Browsing by Author "Nguyen, Viet-Dung"

Filter results by typing the first few letters
Now showing 1 - 1 of 1
  • Thumbnail Image
    ItemOpen Access
    Multi-objective automatic calibration of hydrodynamic models - development of the concept and an application in the Mekong Delta
    (2011) Nguyen, Viet-Dung; Bárdossy, András (Prof. Dr. rer.nat. Dr.-Ing. habil.)
    Automatic and multi-objective calibration of hydrodynamic models is still underdeveloped, in particular, in comparison with other fields such as hydrological modeling. This is for several reasons: lack of appropriate data, the high degree of computational time demanded, and a suitable framework. These aspects are aggravated in large-scale applications. There are recent developments, however, that improve both the data and the computing constraints. Remote sensing, especially radar-based techniques, provide highly valuable information on flood extents, and in case high precision Digital Elevation Models (DEMs) are present, also on spatially distributed inundation depths. With regards to computation, the use of parallelization techniques brings significant performance gains. In the presented study, we build on these developments by calibrating a large-scale one-dimensional hydrodynamic model of the whole Mekong Delta downstream of Kratie in Cambodia: We combine in-situ data from a network of river gauging stations, i.e. data with high-temporal but low-spatial resolution, with a series of inundation maps derived from ENVISAT Advanced Synthetic Aperture Radar (ASAR) satellite images, i.e. data with low-temporal but high-spatial resolution, in a multi-objective automatic calibration process. It is shown that this kind of calibration of hydrodynamic models is possible, even in an area as large-scale and complex as the Mekong Delta. Furthermore, the calibration process reveals deficiencies in the model structure, i.e. the representation of the dike system in Vietnam, which would be difficult to detect by a standard manual calibration procedure. In the last part of the dissertation the established hydrodynamic model is combined with flood frequency analysis in order to assess the flood hazard in the Mekong Delta. It is now common to state that climate change can lead to a change in flood hazard. Starting from this assumption, this study develops a novel approach for flood hazard mapping in the Mekong Delta. Typically, flood frequency analysis assumes stationarity and is limited to extreme value statistics of flood peaks. Both, the stationarity assumption and the limitation to univariate frequency analysis remain doubtful in the case of the Mekong Delta, because of changes in hydrologic variability and because of the large relevance of the flood volume for the impact of flooding. Thus, besides the use of the traditional approach for flood frequency analysis, this study takes non-stationarity and bivariate behavior into account. Copula-based bivariate analysis is used to model the dependence and to generate pairs of maximum discharge and volume, by coupling their marginal distributions to gain a bivariate distribution. In addition, based on cluster analysis, groups of characteristic hydrographs are identified and synthetic flood hydrographs are generated. These hydrographs are the input for the calibrated large-scale hydrodynamic model of the Mekong Delta, resulting in flood hazard maps for the whole Mekong Delta. To account for uncertainty within the hazard assessment, a Monte Carlo framework is applied yielding probabilistic hazard maps.