Articles
Benefits of real-time sensor-controlled irrigation to optimize the stormwater retention capacity of native vs. non-native green roofs
Article number
1409_39
Pages
297 – 304
Language
English
Abstract
Green roofs are primarily used to mitigate stormwater runoff in Washington, DC and in many cities throughout the U.S., and internationally.
Green roof plants are typically drought-resistant succulent species (e.g., Sedum) which can tolerate hot, dry conditions, but there is increasing interest in using native species to increase biodiversity and provide greater ecological benefits.
However, many native (C3) species are not well-adapted to xeric conditions, requiring the judicious use of irrigation water; the conundrum is providing adequate plant-available moisture without affecting the stormwater retention of green roofs, typically having less than 10 cm soil depth.
Given these constraints, an automated sensor-based irrigation system was installed in replicate Sedum and native-community green roof quadrants on the U.S. Botanic Garden Conservatory roof, to test a precision irrigation capability and quantify the benefits of this approach.
Advanced irrigation control software from Sensorweb, Mayim LLC (Pittsburgh, PA) allows for the continuous averaging of sensor data and micro-pulse irrigation water applications, based on a precise soil volumetric water content (VWC) set point of 16%. Two weather stations and 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-October 2021 averaged 107.2 L m‑2 (10,462 L 97.6 m‑2) for native vs. 186.3 L m‑2 (18,575 L 99.7 m‑2) for Sedum quadrants.
Total precipitation during 2021 averaged 1,113 mm.
The native community ETc range was 19-318 L m‑2 month‑1 vs. Sedum ETc which had a range of 23-351 L m‑2 month‑1. This study showed that this sensor-based irrigation capability maintained a precise soil moisture for optimal plant growth, without significantly affecting the green roof stormwater capacity.
Green roof plants are typically drought-resistant succulent species (e.g., Sedum) which can tolerate hot, dry conditions, but there is increasing interest in using native species to increase biodiversity and provide greater ecological benefits.
However, many native (C3) species are not well-adapted to xeric conditions, requiring the judicious use of irrigation water; the conundrum is providing adequate plant-available moisture without affecting the stormwater retention of green roofs, typically having less than 10 cm soil depth.
Given these constraints, an automated sensor-based irrigation system was installed in replicate Sedum and native-community green roof quadrants on the U.S. Botanic Garden Conservatory roof, to test a precision irrigation capability and quantify the benefits of this approach.
Advanced irrigation control software from Sensorweb, Mayim LLC (Pittsburgh, PA) allows for the continuous averaging of sensor data and micro-pulse irrigation water applications, based on a precise soil volumetric water content (VWC) set point of 16%. Two weather stations and 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-October 2021 averaged 107.2 L m‑2 (10,462 L 97.6 m‑2) for native vs. 186.3 L m‑2 (18,575 L 99.7 m‑2) for Sedum quadrants.
Total precipitation during 2021 averaged 1,113 mm.
The native community ETc range was 19-318 L m‑2 month‑1 vs. Sedum ETc which had a range of 23-351 L m‑2 month‑1. This study showed that this sensor-based irrigation capability maintained a precise soil moisture for optimal plant growth, without significantly affecting the green roof stormwater capacity.
Authors
J.D. Lea-Cox, C. Hall, R. Mims, J. Adams, S. Pell
Keywords
electrical conductivity, irrigation scheduling, wireless data logging, soil volumetric water content
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