Real-Time Remote Soil Moisture Monitoring for Rain Garden Irrigation Efficiency with a Low-Cost Cloud-Connected Datalogger

Abstract

Green stormwater infrastructure tools, such as rain gardens, combat water pollution by mimicking pre-development hydrology in urbanized areas to reduce stormwater runoff. The vegetation in rain gardens takes time to establish and initially requires irrigation to survive prolonged dry spells. In Philadelphia, public rain gardens are irrigated after four days without rain. Irrigation is applied manually and can be costly. To make these efforts more efficient, a real-time, low-cost soil moisture sensing device was developed and deployed in rain gardens across Philadelphia during the summer of 2018. The device monitors site conditions and transmits data wirelessly over the 3G cellular network to a cloud database. The device sent hourly air temperature, humidity, and soil moisture in six rain gardens. Precipitation events resulted in obvious soil moisture changes at the banks and troughs of all garden sites, but irrigation events were largely undetectable in the data. Events with greater total precipitation amounts resulted in more dramatic soil moisture increases; post-rain reductions in soil moisture were correlated with in higher average daily air temperature. If the data collected with the device were used to develop a new irrigation schedule based on real-time soil moisture values, there would have been 16 fewer irrigation events at these sites during the summer of 2018. The reduced irrigation would likely have offset the cost of required instrumentation.M.S., Environmental Engineering -- Drexel University, 201