Flood Hazard and Risk Assessment through Incorporating GIS with Hydrodynamic Modelling: Case Study of Muda River
Muda River has been for many years experiencing seasonal floods and causing serious damage and economical loss to human settlements and property in the Muda basin. The 2003 flood was the most devastating event throughout the history of the river. The geomorphological changes, flood behavior and impacts of the Muda River have been investigated in this study using integration of specialized software packages and computer modeling techniques to envisage the consequent changes projected on the river, and assisting in predicting and communicating the flooding risk. Ground surface roughness was delineated through several field visits to the study area. This ground roughness acts as a significant input data for hydraulic modeling purpose. The results of one-dimensional hydrodynamic modeling showed a wide spatial extension of flooding inundation in the vicinity of the floodplain, and indicated damage severity on households and agricultural land use features located in these highly inundated areas. Hazard assessment and risk analysis on these two land use types revealed that the economical damage of the 2003 flood (RM 27.6 million) was five times than that of the last flood (1982) in a 20-year-period (RM 3.87 million). This enormous loss can be attributed to the dramatic changes imposed on the riverine system by much historical and contemporary unsustainable human exploitation of the Muda basin land assets, increasing its vulnerability to erosion hazards and decreased ground surface roughness. The 100-year flood event model was also reconstructed in order to investigate the effectiveness of the proposed bund in controlling the increase in water depth during extreme flooding conditions. The modeling indicated that the proposed bund has enough capacity to contain safely the flood water, with an additional capacity of containing extra 1.5 m of flooding water without exceeding the breaching point. The modeling result also suggests the effectiveness of the proposed bund structure in reducing the flooding risk, protecting thereby the human activities in the floodplain. On the long run, the engineered river may experience localized geomorphic adjustments without initiating flood hazard; but under futuristic extensive and extraordinary channel instabilities, geomorphic adjustments may become magnified, initiating thereby flooding event in the study area. The computer modeling performed in this study improved the understanding of the long-term behavior of Muda River and its flooding behavior.