Quantifying the volume of water that can be treated or removed over a given time period is needed to efficiently design green stormwater infrastructure. It is recognized that evapotranspiration (ET) can be a substantial pathway for stormwater volume reduction in bioretention systems. However, measuring ET is often difficult and expensive, such as with lysimeters or a mass balance approach. This research explored different ways of approximating ET in green stormwater infrastructure. First, the relationship between stomatal conductance measured with a handheld device and ET was evaluated. Twelve vegetated lysimeters were planted with either Black Chokeberry, Seaside Goldenrod, or Switchgrass during the summer of 2018. Stomatal conductance and the weight of each lysimeter were measured at the beginning and end of each 24-hr data collection period. Fairly strong and statistically significant relationships were observed between evapotranspiration and stomatal conductance in the lysimeters growing Black Chokeberry and Seaside Goldenrod between July 12, 2018 and August 31, 2018 (R2 = 0.76 and 0.51, respectively (n=17)). Some individual lysimeters growing Black Chokeberry and Seaside Goldenrod showed higher correlation during that same period (R2 > 0.75), although the relationship was weak and statistically insignificant for other plants.
This research then explored an approach using thermal imaging to calculate ET by measuring the flux of energy at the canopy surface which was compared to ET measurements given by a traditional mass balance approach. The experimental setup had three benchtop scale vegetated lysimeters planted with Switchgrass. Time lapse thermal images of the Switchgrass plants were taken at 10 second intervals and paired with meteorological data. The data were used in an energy balance to estimate the mass of water lost from the plant/soil system. That mass was compared to the change in weight measured by weighing the plant before and after the data collection period. For comparison, reference ET was also calculated for the vegetated systems using three common reference ET equations. The uncalibrated energy balance equation developed here estimated an averaged ET over 12 data collection days within 1 mm of the mass balance measured ET.
Similar to watershed scale energy balances via satellite thermal imaging, the method derived here could be built upon and used to estimate the water balance and performance of vegetation in green stormwater infrastructure. An energy balance like the one described here may be the only practical way to measure ET in green stormwater infrastructure, and thus, the only way to fully resolve the water balance in these systems. This could have great implications for the design and regulation of green stormwater infrastructure.
|Advisor:||Wadzuk, Bridget M.|
|Commitee:||Traver, Robert G.|
|Department:||Department of Civil & Environmental Engineering|
|School Location:||United States -- Pennsylvania|
|Source:||MAI 82/4(E), Masters Abstracts International|
|Subjects:||Civil engineering, Environmental engineering, Hydrologic sciences|
|Keywords:||Energy, Evapotranspiration, Green, Stormwater, Thermography, Water|
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