9th International Conference on Urban Drainage Modelling
Belgrade 2012
C. B. S. Dotto, R. Allen, T. Wong and A. Deletic
Centre for Water Sensitive Cities, Monash University, Victoria, Australia, 3800 cintia.dotto@monash.edu, ross.allen@monash.edu, tony.wong@monash.edu, ana.deletic@monash.edu
The management and use of water in urban environments to provide resilience to climate change is an increasingly critical challenge for cities and towns in
Australia, and globally. Current trends of growing urban populations and increased urban densities heighten the importance of this issue, as well as increasing the need for accessible, high quality and multi-functional urban landscapes. There is currently no simple-to-use yet scientifically rigorous software tool to support the strategic urban planning and conceptual design decisions required to respond to these challenges. A tool to address this gap is currently being developed by the
Cities as Water Supply Catchments Program – an inter-disciplinary Australian research program on stormwater management in water sensitive cities. The program incorporates: public health risks, water sensitive urban design technologies, climate change and urban micro-climate, aquatic ecosystem dynamics, environmental economics and urban water governance. This paper proposes a modelling framework to integrate research insights and outcomes delivered through the Cities as Water Supply Catchments Program, and develop a strategic planning and conceptual design tool to advance stormwater management as part of the transition to water sensitive cities.
Stormwater, model framework, strategic planning, conceptual design, scenario generation, scenario assessment
The impacts of increasing urbanization and climate change on the environment and its consequences to human health are widely documented. Over the last decade major cities and towns in Eastern Australia have experienced prolonged drought and extreme heat events, followed in 2010 and 2011 by some of the biggest floods on record causing considerable financial losses. Further, the effects of increased urbanization and higher urban densities on urban heat island (UHI) intensify longer duration of heat
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waves trends (Coutts et al., 2007; Alexander and Arblaster, 2009). Human health and human thermal
comfort are negatively impacted by the increase in occurrence and duration of extremes heat events
(Laschewski and Jendritzky, 2002; Loughnan et al., 2010). No less critical, are the negative impacts of urbanization on urban stream hydrology (e.g. Booth and Jackson, 1997) and water quality (e.g Hatt et al., 2004).
Urban communities face a new and critical urban design challenge to ensure that future urban landscapes encapsulate opportunities and technologies to provide resilience to the impacts of climate
change (Wong and Brown, 2009). Understanding current and future rainfall variability is fundamental
to establishing cities as water supply catchments as part of the transition to water sensitive cities. The adoption of Water Sensitive Urban Design (WSUD) has shown great potential in creating more sustainable and liveable cities and towns. For example, excess urban heat can be mitigated by green
infrastructures supported by stormwater (Wong et al., 2011). Stormwater management and in
particular, stormwater treatment and harvesting, can contribute to both water supply and
environmental flow objectives (Mitchell et al., 2007). The use of fit-for-purpose stormwater to
augment traditional water supplies also helps to restore pre-developed flow and water quality conditions and minimise pollution impacts associated with urban areas. Although benefits of stormwater harvesting in transforming cities into more liveable environments can be readily identified, the absence of economic valuation methodologies to assess non-monetary benefits creates challenges in assessing the full value of implementing WSUD technologies. Decision making at all levels of water infrastructure investment is limited by the inability of the water sector to quantify the total economic value provided by WSUD technologies and practices.
A series of literature reviews focused on various aspects of stormwater management in a water
sensitive city (compiled in Wong et al., 2011) identified that: (i) a greater understanding of future
rainfall patterns and their uncertainties is required; (ii) stormwater harvesting systems should be implemented and operated to meet required health and safety standards for water use; (iii) WSUD practices can benefit urban micro-climate and stream health; (iv) society and institutions play an important role in creating water sensitive cities; (v) there is a need to develop an economic valuation tool to assign values to non-monetary benefits of stormwater harvesting; and, (vi) WSUD technologies and practices can contribute to improve liveability in urban environments. There is currently no software tool that is able to integrate these findings. However, such a tool to support the strategic urban planning and conceptual design decisions would greatly support the transition to water sensitive cities and towns.
The subject of this paper is a central part of the Cities as Water Supply Catchments (CaWSC) Program
– an inter-disciplinary Australian research program focused on harnessing the potential of stormwater to overcome water shortages, reduce urban temperatures, and improve waterways health and the landscape of Australian cities. The program incorporates: public health risks, WSUD technologies, climate change and urban micro-climate, aquatic ecosystem dynamics, environmental economics and urban water governance. Industry partners, through their active involvement in the CaWSC Program, inform the research agenda and provide a pathway for the practical application of research outcomes
(see http://www.watersensitivecities.org.au/programs/cities-as-water-supply-catchments for more information about the program).
