**1. Introduction**

In urban areas, various drainage facilities such as pump stations and detention reservoirs have been constructed. Pump stations can prevent the backwater effect in urban streams that leads to flooding in drainage systems. Detention reservoirs can reduce the peak discharge in urban drainage systems. It is difficult, however, to prevent flooding due to extreme rainfall, even though all drainage facilities are designed and constructed using the concept of design flood frequency [1]. Both structural and non-structural measures can be implemented to prevent and reduce flooding. Structural measures are any physical construction used to reduce or avoid possible impacts of flooding, as well as engineering techniques used to achieve flood-resistance and resilience in urban drainage systems. Non-structural measures are any measure not involving physical constructions, which use knowledge or practical operation to reduce flood risks.

Currently, however, drainage facilities are not as effective as expected due to a greater amount of extreme rainfall, impervious areas, and runoff in urban areas. Non-structural measures such as rainfall prediction, flood forecasting, and drainage facility operation have emerged as a new alternative that can support structural measures [2].

Recently, significant attention has been paid to studies on the effectiveness of pump stations and detention reservoirs for disaster prevention. Studies of detention reservoirs have included: optimization of detention facilities using multi-objective genetic algorithms (MOGA) [3], determination of reservoir detention capacity [4], and stochastic rainfall analysis for storm tank performance evaluation in urban drainage systems [5,6]. Studies on reservoir location, parameters, and optimal design capacity have drawn a lot of attention [7,8]. In addition, pump station studies have focused on: the operation of prediction-based rainwater pump stations in urban basins [9], generalized methods for storm water pumping station design [10], and the real time operation of rainwater pump stations [11]. There have also been studies on drainage systems in urban basins, including the assessment of urban drainage system resilience using a hydraulic assessment model [12], and an investigation of the relationships between precipitation and floods [13].

Many studies have investigated the design/operation of rainwater pump stations and the capacity/location of detention reservoirs; however, there have been no previous studies on the cooperative operation of pump stations and detention reservoirs. Cooperative operation is advantageous as pump stations and detention reservoirs are a part of the catchment system and their operation may drastically affect water levels and flooding in the drainage network. This study investigates the cooperative operation of pump stations and detention reservoirs, which are non-structural measures that can compensate for the time-consuming and costly nature of structural measures. Drainage pumps at pump stations and detention reservoirs are operated on the basis of centralized reservoirs (CR) and decentralized reservoirs (DR), with monitoring nodes that consider the drainage system situation and implement cooperative operation when necessary. To maximize flood sharing between each drainage facility, cooperative operation is performed on the basis of the water levels in the pump stations, drainage system, and detention reservoirs. CR operation can improve rapid drainage effectiveness and DR operation can increase detention effectiveness. Cooperative operation between CR and DR combines the advantages of CR/DR operation and effective flood mitigation in urban drainage areas. In addition, we propose and apply the resilience index as a standard for determining the condition of urban drainage systems.
