Determination of Imperviousness and its Impact on Risk Based Urban Flood Modeling

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Floods are the most common and widespread disasters in a tropical country like India. While the reason for flooding in rural areas is mostly due to high river discharge, the same in urban areas is due to increased imperviousness and poor drainage. The tremendous growth of infrastructure without adequate provision for drainage has increased runoff, thereby aggravating the flooding in urban areas. The criticalities in the quantification of imperviousness and its impact on flood modeling and flood management are not very well understood for urban catchments. Flood modeling and identifying the vulnerable zones are the primary step for formulating any flood management strategy. It is also noted from the literature that there are not many studies that integrate risk factor with flood management. Therefore, the objective of the present study is to identify precise method of imperviousness determination for urban catchment in north-east India, study its role on urban flood modeling, utilize the results for flood hazard identification and demonstrating the effectiveness of flood management scheme. Different methodologies have been employed to identify Total Impervious Area (TIA) using remote sensing and GIS technologies. The more hydraulically relevant Effective Impervious Area (EIA) has been estimated by two indirect methods and one semi automated direct method. The importance of appropriate quantification of imperviousness for accurate estimation of surface runoff is brought forth in this study. An empirical relationship between TIA and EIA has been derived for the study area and compared with those reported in the literature. The impact of imperviousness and different rainfall intensities on urban flooding is studied in detail. The study also describes the usefulness of these results for flood risk modeling and proposing suitable flood management scheme. The provision of detention pond as one of the measures for urban flood management has been demonstrated in this study.
Supervisor: P. Sreeja