Author(s): Hao Luo; Scott M. Collis; Irene Crisologo; Daniel Horton; Aaron Packman; Marcelo Garcia

Linked Author(s): Hao Luo, Marcelo Garcia

Keywords: Urban drainage; Flooding; Risk assessment; Extreme events; Mitigation and adaption measures

Abstract: Flooding is the most catastrophic disaster in the US, and escalating climate change is exacerbating it. The extreme daily precipitation events (99th percentile) have been observed to increase by 42% in the Midwest region from1958-2016 and are projected to increase at least 40 percent more by the end of the century, according to the Fourth National Climate Assessment. The integrated urban drainage systems (IUDS) in major metropolises worldwide generally need to upgrade their conveyance and storage capacities to adapt to the changing environment due to urbanization and anthropogenic climate change. For example, the City of Chicago, Illinois, USA, ameliorates their existing massive drainage systems by adding upsized tunnels and storage reservoirs partly to alleviate rain-flood risks at the streets and residential areas. Data about flood risks could help the cities make these events more manageable and less detrimental, but flood maps and flood forecasting techniques generally do not account for pluvial flooding that is directly caused by extreme rainfall in urban settings. Moreover, designing infrastructure towards a flood-resilient city requires planning more comprehensively as the entire urban landscape interconnects and should be considered a system. This study adopted a previously developed modeling package for the IUDS across Chicago, which integrates the hydrological processes at each pre-delineated catchment into a finite difference-based hydrodynamic model for the transient flows conveying in the sewer systems connecting hydraulic structures. Therefore, the model supports dual drainage modeling, which interconnects surface runoff and storm drains. Distinct from previous studies focusing on the characteristics of a subset of the system, this study examined the masterplan to best account for its interconnected nature with the fewest assumptions of inflow boundary conditions. This study first assessed the system vulnerabilities to extreme events via numerical simulations of an array of pre-selected synthetic storms constructed based on regional precipitation characteristics, including extreme events with return periods up to 100 years. Furthermore, a reanalysis of a recorded flood-producing event that occurred in 04/17-18, 2013 was also performed based on diverse high-resolution data and further used to simulate the system response considering storage capacities with and without the inclusion of the deep tunnel system. A spatial representation of predicted city-wide flooding risks was presented in peak flood depths and durations, and the latter is a typical indicator for system resilience. Critical precipitation intensities along with local and global conveyance capacities were identified as the major hurdle of drainage system performance to curb surface waters in case of downpours. Comparable spatial disparities were predicted across the simulated storms and were consistent with the flood insurance claim mapping due to economic and infrastructure statuses.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221341

Year: 2022