This paper proposes a framework to integrate insights and outcomes from the CaWSC Program, and describes the conceptualisation of a strategic planning and conceptual design software tool (model) to support the transition to water sensitive cities and towns. The model is currently under development, with the release of a first version scheduled for late 2013. This paper is the first publication by the
CaWSC Program on the development of this model. Research undertaken through the CaWSC
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Program is ongoing and therefore model functionality and processes may evolve throughout the model development process.
The proposed framework to integrate insights and outcomes from the CaWSC Program is a simple-touse yet scientifically rigorous strategic planning and conceptual design software tool (model) to support the transition to water sensitive cities and towns. The model, together with annual blueprints, research reports, design guidance and demonstration case studies make up a water sensitive city toolkit.
The purpose of the model is to support the planning and conceptualisation of WSUD scenarios, and subsequently evaluate the performance of different scenarios across a broad range of measures. For example, different sustainable stormwater harvesting technologies can be assessed in terms of their treatment and harvesting performance under possible future climate predictions, as well as the urban micro-climate and stream ecology benefits provided. The main outputs of this model will be performance indicators (e.g. volume of harvested water, localised reduction in urban temperature, reduction in pollution loads, etc) that reflect the benefits of WSUD technologies and practices.
Performance indicators for a range of measures will enable a high level economic valuation of the nonmonetary benefits provided by different scenarios. Further, an assessment of the contribution of different scenarios to liveability (i.e. how well societal urban water needs are met by a particular scenario) will be supported.
The model will consist of a number of modules representing specific processes that can be used independently by providing appropriate inputs data and system parameters, or connected as part of an integrated model to assess scenario performance against several indicators.
The model incorporates a two stage process (Figure 1) to support the strategic planning and conceptual design of water sensitive cities and towns: (i) scenario generation through a participatory process with stakeholders, and (ii) scenario assessment, including simulation of WSUD technologies and practices and subsequent bio-physical, economic and liveability assessment. Outputs from the scenario assessment process will enable refinement of proposed scenarios.
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Scenario Generation
Urban
Planning
Community
Needs
Urban
Form
Community
Receptivity
Stormwater
Management
Scenario(s)
Climate
Variability
Hazard
Assessment
Climate
Data
WSUD
Conceptual
Design
Scenario Simulation & Assessment
Bio-Physical
Assessment
Treatment /
Harvesting
Micro-
Climate
Impacts
Stream
Health
Outcomes
Contribution to
Liveability
Economic
Valuation
Participatory Process Simulation process
Figure 1. Schematic diagram of the model. Blue circles represent the modules of the scenario generation stage while green circles represent the modules of the scenario simulation and assessment stage; green boxes stand for the sub-modules of the bio-physical module.
3.1 Scenario Generation
The generation of meaningful scenarios requires context specific input and should therefore be guided by local environmental, social and economic considerations. Participatory methods such as scenario analysis, envisioning and policy experimentation can be used to draw on the diverse perspectives and
experiences of a wide range of stakeholders in defining scenario inputs (Videira, 2010). A
participatory approach to scenario generation will be supported by the model through individual modules that provide inputs and guidance on, for example, defining societal urban water needs and understanding community receptivity to different WSUD technologies and practices. These modules, while not dynamically linked to the scenario simulation, support the identification of meaningful
WSUD scenarios for subsequent assessment. The scenario generation component of the model will also utilise other available information (e.g. strategic plans, contextual trends, planned future developments, and environmental values and condition). Some modules will store data and/or generate outputs, while others will contain guidance based on research insights and outcomes.
A brief outline of each of the proposed scenario generation modules is presented below.
1.
Community Needs WSUD technologies and practices contribute to meeting societal urban water
needs, which in turn contributes to the liveability of a city (de Haan et al., 2011; Adamowicz and
Johnstone, in preparation). This module will assist in defining urban water needs of local
communities that can be influenced by stormwater management through, for example, providing information on societal urban water needs as characterised by existence-relatedness-growth theory. The identification of relevant urban water needs will inform the evaluation of scenario contributions to liveability within the scenario assessment component of the model.
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2.
Urban Planning - This module will support the generation of WSUD scenarios by providing links to relevant high level urban planning guidance and regulations for different states/ regions.
Participatory input from stakeholders will assist in determining additional local strategic and statutory planning considerations.
3.
Community Receptivity - This module will comprise results and observations from studies focused on community norms and community engagement. Information contained in this module will provide guidance on identifying policy tools and capacity building strategies to accelerate the implementation of WSUD technologies and practices and to increase industry/community receptivity.
4.
Climate Variability - This module will provide urban climate predictions (e.g. rainfall, evapotranspiration, temperatures and humidity) and the uncertainty associated with these predictions. The module will store climate data at a spatial resolution of approximately 5km
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and a temporal resolution of approximately 12 minutes. These data will provide inputs to the biophysical assessment module, and will also be able to be accessed for statistical and/or visual analysis of future climate scenarios.
