Comprehensive flood mitigation and management in the Chi River Basin, Thailand

Severe flooding of the flat downstream area of the Chi River Basin occurs frequently. This flooding is causing catastrophic loss of human lives, damage and economic loss. Effective flood management requires a broad and practical approach. Although flood disasters cannot completely be prevented, major part of potential loss of lives and damages can be reduced by comprehensive mitigation measures. In this paper, the effects of river normalisation, reservoir operation, green river (bypass), and retention have been analysed by using integrated hydrologic and hydraulic modelling. Every tributary has been simulated by a process-based hydrological model (SWAT) coupled with the 1D/2D SOBEK river routing model. Model simulation results under the design rainfall event, i.e. flood depth, flood extent, and damages for the situation with and without flood mitigation measures have been compared and evaluated to determine an optimal set of mitigation measures. The results reveal that a combination of river normalisation, reservoir operation, and green river (bypass) is most effective as it can decrease the extent of the 100-year flood event by approximately 24% and 31% for the economic damage. The results of this study will be useful for improving the present flood defence practice in the Chi River Basi

Comparison of Flood Management options for the Yang River Basin, Thailand

The Yang River Basin, Thailand, has always been subjected to flooding, but due to recent developments in land use there is an increase in the vulnerability in several parts of the river basin. To mitigate impacts of flooding, both structural and non-structural measures can be taken. This paper discusses three scenario simulations focusing on flood retardation, retention, and damage mitigation measures. A main tributary was simulated by a process-based hydrological model (SWAT) and coupled to the 1D/2D SOBEK river routing model. The first scenario focused on retarding basins, the so-called natural flood storage, to reduce downstream flood flows by storing excess floodwater in low-lying areas and releasing it after the peak has passed. The second scenario concerned a green river (bypass channel) to provide storage and drainage through a large, shallow retardation basin, and an outlet for water discharge from upstream. The third scenario concerned the effect of dikes to protect areas from inundation. The results show that the green river is the most appropriate solution since it can potentially reduce a 1% to a 10% per year flood event, with a reduction of peak discharges of 14% in comparison to 9.2% reduced by natural flood storage. Copyright © 2010 John Wiley & Sons, Ltd. Le bassin du fleuve Yang, la Thaïlande, a toujours été soumis aux inondations, mais en raison de l'évolution récente de l'utilisation des terres il ya une augmentation de la vulnérabilité dans plusieurs parties du bassin de la rivière. Pour atténuer les impacts des inondations, à la fois structurelles et des mesures non structurelles peuvent être prises. Ce document traite de trois simulations de scénarios mettant l'accent sur le retard des inondations, la conservation, et des mesures d'atténuation des dommages. Un affluent principal a été simulée par un modèle basé sur les processus hydrologiques (SWAT) et couplé à la rivière SOBEK 1D/2D routage modèle. Le scénario s'est d'abord concentré sur les bassins de retardement, ce qu'on appelle le stockage de ces eaux naturelles, pour réduire les flux d'inondation en aval en stockant les eaux de crue excès dans les zones basses et de la libérer après le pic est passé. Le deuxième scénario concerne une rivière verte (canal de dérivation) d'assurer le stockage et le drainage au moyen d'un grand bassin peu profond retard, et une sortie de rejet d'eaux d'amont. Le troisième scénario concerne l'effet des digues pour protéger les zones de l'inondation. Les résultats montrent que la rivière verte est la solution la plus appropriée, car elle peut potentiellement réduire de 1% à 10% par année de l'événement inondation, avec une réduction des débits de pointe de 14% en comparaison à 9,2% réduit par un stockage d'inondation naturelle