Grey Infrastructure Research Articles

Flood legislation and land policy framework of EU and non‐EU countries in Southern Europe

AbstractFloods are a widespread natural hazard affecting people and their assets in regions worldwide, including Southern Europe. Besides coastal floods, the Mediterranean region is highly prone to flash floods driven by short but intense precipitation events. With increasing flood risk due to climate change and socio‐economic conditions, governments are under pressure to reinforce flood protection measures, which could be a great challenge for the weak economies of non‐EU developing countries. This is of particular relevance to achieving international commitments such as the United Nations Sustainable Development Goals. Several policy frameworks have been developed to mitigate flooding risk, at European Union (EU) and global level. These frameworks call for a holistic risk reduction approach where governments, institutions, and households are all responsible for reducing risk. In practice, however, gray infrastructure remains the prevailing flood risk management measure in many countries. Incorporation into national legislation and implementation of the EU policy framework will increase constraints and pressures for non‐EU countries, particularly those strongly committed to becoming EU members in future. This article provides a comprehensive review of policies and measures implemented in four different southern European countries to mitigate flood hazard, and compares governance aspects between EU (Portugal and Slovenia) and non‐EU countries (B&H and Serbia). Understanding governance aspects and the status of flood‐related policy implementation is of critical importance in protecting people and enhancing resilience to climate change impacts. Programs of improvement measures and further integration of sustainable water management with other sectoral policies are required to reduce flood risks.This article is categorized under: Engineering Water > Planning Water Human Water > Water Governance Science of Water > Water Extremes

Reading the Green Landscape: Public Attitudes toward Green Stormwater Infrastructure and the Perceived Nonmonetary Value of Its Co-Benefits in Three US Cities

AbstractGreen stormwater infrastructure mirrors natural hydrologic processes and is presented as an alternative or complement to traditional gray stormwater infrastructure, which uses concrete chan...

A phyto-guide to species selection for optimized South African green infrastructure

In South Africa, rapid environmental degeneration caused by anthropogenic pollution poses a major ecological engineering problem, demanding proper resource mitigation strategies. For the treatment of polluted water and degraded soil systems, green infrastructure (GI) offers an effective, sustainable and affordable nature-based alternative to grey infrastructure. An additive benefit within GI, plant species provide enormous potential to treatment; however, species vary substantially in their pollutant removal and hydrologic performance. South African civil engineers tasked with designing GI often lack expertise and knowledge of plant behaviour and ecosystem dynamics. Therefore, this paper proposes a decision framework to facilitate selection for designing local GI in the form of a phyto-guide, based on existing recommendations and knowledge of removal processes and plant behaviour. Interdisciplinarity at the core of the phyto-guide relies on continuous specialist collaboration with each selection criteria, whilst efficiency and sustainability are considered equally important contributors to successful GI functioning. The spread of invasive alien plants, whether accidental or deliberate, negatively impacts an ecosystem’s capacity to deliver goods and services. Thus, the desire to optimize GI by incorporating effective phytoremediators cannot be prioritised over conservation concerns. In addition, this paper seeks to advance the GI limitation of relying solely on previously identified phytoremediators, by including evaluation criteria of beneficial plant traits as well as plant distribution, behaviour and diversity into the decision-making process for optimized GI. It is recommended that future research engages in discovering less invasive, naturally occurring local species as potential phytoremediators, inspired by South Africa’s rich biodiversity and endemism, as well as conveying the importance of consultation with engineers and ecologists for optimized GI.

Immune-mediated disease associated microbial community responded to PAH stress in phyllosphere of roadside greenspaces in Shanghai

