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HS5.10

EDI
Green infrastructure for sustainable urban hazard management

Urban areas are at risk from multiple hazards, including urban flooding, droughts and water shortages, sea level rise, disease spread and issues with food security. Consequently, many urban areas are adapting their approach to hazard management and are applying Green Infrastructure (GI) solutions as part of wider integrated schemes.

This session aims to provide researchers with a platform to present and discuss the application, knowledge gaps and future research directions of urban GI and how sustainable green solutions can contribute towards an integrated and sustainable urban hazard management approach. We welcome original research contributions across a series of disciplines with a hydrological, climatic, soil sciences, ecological and geomorphological focus, and encourage the submission of abstracts which demonstrate the use of GI at a wide range of scales and geographical distributions. We invite contributions focusing on (but not restricted to):

· Monitored case studies of GI, Sustainable Drainage Systems (SuDS) or Nature Based Solutions (NBS), which provide an evidence base for integration within a wider hazard management system;

· GIS and hazard mapping analyses to determine benefits, shortcomings and best management practices of urban GI implementation;

· Laboratory-, field- or GIS-based studies which examine the effectiveness or cost/benefit ratio of GI solutions in relation to their wider ecosystem potential;

· Methods for enhancing, optimising and maximising GI system potential;

· Innovative and integrated approaches or systems for issues including (but not limited to): bioretention/stormwater management; pollution control; carbon capture and storage; slope stability; urban heat exchange, and; urban food supply;

· Catchment-based approaches or city-scale studies demonstrating the opportunities of GI at multiple spatial scales;

· Rethinking urban design and sustainable and resilient recovery following crisis onset;

· Engagement and science communication of GI systems to enhance community resilience.

Co-organized by GM12/NH1
Convener: Daniel GreenECSECS | Co-conveners: Lei LiECSECS, Jorge Isidoro
Presentations
| Thu, 26 May, 13:20–16:34 (CEST)
 
Room L2

Thu, 26 May, 13:20–14:50

Chairpersons: Daniel Green, Helen Brooks, Lei Li

13:20–13:25
5-minute convener introduction

13:25–13:27
Section 1: Experimental monitoring of GI systems

13:27–13:34
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EGU22-333
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ECS
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On-site presentation
Jeremy Teale and Julia L.A. Knapp

Nature based solutions to urban flooding have drawn growing attention in recent years as climate change models predict a catastrophic increase to flood-risk in the UK and around the world. The lack of systematic empirical evidence to support Natural Flood Management (NFM) initiatives still presents a key barrier to the widespread implementation of NFM techniques. The disconnect between practitioners and academics in the field also remains a central issue to be addressed to improve uptake and acceptance of NFM by landowners.

Urban centres in the Wear Catchment in Northeast England are substantially affected by flooding. In this study, we assess the effectiveness of several earth bunds in creating temporary storage of flood water in the upper catchment of the Wear. For this purpose, we assess flood storage frequency and record the impacts of flood storage on bund structure. Arduino-based water sensors in each of the five bunds record the frequency of flood storage, which is related to precipitation intensity and volume. Changes in soil hydraulic conductivity and soil chemistry are also measured throughout the year to assess changes in infiltration capacity as a measure of bund stability. Finally, vegetation surveys are carried out to gain insights on soil recovery after the installation of the bunds, providing a measure of suitability for the land to be used for grazing.

Working closely with the Environment Agency and the landowner, this work aims to develop an improved understanding on the importance of the design requirements and location setting for the installations. We hypothesise that the varying build quality and placing of the bunds in relation to the stream will directly impact the regularity with which the bunds become active storage. This project adds to the evidence base of NFM in the UK and is of direct consequence to practitioners around the world seeking to improve NFM methods.

How to cite: Teale, J. and Knapp, J. L. A.: Assessing the use of earth bunds as Natural Flood Management features, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-333, https://doi.org/10.5194/egusphere-egu22-333, 2022.

13:34–13:41
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EGU22-2949
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ECS
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On-site presentation
Dante Föllmi et al.

Abstract

Green roofs received increased scientific attention with respect to climate adaptation in urban environments for their hydrological, biodiversity and insulative capacities. Yet, the thermal properties of roofs with an additional water layer underneath the vegetation substrate (blue-green roofs) are not well represented in scientific research. In this field study, we examined the impact of surface temperatures, indoor temperature and insulative properties of blue-green, green, and conventional gravel/bitumen roofs in the city of Amsterdam for early 20th century buildings. Temperature sensor (IButtons) results indicate that outside surface temperatures of blue-green roofs were more stable than for conventional roofs. For instance, for three warm periods during summer (2021) surface substrate temperatures peaked much higher for gravel roofs (+8 oC) or bitumen roofs (+18 oC) than for blue-green roofs. On top of that, during a cold period in winter average water crate layer temperatures remained 3.0 oC higher and much more stable than substrate temperatures of blue-green roofs and conventional roofs, implicating that the blue layer functions as an extra temperature buffer. The effect of lower daily variation of surface temperatures in winter and summer is also reflected by inside air temperatures. Inside temperatures showed that locations with blue-green roofs are less sensitive to outside air temperatures, as daily temperature fluctuations (standard deviations) were 0.19 and 0.23 oC lower for warm and cold periods, respectively, compared to conventional roofs. This effect seems rather small but comprises a relatively large proportion of the total daily variation of 24% and 64% of warm and cold periods respectively.

