Green Infrastructure and Water: An Analysis of Global Research

A deep dive into green infrastructure failures using fault tree analysis

Green Infrastructure has transformed traditional urban stormwater management systems by fostering a wide range of service functions. Despite their popularity, green infrastructure's performance can deteriorate over their lifecycle, leading to operational failures. The operation of green infrastructure has predominantly relied on reactive maintenance strategies. To anticipate malfunctions and enhance the performance of green infrastructure in the long run, failure data needs to be recorded so that deterioration processes and component vulnerabilities can be recognized, modelled and included in predictive maintenance schemes. This study investigates possible failures in representative GIs and provides insights into the most important events that should be prioritized in the data collection process. A method for qualitative Fault Tree Analysis using minimal cut sets are introduced, aiming to identify potential failures with the minimum number of events. To identify events of interest fault trees were constructed for bioswales, rain gardens and green roofs, for three groups of service function failures, namely runoff quantity control, runoff quality control and additional service functions. The resulting fault trees consisted of 45 intermediate and 54 basic events. The minimal cut set analysis identified recurring basic events that could affect operation among all three green infrastructure instances. These events are 'trash accumulation', 'clogging due to sediment accumulation', and 'overly dense vegetation'. Among all the possible cut sets, events such as 'plants not thriving', 'invasive plants taking over', and 'deterioration caused by external influences' could potentially disrupt most of the service functions green infrastructure provides. Furthermore, the analysis of interactions between component failures shows vegetation and filter media layer failures have the highest influence over other components. The constructed fault trees and identified basic events could be potentially employed for additional research on data collection processes and calculating the failure rates of green infrastructure and as a result, contribute to a shift toward their proactive operation and maintenance.

Influence of Low-Impact Development in Flood Control: A Case Study of the Febres Cordero Stormwater System of Guayaquil (Ecuador)

Urban flooding is a major problem in many coastal cities. The rapidly shifting patterns of land use and demographic increase are making conventional approaches to stormwater management fail. In developing countries such as Ecuador, a lack of monitoring, financial constraints and absence of proper policies exacerbate flooding problems. This work assesses the implementation of two Low Impact Development strategies (LIDs), namely, green streets and rain barrels, as nature-based solutions to mitigate flooding problems. The use of the “Stormwater Management Model” (SWMM) helped to contrast the new approach with the current state of the drainage system, including normal and extreme scenarios. With an implementation of 1.4% (19.5 ha) of the total area with LIDs, the reduction of runoff for short events (200 min) is around 20%, and for extreme events (within 24 h) is around 19% in comparison to the conventional approach. Flooded nodes were reduced to 27% for short events, and to 4% for extreme events. The peak flooding system had a reduction to 22% for short events and 15% for extreme events. These highlights help to increase city resilience, and authorities and stakeholders should engage in climate actions to reduce flood risks complementing drainage operations with nature-based solutions. Moreover, calibrated results in this article serve to increase awareness among municipal authorities regarding the importance of maintaining flooding records to improve modelling results for decision-makings processes.

Impacts of Zagreb’s Urban Development on Dynamic Changes in Stream Landscapes from Mid-Twentieth Century

Urban streams constitute a valuable form of multi-functional blue and green infrastructure (BGI) and can support urban development to generate ecosystem, social, and economic benefits. In global cities, planning for BGI enhancement contributes to climate change adaptation, ecosystem restoration, community health and wellbeing, improved quality of life, etc. This research aims to assess the dynamics of stream landscape change in Zagreb as well as the influence of urban development on the blue and green landscape and related urban values. The analysis of landscape features and their planning is conducted at the level of the stream system of the whole city of Zagreb and at the level of two stream sequences by superimposing spatial data from cartographic sources. By developing an urban planning-social-ecological approach to evaluation, monitoring, and management, a quantitative and qualitative trend in stream landscape changes is identified and indicators for detecting areas of critical urbanization pressure are established. This research confirms the trend of negative changes in the urban BGI, evident in the present state (interruption of open streams, and the reduction, fragmentation, and disconnection of blue and green landscape), as well as in the planned neglect (plans for further stream closures and reduction in public green areas). Stream landscape potential is emphasized as one of the greatest urban assets for improving the system of BGI, and areas needed for their prioritization in urban planning measures, directed towards an increase in multiple landscape values, are determined.

