Measurements of Nearshore Waves through Coherent Arrays of Small-Scale, Free-Drifting Wave Buoys

Abstract

Along the coastlines, surface gravity wave breaking occurs in complex spatial and temporal patterns that have significant impacts on coastal erosion, transport of scalars and coastal flooding. Numerical models are used to predict these processes but many models lack validation against measurements during storm events. To fill the need for more nearshore wave measurements during extreme conditions, we created a large dataset of measurements of nearshore waves through the deployment of coherent arrays of small-scale, free-drifting wave buoys called microSWIFTs. The measurements were collected over a 27-day field experiment in October of 2021 at the US Army Corps of Engineers Field Research Facility in Duck, NC. The microSWIFT wave buoy developed in this project is a scaled-down cylindrical version of the original SWIFT (Surface Wave Instrumentation Float with Tracking) wave buoy with a length of 21 cm and a diameter of 9 cm. The microSWIFT is equipped with a GPS module and Inertial Measurement Unit (IMU), where the global position, horizontal velocities, rotation rates, accelerations, and heading of the buoy are all measured directly and vertical velocity and sea surface elevation are computed from these measurements. While many other small wave buoys have been developed, the deployment of the microSWIFTs as large coherent arrays is a novel deployment strategy for surf zone drifters and leads to more robust statistics of measurements and the ability to observe larger spatial areas. The dataset spans 1,154 individual microSWIFT drifts over a range of 73 separate coherent arrays. Over all of the separate coherent arrays, 24.7 hours of data were recorded during the experiment. The offshore wave conditions during the field experiment had significant wave heights ranging from 0.1 meters to 3 meters and peak wave periods ranging from 4 seconds to 20 seconds over the entire experiment. This dataset is used to investigate the transformation of waves in the surf zone and the location of individual breaking waves. Future goals using this dataset are to test and validate phase-resolved and phase-averaged wave models in the nearshore environment.