Green Roof: Performance

TSS Reduction

The performance results for Rainwater harvesting practices, located within TRCA's watershed originate from two sites:

• Kortright Green Roof (Vaughan)
• York University (North York)

The mean performance value recorded at each of the green roof facilities, was to measure their ability to remove Total Suspended Sediments (TSS), which was calculated based on 24 separate recordings from 2003-2004, and 2008 at both of the aforementioned locations listed above.

As can be seen in the corresponding boxplot the mean performance removal efficiency of the rainwater cistern practices monitored are well below the suggested guideline of 30 mg/L (Canadian Water Quality Guideline (CWQG), or (background (assumed at <5 mg/L)+ 25 mg/L for short term (<24 hour) exposure) (CCME, 2002; (TRCA, 2021).

The median value of the 24 samples taken was 1.25 mg/L whereas the mean was 2.80 mg/L, with a 0% guideline exceedance.

Phosphorus Reduction

The performance results for Rainwater harvesting practices, located within TRCA's watershed originate from two sites:

• Kortright Green Roof (Vaughan)
• York University (North York)

The mean performance value recorded at each of the green roof facilities, was to measure their ability to remove Total Phosphorus (TP), which was calculated based on 24 separate recordings from 2003-2004, and 2008 at both of the aforementioned locations listed above.

As can be seen in the corresponding boxplot, the mean performance removal efficiency of the green roof practices monitored is not meeting the acceptable upper extent range of nutrients as it is 0.03 mg/L (30 µg/L) (Environment Canada, 2004; OMOEE, 1994).

The median value of the 24 samples taken was 0.19 mg/L whereas the mean was 0.30 mg/L, with a 100% guideline exceedance. Given the small sample size of just 24 grab samples further monitoring projects will be required to ensure that the results collected are as accurate as possible to ensure these practices can meet federal and provincial governments' guideline requirements for TP stormwater quality. These results were the highest of all practices monitored.

Please refer to the Phosphorus page and the additives page for more information on how LIDs can reduce contaminant loading in stormwater

Recent Performance Research

• (O'Hogain et al. 2012) - Physicochemical and microbiological quality of harvested rainwater from an agricultural installation in Ireland
  • This research study conducted by the Dublin Institute of Technology was commissioned by the federal government to assess the feasibility of utilizing rainwater to replace treated mains for non-potable uses (bathing, irrigation, etc.) on an agricultural property. Two different rainwater harvesting configurations were developed and the results collected over a 1-year period found that median TSS levels were 3.0 mg/L for configuration 1 and 3.5 mg/L for configuration 2. The only parameter that did not comply with local drinking water regulations were the levels of iron, lead and ammonia collected in the cistern of configuration 1 and just ammonia for configuration 2 (O'Hogain et al. 2012).

Schematic drawing of a RWH system with larger capacity for residential or commercial usage. In this schematic pre-storage filtration is used to prevent excess sedimentation, leaves and detritus from entering the system. A piping network delivers water to the tank and a first flush diverter can be installed to diver the first 1-3 mm away from the storage container and be deposited as overland flow, preserving the quality of water for later use (DeBusk and Hunt, 2014.

Total suspended solids

Toronto and Region Conservation Authority

A thin layer of vegetation and growing medium installed on top of a conventional flat or sloped roof, also referred to as living roofs or rooftop gardens.

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

Tank used to store rainwater (typically roof runoff) for later use.

Total phosphorus

Refers to the conditions in which an organism lives and survives or the conditions in which an organism resides. These conditions can be described as aspects of a “physical”, “social” or an “economic” environment, depending on the perspective perceived by the observer.

The total mass of a pollutant entering a waterbody over a defined time period.

The net amount of something (e.g. chemical, such as phosphorus), calculated as the product of concentration and volume in a given time. Some BMPs significantly reduce loading of pollutants to the environment by reducing volume more so than concentration.

Surface runoff from at-grade surfaces, resulting from rain or snowmelt events.

Human application of water to agricultural or recreational land for watering purposes. City of Toronto Wet Weather Flow Management November 2006 47

The practice of intercepting, conveying and storing rainwater for future use. Captured rainwater is typically used for outdoor non-potable water uses such as irrigation, or in the building to flush toilets.

Rainwater harvesting.

The technique of removing pollutants from runoff as it infiltrates through the soil.

Deposition of material of varying size, both mineral and organic away from its site of origin by the action of water, wind, gravity or ice.

Settling-out or deposition of particulate matter suspended in runoff.

The delivery of a disproportionately large load of pollutants during the early part of storms due to the rapid runoff of accumulated pollutants. The first flush of runoff has been defined several ways (e.g., 10 mm per impervious area).

Initial pulse of stormwater runoff which picks up the pollutants that have settled on surfaces during the dry period. The first flush contains the highest pollutant concentrations.

Open space floodway channels, road reserves, pavement expanses and other flow paths that convey flows typically in excess of the capacity of the Minor Drainage System.

A biological community, including humans and their natural environment.

The practice of intercepting, conveying and storing rainwater for future use. Captured rainwater is typically used for outdoor non-potable water uses such as irrigation, or in the building to flush toilets.