Byunghyun Kim

An Analysis Method of 1D Hydrodynamic Model Based on GIS for Flood Inundation Mapping

Flooding as one of the major natural disasters affects country`s economy. Most country is establishing a flood inundation maps as a non-structural measures to prevent damages from an abnormal flooding over the design criteria of hydraulic structures such as dams, storages, and levees et al. This study suggests method to establish GIS based inundation map induced by dam-break flood simulated by 1D hydrodynamic model(DAMBRK). In this study, the dam-break hydrograph were simulated by various scenario events and especially for the extreme event, peak discharge, peak water surface elevation, arrival time of flood wave and peak water surface elevation are calculated by flood routing at the control points and peak water surface elevation was compared with levee height to detect inundation. In addition, the detailed flood inundation mapping processes at each water level linking with GIS are presented in this study. The proposed method to establish a flood inundation map is able to complement the limitation of 1D hydrodynamic model in analyses of flood plains.

Development of Two-dimensional Finite Volume Model Applicable to Mixed Meshes

In this study, 2D finite volume model, which can apply to the mixed meshes that is effective to treat the complicated topography such as a natural river, is developed. To do so, an algorithm for finding the neighbouring cell of a computational cell is introduced, and fluxes are computed using the HLLC approximate Riemann solver at each interface between a computational cell and it`s neighbouring cells. Moreover, in order to numerically treat the bed slope which has important effect on the balance between flux gradients and sourte terms, different formula to compute the bed slope for rectangular and triangular mesh are applied. The developed model is applied to analyze dam-break in an experimental channel with bend and Malpasset dam-break in France. The two cases consist of mixed meshes and the suggested method is validated for the experimental channel and natural channel by comparison with the experimental data, field data and computed results.

Modification of MUSCL Scheme for Application of Non-uniform Grid

This paper presents a new and simple technique to perform MUSCL reconstruction for solving 2D shallow water equations. The modified MUSCL scheme uses weighted area ratio to apply non-uniform grid in stead of the previous method that equally distributed the difference of conservation variables to each interface. The suggested method can physically reconstruct conservation variables in case of uniform grid as well as non-uniform grid. In this study, Unsplit scheme applicable to unstructured grid is used and efficient slope limiter of TVD scheme is used to control numerical oscillation which can be occurred in modified MUSCL scheme. For accurate and efficient treatment of bed slope term, the modified MUSCL scheme is coupled with the surface gradient method. The finite volume model applied to suggested scheme is verified through a comparison between numerical solution and laboratory measurements data such as the simulations of isolated building test case and Bellos`s dam break test case.

Flood inundation analysis resulting from two parallel reservoirs' failure

AbstractThe DAMBRK is applied to Janghyeon and Dongmak reservoirs in Namdaecheon basin, where two reservoirswere failed due to Typhoon Rusa in 2002. Relaxation scheme is added to DAMBRK to consider the tributary cross-section because two reservoirs are in tributary valleys. In addition, this study suggests the method to utilize the reservoir breach formation time of ASDSO (2005) and empirical formulas for peak break outflow from dam to reduce the uncertainty of reservoir breach formulation time. The single break of Janghyeon reservoir and consecutive break of Janghyeon and Dongmak reservoirs with the suggested method are considered. While the breach discharge from reservoirs rushes down, the discharge and water surface elevation along the river are predicted, and the predictions show the attenuation phenomena of reservoir break floodwave. The applicability of the model is validated by comparing the predicted height with field surveyed data, and showing good agreements between predictions and measurements.Keywords:Two parallel reservoirs, Reservoir failure, DAMBRK, Flood inundation area

Treatment of the Bed Slope Source Term for 2-Dimensional Numerical Model Using Quasi-steady Wave Propagation Algorithm

Two dimensional numerical model of high-order accuracy is developed to analyze complex flow including transition flow, discontinuous flow, and wave propagation to dry bed emerging at natural river flow. The bed slope term of two dimensional shallow water equation consisting of integral conservation law is treated efficiently by applying quasi-steady wave propagation scheme. In order to apply Finite Volume Method using Fractional Step Method, MUSCL scheme is applied based on HLL Riemann solver, which is second-order accurate in time and space. The TVD method is applied to prevent numerical oscillations in the second-order accurate scheme. The developed model is verified by comparing observed data of two dimenstional levee breach experiment and dam breach experiment containing structure at lower section of channel. Also effect of the source term is verified by applying to dam breach experiment considering the adverse slope channel.

Establishment and Application of Neuro-Fuzzy Real-Time Flood Forecasting Model by Linking Takagi-Sugeno Inference with Neural Network (I) : Selection of Optimal Input Data Combinations

The objective of this study is to develop the data driven model for the flood forecasting that are improved the problems of the existing hydrological model for flood forecasting in medium and small streams. Neuro-Fuzzy flood forecasting model which linked the Takagi-Sugeno fuzzy inference theory with neural network, that can forecast flood only by using the rainfall and flood level and discharge data without using lots of physical data that are necessary in existing hydrological rainfall-runoff model is established. The accuracy of flood forecasting using this model is determined by temporal distribution and number of used rainfall and water level as input data. So first of all, the various combinations of input data were constructed by using rainfall and water level to select optimal input data combination for applying Neuro-Fuzzy flood forecasting model. The forecasting results of each combination are compared and optimal input data combination for real-time flood forecasting is determined.

Risk Assessment of Levee Embankment Applying Reliability Index

General reliability assessment of levees embankment is performed with safety factors for rainfall characteristics and hydrologic and hydraulic parameters, based on the results of deterministic analysis. The safety factors are widely employed in the field of engineering handling model parameters and the diversity of material properties, but cannot explain every natural phenomenon. Uncertainty of flood analysis and related parameters by introducing stochastic method rather than deterministic scheme will be required to deal with extreme weather and unprecedented flood due to recent climate change. As a consequence, stochastic-method-based measures considering parameter uncertainty and related factors are being established. In this study, a variety of dimensionless cumulative rainfall curve for typhoon and monsoon season of July to September with generation method of stochastic temporal variation is generated by introducing Monte Carlo method and applied to the risk assessment of levee embankment using reliability index. The result of this study reflecting temporal and regional characteristics of a rainfall can be used for the establishment of flood defence measures, hydraulic structure design and analysis on a watershed.