How to cite: Föllmi, D., Corpel, L., Solcerova, A., and Kluck, J.: What is the thermal effect of ‘blue’ in blue-green roofs? A quantitative case study on the insulative effects of blue-green roofs in Amsterdam, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2949, https://doi.org/10.5194/egusphere-egu22-2949, 2022.

13:41–13:48
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EGU22-3745
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ECS
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Virtual presentation
Long Jiang and Ting Fong May Chui

Multi-stage constructed wetlands (CWs) are widely used for water quality improvement, especially in the treatment of wastewater. Many studies focus on their treatment efficiency under steady loading, but fewer studies consider their stability and sustainability under variable conditions. This study monitors the hydrology and water quality at the multi-stage CWs in the Hong Kong Wetland Park. Five wetland units along the flow path are examined for their long-term performance and sustainability in terms of water quality under seasonal changes, storm events, and shock loadings of pollutants. Time-series statistical analysis indicates that the multistage design well achieves stable performance. Each wetland unit has certain roles and they work together to achieve good performance. The reliability analysis shows that the CW system can largely buffer the fluctuations from most disturbances. While the resiliency analysis also shows that most water quality indicators could recover in a few days after the fluctuations. The water levels recover quickly but it was difficult to return to original water levels in multi-stage CWs. Besides, a numerical model is developed, calibrated, and utilized to predict future water quality changes. This will help evaluate measures to improve the sustainability of multi-stage CWs by simulating water quality changes under different influent concentrations and rainfall conditions. This study could provide appropriate recommendations and early warnings for wetland management and improvement.

How to cite: Jiang, L. and Chui, T. F. M.: Sustainability of a multi-stage free water surface constructed wetland in terms of water quality under changing conditions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3745, https://doi.org/10.5194/egusphere-egu22-3745, 2022.

13:48–13:55
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EGU22-3941
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Virtual presentation
Rasool Erfani et al.

Sustainable drainage systems (SuDS) design and management can contribute to a healthier and greener urban development. We show how the inclusion of innovative approaches to SuDS namely the plasma engineering can lead to a more effective and less detrimental water quality treatment. The treatment method using Dielectric Barrier Discharge Plasma actuator, can be retrofitted to the current urban setting, it is cheap and provides efficient alternative for water purification and pollution treatment. We present its environmental benefits causing minimal impact to the surroundings while controlling and managing the pollution. We investigate this in both the city and catchment scale contexts.

How to cite: Erfani, R., Ciric, L., and Erfani, T.: Plasma water quality treatment for SuDS development, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3941, https://doi.org/10.5194/egusphere-egu22-3941, 2022.

13:55–14:02
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EGU22-6104
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ECS
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On-site presentation
Elisa Costamagna et al.

Green and blue infrastructures are an innovative solution to contrast climate changes (SDG 13 of UN 2030 Agenda) and increase cities resilience (SDG 11), using a smarter water management that transform wastewater into a new resource for non-potable reuses. Due to the lack of horizontal surfaces in urban areas, green walls are one of the most suitable nature-based solution to treat greywater (i.e. the portion of household wastewater that exclude toilet flush and kitchen sink). Green walls allow for a multidisciplinary approach, providing multiple benefits such as thermal and acoustic regulation, biodiversity preservation, decreasing heat islands effects and removing CO2, improving life quality and buildings value.

Green walls have also been proposed for treating the large amount of greywater that is daily produced (e.g. around 100 L/PE/die in Italy), an approach that also provides urban green while reducing the need of irrigation water. Following previous work on a pilot system, this study aims to improve the green walls design and test its resilience to variations in the flow rate of greywater fed to the green wall. Two panels have been built in which synthetic greywater flows by gravity along three levels of pots with different plant species. The 18 pots (arranged in a 3x3 matrix in each panel) have been filled with a mix of coconut fibre and perlite (1:1 in volume) and fed with greywater, and output water samples have been collected almost weekly from June to December 2021. The control panel has been regularly fed with 24 L/die/col (standard flow rate), the other has been fed with different flow rates (standard, underflow, overflow and maintenance) that usually changed after three weeks. Different parameters (e.g. TSS, BOD5, COD, DO, TN, TP, MBAS), have been monitored in the outflow of each pot and average performances of each level has been evaluated. Results indicate a good efficiency of the green wall in removing contaminants even when the provided flow rate is not constant.

The treatment performances increase along the columns in both panels and the first two levels guarantee a good compounds removal during standard flow and underflow rates. On the other hand, the overflow rate caused a performances decrease in the variable flow panel for many parameters, followed by a visible plant stress. However, one week of standard flow rate was sufficient to reduce the negative effects of the three- weeks-overflow. This demonstrated the resilience of the green wall facing flow variability, that can be caused by seasonal variation or system failure.

How to cite: Costamagna, E., Raffaelli, B., Fiore, S., and Boano, F.: Resilience to flow rate variability in a green wall for greywater treatment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6104, https://doi.org/10.5194/egusphere-egu22-6104, 2022.

14:02–14:09
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EGU22-9488
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ECS
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Highlight
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On-site presentation
Anna Zeiser et al.

