains from the inundation frequency (IF) data derived from over 32 years of composite optical remote sensing data. The new method was tested and validated over the Curuai floodplain in the lower Amazon River, where the entire bathymetry was surveyed in 2004, and water level gauge data has been available since 1960. The depth was estimated based on the relationship derived from IF and surveyed depth data, and the results were compared to those retrieved from bare-Earth DEM. We further assessed the sensitivity of the approach by analyzing the deepest part of the lake (i. e., permanent water body ~ 8m) with high IF, as well as the effect of gradual sedimentation in the lake over time. The results showed that the model is highly accurate and sensitive to IF changes even in the permanent water body areas, suggesting that this model can be used in other seasonal lakes worldwide with turbid-waters, where large-scale bathymetry surveys are not feasible due to high operation costs.
    WOS© Citations 7Scopus© Citations 8  271  107
  • Publication
    Open Access
    Local rainfall or river overflow? Re-evaluating the cause of the Great 2011 Thailand flood
    (2020)
    Ho, Huu Loc
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    Chitwatkulsiri, Detchphol
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    Lim, Jana
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    Yun, Sang-Ho
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    Maneechot, Luksanaree
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    Minh Phuong, Do
    The Great 2011 Thailand flood is one of the most catastrophic flood disasters recorded worldwide in modern history, which covered about 100,000 km2 of the country and resulted in 813 casualties and incurring US$ 46 billion in economic losses. In this paper, we re-evaluate the flood event to identify the root source of the catastrophe. By analyzing hydrological data from gauge stations along the Chao Phraya River (CPR) and remote sensing data, we decoupled the volumetric contributions of river overflow and local rainfall to the lowland reach of the basin and found that the latter contributed most to the flooding. More specifically, out of the total of 77.6 km3 of floodwaters estimated, 73.7% was from precipitation, while only 26.3% was from river discharges. This finding differs from the official reports or previous studies, which attributed the main cause of the river overbank flow. Therefore, it is also inferred that the upstream dam operations would have been only marginally helpful in mitigating the flood since rainfall made up most of the floodwaters in the downstream reach of the river. Our finding offers a new perspective that the local rainfall could be a significant source of the floodwater, rather than river overflow in the lower reaches of a large monsoonal river system in Southeast Asia. Thus, this paper contributes to the understanding of complex flood processes in large river basins and provides fresh insights for efficient flood control and stormwater management.
    WOS© Citations 26Scopus© Citations 28  158  87
  • Publication
    Metadata only
    Mainstreaming ecotourism as an ecosystem-based adaptation in Vietnam: Insights from three different value chain models
    (2022)
    Ngo, Thi Thu Trang
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    Nguyen, Thi Quynh Trang
    ;
    Ho, Huu Loc
    ;
    This paper investigates the implications of value chain models in mainstream ecotourism as a potential ecosystem-based adaptation in developing country contexts via three case studies across Vietnam, including Lai Chau, Lam Dong and Dong Thap. While the models of the two former two are similar, Dong Thap employs a special unit known as Destination Management Unit, or DMO, to help manage the operations of ecotourism. In this study, a mixed method approach was applied, including both in-depth group discussions and questionnaire-based surveys collecting inputs from tourists and the local tourism business households. For data analysis, we employed two multivariate analysis methods, including multi correspondence analysis and hierarchical cluster analysis. From a tourist’s perspective, DMO provides insurance for services and eliminates intermediate fees. It creates trust in services, improving overall satisfaction, which is a key element for tourist retention. Furthermore, DMO can ensure fair competition, producing a sustainable environment for ecotourism development in the area. However, from business households’ perspectives, the effectiveness of the DMO is still subpar. In contrast, in the case of Lai Chau, we found positive support from the government for tourism activities. The role of the government in the promotion of tourism in Lai Chau can be seen through marketing efforts and the organization of publicity events. In essence, even without the establishment of a dedicated management unit, the management and development of ecotourism can be streamlined should there be effective participation from the government. The findings herewith present an inclusive strategy or instruction for the application of the DMO in a particular area. Empirical results from Lai Chau and Dong Thap point that application without localization is unfeasible. For that matter, localization is key for its application, which requires instruction from the government. Secondly, the improvement of the resource may enhance the experience of the tourists and possibly attract higher travel. The resources mentioned included tangible resources such as infrastructure, accommodation, information access and intangible resources such as human resources and local identity. Lastly, we recommend that DMO should present as the moderator in the value chain of ecotourism which promotes the healthy connection among the members in the ecotourism value chain.
    Scopus© Citations 1  172