A preliminary identification of the relevant modelling tools for WSUD has been undertaken and a selection of relevant models is given below. These models are continuously being updated and so each model is linked back to its webpage.
The Model for Urban Stormwater Improvement Conceptualisation (MUSIC) is a stormwater quality assessment tool developed by eWater. The model is used to analyse the conceptual designs of stormwater infrastructure and places particular emphasis on water quality objectives (Elliott & Trowsdale, 2007). MUSIC models downstream flow control and water quality benefits achieved through the installation of structural Best Management Practices (BMPs) (Lloyd et al., 2002). First developed in 2001, the software is designed to help urban stormwater professionals create and visualise strategies to tackle problems associated with stormwater hydrology and pollution impacts (eWater, 2011a). MUSIC can operate over a range of spatial and temporal scales; the model can simulate catchments of 0.01 to 100km2 with time steps ranging from 6 minutes to 24 hours. The basic operations of the software model include: (Lloyd et al., 2002)
- Determining the probable water quality being released from urban catchments.
- Predicting the performance of structural BMPs in protecting water quality.
- Designing an integrated stormwater management system.
- Evaluating the success of potential designs against a range of water quality standards.
MUSIC enables designers to model both the stormwater quantity and quality characteristics of stormwater systems for catchments of varying size. The program incorporates a range of treatment measures either individually, within a treatment train, or as distributed treatment measures (Singh et al., 2008). MUSIC helps decision makers in the planning and design phases by simulating the stormwater quality performance of different conceptual designs (eWater, 2011a).
MUSIC should not be confused with Urban Developer (Section 13.4.3). MUSIC models the impact of treatment train technologies on stormwater quality, whereas Urban Developer considers all elements of the urban water cycle (stormwater, wastewater and potable water) and assists in considering potential management strategies including reuse, alternative supply options and water efficient appliances (Feilin, 2012).
MUSIC is a useful tool with which to link government policy regarding water quality standards to stormwater quality technology (Lloyd et al., 2002). This is illustrated in a case study of Redland City Council in Australia that used MUSIC to evaluate the designs submitted with development applications (eWater, 2011b). The model allows authorities to quickly check the adequacy of designs in meeting the required standards, thereby saving time for both the authorities and the developers (eWater, 2011b).
The latest version of MUSIC, i.e. MUSIC 5.1 was released in July 2012. One of the major advancements within MUSIC 5.1 is the ability to better model stormwater harvesting and reuse. It is possible to specify a reuse demand and model how well this can be met.
The Source Loading And Management Model (SLAMM) was developed by PV & Associates as a planning level tool. The software’s basic capabilities involve predicting flow and pollutant discharges from a broad range of development scenarios with many different combinations of stormwater controls (PV & Associates, 2011b). SLAMM is capable of calculating mass balances for dissolved and particulate pollutants for different development scenarios and rainfall events (Pitt & Voorhees, 2002). It was initially developed in the 1970’s to model the interactions between sources of urban runoff pollution and water quality. Since then the software has expanded its scope to include a range of source area and outfall control measures such as infiltration devices, detention ponds, porous pavement and swales (PV & Associates, 2011a).
SLAMM is based on actual field observations with limited reliance on purely theoretical concepts that have not been confirmed or documented in the field (Pitt & Voorhees, 2002). SLAMM places special emphasis on small storm hydrology, as the vast majority of stormwater quality issues are associated with smaller rainfall events (PV & Associates, 2011a). In order to model these events more accurately, SLAMM includes unique process descriptions which allow a more accurate prediction of flows and pollutant loads for a given rainfall event (Pitt & Voorhees, 2002, PV & Associates, 2011b).
SLAMM is currently undergoing an extensive overhaul prior to it being re-released; further details on this program will therefore only be provided once the new version has undergone its testing phase and the results have been published (sometime in 2013).
The System for Urban Stormwater Treatment and Analysis INtegration (SUSTAIN) was developed as a GIS-based decision support tool by Tetra Tech in conjunction with the Environmental Protection Agency (EPA). The EPA report on the SUSTAIN model (Shoemaker et al., 2009) provides an overview of the model and its capabilities.
SUSTAIN is a tool capable of performing a comprehensive analysis of stormwater management strategies at multiple scales. SUSTAIN helps to evaluate, select and place structural BMPs within a given catchment on the basis of user-defined cost and effectiveness criteria. SUSTAIN provides a mechanism that enables the evaluation of the most appropriate location, type and cost of stormwater BMP’s to achieve specified water quality goals. SUSTAIN was developed by combining publically available modelling techniques, management costs and optimisation tools within a geographic framework.
