Inundation of Stormwater Infrastructure Is Common and Increases Risk of Flooding in Coastal Urban Areas Along the US Atlantic Coast

Abstract

Stormwater infrastructure can manage precipitation‐driven flooding when there are no obstructions to draining. Coastal areas increasingly experience recurrent flooding due to elevated water levels from storms or tides, but the inundation of coastal stormwater infrastructure by elevated water levels has not been broadly assessed. We conservatively estimated stormwater infrastructure inundation in municipalities along the Atlantic United States coast by using areas of high‐tide flooding (HTF) on roads as a proxy. We also modeled stormwater infrastructure inundation in four North Carolina municipalities and measured infrastructure inundation in one of the modeled municipalities. Combining methodologies at different scales provides context and allows the scope of stormwater infrastructure inundation to be broadly estimated. We found 137 census‐designated urban areas along the Atlantic coast with road area impacted by HTF, with a median percent of total road area subject to HTF of 0.16% (IQR: 0.02%–0.53%). Based on 2010 census block data, the median number of people per urban area that live in census blocks with HTF on roads was 1,622 (IQR: 366–5,779). In total, we estimate that over 2 million people live in census blocks where HTF occurs on roadways along the US Atlantic coast. Modeling results and water level measurements indicated that extensive inundation of underground stormwater infrastructure likely occurs at water levels within the mean tidal range. These results suggest that stormwater infrastructure inundation along the US Atlantic coast is likely widespread, affects a large number of people, occurs frequently, and increases the occurrence of urban flooding.

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

“…These estimated flood thresholds are referred to as common impact thresholds. The use of these thresholds is now standard practice in regional and national coastal flood hazard studies in the US (Dusek et al., 2022; Ghanbari et al., 2019; Gold et al., 2022; Li et al., 2022, 2021; Thompson et al., 2021), despite their limitations (e.g., Section 4.2). Most recently, this approach has been used to estimate flood thresholds in China (Li et al., 2023).…”

“…DEMs can only natively resolve direct marine flooding processes. Considerable additional modeling is required to resolve drainage networks and groundwater processes, which has so far only been attempted on local scales (Gold et al., 2022; Habel et al., 2020; Prakash et al., 2020). The consideration of flooding from all three mechanisms is a further advantage of impact‐based threshold methods, which use water levels at tide gauges during flood events as a proxy for observed regional impacts without needing to explicitly model the flow (Hague et al., 2019; Moore & Obradovich, 2020).…”

Data From the Drain: A Sensor Framework That Captures Multiple Drivers of Chronic Coastal Floods

“…The tidal cycle now takes place on higher average sea levels, resulting in “sunny‐day” flooding of roadways during high tides. Because sea water infiltrates drainage systems at even low tidal levels (Gold et al., 2022), ordinary rain storms can now cause flash floods. We refer to locations that experience flooding multiple times per year, from drivers other than extreme storms (e.g., tropical cyclones, nor'easters), as chronically flooded.…”

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

“…The tidal cycle now takes place on higher average sea levels, resulting in "sunny-day" flooding of roadways during high tides. Because sea water infiltrates drainage systems at even low tidal levels (Gold et al, 2022), ordinary rain storms can now cause flash floods. We refer to locations that experience flooding multiple times per year, from drivers other than extreme storms (e.g., tropical cyclones, nor'easters), as chronically flooded.…”