With the emerging climate crisis and increasing human activities, many riverine and coastal communities have experienced intensified flooding and associated damages. There is a need to re-evaluate flood risk as to better understand the hydrological and hydraulic response of the intense storm events. Furthermore, the properly defined flooding zones may provide valuable guidance regarding community safety, possible future development, and flood insurance. To achieve this goal, this study uses the watersheds of riverine community as an example. The rainfall-runoff analysis is applied to evaluate the hydrological response such that one may adequately incorporate the climate change and LULC change. The floodplain and floodway analysis are then carried out with 1D-steady, 2D- unsteady, and combined 1D-steady and 2D-unsteady hydraulic analysis. This study aims: (1) evaluating the advantage and challenges if both 1D-steady and 2D-unsteady hydraulics analysis are necessary for the main-stem of the stream; (2) comparing the performance of combined hydraulics analysis with 1D-Steady (or 2D-Unsteady) analysis for flood-prone zone; and (3) evaluating and comparing the floodway extent of different hydraulics analysis approach. In summary, this study will provide valuable information to guide reasonable floodplain and floodway analysis for riverine communities.
