Fabian Funke

Graph showing an overview of flooding problem, the SDB framework and its application in the two topographical cases, the role of SDB chart in co-designing Green-Grey Infrastructure. Storage and discharge are two fundamental solutions to strengthening pluvial flood resilience. Recent studies reveal that many urban catchments operate under a persistent storage–discharge imbalance, driven by urban densification. This ‘imbalance’ raises concerns in hydrologic, economic, spatial, and social aspects. This research aims to quantify the balanced relationship between storage capacity and discharge capacity (storage discharge balance, SDB) for pluvial flood protection and provide planning strategies for different urban topographies. We suggest and apply a quantification method using different modelling tools, hydrological and hydrodynamic models, in two cases with distinct physical and socioeconomic characteristics: one in a flat polder area in Nanjing, China, and the other in a sloping hilly area in Feldbach, Austria. By comparing these cases, insights are gained into the modelling methods, results, and proposed strategies for each context. The use of the SDB chart mapping framework supports the identification of both short- and long-term targets, as well as dynamic pathways toward enhanced flood resilience. These insights will facilitate multidisciplinary dialogue on key constraining factors, thereby enabling the co-creation of an actionable solution. While the quantitative findings are context-dependent, the novel approach can be applied to other cities to facilitate their resilience planning.

Climate change is severely affecting all regions of the world, and urban water management has become a major urban challenge. Although nature-based solutions (NBSs) have been widely implemented in developed countries in the Global North to address stormwater-related challenges in urban areas, implementation of such approaches in Viet Nam and other Asian countries remains limited. In addition, comprehensive and critical reviews of NBS adoption and development processes in Viet Nam are scarce. This study aims to clarify several aspects through a literature-based review: to understand the development of urban water management in Europe and Asia (China and Southeast Asian countries) along with the drivers for NBS implementation in Viet Nam, to explain the barriers to NBS adoption in Viet Nam, to present feasible solutions for promoting NBS adoption, and to explore future perspectives for NBS development in the context of Viet Nam. Although significant barriers exist, opportunities for NBS implementation are evident. The findings of this study can be used to promote NBS in other municipalities in developing countries.

Urban drainage operation, management and rehabilitation can be divided into two distinct segments: traditional grey infrastructures (i.e. pipes and associated components) and green infrastructures. For piped systems this boils down to maintaining the operational safety, stability and tightness of the sewers and special structures. However, this chapter provides an overview on both realms and highlights that, while there is a lot of standardization for grey infrastructures, the knowledge on green ones is much more fractured. They are often composed of both engineered and natural elements such as pipes, flow control systems, vegetation, micro-organisms in the soil or growing media, and also deliver a broad range of beneficial services to our communities and their inhabitants. Existing terminology for pipe networks is adapted by defining a similar distinction for green infrastructures based on the severity of the necessary actions. There will be no focus on other special structures and machinery. Adopting these distinctions, this chapter consists of three parts: (1) pipe network operation and maintenance (O&M), (2) structural rehabilitation of pipe networks and the connected manholes and (3) green infrastructure rehabilitation including O&M focusing on some examples. Consequently, this chapter can be used as guidance on available technologies, existing guidelines and research gaps.

This study employs a comprehensive multi-objective efficiency index (EI) to assess urban flood mitigation strategies. The EI enables the simple interpretation of a mitigation strategy’s efficiency with a value range between −1 (low efficiency) and 1 (high efficiency), which represents a practical communication tool for decision makers, engineers, and researchers. This was tested at the study site of Feldbach (Austria) with an integrated 1D–2D urban flood model and a distributed hydrological model. A total of 112 scenarios were analysed for six mitigation strategies, which were built from three future challenge scenarios, two observed heavy storm events, and two hydrological pre-conditions. For the given study site, the analysis identifies mitigation strategies implemented in rural boundary areas as the most effective. A novel aspect of this study is the consideration of the urban water balance change, highlighting its impact on the EI. The analysis highlights the importance of analysing each relevant process separately to determine the EI in order to understand why a mitigation strategy is more or less efficient.

In recent years, sustainable urban drainage systems (SUDSs) have become increasingly popular, sometimes taking over large parts of conventional stormwater management. SUDSs are usually designed using simple design procedures based on statistical rainfall data, without long-term simulations or real rainfall events. In addition, there is little experience of how SUDS respond to potential failures and malfunctions, often caused by ageing infrastructure and lack of asset management. Based on these two factors influencing the hydrological performance of SUDS, this study investigates the sensitivity of seven different SUDSs to rainfall events and malfunctions. The study was conducted using the SWMM 5.2 modeling software and the low impact development (LID) module was implemented for a period of 60 years. The SUDS are studied as individual infrastructure and as part of a small urban catchment. The results show that only the green roofs and rainwater cisterns have a statistically significant correlation between the length and return period of rain events and runoff values, with higher correlations for longer rain events. In contrast, the failures and malfunctions investigated can have a significant impact on the hydrological performance of SUDS. In particular, the design return period of SUDS was occasionally significantly exceeded for the strong malfunction scenarios studied.

Urban drainage is subject to a variety of external influencing factors that can have a negative impact on hydraulic system performance. These include changing precipitation characteristics due to climate change [1], an increase in sealed surfaces due to advancing urbanisation [2], but also further failures and malfunctions [3] in the technical grey and green infrastructure. With an increasing share of decentralised urban stormwater measures and uncertainties regarding responsibility, care and maintenance of these facilities, an increase in malfunctions can be assumed [4]. In this work, we are investigating common malfunctions in urban drainage systems with 1D/2D urban flood model in a virtual urban study site. The goal is to highlight differences between the failures and malfunctions in both grey and blue-green infrastructures for different design rainfall events (Type Euler II) and compare them to other possible scenarios like climate change and urbanization.For the research, a model of a small virtual urban study site (1.5ha) is developed with the commercial software PCSWMM2D [5], which represents a small part of an urban catchment. It includes the following sub-structures and assets: i) combined sewer system, ii) urban stream, iii) urban structures including buildings, marketplaces, streets, bridges, pathways, and underbridges and iv) four sustainable urban drainage system (SUDS) structures (green roofs, permeable pavements, swales and bioretention cell). Connected to the combined sewer system are three border areas (30ha, 10ha, 10ha), representing inflows from outside. The urban drainage infrastructures and SUDS were designed based on a design rainfall (Euler Typ II) event with a 5-year return period and 1-hour event duration.In total 12 different scenarios were designed for the virtual urban study site i) the SUDS-base-scenario which includes four different green infrastructure assets, ii) three reference scenarios with climate change, urbanisation and wet preconditions and iii) the malfunction-scenarios with seven single malfunction scenarios and one worst case which is all of the single scenarios combined. Each scenario was run with design rainfall events with an Euler II distribution and interval lengths between 15 minutes and 24 hours as well as return periods between 1 and 100 years.To compare the different scenarios and assess their severity for the urban area we used 3 different objective values. i) The maximum water depth in the vulnerable infrastructure (underbridge), ii) the flooded area with water depths > 10cm and iii) the total combined sewer overflow emissions released into the urban stream.Results show a clear difference between the different malfunction scenarios, with a higher influence of malfunctions in grey than in green infrastructures. In most cases, the reference scenarios climate change, urbanisation and wet preconditions show higher values than the malfunctions scenario. All scenarios are highly dependent on the rainfall event characteristics, with no differences in the objective values compared to the base case for low return periods and rising differences for medium to high return periods.