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1D2D Modelling of Sediment Transport and Deposition from Flash Floods: A Case Study in the Nam Chun Watershed, Thailand

Masters, Kerice Venessa (2009) 1D2D Modelling of Sediment Transport and Deposition from Flash Floods: A Case Study in the Nam Chun Watershed, Thailand.

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Abstract:The rapid population growth in Thailand within the last decade has significantly intensified soil degradation, causing farmers to infringe on forests for the expansion of agricultural fields predominantly in upland areas. This has led to intense flooding events, accelerated soil removal, transport and deposition in the low lands. The aim of this study was to test and broaden the use of an existing tool for modelling two dimensional sediment transport and deposition during flash flood events over complex topography. To model the sedimentation processes, in the lowland flood plain of the Nam Chun Watershed, in Thailand, this study applied a physically based hydrological model (LISEM) to estimate the sediment yield from the upland catchment and a coupled onedimensional/ two-dimensional (1D2D) hydraulic model (SOBEK) to model the propagation of flash floods and sediment transport and deposition in the lowland floodplain. In the upstream catchment, model parameters were extracted from previous studies and integrated with a new fieldwork campaign. To improve outputs from previous years, a base flow was added to the total discharge exiting the catchment. The calibration of the LISEM model was carried out by comparing the simulated results versus measured hydrographs. The calibrated hydrographs from LISEM were used as the upstream boundary condition in the SOBEK schematisation. The innovative aspect of the study is the application, of a two-dimensional Water Quality (2DWAQ) module in SOBEK, which was originally used to model sediment transport and deposition for riverine floods. The hydrodynamics are computed for 1D and 2D in one integrated calculation. For the Water Quality, the calculation procedure is different; the 1D and 2D domains are calculated separately. The Water Quality model and the Flow model exchange information about the 1D-2D connections during every time step. For the purpose of validation, probable deposition zones were delineated based on four group interviews carried out in villages that have been most affected by flash floods in the study area. The results proved the applicability of the tool to flash flood events. However, a more detailed method of validation is recommended. To realistically model such hydrological processes a good knowledge of the historic events, soil properties and topography in the study area along with a meticulous validation strategy is crucial. Keyword: LISEM, SOBEK, 2DWAQ, Erosion, Flash Floods, Two-Dimensional
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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