Examining Terrestrial and Subterranean Sediment Sources and Transport Processes In An Urban Sewershed With An Entirely Buried Stream Network, Washington, D.c., Usa

Excessive fine-grained sediment runoff due to anthropogenic activities is a major concern for the ecological health of watersheds worldwide, and especially so for urban areas. In older cities, such as Washington, D.C., urbanization occurred decades ago, but ongoing construction is still prevalent. Dated grey infrastructure, the human-engineered network of buried pipes and reservoirs used for managing water resources, can amplify existing issues with sediment runoff and associated pollutants. This infrastructure was generally designed to quickly transport stormwaters away from urban areas and contributes to urban stream syndrome. Furthermore, recent studies have suggested that as this subterranean infrastructure ages it fractures and breaks down, allowing surrounding soils to infiltrate the buried drainage network. The composition of and the extent to which this possible sediment source contributes to urban sediment runoff is poorly understood and rarely accounted for, even indirectly. In our study we sought to examine sediment sources and transport processes in an urban watershed with an entirely buried drainage network using the sediment fingerprinting approach, with specific attention paid to discriminating between terrestrial and subterranean sources. We develop and demonstrate here multiple novel approaches to sampling subterranean sources including augering, sampling manholes, and entering the buried drainage network itself. The results of this study may inform urban sediment reduction managers and infrastructure engineers and allow for targeted sediment reduction responses.