With city growth, the development of vacant or under-used land parcels is becoming more common compared to the past. The current ‘water-sensitive urban design (WSUD)’ approach to such development will improve resource efficiency, liveability, and the amenity of cities, especially natural water systems. However, there is a need to quantify the water performance of site-scale WSUD options, especially about how these options impact the ‘natural’ and ‘anthropogenic’ flows in the urban water cycle. This study reviewed research about site-scale applications, summarizing the urban water cycle studies from before development to after development. Key findings (i) include very big margin was quantified by (a) water retention (30–100%) and (b) portable water demand reduction (18–100%) for selected site-scale WSUD options through six research studies; (ii) still unclear about the selected site-scale WSUD options’ interaction performance in the urban water cycle between each water accounts, and (iii) need to clarify the site-scale WSUD option's contribution under specific rainfall scenarios. In summary, this study aims to review the literature on the urban water cycle; review the effects of site-scale WSUD options in the urban water cycle; review the water mass balance and relevant evaluation application, and highlight the opportunities for the future urban water cycle studies.

  • Reviews the literature on the urban water cycle, including before development, after development, and after development with WSUD.

  • Reviews the effects of site-scale WSUD options in the urban water cycle.

  • Reviews the water mass balance and relevant evaluation application.

  • Highlights the opportunities for future urban water cycle studies.

Graphical Abstract

Graphical Abstract
Graphical Abstract

The population growth and the movement of people from rural to urban areas cause land-use changes in the form of urbanization (Fletcher et al. 2015). The urbanization process replaced large areas of natural ground with impervious surfaces, such as roofs, roads, parking lots, and footpaths in the urbanized landscape. These activities lead to a massive and comprehensive change to the hydrological system across a range of spatial scales in the urban water cycle, including catchment-scale (city, street, and cross-street levels) and site-scale (householder level). For example, stormwater runoff and sedimentation have had a rapid increase with urbanization (Meyer & Turner 1992; Booth & Jackson 2007; Novotny et al. 2010). Increased stormwater runoff has directly affected a wide range of pressures, such as a crisis of water quality (Astaraie-Imani et al. 2012), sedimentation and erosion issues (Nie et al. 2011), risk of flooding (Wahl & Plant 2015; Raadgever & Hegger 2018), waterborne diseases (Hunter et al. 2001), pollution of underground water (Lenny et al. 2011), aquatic species issues (Quattro et al. 2002), and acidification of water bodies (Grunewald & Schoenheinz 2014).

In the natural water system, increased impervious surfaces reduce the infiltration and evapotranspiration (Ball et al. 2019), thereby increasing the stormwater runoff (Thom et al. 2020) and changing urban hydrology characteristics greatly. The increased stormwater runoff leads to many flooding issues such as overland flow flooding in the urban area (Maksimović et al. 2010). Overland flow flooding mitigation is a big challenge for all urban planners, which is water that runs across the land after rain, either before it enters a creek or stream, or after rising to the surface naturally from underground (Jain & Singh 2019). Unlike river flooding, overland flow flooding significantly impacted sub-catchments rather than the whole city, which poses a greater hazard to localized areas, but on-site flood mitigation solutions and their functions are unclear (Maksimović et al. 2010). Additionally, in the anthropogenic flow system, the amount of potable water keeps increasing, and many cities are facing high pressure because of the rapid increase in water supply (Commonwealth of Australia 2015). Are there any water management solutions that can mitigate overland flow flooding and reduce the potable water demand within the urban water cycle?

As a broader urban stormwater management framework, water-sensitive urban design (WSUD) is an approach to the planning and design of urban environments that support healthy ecosystems through smart management of water, it manages all water streams as a resource (Fletcher et al. 2013), promotes recycling, and mitigates the impact of urban stormwater through the shift of the landscaped features to solve both water quality (Wong 2015) and water quantity issues (Ball et al. 2019). WSUD has been recognized as an innovative way to restore the natural hydrological cycle, including stormwater runoff and groundwater restoration (Ozgun et al. 2017). The implementations of WSUD involve removing sections of the deteriorated concrete riverbank and undertaking environmental rehabilitation of the riparian zone; introducing more distributed biorientation tanks; and connecting distributed WSUD designs to natural waterways (Chesterfield et al. 2016; Ball et al. 2019). To date, several studies have examined the response of stormwater runoff and potable water demand to city-region scale (Meng et al. 2022) and street-scale (Meng & Kenway 2018) through WSUD, but it is still unclear for the understanding of site-scale landscaped features through WSUD implementations, like rainwater tanks, detention tanks, and green roofs (Li et al. 2019). Furthermore, how do site-scale WSUD options restore the water cycle in the urban catchment, and what is an urban water cycle?

