Numerical Computation of Underground Inundation in Multiple Layers Using the Adaptive Transfer Method

Abstract

Extreme rainfall causes surface runoff to flow towards lowlands and subterranean facilities, such as subway stations and buildings with underground spaces in densely packed urban areas. These facilities and areas are therefore vulnerable to catastrophic submergence. However, flood modeling of underground space has not yet been adequately studied because there are difficulties in reproducing the associated multiple horizontal layers connected with staircases or elevators. This study proposes a convenient approach to simulate underground inundation when two layers are connected. The main facet of this approach is to compute the flow flux passing through staircases in an upper layer and to transfer the equivalent quantity to a lower layer. This is defined as the 'adaptive transfer method'. This method overcomes the limitations of 2D modeling by introducing layers connecting concepts to prevent large variations in mesh sizes caused by complicated underlying obstacles or local details. Consequently, this study aims to contribute to the numerical analysis of flow in inundated underground spaces with multiple floors.

Inundation Risk Assessment of Underground Space Using Consequence-Probability Matrix

“…In the previous study [5], the inundation analysis model was validated against an urban flooding problem. Targeting on the identical application site used in this study, the inundation results (flow depth and velocity) were intensively analyzed and parameter calibrations, including roughness coefficient and turbulent eddy viscosity, were mentioned.…”

“…Targeting on the identical application site used in this study, the inundation results (flow depth and velocity) were intensively analyzed and parameter calibrations, including roughness coefficient and turbulent eddy viscosity, were mentioned. Following-up research of [5], this study presented the methodology of acquiring risk level considering both flood intensity and evacuation difficulty.…”

“…The governing equations of the two-dimensional flood analysis model for computing the hydrodynamic process of underground inundation stem from the conservation principles of mass and momentum [5]. ∂h ∂t…”

“…The level of evacuation difficulty was then estimated based on the evacuation time considering walking speed. According to [5], the velocity magnitude of the application site ranged from 0.0 to 1.8 m/s when water having a flow depth of 1.0 m kept entering from the main entrance of the ground floor. With these velocity values and subsequent inundation depth formation, the flow intensity may vary from low to medium to high.…”

“…Previous researches on urban inundation have normally been performed at the watershed scale and have typically involved flooding analysis of the targeted region, sewer network analysis, and impact evaluation of flood prevention measures. But there is a shortage of hydrodynamic-based modeling that analyzes, in detail, the flow submerging underground spaces [5].…”