SEDIMENT DYNAMICS OF THE LOWER JAMES RIVER

The lower James River extends ~180 km across the Virginia coastal plain from Richmond to the southern Chesapeake Bay. The James is one of the largest rivers in VA by both length and discharge (mean: 194 m³/s; max: 8863 m³/s), and serves as an important location for shellfish aquaculture. Despite high-profile historical instances of severe contamination, relatively few studies have investigated sediment transport dynamics in the lower James. In this study, we analyze time-series data of water velocity, temperature, salinity, and suspended sediment concentration from a single location ~50 km from the river mouth, with the goal of understanding the relative importance of river hydrography and marine tides on controlling sediment deposition. The first instrument deployment runs from November 2018 to February 2019, with subsequent deployments occurring in ~3-month intervals. Time-series observations are complemented by discrete along- and cross-channel surveys of water-column properties and sediment grab samples and shallow (<50-cm) cores collected on the dates of instrument deployment (i.e., 3-month intervals). The sediment grabs will be analyzed for their textural and radiochemical properties, to understand change on seasonal time scales. We expect profound variation in sediment transport and deposition across season, as the study area is located in a particularly dynamic region of the lower James. During flood conditions, which can occur periodically from winter through spring, we expect this location to behave like a tidal river; water level and velocity are controlled by the tidal stage, but the water remains entirely fresh. During periods of relatively low river flow, we expect conditions to be estuarine in nature; horizontally-stratified salinity profiles, and the potential for localized deposition at the estuarine turbidity maximum (ETM). Each of these hydrologic regimes will impact the nature of sediment transport and deposition, with potentially important implications for recreation and industry on the lower James River.