The urban water cycle is the water movement between water accounts in the urban area. In the pre-development phase, the urban water cycle presented the ‘natural’ water flows; in the after development phase, the urban water cycle combined the ‘anthropogenic’ flows with ‘natural’ water flows in the urban water cycle. Figure 1 presents three water mass balance concept models to compare the water account changes under different scenarios: they are before the development model (natural water cycle), after the development model (business as usual), and after development with the WSUD model (the sustainable model with site-scale WSUD options).

Figure 1

Concept model to present water mass balance in (a) before development, (b) after development, and (c) after development with WSUD models. P: precipitation; ET: evapotranspiration; GI: groundwater; Rs: stormwater runoff.

Figure 1

Concept model to present water mass balance in (a) before development, (b) after development, and (c) after development with WSUD models. P: precipitation; ET: evapotranspiration; GI: groundwater; Rs: stormwater runoff.

Close modal

Figure 1(a) shows people to observe the before development phase of the urban water cycle and shows the natural movement of water without human intervention. This first phase consists of three main processes, including evaporation and transpiration – liquid changing to vapour, in the example, evaporation occurs when water in oceans, lakes, and rivers warms and turns into a gas, rising to the air; the second process consists of plants releasing water into the air in a process called transpiration; then there is precipitation – when liquid or solid water falls to earth, which is when the clouds eventually become too heavy and the water falls back to the earth as rain, hail, sleet, or snow; and finally, infiltration, percolation, and runoff – liquid water absorbed into the earth, which is the water that falls to the earth and then flows into waterways (runoff), absorbed into the ground (infiltration) or aquifers and underground water pockets (percolation) (Wong et al. 2013).

The second phase is about after development in the urban area with anthropogenic flows, urbanization disturbs groundwater, and evapotranspiration flows through the sealing of native soils with impervious surfaces and through modifications to the subsoil by constructed drainage and other infrastructure (trenches and excavations, e.g. water supply), and at the same time, stormwater runoff increases (Figure 1(b)). To have a better understanding of the urban water cycle in the city development, Wong et al. (2013) highlighted four main human water streams in the urban water cycle (Figure 1(b) and 1(c)). These streams are dams and water treatment plants, dams are used to capture rain, and the water is cleaned at a water treatment plant before being pumped into underground pipes; water storage, which is the clean water, is stored in water reservoirs and towers until it is needed; stormwater drainage, water runoff from buildings and streets is collected in stormwater drains, where it flows to the ocean; and the last stream, sewage treatment, which is water after you use it, water is piped to a sewage treatment plant to be cleaned and treated and the clean water or effluent is then returned to waterways at the outfall (Wong et al. 2013).

The third phase is the after development with WSUD applications, which is a contemporary approach to the planning and design of urban environments that are ‘sensitive’ to the issues of water sustainability, resilience, and environmental protection (Wong et al. 2013). In this phase, WSUD applications are assisted to reduce runoff and increase evapotranspiration and infiltration to soil profiles (Coombes 2015). Integrated WSUD solutions often meet multiple objectives (such as water supply, stormwater drainage, management of stormwater quality, provision of amenities, and protection of waterways) and are dependent on linked interactions with surrounding infrastructure. Importantly, the limitations of design processes are not always apparent and diligence is required to ensure that substantial problems are avoided (Coombes 2015).

In the after development phase and after development with the WSUD phase (Figure 1(b) and 1(c)), the urban water cycle improves urban water resource management and combined the water-related component systems, such as water supply, treatment, demand, distribution, wastewater collection, surface water and groundwater quality, and quantity control (Figure 1(b) and 1(c)). There are three main aspects in this cycle; the first aspect is the water supply infrastructure to influence the design so that the supply matches the demand (Bach et al. 2014); the second aspect is understanding the influence of urbanization on natural hydrological flow (Haase 2009); and thirdly, water mass balance is recommended as an important tool to assess water performance in the urban water cycle (Mcpherson 1973).

In the past, most urban water cycle models only focused on the quantitative simulation of either anthropogenic water flows or natural water flows for catchment-scale which is a big area, such as city, cross-street, and street levels. For example, Aquacycle and Single-source Urban Evaporatranspiration-interception Scheme (SUES), two of the most common urban water cycle models, only focus on the water cycle for natural flows at a catchment scale. Some other researches only focus on catchment-scale anthropogenic water flows (Peña-Guzmán et al. 2017). Currently, some scholars who started the research concentrate on the input and output of both ‘natural’ and ‘anthropogenic’ flows at the catchment level, but very limited studies focus on water flows at a site level.