Trees in urban environment face plenty of problems that hamper vital and long-standing growth, which would be essential to counteract urban heat island effect. The major issue is a tremendously reduced volume of appropriate rooting space due to impervious surface and highly condensed underground in the immediate surrounding. Sponge city substrate based on the model of Stockholm promises to provide conditions suitable for root growth even underneath sealed surfaces. This innovative type of substructure construction method consists of unconsolidated fine substrate flushed into the voids of edged stones that serve as load-bearing structure. If well-designed in a function-oriented manner, the volume of sponge city substrate is able to serve as an underground retention basin saving soil water for transpiration and enabling excess water to infiltrate further into the groundwater. To support the creation of such highly functional substrate-pore systems, knowledge about the effects of different materials and methods on the hydrological functions is needed.

In Austria several projects using sponge city for urban tree planting have been implemented in recent years in various cities and municipalities. In order to increase the understanding of the system in hydrological, soil physical and implementational terms and to enable improvements and identification of reasons for malfunction, research is performed at laboratory, lysimeter and field scale. The latest monitoring project has been built in a small street in Graz, where both sides next to the street have been excavated and rebuilt with sponge city substrate. Two different substrate types have been used and 9 trees have been newly planted. The closest monitored part consists of about 100 m³ sponge city substrate, 4 trees and various types of surface design and usage including parking space, perennial plantings and a seepage basin with topsoil passage for purification of street water. Sensors measuring matric potential, volumetric water content, electrical conductivity, soil temperature, sap flow and water inflow from roof and street deliver the basic data to calculate the full water balance within this area and set up a water balance model offering the opportunity to assess the impact and potentialities of sponge city substrate in various temporal and spatial scenarios.

Coupling data from sponge city lysimeters, laboratory experiments and other field monitoring sites an estimation of ecosystem services accomplished by this innovative construction type will be attempted. Focus will be put on retention behaviour for heavy rainfall, plant water availability as well as tree vitality, growth and transpiration.

How to cite: Zeiser, A., Murer, E., Strauss, P., Zimmermann, D., and Weninger, T.: In-situ evaluation of sponge-city-type sites for urban trees to tackle flooding and heat islands , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9488, https://doi.org/10.5194/egusphere-egu22-9488, 2022.

14:09–14:16
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EGU22-13418
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Highlight
Daniel Green et al.

Bioretention cells, also referred to as ‘rain gardens’, are Green Infrastructure features with a functional role of managing urban flood risk and relieving pressure on traditional grey infrastructure systems. These Sustainable Drainage Systems (SuDS) rely on the use of soil and vegetation to attenuate and discharge stormwater via infiltration into the ground or via underground outlets into sewer networks whilst filtering pollutants in urban runoff and providing value to public space. Soil makes up a large proportion of these systems and plays a key role in providing the storage capacity for retaining stormwater and determining outflow discharges. This role is typically characterised using laboratory or in-field surface assessments of saturated hydraulic conductivity (Ksat), which provide an empirical assessment of SuDS performance. Guidance suggests that SuDS substrates should have a Ksat that ensures that systems are able to collect and store runoff to provide water retention without becoming waterlogged before the next rainfall event. However, in-field evaluations are rarely conducted due to cost and testing rarely identifies variation with depth through the soil profile.

This paper presents in-field Ksat testing from four-purpose built, vegetated bioretention cell lysimeters at the UKCRIC National Green Infrastructure Facility, Newcastle-upon-Tyne, UK, commissioned as part of the Engineering and Physical Sciences Research Council (EPSRC) project ‘Urban Green Design and Modelling of SuDS’ (EP/S005536/1). Ksat was measured using a Soil Moisture Equipment Corporation Guelph Constant Head Field Permeameter to obtain stratified Ksat values throughout the 750 mm deep soil profile of the lysimeters. Ksat was assessed in the context of four different vegetation treatments, including an unvegetated control lysimeter, an amenity grass covered lysimeter and two mono-cropped lysimeters planted with Iris sibirica and Deschampsia cespitosa.

Results show that Ksat values are systematically variable through the soil column and are a function of confining pressure with soil depth and wash through processes. Trends in porosity with soil depth are shown to be comparable across all lysimeter planting styles with some subtle differences associated with vegetation planting. All lysimeters feature higher Ksat values at the near-surface (ranging from 160.2 – 648.0 mm/hr at 0 – 100 mm depth), thought to be due to weathering and wash-through processes associated with near-surface soil strata being exposed to prevalent weather conditions. Where larger vegetation is present, higher Ksat values are recorded, reflecting the presence of root-derived preferential flow pathways. The depth of elevated near-surface Ksat values reflects the rooting depth and structure of the plant species studied.

The use of a single Ksat value does not adequately capture the spatially variable hydraulic properties of bioretention systems. The results presented herein also have implications for SuDS design and maintenance, suggesting that the hydraulic properties of these systems may change through time. Consequently, SuDS scheme planners and developers should conduct multiple assessments of Ksat through the soil profile to provide robust empirically-based model parameter values to ensure that systems are fit for purpose.

How to cite: Green, D., Goddard, A., and Stirling, R.: Stratified hydraulic conductivity testing of green infrastructure: A lysimeter bioretention cell study , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13418, https://doi.org/10.5194/egusphere-egu22-13418, 2022.

14:16–14:23
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EGU22-8387
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Highlight
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Virtual presentation
Francesco Bettella et al.

