2018 ASHS Annual Conference

We are monitoring green roof and urban tree systems in Washington, DC using wireless sensor networks for the continuous assessment of stormwater performance. One of these systems is at the U.S. Tax Court, where mature bald Cypress trees (Taxodium distichum) surrounded by zoysia grass (Zoysia japonica), are irrigated using runoff water collected from the roof and a hardscape plaza. The objectives of the study were provide daily and seasonal transpiration data for these two plant components, to understand how efficient this urban landscape is in mitigating the cost of potable water for irrigation, and additionally reducing stormwater drainage (impervious) fees, by quantifying the total runoff applied to this landscape on an annual basis. The tree/grass system is planted in a concrete overpass over the US 295 highway that passes underground at that location. Ten replicate Cypress trees and approximately 75m² of zoysia are monitored using a combination of soil moisture sensors, flow meters and a number of environmental (weather station) sensors. Data are logged using EM50R radio dataloggers (Meter-Group, Inc, Pullman, WA) on a 5-minute basis, and transmitted to a computer and radio basestation on site. Data are then assimilated into a database and charted graphically using Sensorweb™ software (Mayim, LLC, Pittsburgh, PA). Real-time data are available to irrigation managers over the internet through a password-protected site. Sensor data provide daily rainfall and irrigation inputs, reference evapotranspiration (ETo), and estimated daily crop water use (ETc), from soil moisture (Kc) data at three depths, integrated using the Penman monteith and a water balance model. During 2015, the water use of the cypress trees totaled 127,213 L compared to 47,438 L for zoysia. During 2016, the water use for cypress vs. zoysia was 152,496 and 61,737 L, respectively and 66,806 and 76,482 L from April through July, 2017. The total value of Stormwater Retention Credits based on the variable contract price in Washington, DC was $20,924, $46,285 and $128,757 for 2015, 2016 and 2017 respectively.