When the boundary of the water system and all relevant subsystems have been defined, then the challenge is to quantify water flows into and out of the urban water cycles and also the flow between water-related component systems. The accurate data outcome can develop a fully labelled flowsheet. After the quantification of each flow, a balance of a conserved quantity can be generated (Equation (1)). In this equation, accumulation means the change in storage and this element is the act of building up in the system. Input and output represent the flows entering or leaving the system. Generation and consumption represent the flows produced or consumed within the system.
formula
(1)

The current water management model is focused on local hydrological flow movement in a catchment-scale study. This means that local precipitation, stream, and groundwater are treated as inputs; and the outputs are stormwater runoff, groundwater infiltration, and evapotranspiration. When the water research area is the whole catchment, this system focuses on water movement without considering influences outside of the system, treating the catchment as a whole (Cisakowski et al. 2011). For water movement outside of the system, there is a high probability that it will be impacted by population increases, urbanization, and climate change. For example, an urban area with continued population growth requires more water supplies. However, in most cases, water sources are outside the urban catchment boundary and are not included in the urban water system. Further, urbanization and climate change could introduce extra water flows to the local water cycle, such as flooding and irrigation across the boundary (Cisakowski et al. 2011). So, what is the site-scale WSUD option's function in flood mitigation and water demand reduction?

The term WSUD is commonly used to reflect a new paradigm in the planning and design of urban environments that is ‘sensitive’ to the issues of water sustainability and environmental protection (Nunes et al. 2011). Since the 1990s, WSUD began to be used in Australia, with the first known reference to it in 1992 and then shortly after in a report prepared for the Western Australian Government in 1994 (Fletcher et al. 2015). In the years that immediately followed, the concepts of WSUD were fleshed out through a series of position papers by Wong and others (Lloyd et al. 2002; Wong & Brown 2009). Lloyd et al. (2002) described WSUD as a philosophical approach to urban planning and design that aimed to minimize the hydrological impacts of urban development on the surrounding environment. Stormwater management is a subset of WSUD directed at providing flood control, flow management, water quality improvements, and opportunities to harvest stormwater to supplement mains water for non-potable uses (Lloyd et al. 2002).

WSUD is an integrated method through the better setting and aligning of water issues in urban planning, which includes both site-scale WSUD and catchment-scale WSUD applications. It is not merely to address water issues but also involves water-related economic, social, and governance problems (Wong & Brown 2009; Chesterfield et al. 2016). In this process, retention, infiltration, evapotranspiration, treatment, and harvesting are the main philosophy behind WSUD – minimizing the impact of development on the natural hydrological system in terms of water flow. Generally, catchment-scale WSUD applications are designed to reduce the harm it causes to the rivers and creeks directly, and two common catchment-scale WSUD applications are biofilter systems and constructed wetlands (Zhang et al. 2019). Through the catchment-scale WSUD applications, scholars found that both water quality and the hydrological regime of the urban waterway system have improved, bringing the water cycle closer to its near natural state (Shahzad et al. 2022). Further, researchers highlighted that those larger systems are recommended to ensure reliable performance in pollution reduction, flow frequency mitigation, and reliability as an alternative water supply within the implications of climate change on future rainfall (Zhang et al. 2019).

WSUD options were introduced to the urban water cycle studies as solutions to restore the urban water cycle at a high level, such as artificial wetlands, basins, and swales. However, these catchment-scale WSUD options are not designed to capture minor flows, such as overland flows at the site-scale level. On the site-scale level, there is a high demand to find appropriate WSUD options to capture overland flows because the overland flow excesses rainfall runoff from homes, driveways, and other surfaces that can lead to flooding. Indeed, overland flow flooding can be unpredictable runs across the land after rain, either before it enters a creek or stream, or after rising to the surface naturally from underground. Consequently, overland flow makes more severe damage to the properties if they are located far away from the catchment scale of WSUD sites.

As a solution, site-scale WSUD applications could catch minor flows as they treat and return stormwater into the ground, helping to recharge natural groundwater and stream baseflows in a small area (Moravej et al. 2022; Shahzad et al. 2022). The application of site-scale WSUD would take the local climate into account and restore the natural hydrological cycle; however, most of the site-scale WSUD technologies will not connect with creeks or rivers directly because the linear connection is difficult (Meng & Kenway 2018).

This paper reviews the site-scale WSUD options in the urban water cycle studies; however, there is only limited research to demonstrate and list the impacts on groundwater infiltration and evapotranspiration. To have a more balanced review of the site-scale WSUD options for the urban water cycle, this paper reviewed water retention and potable water demand reduction in the urban water cycle in a quantitative manner (Table 1). Table 1 lists the existing research on main site-scale WSUD options’ performance in water retention and potable water demand reduction. These site-scale WSUD options include rainwater reuse and detention, green roof, horticulture garden, grasscrete, and linear park (Kuller et al. 2017; Meng & Kenway 2018).