The consequences of climate change are exacerbated by land-use changes, which affect the control of rainfall-runoff relations and the impact on flooding hazards. Effectively, urbanization is constantly contributing to the increase of impervious areas and reducing the time-to-peak. The effect of Natural Water Retention Measures (NWRMs) in the mitigation of these phenomena is known. Nevertheless, this kind of sustainable infrastructures are still poorly known by citizens and administrators, and consequently barely adopted in many parts of the European Countries. The LIFE BEWARE project aims to enhance hydraulic safety and spread good practices on rainwater management by promoting and facilitating the adoption of NWRMs in the Altovicentino, a highly rainy foothills area in Northern Vicenza Province (Veneto Region, Italy). In order to support the dissemination activities, some full-scale NWRMs have been realized in the area of intervention of the project. The hydrological functioning of these nature-based green infrastructures is continuously monitored thanks to the installation of devices measuring inlet and outlet runoff. The aim of this research is to present the realized NWRMs and the adopted monitoring system, and to analyze the data collected during the firsts two years. Results show that at this field-scale experiment all the monitored interventions were able to manage almost all the rainfall events occurred during these two years and the fraction of the rainfall runoff that reached the outflow was always less than 2%. Finally, the research provides insights in better understanding the behavior of NWRMs exposed to different weather and environmental conditions. This also adds some useful information at the design phase of such green infrastructure.

How to cite: Bettella, F., Bortolini, L., Baggio, T., and D'Agostino, V.: Hydrologic performance of Natural Water Retention Measures: outcomes from the LIFE BEWARE project test site , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8387, https://doi.org/10.5194/egusphere-egu22-8387, 2022.

14:23–14:30
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EGU22-9353
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ECS
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Highlight
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On-site presentation
Giulia Mazzarotto et al.

In recent decades, due to on-going urbanization and changes in rainfall patterns, urban drainage systems are facing increasing challenges. The expansion of impermeable surfaces and the increase of both frequency and intensity of rainfall events, are responsible for the augmented peak-flows and heavily polluted stormwater volumes conveyed by combined sewer overflows to water bodies. The need of assessing these challenges to mitigate the impact on water bodies’ quality has prompted International Authorities to develop standards and scientific communities to find solutions for an effective stormwater management.

Sustainable Drainage Systems are effective at-source stormwater management solutions designed for collecting, retaining, and infiltrating direct rainfall and runoff from impervious surfaces. When properly applied in the urban drainage system, they mitigate pollution coming from wash-off of impervious surfaces and reduce both volumes and flood peaks conveyed to the drainage system.

Among others, Permeable pavements (PPs) and infiltration trenches (ITs) are two solutions that can be easily retrofitted into the urban environment. PPs reduce surface runoff allowing direct infiltration of rainfall, whereas ITs collect runoff from nearby impervious surfaces. Both can temporally store relevant amount of water which is then slowly released to deeper native soil layers. Moreover, these systems act as filters trapping solids and pollutants onto or into the filter layers. However, physical clogging related to particle accumulation on the surface or inside the porous media reduce permeability of the system decreasing infiltration rates along time. This is a crucial aspect affecting both PPs and ITs effectiveness that must be accounted in the urban environment maintenance plans.

A large-scale laboratory model is currently under development to analyze the main physical processes and to assess the efficiency starting first from the PPs. To this aim, a laboratory facility (Lora et al., 2016), built in the Laboratory of Hydraulics and Hydraulic Works of the Department of Civil, Environmental and Architectural Engineering (University of Padova), is being rearranged. The facility consists of a reinforced concrete box 6 m long x 2 m wide, and the height varies from 3.5 to 0.5 m. It is equipped with 50 openings on each lateral side for the insertion of probes (e.g. water content reflectometers - WCR) to continuously collect long term monitoring data in different positions. The end side of the facility is made of porous bricks allowing subsurface runoff to drain into a V-notch stream gauge. Another stream gauge is installed to measure exceeding surface runoff. During experiments, steady rainfall intensities ranging from 50 to 150 mm/h will be produced with a specifically designed rainfall simulator.

Suitable materials for the filter layers package will be laid for 1 m total depth assessing filtration processes through the probes in three positions along the vertical. The rainfall simulator will be rearranged to guarantee uniform rainfall distribution on the PP surface characterized by a mild slope (about 2-3%).

In the first set of experiments, the characteristics of the investigated PP will be tested in clear water condition, thus without adding suspended solids, to define the maximum infiltration capacity.

How to cite: Mazzarotto, G., Camporese, M., and Salandin, P.: Assessing Physical Processes of Permeable Pavements with a Large-Scale Laboratory Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9353, https://doi.org/10.5194/egusphere-egu22-9353, 2022.

14:30–14:32
Section 2: Upscaling field-collected GI data

14:32–14:39
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EGU22-9465
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Highlight
Pierre-Antoine Versini et al.

Nature-based Solutions are presented as relevant features to make the cities more resilient in a context of global change. By providing ecosystem services, they are considered as particularly efficient solutions to mitigate urban heat islands and floods, while preserving biodiversity. Nevertheless, despite this consensus, it is still very difficult to quantitatively assess these services. Some methodologies and tools have therefore to be developed to better understand the thermo-hydric behavior of such infrastructure in relation with biodiversity, and to assess their performances across scales.

This presentation aims to present the work carried out to solve these issues through two current projects dedicated to NBS. On the one hand, the French ANR EVNATURB project aims to develop an operational platform to assess some of the eco-system services (ie stormwater management, cooling effect, or biodiversity conservation) provided by NBS at the district scale. On the other hand, the LIFE ARTISAN project deals with the creation of a framework to promote NBS for the implementation of the national plan for adaptation to climate change (PNACC) in France by improving scientific and technical knowledge. Both aim to develop and disseminate relevant tools for project leaders (for the design, sizing, implementation and evaluation of ecosystem performance).

