Blue and Green Cities: The role of blue-green infrastructure in managing urban water resources
While traditional grey infrastructure systems have, over many decades, proved to be effective in collecting stormwater runoff and draining it from the city, reliance on them has led to numerous unintended negative consequences relating to water quantity and water quality. They include increased peak flows and total discharges from storm events, enhanced delivery of nutrients and toxins degrading aquatic habitats in urban waterways, and Combined sewer overflows (CSOs) during wet conditions, exposing urban populations to health risks from waterborne pathogens and toxins.
Climate change and grey infrastructure
Traditional grey infrastructure used to manage stormwater will be challenged by extreme weather caused by climate change. During wet weather events, heavier storms will mean increased amounts of water and wastewater in combined sewer systems for short periods of time. As such, current designs, based on critical ‘design storms’ defined through analysis of historical precipitation data, need to be modified. Meanwhile, during extended periods of dry weather, soils dry up and shrink, resulting in the cracking of water mains and sewers, making them vulnerable to infiltration and exfiltration of water and wastewater. A combination of high temperatures, increased pollutant concentrations, longer retention times and sedimentation of solids may lead to corrosion of sewers, shorter asset lifetimes, more drinking water pollution and higher maintenance costs.
Faced with climate change and environmental degradation many cities are turning to Blue-Green Infrastructure (BGI) solutions to enhance climate resilience as well as restore the health of ecosystems. BGI is a strategically planned network of natural and semi-natural areas, ranging in size from rain gardens right up to green streets, that are designed and managed to deliver a wide range of environmental, economic, and social benefits including improved water quality.
Multifunctionality of BGI
A key aspect of BGI is its multifunctionality, specifically, its ability to perform several functions and provide several benefits within the same spatial area. This means BGI harnesses the interrelationships between vegetation and the water cycle to improve living conditions in the city. In turn, this enhances both sustainable development and water- and greenery-related ecosystem services. There are multiple benefits of BGI including improved water quality, reduced potential for flooding, reduced infrastructure costs, and increased space for communities and wildlife.
Fiscal tools to encourage BGI
Cities can use fiscal tools to encourage the implementation of BGI practices on both public and private properties as well as new developments and existing developments (retrofits). Fiscal tools are easy to implement and provide decision-makers with the flexibility and creativity to tailor programmes to specific priorities or to geographic areas in a community. This enables a city to focus its resources and programme efforts on a more manageable scale and can provide the opportunity to pilot new incentives to determine the potential for city-wide application. Common fiscal tools include stormwater fees/rates, grants, rebates, and installation finance
Mini case study: LA’s stormwater incentive programme
The Los Angeles Department of Water and Power (LADWP) is developing a stormwater incentive programme for the infiltration and on-site use of stormwater from industrial facilities. Under the stormwater incentive programme, all industrial facilities regulated by the Industry General Permit and within LADWP’s service area/areas of interest will be eligible to participate in the program. The total rebate amounts will be based on yield for each respective facility, with the rebate amount of $1,100/acre foot (AF) for infiltration and $1,550/AF for onsite reuse.
Non-fiscal tools to encourage BGI
Cities can implement a variety of non-fiscal tools – voluntary mechanisms– to encourage the development of BGI on public and private land including new developments and retrofits. As non-fiscal tools are less intrusive than fiscal tools, they create less resistance from stakeholder groups and allow policymakers to test and refine programmes that may one day develop into mandatory requirements Common non-fiscal tools include information and awareness campaigns, fast-tracking of BGI project applications by city agencies, pilot and demonstration projects, and leading by example.
Mini case study: Melbourne Water’s Smart City Model
To raise awareness of the benefits of BGI in managing stormwater quality and surface runoff, Melbourne Water has developed the Water Smart City Model. This model is an educational activity suitable for all ages which can be used at community events and festivals. The activity involves the audience building a model city with roads and buildings made from Lego building blocks. Food dye, representing pollutants, is placed on the city and rainfall is simulated over the model, carrying the pollution over the impervious surfaces and into the ‘bay’. A variety of features including rain gardens, rainwater tanks, swales and rooftop gardens are then added. Pollution is again added to the model and rain simulated. The amount of surface runoff is significantly decreased due to the retention capabilities of the new features, reducing risks of flooding. Pollution is also captured in the features so the water flowing into the ‘bay’ is cleaner.
BGI not only enhances the resilience of cities to climate change but provides multiple economic, social, and environmental benefits. A variety of fiscal and non-fiscal tools can be used to enhance the uptake of BGI on public and private land, including incentives for on-site reuse of stormwater and the educating of the public on the benefits of BGI.
The opinions expressed herein are solely those of the authors and do not necessarily reflect the official views of the GGKP or its Partners.