Kim, S.E.; Lee, S.; Kim, D., and Song, C.G., 2018. Stormwater Inundation Analysis in Small and Mediun Cities for the Climate Change Using EPA-SWMM and HDM-2D. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 991–995. Coconut Creek (Florida), ISSN 0749-0208. The increase of rainfall intensity and flash-flood due to climate change are expected to exacerbate flood inundation in urban area. Especially, small and medium cities lacking drainage facilities are more vulnerable to flood inundation than large cities. This study introduces a simplified urban stormwater inundation simulation modelling for the two small and medium-sized cities located in South Korea using the U.S. Environmental Protection Agency (EPA) Storm Water Management Model (SWMM) and a HydroDynamic Model-2D(HDM-2D). EPA-SWMM model which are widely used to the runoff analysis of urban areas c...

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.

Increases in the frequency and severity of extreme rainfall might cause catastrophic submergence of underground spaces. Therefore, it is essential to predict the flood risk for proactive design. This study presents the methodology of acquiring risk level considering both flood intensity and evacuation difficulty. The flood momentum was computed by a 2D hydraulic flow model, and the flood intensity (FI) was employed to evaluate the consequence of flooding. To investigate the level of evacuation difficulty, the spatial layout of rooms, together with walking speed, were considered in the risk analysis process. If stormwater runoff enters an underground space, zones far away from the inlet usually have low risk levels. However, when the level of evacuation difficulty was considered, the risk level was dependent on the evacuation distance and location of the inlet and exit. If people are in zones with a risk level of 4 or 5, a rapid evacuation is necessary for preventing human casualties. The proposed methodology incorporated with the inundation model can be applied to any underground space regardless of the location of stairs, the number of exits, shape of rooms, or layout of the floor. Consequently, it will contribute to mitigating flood damage in an underground space.

We simulated two-dimensional pollutant transport in the tidal reach of the Han River and examined the mixing induced by reversed flow. We used the downstream water surface elevation to reflect the tidal constituents of the Yellow Sea when modeling the flow characteristics. We found that reversed flows were repeatedly created and destroyed as the tide varied. The reversed flow affected the spatial variation of the dispersion coefficients and caused the lateral fluctuations of the dispersion coefficient to increase. The change in the flow direction was related to oscillatory variations in the concentration–time curves, and the horizontal recirculation zone at the front of the reversed flow became a storage area where the pollutant cloud was trapped. The concentration–time curves showed oscillatory changes that corresponded with the temporal variations of the flow direction, and the amplitude of the oscillations gradually decreased. The increases in the time for which the polluted water was retained at the riverine parks can be explained by the oscillations on the falling limb of the concentration curves.

Climate change has increased the damage caused by subtropical rainfall and typhoons in coastal areas. Major flooding factors in coastal areas can be classified as storm surges, river inundation, and inland submergence. Because previous studies usually applied a linear sum of individual inundation components to predict comprehensive flood phenomena, this approach does not consider weighted effects associated with the simultaneous occurrence of complex flooding. In this study, a series of comprehensive flood simulations were performed using two numerical models: HDM-2D and FLUval Modeling ENgine (FLUMEN). The results revealed that an integrated flood analysis considering the effects of inundation flooding, river flooding, and coastal flooding required evaluation of the risk of flooding in coastal cities.