Geomorphic effects and distribution of anthropogenic debris in urban streams

Urban streams are full of garbage: from plastic wrappers to car tires, from shopping carts to construction debris. This garbage degrades the local environment, poses risks to human health, requires repeated volunteer clean up efforts, and may be a significant source of the plastics and microplastics found in lakes, oceans, and coastlines. Yet currently, we have a poor understanding of how garbage moves through and is stored within urban streams, and how it interacts with sediment, wood, and engineered structures along the way. This project seeks to address two fundamental questions: (1) what controls where garbage is found in streams? and (2) what controls what garbage does to channel form and function? With its wide variety of shapes and material properties, garbage is likely to behave in ways that are not predicted or explained by existing models of sediment transport. By measuring how garbage actually behaves in urban streams, this research will improve these models and advance science about the physical behavior of materials in streams and rivers. The results of this research will be useful for guiding litter management in cities and environmental clean-up and restoration efforts. The project will also provide educational opportunities for the public at community festivals and environmental events, as well as undergraduate and graduate students. This project aims to quantify the geomorphic effects of garbage, or anthropogenic debris, in urban streams, by investigating the controls on its distribution and the changes that it produces. Geomorphic assessments, including quantification of anthropogenic macro-debris (>5 cm), conducted in an extensive, multi-city set of stream reaches will quantify its distribution within and across urban stream reaches and its interaction with other stream elements. Time lapse photography and repeat surveys of large debris, streambed topography, and sediment size will quantify debris mobility and geomorphic change as a function of geomorphology and hydrology. Flume experiments will identify the effects of debris properties and interactions among objects on the transport mechanics and geomorphic effects of anthropogenic debris. The field and laboratory work in this project will inform generalizable understanding of how material properties influence the geomorphic function of objects in fluvial systems. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.