WATER SENSITIVE CITIES (WSC) PRINCIPLES

Water Sensitive Cities approaches aim for holistic management of the integrated water cycle. It takes a whole of water cycle approach to water management. All the potential water sources like rainwater/stormwater, water supplies, wastewater, groundwater are not managed in isolation, instead integrated solutions are delivered to provide multiple benefits. Water Sensitive Cities seeks to protect and enhance the health of receiving waterways (e.g. creeks, rivers), reduce flood risk, and create public spaces that harvest, clean, and recycle water.

The Water Sensitive Cities approach advocates that cities should:

Serve as a potential water supply catchment providing a range of different water sources (e.g. water supply, rainwater, recycled water) at a range of different scales (e.g. household, lot, precinct level) and for a range of different uses (e.g. potable, non-potable, gardening) by integrating centralised and decentralised systems.
Provide ecosystem services and a healthy natural environment, thereby offering a range of social, ecological and economic benefits like addressing urban heat island effects.
Consist of water sensitive communities where citizens have the knowledge and desire to make wise choices about water, are actively engaged in decision-making and demonstrate positive behaviour

Water Sensitive Cities interventions such as channel naturalization, bioretention systems, wetlands, constructed waterways, vegetated swales, and retarding basins can be applied at various scales and for a range of benefits. The interventions can also be linked to other EbA options like revegetation, wetland restoration, vegetative control of riverbanks, rainwater harvesting.

Example interventions are described below:

Channel Naturalization or constructed waterway: Channel naturalisation provides an opportunity to replace part of or the entire channel with a natural river form for flood conveyance and to improve aesthetics. It includes removal of the concrete channel and replacement with more natural, vegetated waterway. It provides stormwater treatment, improves flood protection and ecological conditions, and provides a high-quality community asset.

Wetlands: Constructed surface flow wetland systems use enhanced sedimentation, fine filtration and biological uptake processes to remove pollutants from stormwater. Wetland systems can also mitigate flooding and waterlogging by acting as retarding basins. Wetland processes are engaged by slowly passing runoff through heavily vegetated areas where plants filter sediments and pollutants from the water. Biofilms that grow on the plants absorb nutrients and other associated contaminants. In addition to playing an important role in stormwater treatment and waterlogging alleviation, wetlands can also have significant community benefits. They provide habitat for wildlife. They can also improve the aesthetics of new developments and can be a central landscape feature.

Retarding basins: Retarding basins provide temporary storage to retard peak flow rates required for downstream network capacity or to protect natural waterways. Retarding basins are usually designed to attenuate up to the 1% AEP (100-year ARI) flows. Retarding basins can provide both flood control and erosion protection by controlling outlet properties.

Bioretention Systems / Raingardens: Bioretention systems, also known as raingardens, are commonly constructed to meet stormwater quality targets including nitrogen removal but can also mitigate flooding and waterlogging. They are suitable in urban areas and can be implemented at a range of scales. Bioretention systems are vegetated soil filters. Stormwater runoff is treated by draining vertically through a vegetated filter media (typically a sandy loam). Treated stormwater is then collected by a perforated underdrain and directed to the downstream stormwater drainage system.

Pros and cons

Water Sensitive Cities approaches provides environmental benefits as well as social well-being.
Water Sensitive Cities principles consider the whole of water cycle approach and treats all the water source in an integrated manner.
Water Sensitive Cities solutions facilitate social interaction by creating attractive public and private open spaces that can be used for recreation.

Water Sensitive Cities approaches work on cooperation among various government departments and diverse stakeholders which can cause an issue of fragmentation of responsibility.
There is no size fit all approach, the solutions are location specific thus have to be tailored accordingly.

Indicative cost

Water sensitive cities principles implementation can be low to high depending on the interventions adopted. Whilst providing cost estimates is difficult given the broad range of influencing factors across the Pacific, the below table outlines the key components that should be taken into account when estimating a water sensitive cities project budget for a specific location.

