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Spatial pressures in many contemporary cities restrict the construction of surface wetlands of the scales necessary to deliver storm water management and ecosystem services. Alternative means are able to deliver some of these services by harvesting storm water at source and storing it in soils beneath road verges where it can irrigate urban trees and other vegetation. By incorporating vegetation into this storm water management infrastructure both water harvesting rates and storage capacities can be increased. If integrated with street infrastructure on a large scale, water sensitive urban design features and associated vegetation have the potential to make major contributions to improved human health, environmental quality and flood risk mitigation. Infrastructure established to support preliminary investigations in the cities of Mitcham and Salisbury has demonstrated problem-free function of storm water harvesting for street tree irrigation at the local level over seven years.
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Acta Hortic. 1108. ISHS 2016. DOI 10.17660/ActaHortic.2016.1108.8
XXIX IHC – Proc. Int. Conf. on Landscape and Urban Horticulture and International
Symposium on Sustainable Management in the Urban Forest
Eds.: G. Groening et al.
The Council verge as the next wetland: TREENET and
the cities of Mitcham and Salisbury investigate
University of Adelaide, PMB 1 Glen Osmond, 5064, South Australia, Australia; 3University of South Australia,
Keywords:watersensitiveurban design,sustainableurban drainage system,storm water
The global rate and scale of urbanisation is stressing ecologicalsystemsandthe
infrastructure on which cities depend (Andersson et al., 2014; Childers et al., 2014; Wu
2008),withmost ecosystemson Earthnowbeingaffectedbyurban demandsand outputs
(Elmqvistetal.,2013).Urbandevelopmentislargelyimpervious torainfallsoit canaffect
local hydrological cycles (Ferguson, 2010). Accompanying vegetation loss compounds the
hydrological consequences. These impacts together contribute towatershortagesand
flooding(Sheng and Wilson, 2009; Lee andHeaney,2003), urban heatislands (Australian
LocalgovernmentsinAustraliaarelargelyresponsiblefortheprovision and
mattersthroughpreventivemeanssuchastheprovisionof‘green’urban environmentsfor
passiverecreation,includingsportingandactiverecreationfacilities and vegetated
Green urban designs promise increased delivery of ecosystem services from within
cities as well as reduced impacts on surrounding environments. However, increasing
pressureonspace canresult inconflicts betweenacity’sbuilt andnaturalassets.Current
far the largest component of urbanmetabolism(Kennedyetal., 2007). Massive
rain gardens have demonstrated the benefits achievable through retaining and detaining
For functional, financial, human and environmental reasons water storage solutions are
needed which require little space. Technologies such as the TREENET Inlet, permeable
pavements,infiltrationtrenches and‘leakywells’can reduce pressureontraditionalstorm
thecities of Mitcham and Salisbury have demonstratedthat costsaving,lowmaintenance
integrated approach to water management supports other local government initiatives
including climate change adaptation,protectingthehealthandwell-being of citizens and
reducing environmental impacts. Increased evapotranspirational cooling, shading and
example,provideamoretemperature-stablecitywhichwillfurther reduce energy
consumption, greenhouse gas emissions and costs to the community (McPherson et al.,
2005). Similarly, benefits will accrue from ecosystem services provided by trees, such as
improvements in social and psychological health resulting in reduced anxiety and fatigue
To investigate and demonstrate the integration of horticulture and storm water
engineering, purpose-built infrastructure has been established in Salisbury Council’s
suburbanstreetstothenorthofAdelaideinSouthAustraliaand inMitcham tothe south.