Microorganisms in urban greenspaces play key roles in ecosystem service provision and potentially influence human health. Increasing evidence suggests that anthropogenic disturbance poses constant stress on urban microbial communities, yet, as previous studies have focused on non-contaminated greenspaces, it has remained largely unknown how microorganisms respond to anthropogenic stress in roadside greenspaces with contamination. Our previous effort determined phyllosphere PAHs of camphor trees in 84 sites of roadside greenspaces along the urban-rural gradient in Shanghai. Here, we further investigated the phyllosphere microbial communities (PMCs) of the same sites across the same urban categories, including urban, suburban, and rural areas using high-throughput DNA sequencing. We aimed to explore how PMCs, especially those associated with immune-mediated diseases (IMDs), were affected by PAHs and the surrounding land-use types. We found that several microorganisms associated with increasing IMD risk were stimulated by PAHs. The composition of PMCs differed between the three urban categories which can be largely explained by the variation of phyllosphere PAH concentration and the surrounding land-use types. Similar to our previous study, suburban areas were linked with the most potential adverse health effects, where we observed the lowest bacterial diversity, the highest relative abundance of IMD-associated bacteria, and the highest relative abundance of Pathotroph. Urban green-blue infrastructure (GBI) was positively correlated with the diversity of PMCs, whereas urban grey infrastructure tended to homogenize PMCs. Notably, GBI also reduced the relative abundance of IMD-associated and pathogenic microbes, indicating the potential health benefits of GBI in land-use planning. Taken together, our study emphasizes the need to further investigate environmental communities in contaminated traffic environments, as human microbiomes are directly exposed to risky microorganisms.

Developing Green Infrastructure Strategies Based on the Analysis of Sewer System Critical Components

Flooding has presented a significant risk for urban areas around the world. Road inundation is one of the severe consequences leading to traffic issues and congestion. Green infrastructure (GI) offers further potential for stormwater management as an environmentally friendly and sustainable solution. However, sewer system behaviour has been overlooked in GI implementation. This study investigates sewer performance by measuring topological connectivity and hydraulic characteristics, and critical components are identified under different design storms. Three retrofit scenarios, including enlarged pipes (grey infrastructure, Grey I), rain gardens (GI), and the combination of enlarged pipes and increased rain gardens (GI + Grey I), are proposed according to the distribution of critical components. The results show that it is feasible to locate the vulnerable parts of the sewer system and GI site allocations based on the critical components that significantly impact the performance of the entire system. While all three scenarios can mitigate inundation, GI and GI + Grey I perform better than pipe enlargement, especially for runoff reduction during long-duration rainfall. Furthermore, the sewer behaviour and retrofit effect are dynamic under different rainfall patterns, leading to diverse combined effects. The discoveries reveal that the adaptation measures should combine with sewer behaviour and local rainfall characteristics to enhance stormwater management.

Green infrastructure: The future of urban flood risk management?

AbstractUrban flooding is a key global challenge which is expected to become exacerbated under global change due to more intense rainfall and flashier runoff regimes over increasingly urban landscapes. Consequently, many cities are rethinking their approach to flood risk management by using green infrastructure (GI) solutions to reverse the legacy of hard engineering flood management approaches. The aim of GI is to attenuate, restore, and recreate a more natural flood response, bringing hydrological responses closer to pre‐urbanized conditions. However, GI effectiveness is often difficult to determine, and depends on both the magnitude of storm events and the spatial scale of GI infrastructure. Monitoring of the successes and failures of GI schemes is not routinely conducted. Thus, it can be difficult to determine whether GI provides a sustainable solution to manage urban flooding. This article provides an international perspective on the current use of GI for urban flood mitigation and the solutions it offers in light of current and future challenges. An increasing body of literature further suggests that GI can be optimized alongside gray infrastructure to provide a holistic solution that delivers multiple co‐benefits to the environment and society, while increasing flood resilience. GI will have to work synergistically with existing and upgraded gray infrastructure if urban flood risk is to be managed in a futureproof manner. Here, we discuss a series of priorities and challenges that must be overcome to enable integration of GI into existing stormwater management frameworks that effectively manage flood risk.This article is categorized under: Engineering Water > Sustainable Engineering of Water Engineering Water > Planning Water Science of Water > Water Extremes

Urban Pluvial Flood Management Part 2: Global Perceptions and Priorities in Urban Stormwater Adaptation Management and Policy Alternatives

Urban stormwater infrastructure is at an increased risk of being overwhelmed by pluvial flood events due to climate change. Currently, there are no global standards or frameworks for approaching urban rainfall adaptation policy. Such standards or frameworks would allow cities that have limited time, finances or research capacities to make more confident adaptation policy decisions based on a globally agreed theoretical basis. Additionally, while adaptation via blue-green infrastructure is often weighed against traditional grey infrastructure approaches, its choice must be considered within the context of additional policy alternatives involved in stormwater management. Using six global and developed cities, we explore to what extent a standardized hierarchy of urban rainfall adaptation techniques can be established through a combined Analytic Hierarchy Process (AHP) Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) Multi-Criteria Decision Analysis. While regional and stakeholder differences emerge, our study demonstrates that green infrastructure undertaken by public bodies are the top policy alternative across the cities and stakeholder groups, and that there exists some consensus on best management practice techniques for urban stormwater adaptation.