Components	Unit (A)	Number of units (B)	Unit Cost (C)	Budget (B x C)
Establishment Cost
Land (if not already held)	e.g. km²
Planning and design including community outreach	e.g hours
Materials (e.g. seeds, plants, biotextiles)	e.g number
Earthworks (if required)	e.g. m³ soil
Labour	e.g. hours
Reporting to donor (if required)	e.g. hours
Ongoing Cost
Maintenance Cost (materials and labour)	e.g. number and hours
Reporting and Monitoring	e.g. hours

Comparison against conventional approaches

Water Sensitive Cities principles of developing and connecting water(blue) and biodiversity(green) infrastructure can be compared against conventional water supply systems that are heavily dependent on infrastructure (e.g. laying of water pipes and setting up of water and wastewater treatment plants)

Conventional water systems tend to incur larger infrastructure and energy costs.
Conventional water systems are built for single use of water supply whilst a Water Sensitive City approach supports human and ecosystem well-being by providing environmental, economic and social benefits.
Conventional water supply systems are centralised whilst Water Sensitive City approaches aim for a mix of centralised, decentralised and fit-for-purpose water supplies.
Conventional water systems adopt a top-down approach whilst Water Sensitive Cities aim to engage communities in sustainable water planning and management.

Resources

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Materials from the Cooperative Research Centre for Water Sensitive Cities. See https://watersensitivecities.org.au/
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Adoption Guidelines for Stormwater Biofiltration Systems Cities as Water Supply Catchments - Sustainable Technologies. See https://watersensitivecities.org.au/wp-content/uploads/2016/09/Adoption_Guidelines_for_Stormwater_Biofiltration_Systems.pdf

Figure References

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1. Water Sensitive Cities Index: A diagnostic tool to assess water sensitivity and guide management actions. See https://www.sciencedirect.com/science/article/pii/S0043135420309465
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2. Constructed Waterways Design Manual: Part D: Technical Design Elements. See constructed_waterway_design_manual_2019-partD (1).pdf
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3. Water Quality Improvement Options for 4 priority catchments in the ACT: Tuggeranong Catchment. See https://www.environment.act.gov.au/__data/assets/pdf_file/0011/1859897/21_42215-ATTACHMENT-B-2.-Document-8-Report.1.pdf
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4. Retarding basins. See https://www.melbournewater.com.au/water-data-and-education/water-facts-and-history/flooding/retarding-basins
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5. Bioretention basins. See https://www.townsville.qld.gov.au/__data/assets/pdf_file/0013/12226/GUIDELINES_5_Bioretention_Basin_FINAL.pdf

On-ground impacts that the EbA option addresses

Decreasing water availability

Poor water quality

Increasing temperatures in urban areas

Increased occurrence of flooding

Case study

Revitalising Informal Settlements and their Environments (RISE)

Suva, Fiji

RISE is a transdisciplinary research program working on health, environment and water and sanitation. The programme is working on new water sensitive approaches to water and sanitation management in 12 informal settlements in Suva, Fiji along with creating a demonstration site. RISE is co-designing location-specific solutions that integrate green infrastructure, such as constructed wetlands and bio-filtration gardens, to reduce pollution in the environment and strengthen the whole-of-life water and sanitation cycle. It uses the approach of working with communities, governments, local leaders and partner institutions.

RISE aims to enable communities in informal settlements to:

Recycle their own wastewater (both blackwater and greywater)
Harvest rainwater
Create green space for water cleansing and food cultivation
Restore natural waterways to encourage diversity; and
Reduce vulnerability to flooding and climate change.

Tamavua-i-Wai, situated at the bottom of the steep hill, was selected as the first demonstration site to showcase RISE’s water sensitive approaches in an informal settlement in the Pacific Region. The demonstration site showcase whole of water sensitive project lifecycle, to address flooding and sanitation issues, not just the infrastructure by building local support and providing proof-of-concept to support replication and scale -up in pacific Island countries. In this site, the community participated in designing, costing, implementation planning, capacity building of households and government heads and operation and maintenance of the system to deliver multiple co-benefits like:

Waste-water treatment from constructed wetlands
Improved water security using rainwater tanks
Treating greywater using biofilters
Improving access to blue and green infrastructure.

Resources: Revitalising Informal Settlements and their Environments (RISE), https://www.rise-program.org/ and RISE, communities seek to influence global investments for informal settlements, https://www.rise-program.org/news/rise,-communities-seek-to-influence-global-investments-for-informal-settlements
https://www.rise-program.org/news/rise,-communities-seek-to-influence-global-investments-for-informal-settlements