Geospatial modelling of flood dynamics using synthetic aperture radar
Most approaches for modelling flood inundation and depth in lowland settings involve laborious parameterisation of stream channel and floodplain hydraulic characteristics and most require intensive inputs to set up and maintain. Such an approach is unrealistic in Bangladesh with its highly complex and dynamic hydrological network and sparse data collection system. This needs-driven research develops techniques that could be used in an operational, national system for monitoring and assessing floods and for monitoring riverbank erosion and dynamics of river channel morphology. Satellite synthetic aperture radar (SAR) images are used in a consistent, multitemporal data set for the 1998 monsoon flood season. The SAR images are processed and analysed with digital elevation models (DEM) and other spatial data for monitoring floodplain water levels. Compared water levels for the 24-day image acquisition cycle compare with field data by average absolute value difference of 33 cm and with regression coefficient of 0.86. Daily floodwater elevations are simulated through regression relation of the floodplain with conventional river gauge recordings. Flood depth is derived by difference with a DEM and used to create a series of daily flood depth maps that compare with field data by less than 40 cm absolute value difference. Because of the unusually high water levels during the 1998 flood, it is possible that there may have been an unusually direct hydrologic connectivity between the river and the floodplain. Such a relation has yet to be extended to other flood seasons or to other floodplain areas.
A series of spatial data products demonstrates the uses of these daily flood data for flood risk and vulnerability mapping, flood damage assessment, river erosion monitoring, and other applications. Before the methods can become operational, data processing, modelling, and analysis will need to become more quantitative and more efficient. Furthermore, institutional linkages and multi-stakeholder co-operation and involvement will need to be ensured. Bangladesh lacks the financial resources for implementing and maintaining an operational system, however, it has the technical capability and the commitment of development partners.