An Integrated Hydrologic and Hydraulic Flood Modeling Study for a Medium-Sized Ungauged Urban Catchment Area: A Case Study of Tiruchirappalli City Using HEC-HMS and HEC-RAS

Floods are a natural calamity that causes loss of human life and destruction of property. They are caused by riverine, coastal and storm surges, cyclones, and tsunami waves. The primary causes of urban floods are an unusual rise in quantum of rainfall, extreme man-made changes in land-use–land-cover patterns, and consequent detrimental hydrological impacts. There are different methods available for flood estimation like rational formulae and empirical methods for approximate estimation of flood peak discharge, but they cannot be applied widely, and their application is confined to a particular region. The current study first discusses the causes of urban floods and then assesses the appropriate flood modeling methods that can be effectively used for urban catchments. Flood modeling methods deployed internationally and nationally in major- and medium-sized cities are discussed, and the research gap is identified. The advantages and demerits of each method are analyzed, and the parameters involved are also identified. An integrated modeling approach is chosen for this case study. In India, only coastal megacities have been considered for flood modeling studies thus far. There have been no research studies conducted on medium-sized urban catchment areas using an integrated modeling approach. Therefore, the present article reviews all the features of a novel integrated flood modeling approach which can be adopted for a medium-sized dendritic pattern ungauged urban catchment area. © 2020, The Institution of Engineers (India).