Monitoring tides, currents, and waves along coastal habitats using the Mini Buoy

Abstract

Intertidal habitats are shaped by the actions of tides and waves which are difficult to monitor in shallow water. To address this challenge, the “Mini Buoy” and associated open-source App were recently developed for the low-cost and long-term monitoring of tidal inundation and current velocities simultaneously. The Mini Buoy is a bottom-mounted float that measures tilt to infer near-bed hydrodynamics. Here, we present significant updates to the Mini Buoy and App. Two new Mini Buoy designs were calibrated: the “Pendant” that requires minimal assembly for deployment, and the “B4+” that can also measure wave orbital velocity. Comparisons against industry-standard water-level and velocity sensors deployed in the field showed that each new design was effective at detecting tidal inundation (overall accuracy of 86–97%) and current velocities (R² = 0.73–0.91; accuracies of ± 0.14–0.22 m s⁻¹; detection limits between 0.02 and 0.8 m s⁻¹). The B4+ could reasonably measure wave orbital velocities (R² = 0.56; accuracies of ± 0.18 m s⁻¹; detection limits between 0.02 and 0.8 m s⁻¹). Reducing the sampling rate to prolong survey durations did not markedly reduce the precision of velocity measurements, except in the original Mini Buoy design (uncertainty increased by ± 2.11 m s⁻¹ from 1 to 10 s sampling). The updated App enhances user experience, accepts data from any Mini Buoy design, is suitable for generic use across any tidal setting, and presents multiple options to understand and contrast local hydrodynamic regimes. Improvements to the Mini Buoy designs and App offer greater opportunities in monitoring hydrodynamics for purposes including ecosystem restoration and flood risk management.