Water harvesting strategies used by the cities of Mitcham and Salisbury include
the subject of this paper. At the streetscape scale, devices used include permeable
Allofthesesystemsharvest‘firstflushstormwaterrunoffto mitigate pollution loads
Permeable pavements have been developed over several decades (Ferguson, 2010;
application in Australia remains relatively limited in comparison to impermeable
Construction details and aspects of the two different permeablefootpathpavement
designsunder investigationare detailed in Johnsonet al. (2011a). Permeableinterlocking
concrete brick footpath surfaces are supported by a layer of crushed rock (20 mm
and68mminanother;thewaterthensoaksintounderlyingsoils. The smaller capacity
level’); the larger capacity design has the screenings formed into a swale (‘perm-swale’)
beneath the footpath to encourage deeper root growth beneath its center (Johnson et al.,
Developed by not-for-profit tree research organisation TREENET Inc., the TREENET
inlet device harvests storm water from the road for watering tree root zones in adjacent
verges. Severalhundred TREENETinlets have been installedacrosseightlocalgovernment
authoritiesinthreestatesofAustralia.Thiscurrentresearch is providing data to better
inform the application of this technology in future by investigatinglifecyclecosts,
TREENETinletdevices(Figure1)arecastintoconcretekerbstodivertstorm water
wells(Figure2)constructedinthevergeuntilthelimitofthe well and the infiltration
capacityofitssurroundingsoil arereached.Theshallowdepressionintheguttercreatesa
small pool which reduces flow velocity marginally, thereby establishinganeddywhich
Several designs have been developed in the search for the optimalleakywellfor
localrainfallpatterns, catchmentarea,vegetationproximityandtype,andaccessibilityfor
Roadsideleakywellsandinfiltrationtrencheswithcapacitiesranging from 10 L to
7 kL have been constructed. Those connected to TREENET Inlets range between 65 and
150L;thesmallerbeingusedinshallowsoils and the larger at sites wheredrainage isa
hasa capacityof 50 L. Optimising design capacity ona cost-benefit basis requiresfurther
sampleswill be collected from thebasesoftheleakywellsduring late2014 and through
2015, to be analysed for pollutants including phosphates, nitrates,heavymetalsand
suspended solids. Soil samples collected from the sites during construction of the leaky
wells, and additional samples to be taken in 2016, will be analysed and compared to
inthecitiesofMitchamandSalisbury since 2007withnooperationalfailuresorproblems
screenings which fill them; the water then percolating into surrounding soil. Percolation
rates after seven years of operation appear consistent with those immediately following
40timesperyear.Builtattheendofaseveredrought,waterrecharge wasanticipated to
causesubstantialsoilheave,potentiallydislodgingthe newkerbing.Noimpactshavebeen
leaflitter and fruit producedby a matureavenue ofWhite cedar (Meliaazedarach)street
waterenteringthetrench,afterthreeyearsofoperationthesystem was measured to be
root systems which take advantage of the additional water, with hydraulic redistribution
around the trenches and sustaining prolonged storm water harvesting. Several similar
systemshaveremainedfullyoperationaloversimilartimespanswithno maintenanceand
locations for over two years. At one site a large river red gum(Eucalyptuscamaldulensis)
treehadlifted kerbingby approximately 100mm, creatingpoolingalongthestreetwhich
on surrounding infrastructure. As road-sweeper access is difficult at this site, sediments
regularly build up in the inlets’ pools. This has been observed to only marginally reduce
infiltration rates however. Adequate drainage is possibly sustained by the inlets in the
absence of maintenance due to high hydraulic conductivity of the built-up sediments. At
been observed to occupy screenings in the leaky wells within the first spring after
construction, suggesting that hydraulic redistribution of waterfromthewellsto
of preliminary observations warrant reporting at this stage however. All of the average
annual rainfall of 546 mm incident upon the permeable research pavements has been
intercepted and managed in situ since September 2009, with no runoff and discharge to
receivingwatersresultingandnonegativeimpactsonthepavements themselves or
Between2011and2014surfacelevelmovementduetomoistureinduced soil
reactivityappearedsimilar atpermeable andimpermeable controlpavements.Soil ‘heave’
+7 to +31 mm at ‘perm-level’ sites, and +10 to +30 mm at ‘perm-swalesites(relativeto
February2011levels).LevelsrecordedonApril 8,2014of+18to-25mmatcontrolsites,
-4to-20mmat‘perm-levelsitesand+11to-22mmat’perm-swale’ sites (relative to
controls.Theserelativelyminorsurface levelfluctuationsobservedonmoderatelyreactive
soilsalongthe320mlong researchsite,andtheabsence ofdiscontinuitiesinlevelsatthe
interchangesbetweenpermeableandimpermeablesurfaces,suggest that permeable
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... The exfiltration rate determines the storage availability before the arrival of a new storm event. This parameter is a function of the native soil type, filter medium properties and hydraulically efficient fissures in adjacent soil attributed to the presence of tree roots (Johnson et al., 2016). The installed kerbside leaky well systems across the catchment exfiltrated 100 L in approximately 10 h. ...
... exfiltration rate of up to 0.005 L/s resulting in a 14% greater annual retention over the present case (Fig. 12). Previous research (Johnson et al., 2016) on the impacts of tree roots as conduits for both uptake and preferential flow pathways has indicated that the hydraulic redistribution phenomenon can occur immediately upon the installation of kerbside leaky well systems. This suggests that the present systems can potentially be expected to retain 14% more runoff annually than expected due to the presence of tree roots. ...
