Now showing 1 - 4 of 4
  • Publication
    Open Access
    Inferring floodplain bathymetry using inundation frequency
    (2020) ;
    Emadzadeh, Adel
    ;
    Enner, Alcantara
    ;
    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
    Characterizing channel-floodplain connectivity using satellite altimetry: Mechanism, hydrogeomorphic control, and sediment budget
    In this study, a mechanism of channel-floodplain seasonal connectivity over a full hydrological year is assessed mainly utilizing satellite radar altimetry data (Jason-2) in a floodplain along the Amazon River. The proposed observation-based approach employs the concurrent measurement of water levels (WLs) over river and floodplain, analyzing seasonal changes in water surface height differences between the two water bodies. Hydrological connectivity thresholds at different stages during the rising phase were identified, and then validated using field data and remote sensing-driven surface suspended sediment maps. Successful decoupling of the two indiscrete flooding processes during the rising phase: channelized and overbank dispersion processes, is one of the major outcomes of this study. Different roles of the connectivity processes on floodplain hydrogeomorphology are highlighted that channelized flows determine inundation frequency, residence time and development of positive topographic features in the floodplain; while overbank flows contribute good part of the seasonal water storage and sediment budget in the floodplain, and tends to smooth positive topography built by channelized flows. The zones of overbank flooding, however, are rather localized due to the well-developed natural levee complex and stable channel-dominated floodplain along the river bank. Lastly, the presented approach is straightforward based on the publicly available operational dataset and therefore it may be readily adapted by non-remote sensing experts. Thus, along with the emergence of new radar altimetry platforms, such as ICESat-2 or Jason-3 that could measure WL of smaller lakes, the proposed approach offers the potential to contribute to research on channel-floodplain systems in other rivers at a global scale.
    WOS© Citations 29Scopus© Citations 36  289  167
  • Publication
    Open Access
    Local rainfall or river overflow? Re-evaluating the cause of the Great 2011 Thailand flood
    (2020)
    Ho, Huu Loc
    ;
    ;
    Chitwatkulsiri, Detchphol
    ;
    Lim, Jana
    ;
    Yun, Sang-Ho
    ;
    Maneechot, Luksanaree
    ;
    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
    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 78  336  283