Modeling Urban Flooding and Drainage Systems

Modeling Urban Flooding and Drainage Systems

Urban flooding is increasingly intensified by the dual pressure of rapid urbanization and the growing frequency of extreme meteorological events, which clearly reveal the structural limitations of traditional drainage systems. A significant research gap exists in the seamless integration of surface runoff with subsurface sewer dynamics, as many conventional models fail to accurately simulate the complex bidirectional flow that occurs when pressurized networks overflow back onto the streets through manholes and inlets. This interaction, known as 1D/2D coupling, is often oversimplified in standard engineering practices, leading to underestimations of flood risk. Furthermore, while the Rain-on-Grid approach offers a superior spatial representation of rainfall by applying it directly to a computational mesh, its implementation across diverse global urban morphologies remains inconsistently documented. There is a critical need for more robust, integrated 1D/2D modeling frameworks that can handle high-resolution topographic data and the specific hydraulic roughness of dense cityscapes. Current literature also lacks comprehensive comparisons of how these integrated models perform across different climatic zones and urban layouts, leaving a significant gap in our ability to design resilient cities capable of withstanding the next generation of climate-driven catastrophes

The primary objective of the research is to develop an integrated hydraulic framework that captures the complex interaction between sewer networks and overland flow using HEC-RAS 2D and EPA SWMM. The study aims to recreate the inundation dynamics of extreme events to understand how storm surges and high-intensity rainfall synchronize to cause systemic failure. By evaluating the Rain-on-Grid technique against traditional methods, the research seeks to optimize flood prediction accuracy and provide a scalable modeling methodology applicable to various coastal and inland cities worldwide.

The methodology centers on a dual-software coupling that solves the governing equations of unsteady flow to capture the dynamic nature of urban flooding. EPA SWMM is utilized to model the one-dimensional pipe hydraulics by solving the 1D De Saint-Venant equations, allowing for an accurate representation of wave propagation and surcharge within the sewer network. Simultaneously, HEC-RAS 2D handles the surface water movement across the urban landscape by solving the 2D Shallow Water Equations (SWE). The Rain-on-Grid technique is applied by distributing net precipitation directly onto a high-resolution computational mesh, which accounts for urban micro-topography and spatially varying land cover.