The popularity of subsurface distributed storage-based kerbside stormwater infiltration systems is increasing because they can be integrated within the strict spatial constraints of existing infrastructure. Distributed systems operate based on the concept of spreading a limited amount of storage throughout the catchment area to achieve runoff management objectives. Storage can also limit the performance of urban stormwater systems. This study investigated the role of storage capacity, especially the volumetric capacity and the emptying time, in the performance of kerbside leaky well systems in a residential catchment area with a native clay soil environment. A detailed, process-based deterministic hydrological model was used to analyze hydrologic storage via a continuous simulation approach. The model was calibrated against catchment outflows measured with stormwater infiltration devices. Individual kerbside infiltration systems were also calibrated to monitor the behavior of on-site kerbside infiltration systems. By using approach of continuous simulations during designed scenarios, this study considered the prestorm storage availability in the hydrological analysis. The results demonstrated that hydrologic storage greatly influences the performance of kerbside leaky well systems during higher-intensity storms. In addition, the results show that distributing a stormwater storage volume equal to thirty-five 1-kL rainwater tanks across the catchment area as a kerbside infiltration system could notably reduce the runoff flow rates and volumes. The results further highlight that the addition of more homes within the connected area could diminish the stormwater reduction benefits achieved through the installation of a distributed kerbside infiltration system.
... More recently, a focus on liveability and urban greening has encouraged the increased adoption of infiltration facilities for passive street tree irrigation in urban environments (Payne et The kerb side tree inlet ( Fig. 1) with a leaky well is a relatively new approach to infiltration, specifically designed to harvest stormwater for street tree irrigation. Leaky well infiltration systems are designed to harvest road runoff and to allow subsequent exfiltration to the surrounding soil where the water may be potentially used by street trees (Johnson et al., 2016;Sapdhare et al., 2018). While the infiltration capacity of the system may be expected to decrease over time due to sediment clogging Kandra et al., 2015), previous research has reported that vegetation or tree roots can create micropores which maintain hydraulic conductivity (Bartens et al., 2009). ...
... However, current weaknesses in the MUSIC modelling approach include the inability to model the influence of vegetation on the performance of infiltration based systems in urban areas. Street trees have been shown to increase the overall performance of infiltration systems in urban areas (Johnson et al., 2016) and further research is required to determine how this influence can be included in MUSIC simulations, or in other urban runoff simulation tools such as SWMM. ...
Kerb side inlets with adjacent leaky wells are an emerging tool to harvest stormwater and to reduce runoff volumes and peak flow rates. This is achieved by collecting the first flush runoff into kerb side storages and infiltrating this water into the surrounding soil, thereby also reducing stormwater pollutant loadings. The hydraulic performance of the kerb side inlet, filter media and surrounding soil are key factors in the performance of these systems. However, no field or laboratory data are currently available for the hydraulic performance of a kerb side tree inlet pit. In this study, 12 tree inlet pits were constructed and filled with various media types including gravel, water treatment solids (a recycled waste product), sandy loam and clay to examine (1) leaky well infiltration rates (2) emptying times of the wells and (3) the well capacity (runoff storage volume) before and after runoff filtering through the wells. Using a laboratory model, the water harvesting performance of the kerb side inlet plate was also examined for various road longitudinal slopes. Using the field and laboratory data, simulation of the well performance was undertaken using the Model for Urban Stormwater Improvement Conceptualisation (MUSIC) to assess the capacity of these systems to reduce runoff volumes at the residential street scale. It was hypothesised that the type of filter media used in leaky well systems has a significant impact on the infiltration rate, regardless of the native soil type through which the stormwater eventually infiltrates. The results showed that the infiltration rates of systems filled with gravel were significantly higher than for the other media types, and this was followed by water treatment solids, sandy loam and clay. The results of the MUSIC modelling indicated that 2.8% of the mean annual runoff volume in the catchment could be harvested by the systems at the case study site. It was found that selection of high infiltration rate media and regular maintenance are the key factors for maintaining long-term performance of these systems.
... Curbside stormwater harvesting systems are a form of WSUD that have been developed to intercept runoff from sealed urban surfaces and direct the captured runoff into the root zone of street trees (Grey et al., 2018;Johnson et al., 2016;Szota et al., 2019). Research into curbside infiltration measures is limited, but some studies have reported on the application of these systems in mainstream stormwater management. ...
