OOS 15-1 - Comparing runoff from green roofs planted with native and sedum species in the mid-Atlantic US

A green roof consisting of four individual quadrants was installed and instrumented on the East and West sides of the U.S Botanic Garden Conservatory in Washington, DC in 2019. One quadrant on each side were planted with a traditional Sedum-based community, the other quadrant with a native-based plant community. The objectives of a four-year study (2020-2023) were to (1) install a sensor-based precision irrigation system that would ensure non-stressed soil moisture contents for each community, but not negate the stormwater retention capacity of each quadrant; (2) monitor the performance of each quadrant with a range of soil and environmental sensors, and calculate the daily water for storms of varying sizes; (3) calculate the stormwater retention and performance of each community, and (4) the potential stormwater credits (economic and ecosystem services) for native and Sedum plant communities, based on the average Washington, DC stormwater credit trading prices for each year.

The advanced irrigation control software (Sensorweb™, Mayim LLC, Pittsburgh, PA) allowed for continuous averaging of soil moisture sensor (TEROS-10; Meter-Group, Pullman, WA) data and automated precision control of irrigation events, based on a soil volumetric water content setpoint of 16%. Repeated micro-pulse (180 sec on; 120 sec off) sub-irrigation drip events (if /when needed) maintained adequate soil moisture and plant performance without substantially affecting the overall substrate stormwater capacity. Two weather stations and additional drain gauge sensors in each block allowed for the calculation of daily water balances (rainfall + irrigation water - runoff + plant evapotranspiration, ETc) for each quadrant throughout 2020 and 2021. Total irrigation volumes from May – Oct, 2021 averaged 107.2 L / m2 (10,462L / 97.6 m2) for native vs. 186.3 L / m2 (18,575 L / 99.7 m2) for Sedum quadrants. Total precipitation during 2021 averaged 1,113 mm. Native community ETc ranged from 19 - 318 L / m2 / month vs. Sedum ETc ranged from 23 - 351 L / m2 /month.