In this study, we conducted storm surge inundation modeling considering estuarine discharge from heavy rainfall during storm events. As the tropical cyclone involves storm surge and heavy rainfall, it causes more complex damages in low-lying coastal city with the estuarine discharge. We combined Delft-3D, hydrodynamics model with HEC-HMS, hydrology model in order to simulate storm surge inundation in low-lying coastal city during a tropical cyclone. In the coupled model, we calculated runoff caused by rainfall using HEC-HMS and utilized it as river boundary condition. Also, we considered tide motion using TPXO 7.2 model and calculated typhoon's wind field with Holland's model. As a result, during the tropical cyclone there wasn't any significant difference in sea level rise. However, the inclusion of river flow resulted in large difference with respect to inundation. In addition, we can confirm that maximum inundation depth and inundation area calculated by the model considering river flow are in more agreement with real observation. From the results, we can conclude that maximum inundation depth and inundation area due to tropical cyclone are significantly influenced by river flow in coastal cities with river inflow.

Recently, the average global temperature has increased by 0.85°C and global warming is accelerating due to increased pollution of the environment. The climate change has increased the sea level and has increased frequency and intensity of extreme events such as cyclone, heatwave, drought and flooding(IPCC, 2014). Among them, Typhoons are natural disasters that cause sea level rise due to low pressure in the oceans, and wave overflow by winds. Typhoon Haiyan, which caused huge damage to the Philippines, Vietnam and neighboring areas in November 2013, had a central minimum pressure of 895hPa and a maximum wind speed of 90m/s. It was the 11th lowest pressure in the North Pacific (Mori et al., 2014). The damage was about 6,300 deaths, 1,061 missing and 28,689 wounded (Lagmay et al., 2015), and the Philippine government estimated property damage amounted to 12.9 billion USD. It is expected that the frequency of super typhoons such as Haiyan, which causes such enormous damage, will be increased by the sea level temperature due to recent climate change (Mei and Xie., 2016). Here, a super typhoon is defined as a typhoon with a maximum wind speed of 130 knot (67 m/s) at the center of a typhoon, accompanied by rainfall of 1000 mm or more per day according to the definition by Joint Typhoon Warning Center. In addition, it has been accompanied by a strong storm, which causes a concentrated heavy rainfall that causes a lot of rain in a short time. This concentrated heavy rain raises the water level of the river causing river flooding. Typhoon Chaba which occurred in October 2016, caused concentrated heavy rainfall up to 132mm for one hour at Ulsan, South Korea and, as a result the Tae-Hwa river was flooded and the entire basin area was paralyzed. This precipitation is equivalent to 500 years of return period (Nak-Dong River Flood Control Office., 2017). These concentrated heavy rains suddenly increased in water level over time and quickly hit the area. As mentioned above, typhoons cause serious flood damage to the oceans and rivers, in a coastal city where the ocean and the river are adjacent to each other, a complex interaction between the ocean and the river causes serious flood damage.

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