Distributed infiltration systems can benefit downstream water bodies by reducing the runoff flowrate and volume discharges from the catchment. Investigating their runoff flowrate and volume reduction potential at the catchment scale will inform decision makers regarding their efficacy for managing catchment outflows. To this end, we conducted field investigations at the residential catchment scale for three years. The study monitored the catchment for one year before the installation of leaky well systems (preinstallation) and two years after installation (postinstallation). The hydrological model, calibrated to preinstallation catchment outflows, acted as a virtual control tool. Runoff flow outputs from the control model and two years of monitored runoff flow data from the postinstallation period were analysed using statistical methods. The statistical tests showed a significant 13% reduction in average flowrates in storms with a corresponding runoff flowrate of 50 L/s. The study further reported the ability of infiltration systems to reduce runoff volume in the catchment by 9%. This reduction was not significant, however, as per the results of the statistical analysis. We then fitted the generalized linear model (GLM) to the monitored and simulated runoff volume data. This enabled us to break down the effect of curbside infiltration systems on runoff volume according to corresponding peak flowrates during the storm. The results of the two-way ANOVA performed to detect significant differences in the regression slopes of the GLM indicated that curbside infiltration systems significantly reduced runoff volume for storms when the runoff flowrates remained below 100 L/s. The article can be dowloaded free for next 50 days from this link
... Reduced flow velocity due to greater cross-sectional area in the gutter established an eddy in the pool which deposited larger sediments away from the capture slot. In this way, clogging of the inlet may be reduced and routine mechanized street sweeping used to remove deposited sediment [23]. ...
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The conveyance of stormwater has become a major concern for urban planners, considering its harmful effects for receiving water bodies, potentially disturbing their ecosystem. Therefore, it is important to characterize the quality of catchment outflows. This information can assist in planning for appropriate mitigation measures to reduce stormwater runoff discharge from the catchment. To achieve this aim, the article reports the field data from a typical urban catchment in Australia. The pollutant concentration from laboratory testing is then compared against national and international reported values. In addition, a stochastic catchment model was prepared using MUSIC. The study in particular reported on the techniques to model distributed curbside leaky wells with appropriate level of aggregation. The model informed regarding the efficacy of distributed curbside leaky well systems to improve the stormwater quality. The results indicated that catchment generated pollutant load, which is typical of Australian residential catchments. The use of distributed storages only marginally improves the quality of catchment outflows. It is because ability of distributed leaky wells depended on the intercepted runoff volume which is dependent on the hydrological storage volume of each device. Therefore, limited storage volume of current systems resulted in higher contributing area to storage ratio. This manifested in marginal intercepted volume, thereby only minimum reduction in pollutant transport from the catchment to outlet. Considering strong correlation between contributing impervious area and runoff pollutant generation, the study raised the concern that in lieu of following the policy of infill development, there can be potential increase in pollutant concentration in runoff outflows from Australian residential catchments. It is recommended to monitor stormwater quality from more residential catchments in their present conditions. This will assist in informed decision-making regarding adopting mitigations measures before considering developments.
... Recent literature further grounds the multiple benefits of verge gardens as NBSs in cities. Verge gardens have great potential to facilitate rain-water run-off capture (Johnson et al., 2016) and enhance biodiversity conservation (Lin et al., 2015). The road verge garden is essentially an extensive green corridor network that increases plant diversity, reduces the impacts of fragmentation and facilitates the dispersal and movement of pollinators and wildlife (Phillips et al., 2020). ...
Australia is currently grappling with a range of social and environmental challenges, many of which impact the way our public health system, and society more broadly, function. In this short communication paper we explore urban agriculture in Australia as a Nature-Based Solution (NBS) to address some of the ecological, social, economic and health challenges facing the continent. We argue that urban agriculture has the potential to mitigate the effects of climate change extremes while simultaneously providing multiple benefits such as improving wellbeing, people-nature connections, and food security. We present three exemplar case studies diverse in geography, context and governance from Queensland, Tasmania, and New South Wales exploring verge gardening, market gardening, and a community greening program respectively to highlight the benefits of urban agriculture as a NBS. We advocate that various forms of urban agriculture need to be researched and considered for their potential impacts and multiple benefits to be fully supported, governed, and understood in light of the social-ecological challenges Australian cities face.
... In 2002, TREENET Inc. developed the TREENET inlet, a novel kerb side inlet to harvest road runoff for passive irrigation of street trees. This inlet, coupled with a leaky well infiltration pit ( Fig. 1), is an emerging WSUD tool that has been installed in Australia to reduce runoff volume, reduce mains water demand and improve stormwater quality (Johnson et al. 2016). In its most common configuration, one leaky well infiltration pit is installed adjacent to a tree or ideally between two trees in Responsible editor: Philippe Garrigues * Harsha Sapdhare a street. ...
