Fecal Bacteria Contamination of Floodwaters and a Coastal Waterway From Tidally‐Driven Stormwater Network Inundation

Abstract

Inundation of coastal stormwater networks by tides is widespread due to sea‐level rise (SLR). The water quality risks posed by tidal water rising up through stormwater infrastructure (pipes and catch basins), out onto roadways, and back out to receiving water bodies is poorly understood but may be substantial given that stormwater networks are a known source of fecal contamination. In this study, we (a) documented temporal variation in concentrations of Enterococcus spp. (ENT), the fecal indicator bacteria standard for marine waters, in a coastal waterway over a 2‐month period and more intensively during two perigean spring tide periods, (b) measured ENT concentrations in roadway floodwaters during tidal floods, and (c) explained variation in ENT concentrations as a function of tidal inundation, antecedent rainfall, and stormwater infrastructure using a pipe network inundation model and robust linear mixed effect models. We find that ENT concentrations in the receiving waterway vary as a function of tidal stage and antecedent rainfall, but also site‐specific characteristics of the stormwater network that drains to the waterway. Tidal variables significantly explain measured ENT variance in the waterway, however, runoff drove higher ENT concentrations in the receiving waterway. Samples of floodwaters on roadways during both perigean spring tide events were limited, but all samples exceeded the threshold for safe public use of recreational waters. These results indicate that inundation of stormwater networks by tides could pose public health hazards in receiving water bodies and on roadways, which will likely be exacerbated in the future due to continued SLR.

Wind and rain compound with tides to cause frequent and unexpected coastal floods

“…A growing body of literature has identified impacts of chronic coastal floods to people, businesses, and communities, with impacts spanning traffic delays (Hauer et al, 2023), water quality risks (Carr et al, 2024;Macías-Tapia et al, 2021), reduced economic activity (Hino et al, 2019), property damage (Moftakhari et al, 2018), and changing development patterns (Buckman and Sobhaninia, 2022). Given the limited data describing this type of flooding and the lack of validated models capable of resolving flood drivers at relevant spatial and temporal scales, relating impacts to flood mechanisms remains difficult, constraining our understanding of the social and economic burden of these floods.…”