5.
Hazard Assessment This module will compile the findings of public health hazard and risk assessments of decentralised stormwater harvesting systems. It will provide guidance on how to implement and operate stormwater harvesting and use systems to meet the required health and
safety standards for potable and non-potable water use (Wong et al., 2011). It will also provide
links to relevant national and state regulations and guidance on water recycling and pollution control.
A participatory process, supported by the above modules and other relevant information, will be used to generate a series of stormwater management strategies and associated scenarios. Scenarios will include targets (typically a target range) for performance indicators including water supply security, water pollution reduction and local flood protection.
3.2 Scenario Assessment
WSUD scenarios generated through a participatory process with stakeholders will inform the simulation and assessment process, which will incorporate the following modules:
3.2.1 WSUD Conceptual Design Module
This module incorporates the exploratory software tool UrbanBEATS to simulate a range of WSUD
scenarios based on decentralised water management strategies (Bach, 2012). The module generates
indicative conceptual designs of WSUD technologies and practices for a given scenario by determining where and how WSUD technologies and practices can be implemented within the urban landscape to meet specified targets. It focuses on the generation of a number of possible realisations of
WSUD scenarios that can achieve the specified targets within urban planning constraints based on planning regulations for a given city/region. It uses location specific design curves to determine, for example, required treatment level for different WSUD technologies. For Melbourne, design curves for
treatment performance of specific WSUD technologies developed by Melbourne Water (2005) will be
used.
The indicative conceptual design of WSUD technologies and practices is based on default design parameters (e.g. 0.4 m depth for raingardens; 72 hours of detention time for wetlands). As such, these indicative conceptual designs do not replace the need for detailed design development and are not
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suitable as final design options. Further design development, including more detailed modelling (e.g. using MUSIC by eWater CRC, 2009) is required to develop specific design options.
Outputs from this module include a series of possible configurations (realisations) for each WSUD scenario which are subsequently used as inputs to the bio-physical assessment sub-modules.
3.2.2 Bio-Physical Assessment Sub-Modules
The bio-physical assessment component currently includes three modules:
1.
Stormwater Treatment and Harvesting This sub-module will evaluate the treatment and harvesting performance of the different WSUD realisations generated by the conceptual design module. Predicted future rainfall and evapotranspiration data stored in the climate variability module will provide inputs to this sub-module to enable an assessment of the impacts of climate variability and uncertainty on treatment and harvesting performance. The sub-module generates
flow (runoff) from pervious and impervious surfaces (McCarthy et al., 2011) and simulates pollutant generation using the stochastic approach adopted in MUSIC (eWater CRC, 2009). The
treatment and harvesting efficiency of the different realisations will be simulated using a
simplified version of the Universal Stormwater Treatment Model (Wong et al., 2001).
Outputs of this sub-module include time series of pre and post-treatment flows and pollutant concentrations which are used as inputs to the micro-climate and stream ecology sub-modules.
Outputs from this sub-module may also be used by the economic valuation and contribution to liveability modules.
2.
Micro Climate Impacts - This sub-module will evaluate the urban micro-climate benefits of different WSUD realisations generated by the conceptual design module. Cooling effects, particularly in relation to mitigating urban heat extremes will be evaluated.
It is known that air temperature is related to land surface temperature (LST) for the different land
covers (Mildrexler et al., 2011). As such this sub-module consists of relationships between the
percentage of different land covers, e.g. grass, tree or impervious, and the measured LST from a satellite image. These relationships will point how different WSUD modelled realisations (i.e. output from the WSUD conceptual design module) contributes to reducing peak urban temperatures. The sub-module can also be used as a standalone if the user provides, for example some desired percentages of different land covers.
In addition to predicting reductions in local temperatures under extreme heat conditions, this module will also provide information on changes in evaporation and soil moisture achieved by different WSUD realisations.
3.
Stream Health Outcomes This sub-module will assess the impacts of different WSUD configurations on stream health. It will calculate an environmental benefit index based on four sub-indices: (i) the reduction in flow frequency; (ii) equivalence between the pre-urban volume of subsurface flows and filtered flows from stormwater treatment and harvesting technologies; (iii) median concentrations of suspended solids (TSS), phosphorous (TP) and nitrogen (TN) in filtered
flows from such interventions; and, (iv) reduction in total untreated runoff (EBI - Little
Stringybark Creek, 2012).
The sub-indices are of direct ecological relevance to streams and therefore the environmental benefit index (the output from this sub-module) will indicate how different WSUD realisations contribute to restoring post-development hydrology towards pre-development conditions. Outputs of the stormwater treatment and harvesting sub-module (e.g. flow volumes for pre-urban and pre
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and post WSUD implementation, and water quality performance) provide inputs to the stream health module.