Table 1

Overview of WSUD options and their functions (based on Kuller et al. (2017); Meng & Kenway (2018)) in a quantitative manner to compare how much change in water retention and potable water demand reduction caused by site-scale WSUD options

DetentionGIETWater retentionTreatmentHarvestingPotable water demand reduction
Rainwater tank N/A N/A N/A N/A N/A ✓ 34–92% (Sharma et al. 2015
Detention tank ✓ N/A N/A N/A N/A N/A N/A 
Green roof ✓ N/A ✓ 53–99% (Verbeeck et al. 2014)
58–98% (Whittinghill et al. 2014)
55–88% (Shafique 2018
✓ ✓ 18–22% (Alamdari et al. 2018
Horticulture garden ✓ N/A ✓ 100% (Verbeeck et al. 2014✓ N/A N/A 
Grasscrete ✓ N/A ✓ 50% (Verbeeck et al. 2014✓ N/A N/A 
Linear park ✓ ✓ ✓ 30–83% (Ngo et al. 2016✓ N/A N/A 
DetentionGIETWater retentionTreatmentHarvestingPotable water demand reduction
Rainwater tank N/A N/A N/A N/A N/A ✓ 34–92% (Sharma et al. 2015
Detention tank ✓ N/A N/A N/A N/A N/A N/A 
Green roof ✓ N/A ✓ 53–99% (Verbeeck et al. 2014)
58–98% (Whittinghill et al. 2014)
55–88% (Shafique 2018
✓ ✓ 18–22% (Alamdari et al. 2018
Horticulture garden ✓ N/A ✓ 100% (Verbeeck et al. 2014✓ N/A N/A 
Grasscrete ✓ N/A ✓ 50% (Verbeeck et al. 2014✓ N/A N/A 
Linear park ✓ ✓ ✓ 30–83% (Ngo et al. 2016✓ N/A N/A 

The first option analyzed in site-scale WSUD is rainwater reuse (Figure 2). Rainwater tank systems have been used as local harvesting and water supply source in many areas (Memon & Ward 2015; eWater 2016). In recent times, rainwater harvesting systems have become an important water supply source in urban areas where water supply systems are not sustainable. Harvested rainwater can also provide an ‘improved’ drinking water source in urban and peri-urban areas of developing countries where surface water can be contaminated by faecal pathogens, and/or good quality groundwater is not readily available (Sharma et al. 2015). An analysis of 62 cities in Southern Brazil indicated that rainwater harvesting could potentially reduce potable water demand by 34–92%. However, this analysis did not consider the seasonality of demand, or the dynamics of roof runoff volume, available storage volume, and demand (Sharma et al. 2015). Unharvested rainwater has led to much overland flow flooding in the past. More rainwater tanks provide high stormwater harvesting capacity and reduce more potable water demand.

Figure 2

(a) New residential dwelling with rainwater tanks, (b) linear park/garden with WSUD functions, (c) new building with stormwater detention tank, (d) horticulture garden, (e) green roof, and (f) green fence. The figure is adapted from Meng & Kenway's research in 2018 (Meng & Kenway 2018).

Figure 2

(a) New residential dwelling with rainwater tanks, (b) linear park/garden with WSUD functions, (c) new building with stormwater detention tank, (d) horticulture garden, (e) green roof, and (f) green fence. The figure is adapted from Meng & Kenway's research in 2018 (Meng & Kenway 2018).

Close modal

The stormwater detention tank has also been proposed as an alternative stormwater management option that aims to slow down the rain off from high imperviousness areas to the pipeline system under the streets (Figure 2). In newer areas, the stormwater drains have been engineered to allow for rainwater runoff from the whole street. In some older areas, with the number of dwellings per street rising, the urban development places extra pressure on infrastructure, and water authorities often require detention systems to alleviate this. However, it is unclear of the performance of detention tanks in overland flow flooding and the urban water cycle.

The third selection for future urban planning is the green roof option (Imteaz et al. 2011) (Figure 2). Researchers from Europe and Australia have identified that green roofs can reduce rainwater runoff in the urbanized area (Mentens et al. 2006; Victorian Government 2014). In fact, the green roof not only affects stormwater runoff, maximum thermal insulation, and supplies more biodiversity space but also has social and economic benefits, i.e., some green roofs can be planted with edible food (Vanwoert et al. 2005; Feng et al. 2016). In most green roof projects, the grass roof can be chosen to replace more traditional roofs due to lower requirements for building structures.

