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

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