The presentation of the results is particularly focused on monitored pilot sites and modelling platforms developed during these projects. In addition to these scientific investigations devoted to the thermo-hydric balance, some specific literature reviews and interviews were conducted to facilitate the choice of the more efficient species to implement, and the way to arrange NBS to optimize their performances. One of the results of this work is a dedicated database related to the a priori main ecosystem functions provided by plant species, and a list of quantitative indicators relevant for an urban project (certification, labelling, compliance with local regulations, ...) and that NBS can comply. Then this presentation concludes on remaining research gaps that have be to filled on this topic.

How to cite: Versini, P.-A., Al Sayah, M., Duffaut, C., and Schertzer, D.: How to choose the most relevant Nature-Based Solutions and to assess their performances? Insight from two projects implemented on the French territory. , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9465, https://doi.org/10.5194/egusphere-egu22-9465, 2022.

14:39–14:46
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EGU22-369
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ECS
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Highlight
Timothy Tiggeloven et al.

In order to mitigate the expected increase in coastal flood risk it is critical to better understand how adaptation measures can reduce that risk, including Nature-based Solutions. We present the first global scale assessment of the (future) flood risk reduction and the benefits mangrove restoration. Unlike previous studies on Nature-based Solutions, we provide a quantitative assessment of mangrove restoration and nature contributions to people in terms of monetary flood risk reduction, people exposed to flooding, and poverty indicators. We find that mangrove restoration is an effective measure to contribute to future flood risk reduction and estimate that a large share of future flood risk may be reduced by implementing mangrove restoration. Our estimates indicate that nature-based solutions like mangrove restoration constitute promising complementary measures to other adaptation measures (e.g. structural measures). We further indicate that the benefits of mangrove restoration are unevenly distributed across the population in terms of poverty, and show that only looking into property damages and people exposed is not enough to understand the range of impacts of adaptation on population distributions. Even though this study can only be used as a first proxy analysis or indicative, it provides valuable insight into the feasibility of mangrove restoration at the global scale, and supports the need for sustainable adaptation and global assessmenst of Nature-based Solutions. Furthermore, implementing adaptation measures, such as mangrove restoration, in developing countries will contribute to the resilience of people in poverty, poverty alleviation and help tackle poverty traps.

How to cite: Tiggeloven, T., Mortensen, E., Worthington, T., de Moel, H., Spalding, M., and Ward, P.: Nature-based Solutions, mangrove restoration and global coastal flood risk reductions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-369, https://doi.org/10.5194/egusphere-egu22-369, 2022.

14:46–14:50
Short discussion and concluding remarks prior to comfort break

Thu, 26 May, 15:10–16:40

Chairpersons: Daniel Green, Lei Li, Helen Brooks

15:10–15:12
Convener introduction

15:12–15:14
Section 3: Numerical modelling and GIS approaches within GI research

15:14–15:21
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EGU22-1444
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On-site presentation
Elena Cristiano et al.

The modern society is facing multiple challenges, that are reshaping urban areas: the fast population growth, with a consequent high urbanization, combined with an increase of the average temperature and an intensification of extreme rainfall events, facilitates the pluvial flood risk in cities. Several solutions have been proposed in the literature to mitigate the runoff generation from rooftops and to contribute to a sustainable water management. In this context, multilayer blue-green roofs incorporate the high retention capacity of traditional green roofs with the storage capacity that characterizes rainwater harvesting systems. Moreover, these innovative nature-based solutions present countless benefits for the creation of smart, resilient and sustainable cities, e.g., they contrast the urban heat island, reducing the surrounding air temperature, they contribute to the building thermal insulation, limiting the energy consumption, they attract multiple species of insects and small animals, increasing the biodiversity, etc. 

The potential impacts of multilayer and traditional blue-green roofs and rainwater harvesting systems on the runoff generation reduction have been investigated mostly at local scale, analysing the impact of the installation of these tools on single buildings. However, in order to estimate and to evaluate the potential benefits and limitations for a sustainable urban development, it is fundamental to simulate the potential implications of a large-scale installation of these tools on large neighbourhoods or entire cities. For these reasons, in this work we simulate the installation of multilayer blue-green roofs on all the suitable roofs of the cities of Cagliari and Perugia (Italy). Thanks to the two multilayer blue-green roofs, installed in Cagliari and Perugia as part of the EU Climate-KIC Polderroof field lab project, it was possible to calibrate an ecohydrological model to simulate the potential retention and storage capacities of these nature based solutions. The potential discharge reduction and water storage capacity at large urban scale are discussed using as input for the model long historical time series of local rainfall and temperature.

How to cite: Cristiano, E., Annis, A., Viola, F., Deidda, R., and Nardi, F.: Large scale installation of multilayer blue-green roofs as solution for a sustainable urban water management, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1444, https://doi.org/10.5194/egusphere-egu22-1444, 2022.

15:21–15:28
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EGU22-3983
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ECS
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Highlight
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Virtual presentation
Jérémie Bonneau et al.