Two water retention studies have shown that water retention from the green roof option is 53–99% in Verbeeck's research and 58–98% in Whittinghill's research (Verbeeck et al. 2014; Whittinghill et al. 2014). In Whittinghill's research, stormwater retention (%) of extensive green roofs vegetated with a mix of Sedum species, a native prairie mix, and a fertilized vegetable and herb garden for light, medium, and heavy precipitation events from the growing seasons of 2009–2011 and the number of observations for each green roof treatment and rain event size combination from total 12 plots (Whittinghill et al. 2014). Further, Shafique (2018) summarized that the water retention (%) from the green roofs ranges from 55 to 88% to verify the previous research in 2014, which is based on seven studies about the green roof's hydrological performance in different regions all around the world, including Sweden, Germany, USA, Italy, China, and the UK. As for potable water demand reduction about the green roof, Alamdari et al. (2018) found that in some places, the runoff capture might decrease to as low as 12% while the water supply reliability would fall to 18%. However, it was also estimated that parts of the regions would experience a lift in reliability as high as 22% in terms of water supply.

The fourth site-scale WSUD option is the horticulture garden, which is another excellent option for water detention that can be used in urban development (Figure 2). Researchers have emphasized that urban development, such as large-area car parks and driveways, leads to stormwater runoff and pollution loads for natural water systems (Nichols et al. 2015).

The WSUD grasscrete option is the fifth site-scale WSUD option to be reviewed in this paper, and it is a green alternative to concrete outdoor surfaces, such as an amenity area in the residential dwelling backyard (Figure 2). Researchers found that permeable material can help increase infiltration performance at an affordable price (Huang et al. 2013). Indeed, grasscrete can be selected to replace traditional solid surfaces in the amenity area in the selected urban development area.

Linear parks can be implemented to connect the previous site-scale WSUD options. It includes subtropical boulevards and neighbourhood shadeways in the urban area (Meng & Kenway 2018). This option transmitted parts of traffic lanes to the ‘natural’ level linear park to connect with drainage systems and waterways in the urban area. A Korean case study showed that with the presence of a list of the linear park in an upstream river, the flood peak downstream decreases by 30–83%, corresponding to two scenarios of rainfall duration with a return period of 1 in 100 years (1% Annual Exceedance Probability (AEP)) (Ngo et al. 2016).

Overall, these site-scale WSUD applications can reduce the volume and peak flow; increase evapotranspiration and infiltration; decrease imperviousness ratio; improve stormwater runoff quality; convert some pollutants into inert substances; add to neighbourhood aesthetics; improve land value; recover biodiversity; and supply an alternative and local water source (Payne et al. 2015; Meng & Kenway 2018). Among these six site-scale WSUD options, there is no single option that can reduce both stormwater runoff and potable water demand at the same time. It requires applying more than one site-scale WSUD option to achieve a multifunction design target in the stormwater management project. Indeed, Figures 1 and 2 demonstrate an overview of site-scale WSUD options in the urban water cycle and how these options shift the water flows between each water account, but researchers still need a quantitative tool to calculate the water account changes in and out of the urban water cycle.

Water mass balance is an equation to describe the water flows into and out of the urban water cycle (Figure 2). During the early-stage studies of the urban water cycle, the equation represents the sum that the water inflows equal to water outflows (the change in storage). In fact, there are two different opinions on water mass balance establishment. The first approach can be applied to the water supply infrastructure to inform the designers so that the supply matches the demand (Bach et al. 2014). The second approach concentrates on hydrological catchments to understand the influence of urbanization on natural hydrological flow (Haase 2009). Based on these two opinions, Kenway et al. (2011) developed the urban water system to study ‘anthropogenic’ and ‘natural’ flows at the same time and highlighted that water resource management needs to treat ‘cities as catchments’ (Equation (4) and Table 2).

Table 2

Urban water cycle analysis through the water mass balance tool

EquationsDefinitionsNatural hydrological flowsAnthropogenic flowsWSUD effects
Equation (2)  (Meng et al. 2022✓ ✓ 
Equation (3)  (Meng et al. 2022✓ ✓ 
Equation (4)  (Renouf et al. 2018✓ ✓ ✓ 
EquationsDefinitionsNatural hydrological flowsAnthropogenic flowsWSUD effects
Equation (2)  (Meng et al. 2022✓ ✓ 
Equation (3)  (Meng et al. 2022✓ ✓ 
Equation (4)  (Renouf et al. 2018✓ ✓ ✓ 

P is unharvested precipitation falling in the urban boundary, i.e. total precipitation less any rainwater or stormwater harvested within the urban system area. C is total centralized (external) water supplies, which include surface waters (Cs), groundwater (Cg), and desalinated water (Cd). D is total decentralized (internal) water supplies harvested from within the urban system area, which includes harvested precipitation (rainwater) (Dp) and harvested surface water runoff (Ds), and bore water (Dg). ET is evapotranspiration, which includes transpiration from plants and evaporation from surfaces. Rs is the runoff of surface water/stormwater discharged from the urban system areas (not including that which is harvested). WW is wastewater discharged from the urban system areas (total wastewater generated less than which is recycled). GI is infiltration into groundwater. Re is reuse/recycling of wastewater and ΔS is the change in the stored water within the defined urban system (Renouf et al. 2018; Meng et al. 2022).

