Low-cost electronic sensors for continuous performance monitoring of raingardens

Key Points:

•  Affordable sensors allow continuous monitoring of soil moisture and hydrological performance in rain gardens.
• Using sensors for predictive maintenance lowers expenses and increases the longevity of rain gardens.

 Rain gardens (RG) are essential for sustainable stormwater management, but their effectiveness relies on consistent maintenance, which is both critical and costly. This study explores the use of low-cost electronic sensors to monitor biofilter conditions and enable predictive maintenance, reducing manual inspections and improving operational efficiency.The experiment involved 15 laboratory-scale columns, replicating the typical structure of rain gardens, with stratified layers: a ponding zone, fine sand filter, coarse sand with mulch transition layer and a gravel drainage layer. The columns were divided into three groups to simulate different conditions: a control group (C) representing optimal performance, a group with preferential flow paths (P) simulating surface erosion, and one with surface clogging (S) due to sediment accumulation. Each column had five sensors to monitor soil moisture and temperature: two Chameleon Soil Water Sensors, two temperature probes, and one Truebner SMT 100 sensors. Data were collected in real time and transmitted to a cloud-based system. To evaluate the columns, simulated rainfall events, reflecting varying intensities and antecedent dry periods based on Melbourne’s historical weather patterns, were applied. The SMT sensor effectively tracked volumetric water content (VWC), identifying peaks from simulated rainfall events and showing variability across different antecedent dry days (ADD). However, Chameleon sensors exhibited performance degradation over time due to soil drying, root growth, and temperature variations. Inflow, outflow, and infiltration rates were measured to assess hydrological behavior, but these data alone were insufficient to differentiate healthy from malfunctioning systems. Consequently, indices were developed to differentiate the hydraulic performance of each group. Parameters such as peak time, peak span, and delay time were identified as notable in diagnosing operational states. For instance, the clogging group exhibited delayed response times and retained less water. In contrast, preferential flow columns displayed immediate responses to rainfall. Post-experimentation, the columns were disassembled to analyze physical changes in soil stratigraphy and assess root development, providing additional insights into the impact of hydraulic malfunctions on overall system health. In conclusion, this research underscores the potential of integrating low-cost sensor technologies into the management of rain gardens. Real-time monitoring not only enhances the reliability and longevity of these systems but also reduces operational costs, contributing to the broader goal of fostering resilient and sustainable urban environments. Future research should refine sensor applications and expand testing under diverse environmental conditions.