Evolution and Characterization of Pressurized Flow Conditions in Stormwater Collection Networks

Intense rain events and sprawling urbanization have contributed to more frequent flash flooding in cities, often due to the pressurization of drainage systems. Stormwater collection networks (SCNs) can become pressurized if their conveyance capacity is exceeded, leading to on-street flooding through backflow out of curb inlets. Due to the complexity of SCN geometry and spatiotemporal rainfall variability, studies evaluating pressurization in stormwater systems have previously been conducted for relatively simple geometries and inflow conditions. Thus, to date there have been few network-scale insights into how pressurization develops, making it difficult to understand drivers that influence pressurization: slope, roughness, connectivity, and inflow rate. The present work evaluates the process of SCN pressurization using numerical modeling through a systematic variation of these variables. Herein, three distinct pressurization mechanisms were identified by using EPA SWMM 5.1 to model idealized SCN topology and junction inflows. New nondimensional flow indexes (NDFIs) are proposed to characterize the pressurization conditions after an initially empty stormwater system reaches steady state under application of hydrographs. This study provides a basis for further systematic evaluation of factors influencing drainage system pressurization, guiding future actions to mitigate urban flash flooding.