Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Elementary study on typhoon-induced coastal urban flooding under multiple factors: A case study in thecity of Pearl River Delta (PRD) during Super Typhoon Mangkhut, 2018
Zhuo Zhang1,2,3, Yang Lu,2,3, Weisheng Zhang1,4, Di Hu2,3, Zhiyao Song2,3
1 Key Laboratory of Flood&Drought Disaster Defense, the Ministry of Water Resource, China
2 Key Laboratory of Virtual Geographic Environment (Nanjing Normal University), Ministry of Education,Nanjing, China
3 Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application, Nanjing, China.
4 River Harbor Engineering Department, Nanjing Hydraulic Research Institute, Nanjing, China

the rapid urbanization in coastal zones in recent decades, the economic
losses against typhoon-induced flooding are also increased
significantly. Moreover, climate change shows a tendency that future
tropical storms will be more intense (Emanuel, 2005) and coastal
inundation will likely worsen as a result of rapid sea level rise in floodprone regions (IPCC, 2016). So, a reasonable plan for coastal flood
prevention and mitigation is vital for human sustainable development.
It is well known that typhoon-induced flooding is driven by twosources, (1) storm surge and (2) rainfall-runoff (Torres, et al., 2015).
Storm surge, together with astronomical tide and waves, form highwater levels which may overtop or breach coastal levee to inundate thelow-lying areas and cause catastrophic consequences. Compared toastronomical tide which can be regarded as a deterministic component
in the total water level, the storm surges are not so simple to determine
due to the complexity of their moving tracks and time-varying
characteristics such as centric pressure, cyclone sizes, etc, which has
been proved to have significant effect on the storm surge (Irish et al.,2008; Zhang et al., 2021a). Moreover, the combined effect of storm
surges and tide leads to more uncertainty while they interact with eachother nonlinearly under the shallow topography (Park and Suh, 2012).
In coastal and estuarine regions, the storm surge would be transformed
under the restriction of coastline and estuary boundary (Ebersole et al.,2010). On the other hand, typhoon can introduce torrential quantities ofrainfall as it move inland (Torres, et al., 2015). Differing from most of
the normal rainfalls, typhoon-induced rainfall is not uniformly
distributed and is featured by short-term intense downpours, causing
localized inland flooding. Moreover, rainfall-runoff and storm surge are
not mutually exclusive flood hazards. The joint hydraulic processes
between the two factors during a typhoon event are of particularimportance and interest in the field of coastal flooding prediction andhazard assessment.

ABSTRACTIn this study, we describe a novel framework of modeling the city
inundation arising from typhoon-induced surge and torrential rainfall
by coupling a well-known ocean model (FVCOM) and a river analysis
system (HEC-RAS 6.0). The FVCOM model is applied to capture thebehavior of surge from deep sea to shallow offshore near PRD. Under
the hydrograph of surge and tide supplied by FVCOM, the HEC-RAS
model is applied to simulate the potential flooding scenarios caused by
the comprehensive effect of surge overtopping and torrential rain
during Super Typhoon Mangkhu in 2018. Then, we analyze theinteraction between pluvial flooding and fluvial flooding in urban
region during the typhoon, and the effect of the spatial heterogeneity of
the roughness arising from different land uses in the city. The main
conclusions can provide useful guidelines and insights on dealing withthe possible storm surge and inundation in future in the cities of PRD.

KEY WORDS: pluvial flooding; fluvial flooding; surge; typhoon;
Pearl River; numerical simulationINTRODUCTION
During events of typhoon, storm surges always pose threat to human
lives in low-lying areas near the coast. Apart from storm surge,
torrential rainfall usually caused a large area of inundated regions aswell as overtopping flood. Overall, typhoon-induced flooding cause
massive direct economic losses every year through damaging thehouses and infrastructure, and also induce indirect losses through theharmful impact on transportation, tourism and industrialization. With2628