Nature-based Sustainable Drainage Systems (SuDS) have been promoted for enhancing urban drainage, as well as offering additional benefits to urban greening and amenity, and engaging communities in the design and adoption of schemes. However, a lack of data on the efficacy of nature-based options means that schemes often use traditional engineering approaches instead of nature-based designs. Where nature-based options are used, most schemes lack long-term monitoring to understand their effectiveness; interventions are rarely designed to maximise their potential and often underperform once constructed. Existing practices also mean that most schemes are led by technical expertise and hence proceed with token public engagement, and lack support for community acceptance and adoption. This is unsustainable and undermines SuDS as a crucial tool for climate adaptation and sustainable urban development.

The SuDS+ approach argues for a radical rethink of the benefits of SuDS, de-prioritising drainage as their primary driver, and instead conceptualising ‘SuDS+’ as a multi-benefit urban development tool with a range of co-, not additional, benefits. In this approach SuDS become a vehicle for enhancing urban design, amenity, and health and wellbeing which can be adapted to meet community needs and aspirations.

The SuDS+ project, a 5-year Defra funded study in the Northeast of England, aims to develop and deliver community-centred SuDS, embedding innovation in collaborative design, as well as pushing forward new technologies and approaches for nature-based urban water management, and co-developing our understanding of what and how to monitor interventions to develop a robust evidence-base for the future.

This paper outlines the key challenges and how the project will aim to tackle these as a call to reimagine SuDS as a vehicle for delivering greener, healthier, more sustainable, and more resilience urban communities.

How to cite: Starkey, E. and Rollason, E.: SuDS+: establishing a new vision for sustainable drainage in delivering  sustainable and resilient urban communities, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3381, https://doi.org/10.5194/egusphere-egu23-3381, 2023.

Population growth and climate change alter the urban water cycle resulting in increasing frequency and magnitude of urban floods. In this study, we compared stormwater response in an urban drainage system between two adjacent urban sewersheds in Buffalo, NY, USA. At the first site (DEL), comprehensive installations of green infrastructure (GI) (i.e. bioretention cells) were carried out, while the second site (SQ) was minimally influenced by GI practices. Stormflow was monitored as pipeflow at both sites for an observation period of five years, three pre-construction and two post-construction years. We identified storm events and calculated event runoff, as excess flow above baseflow. Additionally, we evaluated annual total flow and peakflow (annual and seasonal) between the sites and between pre- and post-construction. Our analyses were confined to snow-free seasons because storage of precipitation in the snowpack confounds the evaluation of the precipitation-runoff relation. The analysis showed that the GI implementation was highly effective in reducing stormflow. Total annual flow was reduced at DEL between pre- and post-construction, while no trend was observable at the minimally influenced by GI SQ. Also, event-based stormflow was reduced through GI implementation across all snow-free seasons. Last, median event peakflow was clearly reduced through GI, especially in spring and summer, whereas results during fall were less clear. Through this hydrometric analysis, this study is among the first that provided evidence for the efficiency of GI in reducing stormflow beyond the plot-scale and thus provides future guidance on flood mitigation in urban environments.       

How to cite: Klaus, J., Busch, P., and McHale, M.: On the effectiveness of green infrastructure to reduce stormflow at catchment scale, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4190, https://doi.org/10.5194/egusphere-egu23-4190, 2023.

Urban population has been increasing worldwide in recent decades and it is expected to continue growing in the coming years. Cities are facing the effects of the climate crisis, which primarily impact the most vulnerable contexts, first and foremost informal settlements. In this context, the growth of informal neighborhoods, home to one billion people¹, poses complex challenges for the cities of today and tomorrow. In these urban areas traditional, informal and formal social dynamics coexist, strengthened by strong community identities and bonds. Major problems are due to the lack of basic services and infrastructure, making these areas more vulnerable to the increasingly frequent and intense extreme rainfall events. 

