Now showing 1 - 10 of 47
  • Publication
    Open Access
    Dramatic decrease of flood frequency in the Mekong Delta due to river-bed mining and dyke construction
    (2020) ;
    Ho, Huu Loc
    ;
    Tran, Dung Duc
    ;
    Yang, Xiankun
    ;
    Alcantara, Enner
    ;
    Merino, Eder
    ;
    Song, Vu Hai
    Here we present a proof of concept evaluation of the impacts of riverbed-mining on river-wetland connectivity by analyzing the temporal trends of the flood frequencies in the Vietnamese Mekong Delta (VMD), whilst accounting for the effect of dyke constructions. We focus on the Long Xuyen Quadrangle (LXQ), which is significant in terms of biodiversity and economic contribution to the VMD as it is one of the most important food baskets of Southeast Asia that depends on seasonal flooding. Our results indicate that the flood frequency in LXQ has decreased significantly over the past 20 years (1995-2015). Time-series analyses of water level data at Chau Doc, Tan Chau, and Can Tho stations confirmed that the overall descending trend is statistically significant (p-value<0.001 and tau ~0.1). However, the river discharge at Kratie showed no significant trend (p-value=0.98) over the same period. This indicates that the flood frequency is associated with the lowering of the riverbed (incision) other than climatic factors. The connectivity analysis also revealed a remarkable drop in the inundation duration after early 2000, which corresponds to the previous observations of the shifting shoreline of the VMD from construction to shrinking. Finally, regression and principal component analyses underpinned the strong causality between the riverbed-mining and the decreased seasonal flooding patterns in LXQ, whilst accounting for the effect of the dyke system over the last decades (R2=0.75). This study offers compelling evidences on the relationship between sand-mining in the river and the disrupted flood regimes in VMD. The reduction in water and sediments that is necessary for sustaining current rates of agricultural production in the long term would endanger the livelihoods of millions of VMD inhabitants.
    WOS© Citations 66Scopus© Citations 75  335  278
  • Publication
    Metadata only
    Geomorphic control on stage-area hysteresis in three of the largest floodplain lakes
    (2022)
    Ang, Wei Jing
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    ;
    Yang, Xiankun
    Hysteresis in floodplain lakes occurs between stage and lake area. Stage-area hysteresis controls the storage and exchange of water and sediments, and is a critical hydrological behavior for lake management. While hysteresis has been repeatedly observed in the floodplain lakes of large rivers, the hydrological mechanism and factors in control have been poorly understood thus far. In this paper, we investigate the role of geomorphology in controlling lake hysteresis, specifically the geologic setting and the lake basin, the lake position relative to the main stem of the river, as well as the influence of lake shape and its internal depositional landforms on inundation dynamics. We study the floodplain lakes along three of the largest rivers around the world: the Curuai Lake of the Amazon River, the Tonle Sap Lake of the Mekong River, and the Poyang Lake of the Yangtze River. The three lakes exhibit a similar counter-clockwise stage-area hysteresis: for a given stage, the lake area is larger in the falling season than in the rising season. Our results indicate that hysteresis is mainly controlled by geomorphology, where the lake shape and basin size lead to delays in the drainage and drop in lake area during the falling season, resulting in counter-clockwise hysteresis. Nevertheless, the lakes are of distinct climatic and geologic-geomorphic settings, representing the variety in the lake types of large rivers. Hence, while geomorphology is the overall driver, unique lake characteristics delay the fall in water extent and shape hysteresis on a case-by-case nature. At Curuai, the complex floodplain morphology (impeded floodplain) complicates and slows the routing of outflow. At Tonle Sap, the lake flows into the river solely through a narrow channel, where a backwater effect restricts drainage. At Poyang, the wide lake shape upstream leads to counter-clockwise hysteresis, while the narrow channel downstream exhibits clockwise hysteresis. Out of the three investigated floodplains, Tonle Sap has the largest degree of hysteresis (0.41), followed by Poyang (0.17) and Curuai (0.13). This trend in hysteresis extent is a result of the different composition of inflow and the lake–river hydrological connectivity, attributed to lake geomorphology. This study is the first to address geomorphology as the primary control over lake hysteresis, which improves understanding of the stage-area curve in empirical and numerical hydrological models, and potentially floodplain management.