This new water mass balance framework aims to: (1) aid resource managers to have a better understanding of the hydrological performance for all water account movements in urban water systems; (2) provide a conceptual model to quantify water storage in each account in order to determine water resource reallocation; (3) identify and quantify the new water flows from within the urban water system, such as wastewater recycling, rainwater, and stormwater reuse; (4) assist water cycle managers and urban planners to simulate hydrological performance under different scenarios in the urban water environment (Kenway et al. 2011).

Furthermore, Kenway et al. (2011) and Renouf et al. (2018) have developed an urban water system evaluation framework, which is founded on a water mass balance, to assist urban planners and water managers to have improved systematic analysis. Through this evaluation framework, Meng & Kenway (2018) proved that site-scale WSUD options can decrease stormwater runoff and assist to bring the hydrological flows back to a ‘natural’ level. Recently, a catchment in Sydney, Australia, with over 1,000 ha was used for demonstration purposes of WSUD in restoring the natural hydrological cycle (Meng et al. 2022). The performance of site-scale WSUD in stormwater management, evapotranspiration, and infiltration was evaluated through water mass balance models on a long timeline and was further assessed under three rainfall scenarios. The results obtained provided a comprehensive evaluation and understanding of site-scale WSUD in a catchment-level application for future development (Meng et al. 2022).

As a model based on the processed description, water mass balance models represent the physical processes observed in the real world (Elliott & Trowsdale 2007). Typically, water mass balance models contain parameters such as stormwater runoff, subsurface flow, evapotranspiration, and channel flow (Elliott & Trowsdale 2007). Water mass balance follows Equation (2) to describe the water that flows into and out of the system. From a hydrological perspective, it represents the sum of water inflow equalling water outflow and the change in this urban hydrological cycle.

In recent studies, the shift of water mass balance was influenced by an impervious fraction change in related WSUD projects (Meng & Kenway 2018). Thus, a modified water balance model was established to link simplified representations of the hydrological processes relative to the catchment (Equation (2)). Equation (3) was established based on Equation (2) without any change in stored water (ΔS), including both impervious and pervious lands, rainfall coming into the system and evapotranspiration, runoff, and infiltration going out of the stormwater system. This modified water balance model simply treated a catchment without any extra water input or water stored in that area (Table 2). Further, scholars brought the estimates of anthropogenic and natural flows together into the urban water mass balance (Equation (4)) (Renouf et al. 2018) using the method described in the original framework of Farooqui et al. (2016) (Table 2). The aim was to achieve a mass balance, such that total inflows equal total outflows, plus any changes in storage, thereby ensuring a comprehensive and accurate account (Equation (4)). Changes in storage were assumed to be zero (Equation (3)). In this context, storage refers to soil moisture and water stored in reservoirs within the urban system. This means no changes in storage (assuming there are stable climatic conditions) and no influence on this stored water. Previous research has shown that WSUD can reduce stormwater runoff in the urban water cycle and help to recover the hydrological cycle (Meng & Kenway 2018; Meng et al. 2022). However, it is unclear about the site-scale WSUD options in the overland flow flooding control in the urban water cycle.

After analysis, within appropriate site-scale WSUD options, scholars highlighted that WSUD technologies can restore natural hydrological flow and reduce potable water demand (Meng & Kenway 2018; Moravej et al. 2022). For example, distributed infiltration systems can benefit downstream water bodies by reducing the runoff flow rate and volume discharges from the catchment (Shahzad et al. 2022). Furthermore, the infiltration decreased by 34% (Moravej et al. 2022) and 62% (Meng & Kenway 2018) in variable cases, and the infiltration deduction decreased by 17% in Moravej's study (Moravej et al. 2022) and decreased by 49% in Meng's research (Meng & Kenway 2018). Next, scholars developed relevant assessment frameworks to evaluate water accounts’ performance in the urban water cycle.

Water performance indicators are the key part to assess water mass balance data through an evaluation framework. In the conventional urban water evaluation framework, water technologies are commonly considered after the urban form has been designed. This overlooks the interactions between urban design and urban water systems and the potential that can be unlocked by better integrating the two. However, it needs to be supported by quantitative evidence of the water performance of design–technology configurations (Moravej et al. 2022).

