Heavy rainfall resulting from climate change can lead to inundation in urban areas; therefore, a proper evaluation of urban drainage systems is required. The proper evaluation of urban drainage systems is an important factor in the design and operation of urban drainage facilities. Many researchers have studied resilience in urban cities and drainage systems. In the 1990s, the concept of sustainability was introduced in urban cities and research on developing sustainable urban development models was conducted [1
]. The role of urban parks in a sustainable city and the meanings, models, and metaphors of resilient cities for various factors such as sporting, relax, being with children, meeting others, escaping from city, walking the dog, being in nature, meditating and getting inspiration were suggested [2
]. A sustainable city model with global sustainability with global capital, city capacity and city condition was determined [4
]. Risk and resilience were incorporated to enhance the sustainability of urban water systems using the concept of ecosystem resilience including potable water use, gross pollutants, cost and social acceptance [5
]. The roles of risk, resilience, and environmentally sustainable cities were studied in order to frame national security and energy policies [6
]. The concept of resilience was introduced based on these studies.
In the 2010s, a new concept of sustainability and resilience in urban systems was proposed. Sustainability and resilience with non-equilibrium, adaptive planning and design considering bus routes and urban drainage swales were applied in the new urban world [7
]. Collaborative research in urban areas to quantify the cost-effectiveness of resilience and integrative flood management was announced [8
]. A resilience-based design and a management paradigm for unpredictable and manmade catastrophic disasters was suggested as well as the concept of sustainable, robust, and resilient water distribution systems [9
]. A conceptual framework for designing, planning, and managing resilient cities was constructed, considering climate change and environmental risk [11
]. The integration of risk and resilience in engineering systems was adapted to manage natural and man-made catastrophes [13
]. A conceptual framework with various factors such as climate change, rapid urbanization, and population growth was created for mitigation, adaptation, and coping strategies [14
]. Resilience-based failure mode effects and a criticality analysis for regional water supply system were proposed [15
]. Recently, various resilience studies on urban systems including various factors emerged.
Recently, resilience in urban drainage systems has been studied though research that focused on the resilience in urban cities and water distribution systems. A global analysis approach considering link failure, flood volume and flood duration was used to investigate structural resilience in urban drainage systems and resilient urban drainage as options for optimized area management [16
]. A social-ecological index for measuring flood resilience and multifunctional urban flood resilience enhancement strategies were suggested [18
]. A global analysis approach considering flood volume was used for the evaluation of functional resilience in urban drainage systems [20
]. Cooperative operation of centralized and decentralized reservoirs was proposed for flood reduction and resilience about flooding volume in urban drainage systems [21
]. Resilience studies applied to urban cities and drainage systems were introduced.
Resilience of urban area to flooding has also been studied. In urban drainage systems, the details of the flooding and the measures were conducted to mitigate such floods in the future [22
]. Reflexivity, knowledge and adaptation were used for describing the potential urban form of a flood-resilient urban area [23
]. A methodology of urban flooding resilience was aimed to be organized into a software tool the choice of vulnerability indicators and the integration of the point of view of various stakeholders [24
]. Learning and action alliances for the integration of flood risk management into urban planning was suggested [25
]. Urban flooding resilience was introduced as a key focus of flooding management [26
The resilience of earlier research focused on the flood volume in urban drainage systems. Failure in urban drainage systems was defined as flooding or malfunctioning of urban drainage facilities [21
]. A regional classification was required because flooding depth is not linked to flooding damage in some areas, but it is linked to flooding damage in other areas. In this study, multi-dimensional flood damage analysis (MD-FDA) was applied to divide the target area into several subareas according to the status of land use and to obtain regional damage functions between flooding volume and damage. The results of minutely flooding volume at each node by rainfall runoff simulation were obtained and were converted to minutely flooding damage. The resilience index for flooding damage was suggested and applied to the target area.
In urban drainage systems, flooding damage can pose a critical threat to human life. In the process of making flooding control plans, it will be useful to have a resilience index based on flooding damage. Flooding volume in subareas is different from flooding damage in subareas because some subareas are immediately damaged by a certain amount of flooding while other subareas are not. A new resilience index based on flooding damage has been suggested.
Multi-dimensional flood damage analysis has been selected to obtain the flooding damage in each subarea. Sintaein basin in Jeongup, Korea, has been selected as a target area. Sintaein basin is divided into five subareas, namely, A1, A2, A3, A4, and A5, according to land use. In subareas of the target area suggested in the previous study, damage functions were used for the conversion from flooding volume to flooding damage [32
]. To obtain the results of flooding volume, the SWMM was used in rainfall runoff simulations.
Synthetic data for rainfall runoff simulations was distributed using the Huff distribution [30
]. The Huff distribution is generally used for the design of drainage facilities in Korea. The third quartile of the Huff distribution was selected because it was appropriate for application in Korea [32
]. Fifteen rainfall events had durations of 30, 60, and 90 min and frequencies of 10, 30, 50, 70, and 100 years, generated by the third quartile of the Huff distribution, which were used for the calculation of resilience in the target area.
The results of flooding volume were converted into the results of flooding damage by damage functions after obtaining the results of flooding volume in each subarea by simulating SWMM. The flooding damage in each subarea was used to calculate the utility performance per minute. The results of the utility performance in each subarea were combined with the results of the utility performance in the target area. The resilience in the target area was calculated by the results of the utility performance. The rainfall events with 100-year frequency were selected because the calculation of resilience requires the determination of extreme rainfall. The resilience decrease as the duration decreased because rainfall events with short duration burden urban drainage systems.
In 30-min duration, the resilience go down at about 10-min and rise up at about 40-min. The result of the resilience in 30-min goes down to 0.4 in 10-year frequency and to below 0.2 in 30-year frequency. The results of the resilience go down to 0.1 in 50-year frequency and to below 0.1 in 70-year frequency. In 60-min duration, the resilience goes down at about 20-min and rises up at 50-min. The results of the resilience in 60-min go down to 0.6 in 10-year frequency and to 0.3 in 30-year frequency. The results of resilience in 50-year frequency and 70-year frequency go down to 0.2. In 90-min duration, the resilience goes down at 30 min and rises up at 80-min. The results of resilience go down to 0.6 in 10-year frequency and to 0.4 in 30-year frequency. The results of resilience go down to 0.3 in 50-year frequency and to 0.2 in 70-year frequency.
In this study, the contents of uncertainty and vulnerability in socioeconomic and physical aspects were not included in estimating flooding damage. Future studies would yield more detailed results if there were uncertainty and vulnerability in socioeconomic and physical aspects. This study excluded the damage to humans and did not consider the total damage of urban areas because there are resident and floating people in urban areas. Age and gender in the damage to humans should be considered. The resilience index based on flooding damage can be used for the evaluation of flood control plans such the installation, replacement, and rehabilitation of drainage facilities. Resilience index can be used as a fundamental indicator for the regional evaluation considering the flooding damage. Because various structural measures such as installation of new pump stations and detention reservoirs and replacement and rehabilitation of sewer conduits need to be evaluated, the resilience index based on flooding damage will support decision making in flood control plans. In future research, the resilience index based on flooding damage will be simplified by reports and recorded data.