Investigating the potential of a 1-D hydrodynamic model for flood inundation modeling and hazard mapping

Flooding is one of the most prevalent and disruptive natural hazards that affect livelihoods worldwide, especially in lower-income countries where proper drainage and flood protection measures tend to be less developed. Floods have become more frequent and intense over the recent decades and are expected to worsen their negative impacts in the future. Managing flood risk requires the evaluation of potential flood hazards and their consequences. Hydrodynamic models are generally employed to predict flood hazards (inundation extent, depth, velocity, etc.). One of the major concerns in flood hazard mapping is selecting an appropriate model structure. This study examines the flood predictions by a one-dimensional (1-D) hydrodynamic model for two geomorphologically distinct river reaches, the Adyar River, Chennai, India, and the Brazos River, Texas, USA. The results are compared against the simulation results of a two-dimensional (2-D) hydrodynamic model. An open-source model, HEC-RAS, with both 1-D and 2-D modeling capabilities, is employed for flood inundation modeling. The inundation patterns predicted by the 1-D model are found to vary significantly in the case of the Brazos River compared to those for the Adyar river. The study suggests that the simulations of flood inundation extent and maximum flow depth are influenced by the 1-D modeling assumptions on flood plains in river reaches characterized by wide flood plains with complex local terrain variations. The 1-D model simulations are also found sensitive to the magnitude of the flood event with respect to the hydraulic capacity of the reach.