Urbanisation and climate change jeopardize the health of peri-urban streams, by yielding decreased baseflow and increased peakflows. Green infrastructure can help protecting and even restoring urban streams by storing, infiltrating and losing urban runoff to evapotranspiration. However, whether green infrastructure implementation at the catchment-scale (and how much) can counter future urbanisation and climate change remains a question of interest for urban managers. We modelled the hydrology of a 20 km2 peri-urban catchment in the western suburbs of Lyon, France with the physically-based, spatially distributed hydrological model J2000P, at the hourly time step. We created 12 future urbanisation scenarios with stepwise increases of impervious cover as well as 36 climate change scenarios based on one climate projection (CNRM-CM5-ARPEGE- ALADIN63-RCP 8.5) and the observed temperature and precipitation records from the city of Orange, which is located 200 km south of Lyon in France. We applied a delta method to transform current hourly rainfall and evapotranspiration timeseries into potential future climate timeseries. We coupled these scenarios to stormwater management strategies, through the integration of a site-scale model of green infrastructure into J2000P. Five stormwater management strategies with increasing implementation of green infrastructure were tested: from ‘no green infrastructure’ to ‘all impervious areas drained into green infrastructure’. 640 scenarios coupling urbanisation, climate and stormwater management scenarios were simulated. For each simulation a range of hydrological indicators were calculated. We found that catchment-scale implementation of green infrastructure could mitigate the hydrological impacts of urbanisation. Sewer overflow were particularly sensitive to green infrastructure and urbanisation. Green infrastructure was however unable to mitigate the impact of climate change on the stream flow regime, because green infrastructure only impacted the urban parts of the catchment that accounted for less than 15% of the whole catchment. Non-urban areas (forests, pastures), which contributed very strongly to the flow regime, were impacted by climate change but not significantly by urban stormwater management strategies. These results can inform urban planners and water managers of the great potential of green infrastructure (reduction of sewer overflows, compensation for urbanisation) but also its limitations (little impacts on catchment scale induced flow peaks and droughts).

How to cite: Bonneau, J., Branger, F., and Castebrunet, H.: Can catchment scale implementation of green infrastructure protect the flow regime of an urban stream facing urbanisation and climate change ? A modelling study in Lyon, France., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3983, https://doi.org/10.5194/egusphere-egu22-3983, 2022.

15:28–15:35
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EGU22-7432
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ECS
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On-site presentation
Sebastian Gürke and Jürgen Jensen

In recent years, heavy rainfall events have caused significant damage in urban areas across Germany. Experiences in coping with pluvial floods show that single measures alone cannot reduce the risk, but the combination of different measures is required. Economic aspects and limited land availability in cities emphasize the demand for multifunctional and sustainable retention areas. In the ongoing research project WaldAktiv*, we investigate the integration of existing urban forest areas into municipal flood prevention. The idea is to direct parts of the surface stormwater run-off into urban forest areas for storage and infiltration to reduce flooding in built-up areas. As study area, we use the district of Siegen-Wittgenstein, which has a high vulnerability to pluvial flooding due to its low mountain range topography. At the same time, with an area share of 71%, it is the most densely forested district in Germany and thus particularly well suited to determine corresponding potentials. However, this aim and other positive synergy effects are countered by (ecological) risks, such as the possible entry of pollutants into the forest areas, which must be taken into account during the studies.

First, potential flow paths and terrain depressions are identified based on a digital elevation model using a topographic analysis. While flow paths are used to delineate the individual catchments, terrain depressions in the urban forest areas represent potential retention basins for stormwater run-off. Although many terrain depressions are found, the analyses show that they are rarely located in suitable areas, so that artificial retention basins may have to be created in certain forest areas. Using hydrological modelling, the capability of the forest soil in terms of infiltration is estimated based on various soil geodata sets. In order to model the measures and assess their effectiveness, hydrodynamic numerical modelling is performed for different rainfall scenarios. In this contribution, we will present methods and current findings of the research project.

* WaldAktiv is a research project, funded by the German Federal Ministry for the Environment, Nature Conservation, Nuclear Safety and Consumer Protection (BMUV) and the district of Siegen-Wittgenstein through the project management of Zukunft – Umwelt – Gesellschaft (ZUG) gGmbH under the grant number 67DAS179.

How to cite: Gürke, S. and Jensen, J.: Studies on the active use of urban forest areas as pluvial flood prevention, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7432, https://doi.org/10.5194/egusphere-egu22-7432, 2022.

15:35–15:42
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EGU22-9356
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Virtual presentation
David Milledge et al.

Flooding is costly and disruptive in the UK and worldwide. Leaky barriers (LBs), small-scale blockages to streamflow, provide multiple environmental benefits. Depending on design, and if installed in sufficient numbers, they could also play an important role in reducing downstream flooding. Leaky barrier installation is proceeding at pace, thousands of cobble dams have been installed in peat gullies across the South Pennines (UK). However, the hydraulics of LBs in general and these cobble barriers in particular is poorly understood. Here we develop a simple model coupling two classical engineering flux estimates: Darcy/Casagrande equations for matrix flow and Colebrook equation for pipe flow (where drains are installed). We test this model against observed stage and discharge measurements for four study features with and without drains to: identify stage-discharge relationships; evaluate model performance for individual features; and apply it to model chains of features of varying design (i.e., LB density, matrix permeability, and pipe diameter). We find that: 1) stage-discharge relationships for cobble dams are concave up and are generally well captured by our simple model; 2) current designs offer relatively little attenuation because they are too permeable; 3) instead, optimal designs have low matrix permeability with pass-forward pipes at their base of a diameter tuned to design flow. Based on these results we hypothesise that LBs will perform best where they are designed to have negative permeability-depth relationships (and thus convex up stage-discharge relationships) and where the form and magnitude of the relationship is optimised to accommodate peak flood discharges.  