    WOS© Citations 3Scopus© Citations 4  46
  • 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
    ;
    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
    Metadata only
    The 2020 Hpakant Jade Mine disaster, Myanmar: A multi-sensor investigation for slope failure
    (2021)
    Lin, Yunung Nina
    ;
    ;
    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  56
  • Publication
    Open Access
    How the saline water intrusion has reshaped the agricultural landscape of the Vietnamese Mekong Delta, a review
    (2021)
    Ho, Huu Loc
    ;
    Low, Mindy Lixian
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    Tran, Duc Dung
    ;
    Sangam Shrestha
    ;
    Yoon, Yong-Jin
    Once a key factor behind Vietnam's successful Doi Moi (restoration) economic reforms, the rice-centered agriculture of the VMD is now confronted by the new pressure of climate change impacts, including the intensifying salinity intrusion (SI). The SI menace has partly triggered the delta-wide emergence of new adaptive livelihood models across the VMD, including the prawn rice rotational crop (PRRC) that is arguably the most prominent. Research on the SI-driving factors is rapidly increasing in numbers, yet little synthesis has been done. Likewise, several studies have investigated the economic benefits of PRRC; less emphasis has placed on environmental and societal aspects, hence the questionable sustainability. This study, therefore, contributes a composite literature review, targeting two SI-related aspects: (i) key factors driving the intensification of SI in recent years across the Mekong Delta, and (ii) current understanding of the sustainability of PRRC. Results from the first review assignment highlight the four key SI-driving factors: riverbed incision, land subsidence, upstream dams, and sea-level rise. Also remarked are the critical absence of studies addressing multiple drivers and the need for a decoupling model to quantify the relative importance of each factor to strategize the adaptive measures. For PRRC, we reveal that while economic benefits have been widely reported, potential negative impacts of this model related to environmental and social aspects are lacking. Therefore, while the lucrative prawn trade might financially benefit the farmers', the economic benefit is marred by the underlying negative environmental impacts and social inequalities, limiting overall sustainability. This study also provides a case study to notify the spatial-temporal trends of PRRC in the last three decades and evaluate the associated geographical and social factors. Kien Giang province was selected as the study site since it is the largest PRRCacross the VMD. The lessons from Kien Giang can also be applied to other transformative agricultural models in both Mekong Delta and other deltas worldwide.
    WOS© Citations 31Scopus© Citations 46  298  11
  • 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 38  74  295
  • Publication
    Metadata only
    Flood risk mapping during the extreme February 2021 flood in the Juruá River, western Brazilian Amazonia, state of Acre
    (MDPI, 2024)
    Mantovani, Jose
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    Alcantara, Enner
    ;
    Marengo, Jose A.
    ;
    Londe, Luciana
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    Cunha, Ana Paula
    ;
    Tomasella, Javier

    Cruzeiro do Sul, a municipality in Northwestern Brazil is recurrently impacted by floods, particularly along the Juruá River. This study presents a comprehensive flood risk analysis by integrating geoprocessing, remote sensing, and hydraulic modeling techniques. Our objectives are to simulate flood extents, identify high-risk areas, and guide sustainable territorial management. Our findings illustrate that the flood impacts are distributed across urban (27%), agricultural (55%), and forest/grassland (17%) landscapes. Historical records and literature reviews also underscore a recurring pattern of extreme floods in the municipality, notably during February’s La Niña events. Some vulnerable urban neighborhoods were identified: Vila Cruzeirinho, Centro, Miritizal, and Da Várzea. These areas are especially susceptible due to their proximity to the river and increased surface runoff during high flood events. By amalgamating various data sources and methods, this research aids decision making for flood mitigation and urban development, fostering resilience against recurrent flooding events in Cruzeiro do Sul.

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