Evaluation of Pollutant Removal Efficiency by Small-Scale Nature-Based Solutions Focusing on Bio-Retention Cells, Vegetative Swale and Porous Pavement

Rapid urbanization, aging infrastructure, and changes in rainfall patterns linked to climate change have brought considerable challenges to water managers around the world. Impacts from such drivers are likely to increase even further unless the appropriate actions are put in place. Floods, landslides, droughts and water pollution are just a few examples of such impacts and their corresponding consequences are in many cases devastating. At the same time, it has become a well-accepted fact that traditional (i.e., grey infrastructure) measures are no longer effective in responding to such challenges. Nature-based solutions (NBS) have emerged as a new response towards hydro-meteorological risk reduction and the results obtained to date are encouraging. However, their application has been mainly in the area of water quantity management with few studies that report on their efficiency to deal with water quality aspects. These solutions are based on replicating natural phenomena and processes to solve such problems. The present paper addresses the question of three NBS systems, namely, bio-retention cells, vegetative swales and porous pavements, for the removal of total suspended solids (TSS), total nitrogen (TN) and total phosphorus (TP) when applied in different configurations (single or networked). The results presented in this paper aim to advance the understanding of their performances during varying rainfall patterns and configurations and their potential application conditions.

Planting Stormwater Solutions: A methodology for siting nature-based solutions for pollution capture, habitat enhancement, and multiple health benefits

Urban areas worldwide must manage stormwater to prevent flooding and reduce pollution. Infrastructure has historically been designed and used for the single purpose of managing stormwater, but this gray infrastructure typically has negative consequences and fails to address other challenges faced by urban areas. As an alternative, vegetated Nature-Based Solutions (NBS) such as bioretention facilities, constructed stormwater wetlands, and outfall retrofits may be used to capture and treat stormwater, while also contributing other benefits, such as reducing urban heat-island effects, increasing carbon sequestration, improving air quality, climate adaptation, and access to open space, and enhancing mental and physical health and urban biodiversity. To optimize these benefits, the siting of NBS can be crucial. We developed a spatially explicit analytical methodology, Planting Stormwater Solutions, to prioritize the siting of vegetated NBS to benefit biological diversity, social and public health, and water quality. Using Los Angeles as a case study, we demonstrate where benefits spatially converge or diverge. We found that while some of the greatest opportunities to benefit biodiversity occur along waterways, the greatest social and public health benefits may be realized for NBS installed in and around heavily developed areas. NBS sited in areas with a high density of commercial and industrial land uses may provide the greatest water quality benefits. Use of our analytical methodology may allow decision-makers with limited resources and multiple challenges to make more informed siting decisions for vegetated NBS.

Preference Heterogeneity of Coastal Gray, Green, and Hybrid Infrastructure against Sea-Level Rise: A Choice Experiment Application in Japan

Coastal zones are bearing the brunt of an increase in the likelihood of extreme events, coupled with sea-level rise (SLR). Conventionally, gray infrastructures, such as seawalls, have been constructed to reduce risks in limited coastal zone spaces. Nature-based approaches, known as green infrastructure, have been used in coastal defense, and their ecosystem-based disaster risk reduction functions (Eco-DRR) have received growing attention. However, both gray and green infrastructure alone have limitations in responding to an ongoing increase in the intensity and frequency of natural hazards. To overcome these issues, hybrid infrastructure, which combine gray and green components, is needed, and they have been receiving growing attention. Meanwhile, a large-scale coastal development requires stakeholder agreement; thus, it is imperative to understand people’s demands and build a consensus between municipalities and coastal citizens in coastal development for long-term resilience. The author administered the online survey across Japan, applying it to the choice experiment, and obtained 840 valid responses. Therefore, this paper clarified the heterogeneities in coastal people’s preferences for coastal ecosystem services provided by gray, green, and hybrid structures in intertidal zones in Japan, recognizing seawalls as gray and coastal pine forests as green infrastructure. Consequently, while coastal citizens acknowledged gray’s coastal defense function, the diverse perceptions toward seawalls for SLR preparation were notable as its scenarios became severe. Another remarkable finding is that nearly 60% of respondents preferred Eco-DRR functions provided by coastal forests with JPY 695 in willingness-to-pay for expanding 100 m in width, even though there are uncertainties in their performances.