How to cite: Milledge, D., Johnson, A., Allott, T., Brown, D., Edokpa, D., Evans, M., Goudarzi, S., Kay, M., Rees, J., Shuttleworth, E., and Spencer, T.: Modelled and observed stage-discharge relationships for cobble leaky barriers with and without pipes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9356, https://doi.org/10.5194/egusphere-egu22-9356, 2022.

15:42–15:49
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EGU22-9468
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On-site presentation
Seokhwan Yun et al.

Urbanization is progressing around the world and the phenomenon of urban heat islands, where the temperature of cities increases compared to the surrounding areas due to climate change, is intensifying. Many strategies are being applied to alleviate urban heat islands, and one of them is urban greening. Urban green areas form shadows to block solar radiation, or change the rate of reflection and emission of heat caused by changes in surface environment. It also has the effect of reducing the surface temperature by increasing latent heat through the evapotranspiration occurring in the leaves. Representative urban greening strategies are street trees, green roof, and green wall. Since the cooling effect varies greatly depending on the weather environment, size of green space, and location, it is challenging to estimate the cooling effect that changes according to various environments. In this study, a three-dimensional urban canopy model was developed to evaluate the effects of various green space. This model, which simulates the copy transfer process between urban elements, first builds a domain consisting of squares of a certain size and calculates the view factor and the sky view factor. Next, the short-wave radiantion and the long-wave radiantion are simulated to calculate the net radiation. Finally, the net radiantion is partitioned into sensible heat, latent heat, and storage heat. This model can be used for efficient green space planning to reduce urban heat.

How to cite: Yun, S., Kim, E., and Lee, D.: Development of a 3D urban canopy model for evaluating cooling effect of urban green space., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9468, https://doi.org/10.5194/egusphere-egu22-9468, 2022.

15:49–15:56
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EGU22-9977
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ECS
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Virtual presentation
Emelie Hedlund Nilsson et al.

In subarctic regions, a significant part of annual precipitation occurs as snow. This creates challenges since (a) the occurrence of rain on snow during melting season might increase runoff peak flow and cause flooding in urban areas and (b) snow needs to be removed from roofs and streets. Current snow management practice includes removal of snow to large deposits outside of cities. Downsides of this approach are the carbon footprint and air pollution caused by transport and the release of untreated polluted melt water to nearby water bodies. One strategy to reduce transport and increase treatment of meltwater could be to integrate snow deposits with existing green infrastructure that manages stormwater within the urban environment, i.e. multifunctional areas.

When studying the potential performance of multifunctional areas with respect to snow management it is important to consider the flood risk that comes with increased snowmelt and rain on snow. Prior studies have evaluated the combined effect of frozen soils, snowmelt and rainfall during the melting season on runoff from urban catchments, but there are no similar studies on facility scale. Hydrological models can be used to investigate these factors and the snow deposit potential, without risking flooding. It is, however, unclear to what extent current urban hydrological models are suited to this purpose. This study aims to explore how hydrological models can be used to predict snow deposition volumes in multifunctional areas and the effect on runoff.

This study used EPA SWMM because it is a commonly used urban hydrological model with a relatively advanced snow management module. The modelled facility was a grassed swale in Luleå, Northern Sweden, receiving runoff from a 60 ha catchment with commercial and light industrial land use.  The swale was separated into 6 identical parts to test different scenarios for the amount and distribution of snow deposited in the swale. The long-term performance of the swale with regard to stormwater quantity was investigated with historical rain and temperature data. Runoff from the catchment to the swales was calibrated based on observed data from late spring 2021.

Hydrological models as a support tool for snow management using green infrastructure shows promising results. Using the model, it was possible to evaluate the effect of snow volume and placement within the swale. Such information can be of great use when designing green infrastructure and snow management strategies. However, SWMM has some limitations in this regard. For example, pollutants such as sediments (gravel, sand and micro plastics) affect the properties and melting behavior of urban snow and the release of pollutants, yet these factors are not represented in SWMM. Differences in the actual melt rate will affect the total volume of snow that can be deposited in the swale, hence this topic requires further research.

How to cite: Hedlund Nilsson, E., Broekhuizen, I., Muthanna, T. M., and Viklander, M.: Evaluation of Snow Management using Green Infrastructure in Subarctic Climate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9977, https://doi.org/10.5194/egusphere-egu22-9977, 2022.

15:56–16:03
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EGU22-10925
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ECS
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Virtual presentation
Marie Meulen and Maider Llaguno-Munitxa

The implementation of Nature-based Solutions (NbS) has become a priority in many cities. The benefits of urban demineralization or ‘greening’ initiatives are manifold and range from the mitigation of the urban heat island effect, reduction of flooding risk, to improvements in the outdoor environmental quality. The positive impact on pedestrian level well-being and comfort is also to be taken into account from not only an environmental, but also a visual perspective, given the psychological benefits induced by the attractiveness to nature, and enhanced walkability of streets and squares.

