Development and Field Validation of a Solar-Powered Smart Buoy for Saltwater Intrusion Monitoring

Abstract

Rising sea levels and seasonal decreases in freshwater discharge are accelerating the penetration of saline water into freshwater agricultural canals, aquaculture, and irrigation systems in low-lying coastal areas, making saltwater intrusion a growing threat. This paper reports on the design, development and field validation of a real-time, solar-powered smart buoy for continuous saltwater intrusion monitoring in agricultural canals. The proposed system comprises a multi-parameter electrical conductivity sensor, a water-level sensor based on a pressure transducer, an ESP32 microcontroller, an energy subsystem powered by photovoltaics, and a cloud-based Internet of Things (IoT) platform capable of automatically sending notifications to a smartphone when predefined salinity thresholds are exceeded. Field experiments were carried out at seven monitoring stations along the Khlong Bang Mot canal, Bangkok, Thailand to assess (1) sensor accuracy, (2) power autonomy, (3) flotation stability, (4) communication reliability and (5) spatial salinity distribution under representative operating conditions. The monitoring platform showed measurement accuracy within the specified ±2% full-scale range for the salinity levels studied, and temperature compensation was effective in minimizing conductivity drift across different environmental conditions. The photovoltaic power subsystem provided ~60 h of continuous autonomous operation per battery charge cycle, and the reinforced buoy structure allowed stable operation at canal wave heights of 5–20 cm with a maximum tilt angle of 20.7° and rapid equilibrium recovery. The field deployment successfully detected localized saltwater intrusion and provided smartphone alerts in real time within 10 s of threshold exceedance. The proposed smart buoy provides a reliable, low-cost, and field-deployable solution for ongoing surveillance of saltwater intrusion in freshwater agricultural canals. The integrated platform combines environmental sensing, autonomous energy management, wireless communication and real-time decision support to provide a practical approach to improve irrigation management, reduce salinity-related agricultural losses and enhance climate resilience in vulnerable farming communities.