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The TREENET inlet is an emerging water-sensitive urban design technology that consists of a novel kerb side inlet coupled with a leaky well infiltration system. The inlets have been retrofitted to existing roads since 2006; however, there is currently little information available on the effectiveness of these inlet and leaky well systems. This study investigated the performance of the kerb side inlets and leaky well system for water quality improvement prior to infiltration to native soil. The leaky wells included four filter media types, namely gravel, water treatment solids, sandy loam and clay. To compare the performance of the four filter media types, batch and column studies were performed in the laboratory. The best performance was observed using the sandy loam as a filter media, followed by clay, water treatment solids and then gravel. The selection of effective media for removal of heavy metals is important as each media type has different pollutant removal capacity, infiltration and clogging performance.
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Researchers and water managers have turned to green stormwater infrastructure, such as bioswales, retention basins, wetlands, rain gardens, and urban green spaces to reduce flooding, augment surface water supplies, recharge groundwater, and improve water quality. It is increasingly clear that green stormwater infrastructure not only controls stormwater volume and timing, but also promotes ecosystem services, which are the benefits that ecosystems provide to humans. Yet, there has been little synthesis focused on understanding how green stormwater management affects ecosystem services. The objectives of this paper are to review and synthesize published literature on ecosystem services and green stormwater infrastructure and identify gaps in research and understanding, establishing a foundation for research at the intersection of ecosystems services and green stormwater management.We reviewed 170 publications on stormwater management and ecosystem services, and summarized the state-of-the-science categorized by the four types of ecosystem services. Major findings show that: (1) most research was conducted at the parcel-scale and should expand to larger scales to more closely understand green stormwater infrastructure impacts, (2) nearly a third of papers developed frameworks for implementing green stormwater infrastructure and highlighted barriers, (3) papers discussed ecosystem services, but less than 40% quantified ecosystem services, (4) no geographic trends emerged, indicating interest in applying green stormwater infrastructure across different contexts, (5) studies increasingly integrate engineering, physical science, and social science approaches for holistic understanding, and (6) standardizing green stormwater infrastructure terminology would provide a more cohesive field of study than the diverse and often redundant terminology currently in use. We recommend that future research provide metrics and quantify ecosystem services, integrate disciplines to measure ecosystem services from green stormwater infrastructure, and better incorporate stormwater management into environmental policy. Our conclusions outline promising future research directions at the intersection of stormwater management and ecosystem services.
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This paper will first look at the timeline of important publications that have been published on sustainable design and have emerged from different schools of thought, to exemplify how gradually the notion of Green Urbanism evolved. It then identifies the intertwined principles for achieving Green Urbanism.
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Within-city green infrastructure can offer opportunities and new contexts for people to become stewards of ecosystem services. We analyze cities as social–ecological systems, synthesize the literature, and provide examples from more than 15 years of research in the Stockholm urban region, Sweden. The social–ecological approach spans from investigating ecosystem properties to the social frameworks and personal values that drive and shape human interactions with nature. Key findings demonstrate that urban ecosystem services are generated by social–ecological systems and that local stewards are critically important. However, land-use planning and management seldom account for their role in the generation of urban ecosystem services. While the small scale patchwork of land uses in cities stimulates intense interactions across borders much focus is still on individual patches. The results highlight the importance and complexity of stewardship of urban biodiversity and ecosystem services and of the planning and governance of urban green infrastructure. Electronic supplementary material The online version of this article (doi:10.1007/s13280-014-0506-y) contains supplementary material, which is available to authorized users.
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Urbanization destroys or modifies native habitats and creates new ones with its infrastructure. Because of these changes, urban landscapes favor non-native and native species that are generalists. Nevertheless, cities reveal a great variety of habitats and species, and, especially in temperate cities, the diversity of vascular plants and birds can be higher than in the surrounding landscapes. The actual occurrence of a species, however, depends on habitat availability and quality, the spatial arrangements, species pools, a species’ adaptability and natural history, and site history. In addition, cities are particularly human-made ecological systems. Top-down and bottom-up activities of planners, land managers, and citizens create the urban biodiversity in general and in detail. Plants and animals in cities are the everyday life contact with nature of the most humans on our earth. The intrinsic interplay of social and ecological systems with a city often forms unique biotic assemblages inherent to that city. To support native biodiversity, landscape architects, conservation biologists, and other groups are linking landscape design with ecosystem structure and function to create and restore habitats and reintroduce native species in cities.
