Abstract

This research investigates the critical factors governing the extent and propagation of urban flooding, and their risks on urban systems. A drainage-catchment-based -2D (Catch) and a 1&2D Rain on Mesh (ROM) FE hydrodynamic flood models were constructed, validated, and compared for case studies of Cambridge and Cleveland. The Catch model directs the volume of run-off in a catchment directly into the pipe system bypassing any localized surface flooding in the catchment. Flooding would occur only when a pipe surcharges and that volume is routed over the surface. In contrast the ROM model distributes the rainfall directly on a 2D mesh, calculates the infiltration at each cell and utilizes the city terrain, road, green-zones and building textures geospatial data to route the surface flow via the shallow flow equations to manholes. The ROM model has coupled 1D pipe inflow/outflow with the surface 2D flow and is able to account for the interaction of surcharge flows as well as surface rainfall flows.

Spatial results of the ROM simulations, see Figure 1, revealed for a range of design storms flood extents 7-9.5 times greater and depths 1.2-7 times deeper across the city during peak flooding, as compared to the Catch model. Additionally, the ROM model effectively identified surface flooding in areas where drainage-based model predicted no flooding. The temporal flood propagation was vastly different between the two models, with the ROM model showing peak flooding that more than 5% of the city remained flooded at the conclusion as compared to the 0% for the drainage-based model. The underestimation of duration and extent of flooding greatly impacts the expected damages on urban infrastructure and current drainage-based models dramatically underestimate this simulation output. Our findings demonstrate that ROM mechanisms, when introduced in pluvial flooding simulations, along with the granular details of city texture incorporated within the model, are critical determinants of the extent and propagation of highly dynamic urban flooding. The results highlight the significance of incorporating ROM approaches and granular city information for more informed and refined pluvial and fluvial regional flood modeling, offering valuable insights into urban flooding impacts.

Plain-language Summary

Catchment-based surface runoff models underestimate the duration and extent of flooding as compared to models that incorporate of rain-on-mesh surface runoff modeling in urban drainage analysis. This underestimation of flood extent and duration leads to underestimation of the expected damages and impacts on lifespan of urban infrastructure. Case studies of Cambridge, Massachusetts and Cleveland, Ohio are presented.