Abstract
An accurate description of hydrodynamic processes in coastal wetlands is needed to improve their management and conservation. As a consequence, higher knowledge of the connected morphological and ecologic processes is achievable. However, it is very costly to collect spatially distributed values of flow velocities over tidal channels and intertidal areas by means of in situ sensors. Also, when deploying sensors, humans perturb the ecosystem, which takes time to recover. In this study, a new low-cost unmanned aerial vehicle (UAV)-based method to measure surface velocities is proposed and validated. The study area is a salt marsh system on the southeast coast of Little Sapelo Island, Georgia, USA. Two unmanned aerial vehicles were used in the survey. A first UAV released a fluorescent dye tracer on marshes and tidal creeks, while a second one tracked its movement by collecting RGB images. Flow direction and magnitude were calculated from the images using a newly developed algorithm. A comparison with velocities measured with an acoustic Doppler current profiler confirmed the effectiveness of the method. Our results indicate that the calculated flow field is affected by vegetation, marsh morphology, and marsh width. In particular, a non-negligible velocity component perpendicular to the creek axes is detected both in ebb and in flood. Our technique proves to be an effective, non-intrusive, low-cost way to survey the two-dimensional hydrodynamics on salt marsh environments at a km scale. Collected data would be beneficial for calibrating and validating numerical models with accurate water flux information.
Highlights
Salt marshes are a crucial environment for ecological, anthropologic, and economic reasons
Vegetation plays an essential role in marsh conservation: it mitigates the effect of meteorological forcing, such as hurricanes and storms, regulates the rate of organic and inorganic deposition, modulates hydrodynamic processes in the marshes, such as flood events [7,8,9], and reduces nitrogen concentration in water [10]
We describe a new method to measure surface flow velocity by tracking dye released over tidal channels and flooded salt marshes in Sapelo Island, Georgia, USA
Summary
Salt marshes are a crucial environment for ecological, anthropologic, and economic reasons. UAV-based surveys are preferred since fixed-camera images limit the extension of the area in which velocities are measured Due to their limited dimension, solid tracers are difficult to detect at 50–100 m altitude. While GPS drifters [39] do not need to be visually tracked, they have low accuracy (~1 m) and large draft (~40 cm) They are not suitable for surveying small tidal channels or shallow vegetated marshes. We describe a new method to measure surface flow velocity by tracking dye released over tidal channels and flooded salt marshes in Sapelo Island, Georgia, USA. Epnogi.n2t0,20a,n8d, 36(4iii) the time needed to swap the batteries, put in a new one, and to chec5kofth24e operability of the UAVs. 12:20 AM
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