A framework for deriving dispatching rules of integrated urban drainage systems

The urban drainage system (UDS) with the integration of new and old, green and gray infrastructures has become an underlying trend, but its sewage dispatch is getting more and more difficult owing to complex network topology, much uncertainty introduced by the lack of empirical data or monitoring system, and consideration of multiple objectives. We propose a novel framework for deriving dispatching rules that allocate the wastewater inflow according to the comprehensive capacity of treatment facilities. The main innovative point of the framework is using the Prophet algorithm to handle sewage volume uncertainty introduced by rainfall. Moreover, we construct a multi-objective optimization model of operating costs and surface water quality and apply it in multiple scenarios. Lastly, we build a decision tree to mine dispatching rules and threshold identification. Taking the Pingshan River Basin, we plot dispatching diagrams and discover the threshold of creating the risk to surface water quality. When the sewage volume reached 18.0 × 105 m³ in winter, water quality exceeded limits. Other than that, the wastewater spatiotemporal allocation placed receiving water quality and operating cost in a competitive relationship. An application of dispatching rules shows that they fill a gap in the scientific and reasonable dispatch of the UDS.

Multi-Objective Model-Based Assessment of Green-Grey Infrastructures for Urban Flood Mitigation

This paper presents the performance quantification of different green-grey infrastructures, including rainfall-runoff and infiltration processes, on the overland flow and its connection with a sewer system. The present study suggests three main components to form the structure of the proposed model-based assessment. The first two components provide the optimal number of green infrastructure (GI) practices allocated in an urban catchment and optimal grey infrastructures, such as pipe and storage tank sizing. The third component evaluates selected combined green-grey infrastructures based on rainfall-runoff and infiltration computation in a 2D model domain. This framework was applied in an urban catchment in Dhaka City (Bangladesh) where different green-grey infrastructures were evaluated in relation to flood damage and investment costs. These practices implemented separately have an impact on the reduction of damage and investment costs. However, their combination has been shown to be the best action to follow. Finally, it was proved that including rainfall-runoff and infiltration processes, along with the representation of GI within a 2D model domain, enhances the analysis of the optimal combination of infrastructures, which in turn allows the drainage system to be assessed holistically.

Environmental and economic benefit comparison between coupled grey-green infrastructure system and traditional grey one through a life cycle perspective

Green infrastructure is increasingly incorporated into the existing urban drainage system, i.e., grey infrastructure, for stormwater management in the context of rapid urbanization and climate change. Whether the coupled green–grey system can yield additional benefits requires quantification of environmental and economic performance. This study proposes a cost-combined life cycle assessment method to evaluate the environmental and economic benefits of coupled grey and green infrastructure system. Compared to traditional assessment methods, this method introduces internal (e.g., material cost, energy cost) and external (i.e., human health, ecological restoration, and pollutants emission) economic costs to conduct assessment. This research identifies key factors (i.e., categories, processes, and substances) of a coupled grey and green infrastructure system in a typical residential area in China. The coupled system is shown to generate higher environmental impacts and economic costs than grey system in the construction stage. The operation stage of coupled system can observe significant environmental and economic benefits. The payback time of related environmental impacts (except for non-carcinogens) and total economic costs is 4 years for the current case study. Noteworthy, a currently existing subsidy scheme would allow to reduce the payback time of total economic costs from 3.78 to 1.18 years. This study provides concrete evidence in support of urban stormwater management.