3.2.3 Economic Valuation Module
The economic valuation module will inform potential investment in water sensitive stormwater management by providing monetary valuations for a number of non-monetary benefits provided by
WSUD technologies and practices. The module will also include information on how key socioeconomic and geo-political factors influence these valuations. Early versions of the model may contain a basic economic valuation module (facilitating increased awareness of non-market benefits) until research activities generating the relevant data are completed.
The primary outputs from this module will be economic valuations of a number of non-market benefits provided by WSUD technologies and practices, informed by socio-economic and geo-political factors.
3.2.4 Contribution to Liveability
This module will assist in understanding how different WSUD technologies and practices can enhance liveability by contributing to societal urban water needs. The module will relate the benefits of WSUD technologies and practices (e.g. reduced stormwater volumes entering urban waterways, extreme heat moderation, increased quality and amenity of urban landscapes and environment biodiversity, and increased recreational opportunities) to societal urban water needs (e.g. accessible and safe drinking
water, public health, property protection, recreation, etc) (de Haan et al., 2011; Adamowicz and
Johnstone, in preparation).
It is unlikely that one stormwater management scenario will meet all the community water needs, and some scenarios may meet particular societal urban water needs while negatively impacting on others.
Therefore, the output from this module is likely to be a series of indices relating to different societal urban water needs, rather than a single liveability index..
3.3 Model Conceptualisation Summary
The proposed framework and conceptualisation will deliver an integrated model where modules and sub-modules may interact as blocks or provide input data to another module. WSUD scenarios are generated through a participatory process, based on a number of contextual inputs (e.g. societal urban water needs, community receptivity to particular WSUD technologies and practices, public health and urban planning regulations). The model supports the integrated evaluation of WSUD realisations through integrated biophysical and socio-economic assessments (e.g. stormwater treatment and harvesting efficiency, impacts on urban micro-climate and stream health, valuation of non-monetary benefits, and contribution to liveability). Alternatively, each module and sub-module can be run independently to explore how particular WSUD technologies and practices may contribute to creating water sensitive places. Each module will provide data and/or information to support the transition to water sensitive cities and towns through strategic planning and conceptual design.
This paper proposes a framework to integrate insights and outcomes from the Cities as Water Supply
Catchments (CaWSC) Program, and describes the conceptualisation of a strategic planning and conceptual design software tool (model) to support the transition to water sensitive cities and towns.
This paper is the first publication on the development of this model. Research undertaken through the
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CaWSC Program is ongoing and therefore model functionality and processes may evolve throughout the model development process.
The proposed model incorporates a two stage process to support the strategic planning and conceptual design of water sensitive cities and towns: (i) scenario generation through a participatory process with stakeholders, and (ii) scenario assessment, including simulation of WSUD technologies and practices and subsequent bio-physical, economic and liveability assessment. Outputs from the scenario generation and assessment processes will enable refinement of proposed scenarios. The model will consist of a number of individual modules and sub-modules that can be coupled to provide an integrated scenario assessment or can be run independently.
The model will support a participatory approach to scenario generation through modules that provide inputs and guidance on, for example, defining urban water needs of local communities and understanding community receptivity to particular WSUD technologies and practices. The scenario generation process will also utilise other available information (e.g. strategic plans, contextual trends, planned future developments, and environmental values and condition). Some modules will store data and/or generate outputs, while others will contain guidance based on research insights and outcomes.
Scenario assessment is based on a conceptual design module (which incorporates the exploratory software tool, UrbanBEATS) to simulate a range of WSUD scenarios based on decentralised water management strategies. It focuses on the generation of a number of possible realisations of WSUD scenarios that can achieve the specified targets within urban planning constraints based on planning regulations for a given city/region. Bio-physical assessment includes three sub-modules: (i) stormwater harvesting and treatment performance (to evaluate the treatment and harvesting performance of the different realisations of WSUD strategies); (ii) micro-climate (to evaluate the urban micro-climate benefits of different WSUD realisations, particularly in relation to mitigating urban heat extremes), (iii) stream ecology (to assess the contribution of different WSUD realisations to stream health through the calculation of an environmental benefit index).
An economic valuation module will inform potential investment in stormwater management by providing monetary valuations for a number of non-monetary benefits provided by WSUD technologies and practices, including information on how key socio-economic and geo-political factors influence the valuations. The ability of different WSUD technologies and practices to enhance liveability by contributing to societal urban water needs will be assessed through a contribution to liveability module.
The model is currently under development with the release of the first version scheduled for late 2013.
A beta version of the tool is being developed through a collaboration between the Australian CaWSC
Program and Innsbruck University, Austria and will be available for testing and industry engagement in September 2012. Future versions of the model may incorporate insights and outcomes from ongoing research into other aspects of water sensitive stormwater management (e.g. local flood protection) and at different scales (e.g. micro-climate benefits at the street scale).
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