Green Roofs

Green roofs have been used as a stormwater Best Management Practice (BMP) for more than 20 years in Germany and have been used in the United States for over decade. However, common acceptance of greenroofs as a structural BMP has been slow in many communities. One reason is the lack of published data on their performance, especially in the United States. A recent literature search on greenroofs yields very few published U.S. studies on the water quantity and quality benefits associated with greenroofs, only two of which were conducted in a university setting (Penn State University and North Carolina State University). In both cases, while the greenroofs being evaluated were constructed at full scale, the constructed roofs were small and constructed primarily for research purposes. 

The green roof constructed at Lawrence Tech was designed as a stormwater BMP in a high-density urban environment, which makes performance data critical. There is also a need to conduct research on green roofs at a variety of locations throughout the United States. Regional differences in hydrology, climate, plant material, and background water quality make the transference of results from one region to another questionable. Finally, there are numerous green roof design configurations and data needed to evaluate the effectiveness of different designs. All of these factors indicate the necessity of more research studies on green roof performance.

Research Overview

Project:research at LTU
Green Roof Monitoring and Evaluation

Project Supervisor:
Dr. Donald Carpenter, carpenter@ltu.edu 

Research Assistant:
Preethi Kaluvakolanu,  prityraju@gmail.com

 

Research Goals:

1. Determine the overall percent of precipitation retained and detained by the green roof.
2. Determine the nutrient loading attenuation capabilities of the green roof.
3. Determine the reduction in ambient temperature associated with the green roof.
4. Determine the reduction in stormwater temperature associated with the green roof.
5. Establish long-term monitoring station capable of determining the temporal performance of the green roof. 

 

Scope of Work:

The green roof is monitored to control peak runoff and make use as a best BMP. The research work includes installation of instruments on the roof, collection of rainfall data and monitoring the performance of the green roof. Currently a portion of the entire green roof, measuring 3496 square feet is monitored.

The green roof performance is compared with two other roofs which include an existing rock ballast roof adjacent to the green roof and conventional roof, acting as the control station. The three roofs will be instrumented to allow a comprehensive evaluation of performance. Various sampling instruments, sensors are equipped on the roofs to evaluate the runoff data.

The data received is then analyzed using Flowlink software and all the related calculations regarding the peak flows are calculated and graphs are generated. This process is followed for the three roofs and a comparison is made on the functioning of green roof. Measurements will be taken both on the water quantity and quality benefits associated with green roofs.

Research Equipment

1. Avalanche Samplers:

Avalanche refrigerated sampler from ISCO is furnished with a refrigerated sampler, used for permanent site or portable, sequential, and composite sampling applications. It is capable of collecting samples from a variety of liquid sources and suited to collect priority pollutant or general purpose samples in multiple bottles or a single bottle. We use 14 bottle configuration samplers, 3 installed at the three sites at Lawrence Tech. These were programmed with all the necessary storm water input and then installed at the sites.

ISCO 730 Bubbler Flow Meter measures the pressure needed to force air bubbles out of the line, the water level is accurately determined. The 6700 Series or Avalanche Sampler then converts the level into flow rate. Three flow meters are installed on the three roofs, connected to the flumes and these record the flow in the sampler.

 

 2. ISCO 730 Bubbler Flowmeter:
 
ISCO 730 Bubbler Flowmeter

 

3. ISCO 674 Raingauge:

The rain gauge connects directly to Avalanche Samplers, uses a tipping bucket design for rainfall measurement. It has an 8-inch diameter orifice which is factory-calibrated to tip at either 0.01 inch or 0.1 mm of rainfall. One rain gauge is installed on the roof of the Science building which acts as the control roof. Flowlink 5 software is used for Data Retrieval & Analysis.

 

4. 4" Palmer-Bowlus Flumes:

Palmer-Bowlus Flumes

Three 4" Palmer-Bowlus flumes are installed at the three sites, beneath the roofs, with the help of  Lawrence Technological University's Campus Facilities. The avalanche sampler along with the 730 Bubbler flowmeter are connected using various hose connections as mentioned in the sampler's manual.

 

5. Temperature Sensors:
 
Temperature Sensors

MicroLite is a small data logger for monitoring and recording temperature, it is the ultimate plug and record data logger. MicroLite data is clearly displayed on the logger's numeric screen and the stored MicroLite data can be downloaded automatically to the MicroLab Lite software. Two loggers are used on the green roofs, one on the ballast roof and the fourth one on the black roof that acts as the control site. Data is set to be recorded for every fifteen minutes and it is collected after a considerable number of days.

 

6. Flowlink software:

The software used for the data retrieval and analysis from the green roofs, calculates the flow discharges, generates graphs and monitors the effective functioning of the roofs. All data is stored in an industry-standard Microsoft Access® database, and can be organized based on monitoring projects or geographic location.

 

green roof