Table 3 lists some main water performance evaluation methods in the urban water cycle, and they can be used to assess the potable water demand, water consumption, natural water accounts movement, and relationships between natural and anthropogenic flows, such as stormwater reuse and greywater recycling (Martinez et al. 2010; Meng & Kenway 2018; Moravej et al. 2022). The current site-scale urban water cycle studies did not fit the gap between the current water mass balance frameworks (Figure 1) and water performance evaluation methods listed (Table 3), as most of the research is aimed at the catchment scale. Nevertheless, there are no relevant studies that can examine the water movements in each site-scale WSUD option through the water mass balance analysis and evaluation framework.

Table 3

Examples of indicators used to describe the site-scale WSUD performance of urban water cycles

SourceIndicatorsDefinitions
Green City Index (EIU 2011Water use per capita Domestic water consumption per capita (liters/person/day). 
Water system leakages The proportion of water lost in the water distribution system. 
Water quality policy Measurements about cities’ policy towards improving the quality of water (surface and centralized water supply). 
Water sustainability policy Measurements about cities’ efforts to manage water management more efficiently. 
City Blueprint (Leeuwen et al. 2012Total water footprint The total volume of freshwater that is used to produce the goods consumed by the society. 
Water scarcity The ratio of total water footprint to total renewable water resources. 
Water self-sufficiency The ratio of the internal use to the total water footprint. A higher percentage indicates more water demand is sourced locally. 
Water system leakages The proportion of water lost in the distribution system. 
Water efficiency Assessment of the comprehensiveness of measures to improve the efficiency of water usage. 
Consumption Domestic water consumption per capita (litres/person/day). 
Attractiveness (amenity) Water used for landscape maintenance as measured by community sentiment in an urban area. 
Asian Water Development Outlook (ADB 2016Household water security The sanitation needs at the household level. 
Urban water security Status of urban water-related services in cities, towns and other urban areas. 
Economic water security Water to be used in economic sectors for sustainable development. 
Urban water metabolism evaluation framework – city scale (Renouf et al. 2018Urban water efficiency per person Domestic water consumption per person. 
Urban water efficiency per unit of functionality Domestic water consumption per unit of urban function. 
Water-related energy efficiency per person Total energy use for the water system per person. 
Water-related energy efficiency per unit of functionality Total energy use for the water system per unit of functionality. 
Nutrient recovery from urban water The proportion of the nutrient load in wastewater that is beneficially used. 
Water supply internalization The proportion of internally harvested/recycled water in total water demand. 
Water use within a safe operating space The rate of centralized water relative to the sustainable urban water allocation. 
Water pollutant load within safe operating space Point-source and diffuse nutrient loads are discharged to surface and ground waters relative to sustainable discharge rates. 
Supporting diverse functions Water is needed to maintain desired functions relative to the water budget for the functions. 
Urban water mass balance assessment – site scale (Moravej et al. 2020)a Hydrological naturalness Hydrological flows of the urban system have changed. 
Imported water use per capita Reliance of the assessed urban system on water mains. 
Water self-sufficiency Reliance of the assessed urban system on water mains. 
Area–pipeline–policy method (natural) (Meng et al. 2022WSUD treatment area The landowner type, topography background, and soil type. 
Suitable to connect with the existing stormwater pipeline network Stormwater pipeline type, stormwater pipeline capacity, and inlet and outlet levels of the connecting point in the pipeline network. 
Support from the local community and government Community engagement; local councils have a policy and financial support. 
SourceIndicatorsDefinitions
Green City Index (EIU 2011Water use per capita Domestic water consumption per capita (liters/person/day). 
Water system leakages The proportion of water lost in the water distribution system. 
Water quality policy Measurements about cities’ policy towards improving the quality of water (surface and centralized water supply). 
Water sustainability policy Measurements about cities’ efforts to manage water management more efficiently. 
City Blueprint (Leeuwen et al. 2012Total water footprint The total volume of freshwater that is used to produce the goods consumed by the society. 
Water scarcity The ratio of total water footprint to total renewable water resources. 
Water self-sufficiency The ratio of the internal use to the total water footprint. A higher percentage indicates more water demand is sourced locally. 
Water system leakages The proportion of water lost in the distribution system. 
Water efficiency Assessment of the comprehensiveness of measures to improve the efficiency of water usage. 
Consumption Domestic water consumption per capita (litres/person/day). 
Attractiveness (amenity) Water used for landscape maintenance as measured by community sentiment in an urban area. 
Asian Water Development Outlook (ADB 2016Household water security The sanitation needs at the household level. 
Urban water security Status of urban water-related services in cities, towns and other urban areas. 
Economic water security Water to be used in economic sectors for sustainable development. 
Urban water metabolism evaluation framework – city scale (Renouf et al. 2018Urban water efficiency per person Domestic water consumption per person. 
Urban water efficiency per unit of functionality Domestic water consumption per unit of urban function. 
Water-related energy efficiency per person Total energy use for the water system per person. 
Water-related energy efficiency per unit of functionality Total energy use for the water system per unit of functionality. 
Nutrient recovery from urban water The proportion of the nutrient load in wastewater that is beneficially used. 
Water supply internalization The proportion of internally harvested/recycled water in total water demand. 
Water use within a safe operating space The rate of centralized water relative to the sustainable urban water allocation. 
Water pollutant load within safe operating space Point-source and diffuse nutrient loads are discharged to surface and ground waters relative to sustainable discharge rates. 
Supporting diverse functions Water is needed to maintain desired functions relative to the water budget for the functions. 
Urban water mass balance assessment – site scale (Moravej et al. 2020)a Hydrological naturalness Hydrological flows of the urban system have changed. 
Imported water use per capita Reliance of the assessed urban system on water mains. 
Water self-sufficiency Reliance of the assessed urban system on water mains. 
Area–pipeline–policy method (natural) (Meng et al. 2022WSUD treatment area The landowner type, topography background, and soil type. 
Suitable to connect with the existing stormwater pipeline network Stormwater pipeline type, stormwater pipeline capacity, and inlet and outlet levels of the connecting point in the pipeline network. 
Support from the local community and government Community engagement; local councils have a policy and financial support. 

