Capturing local nuisance flooding events with HOBO pendant G data loggers in Key West, Florida US

Flooding impacts social, economic, and landscape systems globally. Changing climate and growing coastal populations exacerbate the outcomes of environmental hazards. Due to the spatial variability in exposure and vulnerability, coastal flooding must be understood at high spatial and temporal resolutions. This paper presents a novel deployment technique using inexpensive accelerometers to measure local floods. The technique is tested in Key West, FL, USA using storm drains to deploy HOBO pendant G data loggers. The feasibility of the method is tested by a team of local stakeholders and researchers through four deployments between July 2019 – November 2021. All deployments resulted in 22 sensors successfully recording data, with 15 of these sensors recording flooding. Sensors captured an average of 13.58 inundation events causing the storm drains to be inundated on average 12.07% of the deployment time. Measured inundation events coincide with local National Oceanic and Atmospheric Administration (NOAA) water level measurements of high tides, which shows that high-tide inundation is captured by the accelerometers. Accelerometers are easy to deploy and accurately capture the duration of local flooding. Access to an effective and inexpensive sensor for measuring flood events can increase opportunities to measure local-scale hazards and collect important information with participation by interested parties (e.g., local governments, homeowners, schools etc.). The ease of use and successful recording of loggers can give communities access to flooding data, and in turn, increase their capacity to make data-informed decisions surrounding sea level rise adaptation. 

Methods
The research team — which includes a Key West municipal employee, researchers from Northeastern University and researchers from the United States Naval Academy — use HOBO pendant G data loggers to collect flooding data in Key West. The loggers record acceleration and angular displacement (tilt) in three dimensions, allowing for characterization of three-dimensional motion. For nuisance flooding, the acceleration and tilt are used to record localized flood events since rising water changes the orientation of the buoyant sensors, causing angular displacement and a change in the axis experiencing gravitational acceleration. Storm drains were selected for deployments, providing publicly accessible areas that were both prone to frequent inundation and fixed locations for sensor deployment. Using knowledge of previous flooding events and local expertise, 14 total deployment locations were selected. Each location has a publicly accessible storm drain to attach the loggers. The research team deployed loggers four different times over the period from July 2019 – November 2021. Loggers were programmed to record continuously after a user-specified launch time and sampling rates were specified such that loggers recorded measurements every one minute for the first two deployments and every five minutes for the third and fourth deployments. 

The sum acceleration and the tilt in all three dimensions were downloaded through HOBOware v3.7.21, exported as .csv files and uploaded to RStudio v1.4.1717. Times at which a sensor recorded a flooding event was identified using tilt in the x-direction and z-direction.