THE SIGNIFICANCE OF RUNOFF MECHANISMS IN URBAN FLOODING AND ENVIRONMENTAL INJUSTICE

Economically challenged communities and communities of color are disproportionately affected by environmental contamination and disturbance. Although environmental racism caused by industrial pollution has been made clear for some time, the integrated stresses of climate change and post-industrial blight are now triggering new challenges to life in underprivileged communities. This is particularly true for floodplain communities who have long grappled with urban flooding and compromised water supplies, problems that are now being exacerbated by the impacts of climate change. A challenge in accurately defining flood risk for many floodplain communities is the dearth of field measurements relating rainfall intensity to observations of flow stage. The result is that many floodplain communities are inadequately protected from flooding, and some are never informed when sustained and harmful flooding is imminent. Here, we report on our efforts to address this environmental data gap for the community of Centreville, in Cahokia Height, Illinois. This Black community, situated in the Metro East region of St. Louis, has suffered from chronic flooding since at least 1975. The nearest regularly operating weather station is 5-km away, with the remaining weather stations situated over 15-km away. Streams running through the community remain ungauged, in spite of the fact that ongoing flooding has compromised residential infrastructure and condemned homes. We constructed a community-centered methodology for assessing the causes of flooding in Centreville, working with residents to identify where field observations were most necessary. Field cameras were installed at these locations, which provided observations of ground conditions every 15 minutes. Integrated into hydrological modeling with HEC-HMS, our findings indicate not only a rainfall threshold for flooding, but also the importance of sustained rainfall to driving flood risk. We find that saturated-excess runoff is the principal mechanism by which flooding occurs and identify strategies for informing residents of the likelihood for flood occurrence.