aRest of water performance indicators were based on indicators proposed by Renouf et al. (2018).

The current site-scale WSUD option studies do not account for the effect of these different options on urban water balance accounts, such as the change of stormwater runoff, groundwater infiltration, and evaporation; without a doubt, this is an opportunity for future iterations of the urban water cycle study. Future research could clarify these effects in the real-world environment, especially the interactions between each account and people using them in a collaborative urban design and the planning context are not well understood about how the interaction impacts the overland flow flooding in the different rainfall scenarios.

Future work should focus on the application of site-scale WSUD options in a variety of rainfall scenarios and contexts to further elicit its capacities. Future applications could apply very frequent rainfall events to simultaneously optimize architectural design and technologies to achieve some pre-defined targets through site-scale WSUD options. This would be a multi-objective optimization, maximizing different water performance objectives to check if- and how-, for example, the natural water balance can be achieved. Another research need is the consideration of appropriate season rainfalls in the urban water cycle. For instance, future research may evaluate the performance of the site-scale WSUD options in the urban flood mitigation with certain AEP targets, such as 10% AEP, 1% AEP, and 0.1% AEP. The detention tank is developed from the rainwater tank but with detention purposes. It is recognized to collect, store, and reuse the stormwater but also to mitigate overland flow flooding issues in certain rainfall events (Meng et al. 2022). How will urban planners assess the detention tank's flood mitigation performance with certain rainfall events? To answer the question, the first step is to predicate seasonal rainfalls. These are known to extend hydrological predictions spanning several weeks to months, which can enable proactive planning and adaptive responses. Next, the model can be evaluated in three annual rainfall scenarios (high, average, and low rainfall) to assess the changes in the urban water cycle through the water mass balance model. After that, the research can analyze the flooding information with certain rainfall events. It is necessary to introduce the very wet, average, and very dry scenarios with predicated seasonal rainfall to evaluate flood mitigation performance.

This paper reviewed the development of the urban water cycle and how the site-scale WSUD option interacted with the water cycle. In answer to the research question, this review found that the water performance of design–technology–environment configurations can be partially quantified by (i) water retention and (ii) portable water demand reduction. The site-scale WSUD options have undergone a significant change over the last several decades, moving from a wide range of environmental, sanitary, social, and economic considerations taken into account to an approach focused on both natural hydrological and anthropogenic flows. The profession has thus developed and adopted new models to describe these site-scale WSUD options and is likely to continue to do so, as the transition to a more sustainable and integrated approach occurs. This review has demonstrated that modern tools have evolved in response to restoring water accounts in the urban water cycle.

However, site-scale WSUD, as an integrated water management approach, includes the positive effects on water quality control and water quantity management. Complexities of climate change together with urbanization impacts, which vary spatially and temporally, necessitate the scrutiny of possible adaptation measures in each location, such as overland flow flooding. In such a complex system, future urban planners should focus on identifying factors of site-scale WSUD options impacting on urban water cycle as well as developing location-based adaptation options and practically implementing site-scale WSUD options to minimize the impacts on the urban water cycle.

The author acknowledges Qilin Wang and Long D. Nghiem from the Centre for Technology in Water and Wastewater (CTWW), the University of Technology Sydney for their great support in this project; acknowledges Brooklyn Meng for his proofreading, editing, and great contribution in the project; acknowledges Eric Ruiz from The Hills Shire Council for data collection; and acknowledges Chloe Meng and Chi Zheng's support during the project period.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.

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