Abstract:
Kalu Ganga basin is one of the main waterway basins in Sri Lanka which gets exceptionally
high rainfalls with higher discharges. This report is about how the different zones, having a
higher likelihood of a flood in the Kalu Ganga basin can be identified through remote sensing
and geospatial approach. RRI model was additionally used to get the flood extents to verify
the flood susceptibility map. Six flood influencing parameters (elevation, slope, land use, flow
accumulation, soil, and rainfall) were taken for obtaining a flood susceptibility map with the
AHP method in ArcMap. In the RRI model, the built-in data (Flow Direction, Flow
Accumulation, DEM, Soil, and Land Cover) with observed rainfall data was used for
generating a flood inundation map. The flood susceptibility map has a flood susceptibility area
under the Very High category of 267 km² (8.4%) in the Kalu Ganga basin which is the most
probable flood occurrence area. The flood inundation maps of May 2003, April 2008, and May
2008 have an area of 217.9 km² (6.3%), 193.6 km² (5.6%), and 108.5 km² (3.1%), respectively
with flood depths greater than or equivalent to 1 meter in Kalu Ganga basin where the flood
depths greater than or equivalent to 1 meter cover all the flood depths. In the AHP method, the
rainfall parameter greatly influenced the flood susceptibility map. The built-in data with nr
river value and ns slope values greatly influence the flood inundation map in the RRI model.
The flood susceptibility map from the AHP method in ArcMap has a higher flood potential
area than the flood inundation map obtained from the RRI model, and this is because the
simulated or observed flood maps are always a subset of the flood susceptibility map. The
flood susceptibility map obtained from the AHP method in ArcMap is a flood probability map
and the flood inundation map from the RRI model is a simulated flood map. Therefore, they
are different. However, the flood inundation area occurs within the flood susceptibility map.
The Analytical Hierarchy Process (AHP) method is an alternative quick method of identifying
flood potential areas and it can be applied to any other place around the world for the
prevention and management of flood hazards.
Citation:
Gurung, R. (2022). Flood risk assessment in Kalu river basin Sri Lanka using geospatial techniques and hydrological modelling [Master's theses, University of Moratuwa]. Institutional Repository University of Moratuwa. http://dl.lib.uom.lk/handle/123/21989