Remote bed-level change and overwash observation with low-cost ultrasonic distance sensors

Abstract

Few datasets exist of high-frequency, in situ measurements of storm overwash, an essential mechanism for the subaerial maintenance of barrier islands and spits. Here we describe a new sensor platform for measuring bed-level change and estimating overwash inundation depths. Our MeOw (Measuring Overwash) stations consist of two ultrasonic distance sensors, a microprocessor board, and a camera and are capable of withstanding the impacts of large storm events, can be left unattended to collect data for months to years, and are relatively inexpensive. With the exception of the camera, the MeOw stations are built with all open-source hardware and software. Herein we provide complete instructions for manufacturing the MeOw stations and present observations from a single MeOw station for a three-month (2019) deployment on a frequently overwashed section of Smith Island, VA. The MeOw stations captured three large storm events over the course of the deployment (Hurricane Dorian, Tropical Storm Melissa, and a November nor’easter), as well as several high-tide events. Based on our interpretation of the raw data, bed-level changes occurred throughout the deployment from both storm and non-storm overwash, but were particularly large during Tropical Storm Melissa where initial accretion of approximately 0.15 m was followed by 0.77 m of erosion over three days. The maximum overwash inundation depth occurred during the nor’easter and measured approximately 0.83 m. The variability in bed level over the course of our experiment highlights the importance of in situ high frequency bed-level measurements for constraining overwash inundation depths. MeOw stations are ideally suited for measuring storm overwash — or any process that necessitates tracking bed and water level elevations at high frequency during harsh conditions.