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Urban sustainability is one of the most pressing and challenging tasks facing humanity today because cities are the primary sources of major environmental problems, the centers of economic and social developments, and home to more than half of the world population. While the ecological, economic, and social dimensions of sustainability are equally important in principle, the ecology of cities is arguably least studied. But this situation has been changing rapidly in recent years. In this paper, the author compares and contrasts different perspectives in urban ecology and examines their relevance to urban sustainability. While all perspectives are useful in some ways, the author argues, a landscape ecology perspective that integrates elements of sustainability science seems most comprehensive and effective. This integrative perspective views humans as powerful “ecosystem engineers” or agents that are critically important for developing urban sustainability. It focuses on the human landscape scale that is large enough to include key ecological and socioeconomic processes and small enough to allow for detailed mechanistic studies. The landscape ecology approach also emphasizes the interrelationship between urban landscape patterns and ecological / socioeconomic processes on different scales, and encourages place-based research that integrates ecology with planning, design, and other social sciences.
Eutrophication in coastal ecosystems is often attributed to elevated nitrogen levels. Reducing the amount of nitrogen entering Port Phillip Bay is therefore an important objective for Melbournians. This article details the performance of a pilot scale street tree bioretention system in reducing nitrogen loads in urban stormwater. Three tree species (Eucalyptus polyanthemos, Lophostemon confertus and Platanus orientalis) and three sandy soils of different hydraulic conductivity (4, 95 and 170 mm/hr) were tested in a randomised block design. Over the course of the experiment, all species displayed seasonal height growth patterns with maximum growth rates occurring in late Spring and Summer. Applications of stormwater increased height growth and root length density compared with tapwater applications. Tree growth was similar in the three soils studied. During the warmer months, leachate volumes from the planted systems were significantly less than the unplanted systems due to transpirational drying. Leached nitrogen loads were significantly reduced in systems with a tree. Whilst there were some statistically significant differences in ammonium, oxidised nitrogen and organic nitrogen removal between species, these were not large in practical terms. In December, total nitrogen load removal from stormwater was 82 to 95% in planted systems (L. confertus), compared to 36 to -7% in the unplanted systems
Urban ecology and its theories are increasingly poised to contribute to urban sustainability, through both basic understanding and action. We present a conceptual framework that expands the Industrial → Sanitary → Sustainable City transition to include non-sanitary cities, “new cities”, and various permutations of transition options for cities encountering exogenous and endogenous “triggers of change”. When investigating and modeling these urban transitions, we should consider: (1) the triggers that have induced change; (2) situations where crisis triggers change; (3) why cities transition toward more sustainable states on their own, in the absence of crisis; (4) what we can learn from new city transitions, and non-sanitary city transitions; and (5) how resource interactions affect urban transitions.
Imperviousness is an important indicator of the impact of urbanization on storm water systems. A hydrologic analysis was performed to evaluate long-term impacts from an apartment area in Miami. The result shows that the directly connected impervious area (DCIA), which covers 44% of the catchment, contributes 72% of the total runoff volume during 52 years. Few studies have actually measured the DCIA with a high level of accuracy for residential areas that constitute the largest proportion of urban land. A detailed analysis of urban imperviousness was performed using geographic information systems and field investigations on a 5.81 ha residential area in Boulder, Colo. For this study area, the total impervious area is 35.9% and the DCIA is 13.0%. Transportation-related imperviousness comprises 97.2% of the DCIA. Hydrologic modeling of this area shows about a 265% difference in estimates of peak discharge with imperviousness measured at five,different levels of accuracy. These results suggest the need to focus on DCIA as the key indicator of urbanization's effect on storm water quantity and quality.
Increasingly, city trees are viewed as a best management practice to control stormwater, an urban-heat–island mitigation measure for cleaner air, a CO2-reduction option to offset emissions, and an alternative to costly new electric power plants. Measuring benefits that accrue from the community forest is the first step to altering forest structure in ways that will enhance future benefits. This article describes the structure, function, and value of street and park tree populations in Fort Collins, Colorado; Cheyenne, Wyoming; Bismarck, North Dakota; Berkeley, California; and Glendale, Arizona. Although these cities spent $13–65 annually per tree, benefits ranged from $31 to $89 per tree. For every dollar invested in management, benefits returned annually ranged from $1.37 to $3.09. Strategies each city can take to increase net benefits are presented.