Data from the drain: a sensor framework that captures multiple drivers of chronic coastal floods

Abstract

Tide gauge records are commonly used as proxies to detect coastal floods and project future flood frequencies. While these proxies clearly show that sea-level rise will increase the frequency of coastal flooding, tide gauges do not account for land-based sources of coastal flooding and therefore likely underestimate the current and future frequency of coastal flooding. Here we present a new sensor framework for measuring the incidence of coastal floods that captures subterranean and land-based contributions to flooding. The low-cost, open-source sensor framework consists of a storm drain water level sensor, roadway camera, and wireless gateway that transmit data in real-time. During five months of deployment in the Town of Beaufort, North Carolina, 24 flood events were recorded. 25% of those events were driven by land-based sources – rainfall, combined with moderate high tides and reduced capacity in storm drains – and would not have been detected using tide gauge proxies. This finding suggests that tide-gauge proxies likely underestimate flood frequency in areas where the stormwater networks are at a reduced drainage capacity due to inundation by receiving waters. Our results highlight the benefits of capturing multiple drivers of coastal flooding by instrumenting stormwater networks directly. More accurate estimates of the frequency and drivers of floods in low-lying coastal communities can enable the development of more effective long-term adaptation strategies.

The Global Drivers of Chronic Coastal Flood Hazards Under Sea‐Level Rise

“…Furthermore, several locations on the US Southeast Atlantic, and eastern Australia (Bureau of Meteorology, 2022) have offsets of just 0.15 m between one or more flood levels. This highlights the need for the development of global flood impact databases such as those that already exist for Europe (Ciavola et al., 2018; Haigh et al., 2017) and systematic collection of impact‐based thresholds defined in national and local coastal flood studies (e.g., Ezer, 2022; Gold et al., 2023; Hague et al., 2022; Smith & Juria, 2019; Thompson et al., 2019). Further investment in LiDAR surveys will also improve the coverage of DEMs with small enough vertical errors to distinguish between floods of different severities.…”

“…To study coastal flood hazards, one must ascertain the water levels that pose a threat over the timescale and region of interest (Rasmussen et al., 2022; WMO, 2015). To do this, many studies define coastal flood thresholds that represent the minimum sea level associated with some specified impact (Gold et al., 2023; Hague et al., 2019; Moore & Obradovich, 2020). These can be defined by relevant government agencies (Burgos et al., 2018; Dahl et al., 2017; Karegar et al., 2017; Sweet et al., 2014; Sweet & Park, 2014), or by leveraging social or news media and local monitoring programs (Ezer, 2022; Gold et al., 2023; Hague et al., 2022, 2020, 2019; Hino et al., 2019; Moore & Obradovich, 2020; Ritman et al., 2022; Thompson et al., 2019).…”

“…To do this, many studies define coastal flood thresholds that represent the minimum sea level associated with some specified impact (Gold et al., 2023; Hague et al., 2019; Moore & Obradovich, 2020). These can be defined by relevant government agencies (Burgos et al., 2018; Dahl et al., 2017; Karegar et al., 2017; Sweet et al., 2014; Sweet & Park, 2014), or by leveraging social or news media and local monitoring programs (Ezer, 2022; Gold et al., 2023; Hague et al., 2022, 2020, 2019; Hino et al., 2019; Moore & Obradovich, 2020; Ritman et al., 2022; Thompson et al., 2019). Unfortunately, such thresholds have only been systematically defined in the United States (US) and Australia, limiting their utility for global studies.…”

“…Chronic flooding is defined quantitatively based on the frequency, rather than the severity, of impacts. Definitions vary between studies but 50 days per year is sufficient for flooding to be considered chronic under all published definitions, and is used subsequently (Buchanan et al., 2019; Gold et al., 2023; Sweet & Park, 2014; Thompson et al., 2019). Minor flooding requires the least SLR to reach chronic frequencies and has been the primary focus of most chronic flood studies to date.…”

Compounding of Sea‐Level Processes During High‐Tide Flooding Along the U.S. Coastline

“…(2018). This regression model is adopted by the National Ocean Service (NOS) and is useful to derive flooding thresholds for sites without defined NWS thresholds (Gold et al., 2023). The HTF thresholds provided by NWS and NOS are different along the US coast, with the maximum difference reaching 0.31 m and the median reaching 0.11 m. Choosing the NOS thresholds everywhere leads to different HTF frequencies, but sensitivity testing showed that the conclusions we draw from our analysis hold, and hence we use NWS thresholds throughout (with the exception of Neah Bay).…”