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"In 2011, massive flooding and inundation in the Chao Phraya River basin, in Thailand, causedserious damage to various activities for a prolonged period of time. Although snapshot images ofthe inundated area are available, detailed information including temporal changes of the inundatedareas and the relationship with meteorological and hydrological conditions are not welldocumented, particularly for the middle and upper sections of the basin. Therefore, we conductedan analysis using two types of satellite data, HJ-1A and Envisat, to better understand behavior ofthe large-scale inundation occurred in 2011, focusing on the middle section of the Chao PhrayaRiver basin. In the analysis, water surface in selected domains was extracted using the NDWI valuecalculated from HJ-1A data. The threshold value of the Envisat ASAR image was then adjusted sothat the inundated area estimated from Envisat gives the closest possible match with that estimatedfrom HJ-1A. Finally, the inundated area was estimated for the whole study domain based on thesame threshold value from the Envisat data. Results indicated that the inundated area began toextend along the Yom and Nan rivers in early August and continued to spread down to the NakhonSawan city area until October. A significant increase in inundated areas occurred between Sep. 2and Sep. l3, during which higher rainfall intensity was observed. Even after the water level inrivers receded below the bank-full elevation, large areas were left inundated along rivers,particularly over lowlying marsh and paddy fields. In addition, several areas located far fromrivers were also inundated, which was likely a consequence of water ponding in paddy fields."

"Nowadays, severe flooding frequently occurs in various parts of Thailand resulted from changesin climatic condition and land use patterns. The flooding has caused great damages to propertiesand lives and affects country economy. Experience from the most severe flooding in the northernand central regions of Thailand in the year 2011 reveals that reliable flood warning system is stilllagging. For flood warning purpose, it is necessary to have an accurate flood routing system. Thisstudy is aimed at developing mathematical models for flood routing so as to provide data for floodwarning. Two different models are developed, i.e., kinematic overland flow model and kinematicstream flow model. The finite element method with Galerkin’s weighted residual technique is usedin model development. The second order Runge-Kutta method is applied to solve the set ofdifferential equations obtained from finite element formulation. The developed models are appliedto simulate flows in the Wang river basin in the northern region of Thailand during July 1 -October 31, 2011 when severe flooding occurred in this region. Model calibration is made byadjusting some parameters in the models and comparing the obtained results with measured datarecorded by RID at 5 stream flow gauge stations along the Wang river. For correlation analysis.three statistical indices are determined, these include coefficient of determination, R2, Nash-Sutcliffe model efficiency coefficient, NSE, and coefficient of variation of the root mean squareerror, CV(RMSE). It is found that the model results at the upstream portion of the riversatisfactorily agree with the observed data, with the values of R2 greater than 0.55 and CV(RMSE)less than 0.57. For the downstream portion of the river, there are remarkable differences betweenthe model results and the observed data. The values of R2 are less than 0.35, CV(RMSE) greaterthan 0.76, and the NSE values are less than 0.16. This might be due to some errors in the inputdata, including rainfall pattern, topography, land use, river cross-sectional area, and water seepagealong the river. More detailed field investigation and model calibration are still needed."