In this work, we present the recently launched Europeaid-funded project MUDAR (Mozambique integrated Urban Development by Actions and Relationships), and specifically focus on its component that addresses the dynamics and effects of flooding  in an informal urban area: the Macuti neighborhood in the city of Beira, Mozambique. Macuti is situated on the coast, making it particularly vulnerable to frequent cyclones, one of all Idai, which damaged 49% of its buildings in March 2019². Moreover, it is located on a marshy, purely flat area at the end of an inadequate open drainage network serving the entire city, which is unable to drain the flow at high tide. Macuti, with its almost 17 thousand people (2017), since the early 2000s has been experiencing a rapid growth in spontaneous settlements, which has resulted in a higher population density, with the unbuilt area decreasing by 40% from 2004 to 2022, and soil permeability further reducing in a context where the clayey soil composition already strongly limits rainfall infiltration. These changes, in addition to the inadequate water infrastructure, have exacerbated flooding problems associated with heavy rainfall events (the maximum daily precipitation of the 1990-2020 period was 288.5 mm/day). Investigating the socio-hydrology of flooding in these informal settlements is particularly complex because its requirements for high-resolution topographic, soil, land use and meteorological data, which are very limited in these informal settlements. 

More specifically, we present preliminary outcomes and the proposed project strategy to cope with the intrinsic data scarcity of such context, which is based on carefully designed participatory surveys with local actors. To fill this data gap, a multi-disciplinary approach has been adopted by combining elaborations from satellite image processing (SAR) with in-situ measurements and interviews to inhabitants and professionals. In addition to being involved in providing information about the area, the inhabitants are a crucial actor in the decision-making process for choosing the technical solutions to be implemented. Preliminary results on  flooding dynamics in Macuti neighborhood, as well as on three Nature-Based-Solutions scenarios emerging from the participatory process highlight promising factors that can allow adapting the participatory procedure in similar contexts.

¹French, M., Trundle, A., Korte, I., Koto, C. (2020). Climate Resilience in Urban Informal Settlements: Towards a Transformative Upgrading Agenda. Climate Resilient Urban Areas, 129-153

²UNOSAT-REACH (2019). Mozambique- Beira City -Macuti - Neighbourhood Damage Assessment- As of 26 March 2019. URL: https://m.reliefweb.int/report/3056948

How to cite: Serrao, L., Ottaviani, S., Diamantini, C., Marzadri, A., Ragazzi, M., Paulino, W. A. M., Macueia, F. C. C. E., Chate, H. J., Msopela, A. D. S. V., Antonio, A. M., and Zolezzi, G.: Engaging local communities in planning Nature-Based-Solutions for urban drainage systems - the MUDAR project, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8836, https://doi.org/10.5194/egusphere-egu23-8836, 2023.

Green infrastructure (GI) has become a common solution to mitigate stormwater-related problems such as water quality and flooding hazards. Despite  widespread acknowledgement of GI benefits, there is a lack of decision support methods that allow practitioners to identify optimal locations and evaluate the costs and benefits of numerous spatially distributed small GI practices at larger scales (subwatershed to entire watershed) under uncertainty. To address these needs, an online Cloud-based interactive tool coupling SWMM (Storm Water Management Model) and the Water Research Foundation LID life cycle model, , called Interactive DEsign and Assessment System for Green Infrastructure (IDEAS_GI), is optimized using a noisy genetic algorithm (GA) with life cycle costs and stormwater volume reduction as the primary objectives. To overcome the computational challenge of probabilistic sampling with the noisy GA and to identify significant features for preferable locations, the GA  is merged with an artificial neural network, which acts as a meta-model (surrogate) for the numerical simulation model (SWMM). Post-optimization, machine learning decision trees are also generated that classify the numerous potential solutions generated by the noisy GA into GI coverage classes based on sub-watershed parameters. This framework is applied to a watershed in Baltimore, Maryland, U.S., under multiple budgetary scenarios. The results suggest that the greatest GI investments under the highest and lowest budgetary scenarios should be allocated to subwatersheds closest to the watershed outlet. For the lowest scenario, GI practices should be installed only in subwatersheds closest to the watershed outlet. When the budgetary scenario is highest, GI is sited across the watershed but highest priority is still given to subwatersheds closest to the watershed outlet. On the other hand, the importance of total distance to the watershed outlet is lower for the medium budgetary scenario. In fact, the impacts of different features for preferable GI coverage for these solutions are more complex, don’t follow a consistent pattern, and require more depth to capture the patterns in their corresponding classifier decision trees. In addition to these GI findings, the results showed that the addition of meta-models decreases average computational time required to reach Pareto frontiers similar to the ones generated by the noisy GA by more than 95%.

