An Integrated Framework of Green Stormwater Infrastructure Planning—A Review

Conventional stormwater management infrastructures show low levels of sustainability owing to the consistent impact of urbanization and climate change, and the green stormwater infrastructure (GSI) has been identified as a more sustainable alternative approach. According to a systematic review, the articles and papers concerning GSI planning are fragmented, especially those discussing the planning steps; thus, an integrated framework of GSI planning is developed here to guide forthcoming planning. In the facility aspect, the research status and prospects of four critical planning steps (i.e., objective formulation, type/scenario evaluation, quantity/scale determination, and site selection) are discussed, and a method of quantifying the relationship between GSI and ecosystem services is given. In the ecosystem aspect, ecosystem resilience promotion is regarded as an approach to guarantee the interaction between hydrological processes and ecological processes, which maintains the sustainable provision of ecosystem services produced by GSI in diverse disturbances. Proposals for future GSI planning research are put forward as comprehensive consideration of the two abovementioned aspects to harvest ecosystem services from GSI directly and to promote the anti-disturbance ability of the ecosystem to guarantee the stable provision of ecosystem services indirectly, which are conducive to the social, economic, and environmental sustainability of GSI.

Rapid Assessment and Long-Term Monitoring of Green Stormwater Infrastructure with Citizen Scientists

Green stormwater infrastructure (GSI) has emerged as a promising decentralized management approach to urban stormwater challenges. A lack of data about GSI performance interferes with widespread adoption of GSI. A citizen science program that benefits researchers, lay scientists, and municipalities offers a way to provide these lacking data. We have developed an open-source, transferable green infrastructure rapid assessment (GIRA) protocol for studying the performance of GSI with citizen scientists. This protocol has been tested in six North American cities (New York City, Toronto, Vancouver, Chicago, San Francisco, and Buffalo). In this research we define the performance of GSI in varying geographic, climatic, and maintenance conditions with the intent to create technological, institutional, and management solutions to urban stormwater problems. The GIRA protocol was used by citizen scientists to assess the physical properties and capabilities of bioswales, while small, affordable Green Infrastructure Sensors Boxes (GIBoxes) were used to determine longer-term function across several rain events. Our results indicate that teams of citizen scientists can be effective for collecting and archiving widespread information on the post-installation function of GSI. The effort also showed that citizen scientists had changes in understanding of urban stormwater challenges and the role that GSI can play in solving these problems. We explore the multiple benefits to knowledge, participants, and municipal partners as a result of this research.

How much water can bioretention retain, and where does it go?

Bioretention is a type of green stormwater infrastructure for the urban environment that mimics a natural hydrologic system by reducing peak flows and runoff volumes and encouraging infiltration and evapotranspiration. This study examines the complete water balance of a bioretention system located in Vaughan, Ontario, Canada, between 2018 and 2019. The water balance was further broken down by event size, where the event size was determined by rainfall frequency analysis. Recharge was the largest component of the water balance overall (86 % of inflow), as well as by event size. Evapotranspiration was the next largest water balance component (7 % of inflow overall), and was a significant component of inflow (21 %) when considering only small events (50 % probability of recurrence). Evapotranspiration is a slow but consistent process, averaging 2.3 mm/day overall and 2.9 mm/day during the growing season. Climate change is likely to bring more wet days and higher temperatures, which will impact the bioretention water balance by increasing evapotranspiration and inflow. Design standards for retention targets should be updated based on the most recent rainfall frequency analyses to adjust for changing climate conditions.

Impact of Green Stormwater Infrastructure Age and Type on Water Quality

Green stormwater infrastructure (GSI) has become increasingly common to mitigate urban stormwater runoff. However, there is limited research on the impact of age and type of GSI. This study evaluated nutrient and metals concentrations in the soil water of five different GSI systems located at the University of Portland in Portland, Oregon. The GSI systems included a bioretention curb extension (part of Portland’s Green Street project), a bioretention basin, a bioretention planter, an infiltration basin, and a bioswale ranging in age from 2 to 11 years. Samples were taken from each system during rain events over a 10-month period and analyzed for copper (Cu), zinc (Zn), phosphate (PO43−), and total phosphorus (TP). Copper and zinc concentrations were found to be impacted by GSI age, with lower concentrations in older systems. The same trend was not found with PO43− and TP, where almost all GSI systems had soil water concentrations much higher than average stormwater concentrations. Age likely played a role in phosphorus soil water concentrations, but other factors such as sources had a stronger influence. Phosphorus is likely coming from the compost in the soil mix in addition to other sources in runoff. This study shows that GSI systems can be effective for copper and zinc, but changes to the soil mix design are needed to reduce high levels of PO43− and TP in soil water.