SUSTAIN is only compatible with ArcGIS 9.3.1 and Windows XP. As a result it is now out of date and not compatible with many modern machines. The USEPA currently has no plans to upgrade the software in the near future (Selvakumar, 2012).
The Storm Water Management Model (SWMM) was first developed by the Environmental Protection Agency (EPA) in 1971 and has had several major overhauls over the years (Rossman, 2008). The SWMM User’s Manual (Rossman, 2008) provides a useful overview of the model which is summarised as follows.
SWMM is a software package that enables dynamic rainfall-runoff modelling, and can be used to model long term or single rainfall events. The model simulates the quantity and quality of runoff that emanates from an urban environment. The model consists of two major components, i.e. runoff and routing. The runoff component produces runoff and pollutant load simulations for a number of sub-catchments. The routing component simulates the transportation of runoff through stormwater infrastructure such as pipes, channels, storage and treatment devices (SuDS / BMP’s), pumps, and regulators. SWMM 5 (the latest version) has the capability of evaluating the effectiveness of BMPs. SWMM tracks both water quantity and quality in each designated sub-catchment, as well as the flow rate, flow depth and quality of water at multiple time steps during the simulation. The latest version is easier to operate and more accessible to the current generation of engineers and water specialists, however the models are too complex to be used by non-modelling planners (Elliott & Trowsdale, 2007; Gironás et al., 2010).
SWMM may also be linked to other models, for example Rowan (2001) linked SWMM and MODFLOW using a ‘multiple model broker’, which allows for the exchange or feedback of information between the two models at each time step during the modelling process, and Yergeau (2010) coupled SWMM and MODFLOW models in a study of an urban wetland.
SWMM 5 is not integrated with GIS which requires planners and designers to import and export data between different formats. There are however a range of additional software packages which use SWMM as the core processing / calculation software, but then improve the usability of the software through an improved user interface. This includes a GIS interface with the ability to export results into a range of formats not usually available in the USEPA SWMM 5 package.
Urban Water Cycle Models
Source Urban is a function within Source, that is being made publically available through membership into the Source Modelling Community (Feilin, 2012). Source Urban is designed to represent a wide variety of water sources such as (eWater, 2012):
• River extractions to in-line or off-line reservoirs.
• Direct river extractions.
• Groundwater extractions.
• Alternative sources such as stormwater harvesting and wastewater treatment.
• Decentralised sources such as rainwater tanks.
“In addition to accounting for alternative water sources in the urban environment, Source can also represent urban demand. Satisfying urban demand is the aim of urban water resources managers and this topic has received a large amount of attention and there are, a large number of existing urban demand models. Source does not seek to replace these models; rather it provides a framework in which existing demand models are incorporated through importing existing time series, mathematical expressions or plug-ins. This flexible framework ensures compatibility with existing demand model allowing continuity of data and modelling approached (eWater, 2012)”. The cost of Source varies depending on the size of the company or institution, as determined by the company’s annual turnover.
UVQ (Urban Volume and Quality) was developed to provide a means for rapidly assessing conventional and non-conventional approaches to providing water supply, stormwater and wastewater services to urban allotments, neighbourhoods and study areas. The model is placed in the context of other such models developed internationally through a brief literature review. This is followed by a description of the model and output examples, which is used to illustrate the utility of the model. UVQ is an effective preliminary assessment tool for determining the impacts of urban development options on the total water cycle, as well as the performance of a wide range of non-conventional demand and supply side management techniques (Mitchell & Diaper, 2005).
UVQ is the successor of Aquacycle (Last, 2010; Mitchell & Diaper, 2005). The main improvements were that it added a contaminant balance to the water balance, and there has been an improvement in the user interface (Last, 2010; Mitchell et al., 2007). According to Last (2010), the main strengths of UVQ include: simplicity, rapid runtime and description of the cityscape. Weaknesses include the predominant focus on residential areas, range of indicator outputs, limited availability of water management techniques, and limited consideration of the natural systems.
Mitchell & Diaper (2005) highlight the fact that UVQ was developed “with the objective of maximum applicability to all urban areas in both Australia and Europe”. As a result Mitchell & Diaper (2005) state that UVQ can model a variety of land use types (not just residential); a range of different conventional water infrastructure technologies and account for local climatic conditions. Mitchell et al. (2007) do however recognise that the one disadvantage of UVQ is that it can only handle one climate file, which then assumes a constant climate for the whole model.
