The Insights to River Dunes

NSF Fellow: Danielle Perkins, Coastal Carolina University

Mentor: Dr. Travis Swanson

Our project offers an in-depth view of how riverbeds and tidal flow correlate. Our focus was on a portion of the Lower Ogeechee River, with just under 20 km of the river being surveyed. We wanted to know how dunes inherit “hydraulic information” across the river-tidal transition and how dunes are affected when there is no sediment movement and no tidal flow. Tidal flow takes great effect on the Ogeechee’s riverbed through its daily tidal cycle. The tidal cycle changes the shape and size of the dunes through hysteretic loops. The hysteretic loops respond based on fast and slow floods which determine the type of dunes we expect to see. We measured dune height by taking surveys of the lower and upper portion of the Ogeechee River using an Echosounder. The Echosounder sends sound waves that provide us with snapshots of bathymetry, that are used to look at the riverbed. To analyze and process the data we used Geographic Information System Software (QGIS) to map out dunes, compound dunes, and bed forms. We took a greater interest in the lower survey of 15 km, where there was more tidal river flow. Descriptive data that was able to show about 2,000 dunes coming in an average of 14cm. We were able to find a significant trend (R² = 0.0625) while our dunes show a decrease in variance relatively to the mean. In conclusion we found that hysteretic loops change the variability of dune size as well as influence tidal river flow. For future directions, we could explore how grain size determines how much of sediment is being moved along the riverbed and forming these bedforms.