Sustainable Urban Drainage System (SUDS) modeling supporting decision-making: A systematic quantitative review

Decision Support Systems (DSS) for Sustainable Urban Drainage Systems (SUDS) are a valuable aid for SUDS widespread adoption. These tools systematize the decision-making criteria and eliminate the bias inherent to expert judgment, abridging the technical aspect of SUDS for non-technical users and decision-makers. Through the collection and careful assessment of 120 papers on SUDS models and SUDS-DSS, this review shows how these tools are built, selected, and used to assist decision-makers questions. The manuscript classifies the DSS based on the question they assist in answering, the spatial scale used, the software selected, among other aspects. SUDS-DSS aspects that require more attention are identified, including environmental and social considerations, SUDS trains performance and criteria for selection, stochasticity of rainfall, and future scenarios impact. Suggestions for SUDS-DSS are finally offered to better equip decision-makers in facing emerging stormwater challenges in urban centers.

Water Literacy in the Southeast Asian Context: Are We There Yet?

The water situation in Southeast Asia has changed from one of relative abundance to one of relative scarcity. Conventional water management that strategized around the provision of adequate water supply to users has limited sustainability. Though nations in this region have adopted the United Nations Sustainable Development Plan into their water management framework, successful outcomes are limited thus far. Water literacy has a growing importance for improving water sustainability, especially in developing countries. A literature search was employed to extract data on the different dimensions of water literacy in Southeast Asia including the sources and consumption patterns, water governance and management, and sociodemographic elements as well as the various aspects of water related challenges faced. Results from the review and analysis show that a large proportion of Southeast Asian populations are not part of a water sustainable society, and this presents a major hurdle for the countries to meet United Nations Sustainable Development Goal 6 by 2030. Therefore, active cognitive engagement through the creation of a water literate environment is critical for breaking the chain of water illiteracy and to achieve long-term water sustainability in Southeast Asia countries. Overall, this paper provides a critical analysis on lessons learnt from the region that can be mirrored in other parts of the world.

Effectiveness of Nature-Based Solutions in Mitigating Flood Hazard in a Mediterranean Peri-Urban Catchment

Urbanization alters natural hydrological processes and enhances runoff, which affects flood hazard. Interest in nature-based solutions (NBS) for sustainable mitigation and adaptation to urban floods is growing, but the magnitudes of NBS effects are still poorly investigated. This study explores the potential of NBS for flood hazard mitigation in a small peri-urban catchment in central Portugal, prone to flash floods driven by urbanization and short but intense rainfall events typical of the Mediterranean region. Flood extent and flood depth are assessed by manually coupling the hydrologic HEC-HMS and hydraulic HEC-RAS models. The coupled model was run for single rainfall events with recurrence periods of 10–, 20–, 50–, and 100–years, considering four simulation scenarios: current conditions (without NBS), and with an upslope NBS, a downslope NBS, and a combination of both. The model-simulation approach provides good estimates of flood magnitude (NSE = 0.91, RMSE = 0.08, MAE = 0.07, R2 = 0.93), and shows that diverting streamflow into abandoned fields has positive impacts in mitigating downslope flood hazard. The implementation of an upslope NBS can decrease the water depth at the catchment outlet by 0.02 m, whereas a downslope NBS can reduce it from 0.10 m to 0.23 m for increasing return periods. Combined upslope and downslope NBS have a marginal additional impact in reducing water depth, ranging from 0.11 m to 0.24 m for 10– and 100–year floods. Decreases in water depth provided by NBS are useful in flood mitigation and adaptation within the peri-urban catchment. A network of NBS, rather than small isolated strategies, needs to be created for efficient flood-risk management at a larger scale.