Mapping Mangrove Opportunities with Open Access Data: A Case Study for Bangladesh

Mangroves protect coastal areas against hazards like storms or cyclones by attenuating waves and currents, and by trapping floating debris during extreme events. Bangladesh is a very vulnerable country to floods and cyclones, and part of its coastal system is thus being upgraded to a higher safety standard. These upgrades include embankment reinforcement and mangrove afforestation schemes seawards of the embankments. To further strengthen the implementation of combined green–grey infrastructure in future programs, identifying potential mangrove development sites near the polder systems is a necessary first step. We thus developed a tool to systematically identify mangrove sites throughout the coastal area based on open access data. This method identifies potential sites for mangrove development based on their distance from existing mangrove patches and suggests the required technique to implement the vegetation depending on the rate of coastline change. Our method showed that approximately 600 km of the coastal stretches placed seawards of embankments are within 10 km of existing mangroves, and could thus be potential sites for mangrove establishment. Out of those 600 km, we identified 140 km of coastline where the landwards polders are particularly vulnerable to flooding. The sites with highest restoration potential and priority are located in Galachipa, Hatiya, Bhola, Manpura, Khangona, and Boro Moheshkhali. More detailed data collection and local assessments are recommended prior to executing mangrove afforestation schemes. Nevertheless, this method could serve as a useful systematic tool for feasibility studies that identify mangrove opportunities in data-scarce areas and help to prioritize data collection at the sites of highest interest.

Integrating socioecological indexes in multiobjective intelligent optimization of green-grey coupled infrastructures

Ecological conservation is an important objective in urban runoff management today. Maintaining a sustainable ecological system is as equally important a task as to ensure the safety of drainage systems and runoff management cost control. Thus, the socioecological influences of runoff control infrastructure are innovatively included in a uniform evaluation framework with the control functions and capital investments in this study. These indexes are quantified through hydrological model simulation, life cycle cost analysis, and life cycle assessment. Traditional grey infrastructure and rapidly developing green infrastructure for runoff control are optimized simultaneously. For the trade-off between multiobjectives and configurations of multi-infrastructures, nondominated sorting genetic algorithm-II is utilized to achieve automatic optimization of runoff control infrastructure scale, thereby avoiding the dilemma where manually arranged schemes cannot perform optimally. This multiobjective intelligent optimization is applied to a sponge city pilot region in Wuhan, China, and trade-offs are made in the Pareto optimal solution set. A breakthrough is claimed in quantifying the respective contribution of green and grey infrastructures to the optimal scenario in terms of runoff control function, cost input, and socioecological influence. For socioecological influence, the paybacks can meet the investment in the aspect of toxicity health hazard, pathogenic matter, global warming, terrestrial acidification, and water eutrophication (average socioecological paybacks are 2.0, 2.1, 2.9, 1.9, and 2.1 times to the investments respectively). Results prove the necessity of considering multiobjective optimization and green-grey couple infrastructures in a uniform framework.

Optimizing Green-Gray Infrastructure for Non-Point Source Pollution Control under Future Uncertainties.

Non-Point Source Pollution (NPS) caused by polluted and untreated stormwater runoff discharging into water bodies has become a serious threat to the ecological environment. Green infrastructure and gray infrastructure are considered to be the main stormwater management measures, and the issue of their cost-effectiveness is a widespread concern for decision makers. Multi-objective optimization is one of the most reliable and commonly used approaches in solving cost-effectiveness issues. However, many studies optimized green and gray infrastructure under an invariant condition, and the additional benefits of green infrastructure were neglected. In this study, a simulation-optimization framework was developed by integrated Stormwater Management Model (SWMM) and Non-dominated Sorting Genetic Algorithm (NSGA-II) to optimize green and gray infrastructure for NPS control under future scenarios, and a realistic area of Sponge City in Nanchang, China, was used as a typical case. Different levels of additional benefits of green infrastructure were estimated in the optimizing process. The results demonstrated that green-gray infrastructure can produce a co-benefit if the green infrastructure have appropriate Value of Additional Benefits (VAB), otherwise, gray infrastructure will be a more cost-effectiveness measure. Moreover, gray infrastructure is more sensitive than green infrastructure and green-gray infrastructure under future scenarios. The findings of the study could help decision makers to develop suitable planning for NPS control based on investment cost and water quality objectives.

