Development of the 2D/1D Coupled S-RAT Model for Flooding Simulation Dual Drainage in watershed

Increasing urbanisation and climate change have had a significant impact on urban infrastructure due to the expansion of impervious surfaces. These surfaces lead to excessive runoff, which strains urban drainage systems beyond capacity and often causes damage. Traditional rainfall-runoff models often fail to adequately reflect the specific characteristics and limitations of urban pipe networks. These models typically use the Curve Number (CN) method to categorise land into eight types, including urban areas. This method primarily addresses surface and subsurface runoff without considering important urban infrastructure components such as drainage pipes and storage facilities. Recognising these shortcomings, this paper presents a new concept of distributed rainfall-runoff model, called S-RAT Urban, which incorporates the urban pipe network in the watershed analysis. The model incorporates both temporal and spatial variability of hydrological processes to improve the accuracy of runoff prediction. The model uses a distributed approach that applies the curve number method to better represent urban environments, including the effects of overlooks. The model uses a grid-based input system that uses Digital Elevation Models (DEMs), land use and soil type data to generate flow directions. The traditional two-dimensional (2D) flow direction mapping used in urban areas is converted to a one-dimensional (1D) pipe network model. This conversion is critical to realistically simulate flow through urban drainage systems. In addition, flow within the pipe network is calculated using continuous and impulse equations to provide a dynamic and realistic representation of the urban hydrological response under different weather conditions. This method not only identifies the variability of the hydrological cycle under natural conditions, but also incorporates critical urban infrastructure into the distributed model, providing a more comprehensive and practical tool for urban catchment management.