Fluorescent particle tracers for surface flow measurements: A proof of concept in a natural stream

In this paper, a new particle tracer for surface hydrology is proposed. The approach leverages the complementary advantages offered by particle-tracking velocimetry and traditional tracing technologies, such as dyes and chemicals, toward a practically feasible and low-cost measurement system. Specifically, the proposed methodology is based on the detection and tracking of buoyant fluorescent microspheres through an experimental system that incorporates ultraviolet lamps to elicit the fluorescence response and a digital camera to record the particle transit. This low-cost measurement system can be used in a variety of natural settings ranging from small-scale streams to rills with scales on the order of a few centimeters in hillslopes. The use of insoluble buoyant particles reduces the amount of tracing material for experimental measurements. Further, particles' enhanced fluorescence allows for noninvasive flow characterization, that is, for nonintrusively detecting the tracer without deploying probes and samplers in the water. A proof of concept experiment for the proposed methodology is conducted on the Rio Cordon, a natural mountainous stream in the Italian Alps. Flow measurements at selected stream cross sections and travel time experiments on varying stream reaches are performed to ascertain the feasibility of fluorescent particle tracers. Such experimental findings demonstrate that the particles are visible in complex natural streams and are effective in estimating flow velocities and travel times.