How to cite: Minsker, B. and Heidari Haratmeh, B.: Optimization of Green Infrastructure Networks to Maximize Stormwater-Related Benefits and Minimize Life Cycle Costs Using a Noisy Genetic Algorithm and Machine Learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10670, https://doi.org/10.5194/egusphere-egu23-10670, 2023.

Infiltration-based green infrastructures (GIs) are commonly constructed to effectively storage the excessive stormwater runoff. These GIs exploit infiltration process, as the key natural phenomenon in the hydrological water balance, to detain excessive stormwater volume, especially at the outlet of the peri-urban watershed. Beside many factors playing significant roles in the performance of the infiltration-based GIs, implementing them in shallow groundwater area still represents a challenge that can restrict their widespread adoption. In fact, the groundwater level, if close to the bottom of infiltration-based GIs, can strongly influence the infiltration process. Basically, the shallow groundwater may theoretically play as a boundary conduction and subsequently reduces the infiltration rate.

The present study investigated the activation of an infiltration-based GI located at the outlet of the combined sewer system in the municipality of Sedriano (12,000 inhabitants in province of Milan, North Italy), monitoring the inflow and the water depth over a period of almost two years. Meantime, groundwater level and meteorological measurements were observed (including precipitation, air temperature, solar radiation, wind velocity, and relative humidity). Using these observations, a Water-Balance Model (WBM) was calibrated on the hydrological response of the infiltration-based GI and then, used to simulate how much time is required to empty under a specific precipitation event, and to understand the spatial distributed performances of these measures under different groundwater levels.

The implementation of an accurate WBM can be a useful tool for designing and assessing the performance of the infiltration-based GIs in shallow groundwater environments in peri-urban areas. This study is an integral part of the project Smart-Green (www.smartgreen.unimi.it) that developed online tools for supporting the water utilities to accelerate the transition towards the sponge cities utilizing GIs techniques.

How to cite: Masseroni, D., Niazkar, M., and Cislaghi, A.: Implementing Water Balance Model for Stormwater Management: the case of an Infiltration-Based Green Infrastructure Under Shallow Groundwater Levels, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11430, https://doi.org/10.5194/egusphere-egu23-11430, 2023.

Urban development leads to an increment of impervious cover that drastically reduces infiltration rates and increases the risk of stormwater floods, also reinforced by the rise of extreme events due to climate change.

In this context, urban trees represent a valid system for sustainable stormwater management. They decrease the runoff discharged in the sewer network and/or in the receiving water bodies.

Trees impact the hydrological cycle through the processes of interception, evapotranspiration and infiltration strictly depending on several factors such as tree features, soils properties, climate, and storm event characteristics.

The objective of the study is to propose an analytical-probabilistic approach to model the contribution of urban trees to the restoration of the water cycle, with particular focus on the evapotranspiration component.

How to cite: Marrazzo, G. and Raimondi, A.: The role of urban trees in water cycle restoration, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13613, https://doi.org/10.5194/egusphere-egu23-13613, 2023.

The built environment is being forced to adapt to rising global temperatures and severe weather events such as more intense storms, longer heatwaves etc. The proliferation of impermeable surfaces has over time led to many urban design problems, such as storm surges overwhelming sewers. Increasing urban temperatures are also caused by the built environment, the Urban Heat Island (UHI) effect. These impacts can be tackled through better infrastructure. Permeable paving offers an alternative to many impermeable surfaces, providing a robust surface with the advantage of drainage. Its ability to mitigate heat, however, remains poorly understood.

