A PRELIMINARY CHARACTERIZATION OF ISLANDS IN THE SUSQUEHANNA RIVER

There are nearly a thousand islands in the Susquehanna River drainage basin in Pennsylvania and New York that are mapped as Recent to Late Illinoian stratified drift and outwash deposits (0 to 198,000 yrs). Closer examination of physical characteristics of these landforms such as elevation, shape, location in the river, and island sediment texture and composition suggest multiple origins for the islands. These islands can be preliminarily characterized as anthropogenic influenced islands, bedrock islands, recent and relict alluvial channel bar islands, and incised deltaic and terrace deposits. The majority of islands along the Main Stem of the Susquehanna appear to be recent and relict alluvial channel bar or braid islands. These generally form from alluvium deposited following flood events. Along the upper reaches of the North Branch of the Susquehanna, islands appear to be a mix of alluvial bar and incised delta and terrace deposits. Anthropogenically influenced islands are minor in occurrence but occur throughout the river, most notably as islands related to the construction of infrastructure such as bridges, dams, and canals. Bedrock islands are most prominent in the lower reaches of the Susquehanna.

Islands were examined using aerial photographs, satellite images, and topographic maps as well as Google Earth Pro, GIS data, and historical maps. Using recent imagery, it was found that some incised terrace and delta islands in the northeast undergo incision following flood events. Storms and high discharge events produce streamlets that erode and detach part of the terrace over time.

By characterizing the islands in the Susquehanna River, a better understanding of deposition and erosion in the floodplain may help land planning and mapping of these features. With global climate change and increased precipitation predicted for the future, islands may develop faster from terraces or large islands. An improved understanding of fluvial processes may help us better manage property along the floodplain and floodway.