UVQ represents the catchment using three spatial scales, i.e. site / unit block, local / neighbourhood, and regional / catchment (Elliott & Trowsdale, 2007; Mitchell & Diaper, 2005). This allows for a range of scales and different water management technologies and approaches to be modelled (Elliott & Trowsdale, 2007). UVQ is a volumetrically-based water balance model that can be used for modelling integrated urban water management strategies. It is relatively simple to use, and is freely downloadable. While more complex programs are now available, UVQ can still be used for modelling the urban water cycle.
Urban Developer is a model created by eWater. The model was developed in response to a comment that “to date, no single model offers the ability to undertake the integrated modelling required to assess the performance of integrated urban water management options across the entire urban water cycle” (Hardy & McArthur, 2011).
Urban Developer has been developed as “a flexible and modular modelling environment for the simulation of urban water cycle services systems” (Snowdon et al., 2011). Urban Developer simulates the water supply, stormwater, and wastewater systems at a range of spatial and temporal scales within a single framework to improve the understanding of the potential of integrated urban water management (Snowdon et al., 2011). The key features of Urban Developer are described by Hardy & McArthur (2011) as follows:
- An easy-to-use node-link modelling environment that includes representation of all three urban water cycle service networks: water supply, stormwater, and wastewater.
- Simulation of sub-daily demand and end-use to improve insights into the operation and interactions of water cycle service systems in integrated management frameworks.
- The capability to model using continuous rainfall and climate data as well as supporting AR&R Design Rainfall based assessment of stormwater system components.
- The ability to simulate at temporal and spatial scales commensurate with state and local government planning and approval metrics. For example, Urban Developer can support the estimation of peak discharge and the evaluation of measures to achieve mandated peak discharge reduction targets.
- The ability to group service network elements into sub-networks, reducing the visual complexity of models and allowing the Urban Developer software to be more easily applied at a range of scales.
- Reduced network and computational complexity by using styles: ‘sets’ of configuration parameters that can be reused and applied to multiple node models.
Urban Developer should not be confused with MUSIC (Section 14.3.1) or any other specialised water quality modelling program. Urban Developer considers all elements of the urban water cycle (stormwater, wastewater and potable water) and assists in considering potential management strategies including reuse, alternative supply options and water efficient appliances(Feilin, 2012). It is a useful tool for assisting in the conceptual design of a development. The software is able to analyse the inter-relationships between all the streams of the water cycle and compare conceptual designs against legislative requirements or design targets. The model has support, and is being developed on an on-going basis in order to improve its capabilities of assisting stakeholders to understand the costs and benefits of integrated urban water management. It promises to become, if it is not already, the most advanced modelling tool for managing the urban water cycle at a local to regional scale.
WaterCress (Water Community Resource Evaluation and Simulation System) is a free-to-download model that was developed to analyse the feasibility of conventional and alternative water supply options (Clark et al., 2002; Cresswell et al., 2011; Last, 2010; Mitchell & Diaper, 2005).
WaterCress is a continuous time series, total water cycle model, which simulates the passage of flows through natural and constructed water systems. The model provides statistics on the flows and storages within the water system over the period of modelling, thus providing information on the performance of the system against desired outcomes or against alternative system layouts. It works on similar principles to Aquacycle / UQV and analyses the movement of water volumetrically (Last, 2010; Mitchell et al., 2007). WaterCress is more flexible and may be used up to river basin scale (Last, 2010). This allows the model to consider the whole catchment and better represent a catchment’s boundary conditions. WaterCress’s indicators in this regard are (Last, 2010):
- Reliability of water supply.
- Water quality.
- Average cost.
The Stockholm Environment Institute (SEI) developed the Water Evaluation And Planning system (WEAP) (Mitchell et al., 2007; Rodrigo et al., 2012; Sieber & Purkey, 2011). WEAP is a “GIS-based tool for integrated water resources planning that operates on the basic principle of water balance accounting” (Mitchell et al., 2007).
WEAP operates as a water balance model and can be used to model systems from municipal to agricultural and single sub-basins to complex river systems (Sieber & Purkey, 2011). WEAP is capable of modelling the implementation of the full range of WSUD technologies. A recent study for the USEPA demonstrated its applicability in a study entitled “Total Water Management” (Rodrigo et al., 2012). Rodrigo et al. (2012) used WEAP to model the city of Los Angeles, USA and demonstrated the benefits of a total water management approach.
WEAP has a range of capabilities and can address a wide range of issues including “sectoral demand analyses, water conservation, water rights and allocation priorities, groundwater and streamflow simulations, reservoir operations, hydropower generation and energy demands, pollution tracking, ecosystem requirements, and project benefit-cost analyses” (Sieber & Purkey, 2011).