To address this, a detailed performance evaluation of two permeable paving pads, one a control and the other actively (mains supply) and passively (rainwater retention) watered, was undertaken. The 16 m² permeable paving pads were installed at Imperial College London’s White City campus (London, UK) and monitored over 4 months (July to October 2021). The pads were bounded by a raised impermeable barrier and consisted of a block layer with foundations of grit underneath. Both pads were placed on a slope enabling them to be drained, a weir prevented flooding and a tap allowed for complete drainage. The pads were instrumented with internal heat and water content sensors, as well as surface thermal sensing, and a dedicated weather station. Several artificial wetting events were conducted during the summer of 2021 alongside controlled laboratory work. A significant cooling effect was found (average of 1, and up to 5 of cooling), which was around half that computed for well-watered green space. It was found that the evaporation rate of the wetted pad was dependent on the degree of saturation, with the greatest heat loss efficiency occurring when the grit layer was partially saturated. A variety of secondary observations were also made, including issues around water fouling, and porous bricks. Whilst permeable paving can assist with flood alleviation, is it hoped, through minor design modifications, that it can also help tackle extreme urban heat impacts.

How to cite: Butler, A., Rowan, T., and Paschalis, A.: Investigation of thermal cooling potential of Permeable Paving at an urban trial site in London, UK, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14713, https://doi.org/10.5194/egusphere-egu23-14713, 2023.

In the face of insufficient water resources and the intensification of extreme events caused by climate change, the generation of non-conventional water sources is an option that should become a priority. Wastewater treated is a water resource that with proper post-treatment can be suitable for maintaining the environmental quality of rivers and wetlands or be used for productive activities such as agricultural uses.

Returning water to the environment in similar conditions to its original state is vital to promote its reuse and to help maintain biodiversity. In this sense, the project Integrating circular economy and biodiversity in sustainable water treatments based on constructed wetlands LIFE RENATURWAT aims to demonstrate that it is possible to obtain high quality water from Waste Water Treatment Plants (WWTP) effluents by combining Nature-Based Solutions (NBS) and industrial wastes.

One of the disruptive issues of this project is exactly the use of a waste generated in the integral water cycle itself, concretely during the production of drinking water, to produce quality water from WWTP. This sludge (DWTS) has inert and non-toxic properties, so usually is disposed in landfills, not taking profit of the economic and environmental benefits derived from its valorisation. Nevertheless, the DWTS has adsorbent capacities due to the coagulant used in the drinking water treatment process.

LIFE RENATURWAT plans to use the DWTS as an active substrate in constructed wetlands (CWs) aimed at upgrading treated urban wastewater. This sludge is dewatered and milled to obtain a grain size similar to sand. The DWTS reinforces the wetland technology so that it can be more efficient and can efficiently remove phosphorus and other pollutants at the same time as generating a habitat in itself.

The solution includes two kinds of CWs operating in series. The first is a vertical subsurface flow constructed wetland with DWTS as a filter medium and the second one is a free water surface constructed wetland. The described system is able to remove phosphorus from wastewater even at very low concentrations, achieving an average total phosphorus concentration in the effluent below than 0.1 mgP/l. This is considerably lower than the legal limit set by Directive 91/271/EEC, UWWTD (1 or 2 mg P/l), as well as the so-called sensitive area 0.6 mg P/l. In this way, a wastewater effluent with a very low phosphorus concentration is obtained, without additional consumption of reagents, addressing one of the main problems faced by WWTP managers, which is the eutrophication of the natural environment and compliance with phosphorus discharge limits. Within the framework of this project, two pilot projects have been implemented, one in the Valencian town of Carrícola, and the other in the Los Monasterios urbanisation (Puçol).

How to cite: Oliver, N., Año, M., Almenar, P., Baeza, A., Hernández-Crespo, C., and Martín, M.: Sludge valorisation to obtain high quality water from WWTP, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15822, https://doi.org/10.5194/egusphere-egu23-15822, 2023.