Flood Inundation Mapping and Analysis Using SAR Data at Middle Reach of the Brahmaputra River

Civil Engineering

Guwahati city is one of the cities in Assam which is flooding frequently. This research develops mapping of flood-prone areas which is analyzed as the reasons of flooding. Efficient monitoring and prediction of floods and risk management for large river is quite impossible without the use of Earth Observation (EO) data from space. As a matter of fact, one of the most important problems associated with flood monitoring is the difficulty to determine the extent of the flood area as even a dense network of observations cannot provide such information. The flood extent information is used for damage assessment and risk management, and benefits to rescuers during flooding; it is also very important for calibration and validation of hydraulic models to reconstruct what happened during the flood and determine what caused the water to go where it did. The use of optical imagery for flood monitoring is limited by severe weather conditions, in particular presence of clouds. In turn, SAR (synthetic aperture radar) measurements from space are independent of daytime and weather conditions and can provide valuable information to monitoring of flood events. This is mainly due to the fact that smooth water surface provides no return to antenna in microwave spectrum and appears black in SAR imagery. The objectives of this study is to Identify and classify flood plain using satellite images and analysis of satellite derived water level over Brahmaputra river during monsoon season. The study using Sentinel -1A SAR images in flood water detection, monitoring of spatial extent and propagation of flood inundation were described and analysed in this thesis. The SAR images were first calibrated, filtered, and geometrically corrected. Afterward, threshold method was applied to extract the inundation areas from the SAR images. Probabilistic inundation scenario is developed by combining satellite derived inundation, water level and modified discharge. Due to the penetration capacity of SAR (Synthetic Aperture Radar) data through clouds, it has ability to continuous observation of flood events for producing accurate rapid and cost effective flood mapping. This study illustrates that the SAR data along GIS can be used effectively for flood water mapping, monitoring and analyzing the propagation of flood water in a flood prone area.

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