Today, the green infrastructure (GI) evaluation methods utilized in urban planning processes focus on the quantification of the total greenery ratio making use of remote sensing technologies, or often incomplete geospatial databases. The Normalized difference Vegetation Index (NDVI) deduced from aerial imagery, however, does not match the green infrastructure perception at the pedestrian level. From the geospatial databases, on the other hand, tree location and park areas can be retrieved, however these datasets only provide a partial and oversimplified description of the GI. Strategies for the implementation of range in scale and type. Aside from the diverse tree species, cities are populated by diverse grass fields, bushes, and green walls amongst others. Based on the type and distribution of each GI, the impact on the pedestrian level well-being is different. Thus, the quantification of green infrastructure requires the identification of the distinct GI and their distribution evaluated from a pedestrian perspective.  

Our research investigates a novel methodology to quantify the perception of GI from the pedestrian perspective.  We propose to combine NDVI index metrics computed from high-resolution satellite images, with green view index metrics. Making use of a 360° six-lens camera, videos have been collected for 12 different squares selected based on their varied GI ratios and located in the neighborhoods of Saint Gilles and Molenbeek in the city of Brussels. Through Light Detection and Ranging (LiDAR) scanning technologies, point clouds have also been collected for these sites. Once the remote sensing datasets, video recordings, and scans were completed, through geospatial processing and semantic classification, the distinct GI types and ratios were quantified. Our research methodology enables a comparison between remote sensing, geospatial analysis, and first-person quantification of GI computation, and addresses the need of high-res urban environmental analysis for the development of an accurate GI infrastructural evaluation.

How to cite: Meulen, M. and Llaguno-Munitxa, M.: Pedestrian Level Greenery Perception quantification, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10925, https://doi.org/10.5194/egusphere-egu22-10925, 2022.

16:03–16:05
Section 4: Conceptual Design Framework for GI

16:05–16:12
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EGU22-8783
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ECS
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On-site presentation
Stanislava Boskovic et al.

Cities are open living systems, which rely on the confluence of multiple layers of infrastructure and corresponding services. The interaction among these components is made even more complex by the demands of businesses and governments, together with constraints arising from ecological and environmental considerations. Climate change-related phenomena are putting an enormous strain on cities’ infrastructure, basic services, human livelihoods, public health and well-being. In many parts of the world concerns mount in regard to the scarcity of resources and growing risk of natural disasters (heat waves, urban flooding, droughts).  The converse also holds true, cities are major contributors to climate change through greenhouse gas emissions, notwithstanding other sources of pollution. This, together with the increase in urban growth and urbanization, results in an expansion of urban hazards - including water pollution, disease spread and issues with food security. Despite these pressing issues, we are witnessing an almost paradoxical mismatch between the needs of future cities and the practices currently used in numerous urban projects. A wholesale re-thinking of existing urban design methods at systems level (Systemic Design), is therefore not only necessary, but also provides significant opportunities to explore critical aspects of Blue-Green Infrastructure (BGI) and systematic assessment of possible future scenarios of different scales (local, urban, regional…). Nature-based solutions (NBS) are at the very core of the conception and development of BGI and provide a range of ecosystem services including alleviation of flood risk, mitigation of climatic effects, increase in biodiversity and amenity values, improvements in water quality, and further, rather more intangible benefits related to the residents’ health and wellbeing.

In this work we provide a systemic design as an innovative and integrated approach, based on ecology and ecological design, which introduces the systematic context analysis (environmental, climatic, historic…).  A GIS-based mapping of the context, produced in relation to the functional purpose, can give us synthetic prospects to better understand the potential effectiveness of BGI solutions (design options) in relation to their wider ecosystem. The systemic design approach allows an examination of possible steps to reduce actual cities vulnerability and to explore the main drivers of urban development, climate change mitigation and urban resilience. In this way, the systemic design approach also supports decisions for further planning and anticipates actions for the management of the multifaceted hazards of the entire urban system.

How to cite: Boskovic, S., Puchol-Salort, P., Krivtsov, V., and Mijic, A.: Systemic Design Approach: A Framework for a resilient urban transition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8783, https://doi.org/10.5194/egusphere-egu22-8783, 2022.

16:12–16:19
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EGU22-13180
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ECS
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On-site presentation
Rupesh Shrestha et al.

Urban areas provide a range of benefits to sustain human livelihood and contribute to human well-being through urban ecosystem services. Open spaces in core urban areas of Kathmandu valley in Nepal carries multiple advantages of stimulating social cohesion, offers safe area immediately after a crisis induced by natural hazards, contributes in environmental improvement and mitigates urban flooding. In most urban areas of Nepal, unplanned urbanization has resulted in alteration of landscapes from permeable vegetated surfaces to a series of impervious interconnected surfaces resulting in large quantities of stormwater runoff, requiring wider implementation of water sensitive urban design. After 2015 Gorkha earthquake, several blue-green infrastructure projects are implemented by local governments inside Kathmandu valley in open spaces. This paper presents application examples of green infrastructure projects and through case studies provides a framework for optimization of green infrastructure systems in Nepal. The paper also provides a practitioners perspective on the current state of knowledge, highlights technical challenges in green infrastructure implementation in Kathmandu and points out recommendations to overcome them.

How to cite: Shrestha, R., Jüpner, R., and Thaler, T.: Enhancing Kathmandu’s Urban Design Through Implementation of Green Infrastructures, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13180, https://doi.org/10.5194/egusphere-egu22-13180, 2022.

16:19–16:31
Concluding remarks and discussion

16:31–16:34
Next steps