River inundation satellite images are restricted to make real-time flood inundation maps in many cases. However, such images have significant potential to predict the time, place and scale of a flooding event, and can be very useful in emergency response efforts. The estimation of water extent boundary and flood volume is important to determine a fundamental hazard in flood risk assessment. In this study, an attempt was made to detect surface water in a severe flood event (the 2011 Thai flood) by applying modified remote sensing indices to near-real-time MODIS images. Flood volumes were also calculated for detected flood areas by using a proposed flood inundation level (FIL) model with the Digital Elevation Model (DEM). FILs were verified through field investigation. The results show that the MODIS-FIL combined approach is feasible for automatic, instant flooding detection.