The challenges of urban river restoration and the proposition of a framework towards river restoration goals

River restoration is gaining significance as an approach for river system management, even in urban areas, where the flood risks and morphological imbalances are more evident. In cities, the highly modified environment and the lack of open spaces make it harder to apply the concept of river restoration in its whole extent, raising doubts about the feasibility of adopting restoration approaches for urban rivers. In some cases, the implementation of green and blue infrastructure strategies alone is not enough to support the river restoration goals so the adoption of gray infrastructure is necessary. In order to explore aspects related to the theme, this article discusses four questions proposed from a bibliometric study of urban river restoration: Is it worth restoring urban rivers? How much does it cost? If the watershed is heavily modified, can it sustain the restored fluvial spaces? How can the success of this approach be measured? Throughout the discussion, it is clear that due to cities’ complexity and the absence of available open spaces, there is no simple answer to these questions, each case being unique and deserving particular assessment. However, even when performed partially, without significant positive impacts on the natural environment, river restoration can bring several benefits to the urban environment, creating an opportunity of reintegrating the river as a valuable element of the landscape. Additionally, we propose a framework to assist managers in identifying and implementing potential river restoration actions.

Estimating the cost of coastal adaptation using mangrove forests against sea level rise

ABSTRACT Sea level rise due to climate change poses a serious threat to human populations in coastal areas. In planning possible countermeasures, it is important to consider the potential economic risks and the cost of any proposed adaptation. This paper examines the cost effectiveness of adaptation measures that combine mangrove afforestation (green infrastructure) and dike construction (gray infrastructure) in areas considered to be at risk of inundation. Based on data for 112 countries and regions where mangrove forests are present along the coastline, the global benefit/cost ratio for the combination of dikes and mangrove is approximately 1.5 times higher than the ratio for dike-only protection. It was found that this type of multiple protection scheme can reduce the number of dikes required and the overall cost of adaptation.

Hierarchical management scheme of urban waterlogging risk based on critical rainfall level: a case study of Xining City

With the global climate change and the intensification of human activities, urban waterlogging caused by rainstorm is becoming more prominent, and the problem of urban waterlogging needs to be solved. According to different return periods and drainage standards, a new hierarchical management scheme of urban waterlogging risk is proposed, which is composed of micro source runoff control system, minor drainage transmission system, major waterlogging prevention system and resilience improvment system. Based on long series short duration precipitation data, different critical rainfall levels are calculated considering the relevant drainage and waterlogging prevention standards. The calculation results show that the rainfal level for micro source runoff control system is 15.8mm (i.e. point A). For minor drainage control system, the rainfal level are 20.6 mm and 26.9 mm respectively (i.e. point B and B’). For major waterlogging prevention system, the rainfall level is 53.5mm (i.e. point C). According to these segmentation points, four interconnected urban waterlogging risk management strategies are proposed, i.e. stategy 1.0 focuses on micro scale and aims to promote source runoff control by ‘green infrastructure’, 2.0 focuses on minor scale aims to conduct drainage optimization of ‘grey infrastructure’, 3.0 focuses on major scale aims to improve waterlogging prevention by ‘blue infrastructure’ and 4.0 aims to deal with disaster mitigation by ‘red infrastructure’. Furthermore, the rainfall characteristics, the influence degree of rainfall, and objectives and measures for each stragy are given in detail.

The Ecohydrological Approach in Water Sowing and Harvesting Systems: The Case of the Paltas Catacocha Ecohydrology Demonstration Site, Ecuador

Water sowing and harvesting (WS&H), a term adopted from Latin America, is an ancestral process that involves gathering and infiltration (sowing) of rainwater, surface runoff, and groundwater to recover it (harvesting) later and/or elsewhere. The WS&H systems follow the approaches of integrated water resource management, nature-based solutions and the recovery of ancestral knowledge for water management. In this paper, we present some representative types of WS&H in Latin America, Spain, and Portugal, and then, we focus on the Paltas Catacocha Ecohydrology Demonstration Site in southern Ecuador as a study case. The recovery of such local ecohydrological knowledge in the study case has made enabled the regulation and retention of water in the aquifers through the restoration of artificial wetlands ( cochas ) and stream dams ( tapes or tajamares ). Also, this ancestral way of water management has recently supported and reactivated several biological aspects and human activities. The experience of the Paltas Catacocha site shows that there are more appropriate and sustainable alternatives to gray infrastructure projects for water resources management and denotes the need to study ancestral water and soil management systems.