HISTORIC CHANGES IN THE CHANNEL GEOMETRY AND POSITION OF THE SUSQUEHANNA RIVER FROM CONKLIN TO APALACHIN, NEW YORK, AND THEIR CAUSES

Rivers can threaten riverside communities through bank erosion, deposition, and flooding, necessitating a thorough understanding of the response of river channels to natural and anthropogenic forces. This study examines spatial and temporal changes in channel geometry and planform of the Susquehanna River in the Binghamton (NY) region, in order to determine the relative influence of human activities and natural processes on channel change. This was accomplished by measuring the mode and rate of channel bank migration, analyzing hydraulic geometry in the channel, and comparing changes in these parameters to historic records of river floods, channel change, and engineering works.

Mode and rate of lateral migration were quantified using aerial photographs, taken nearly every decade since 1937. Channel banks were traced in a Geographic Information System (GIS), and their movement was analyzed using eroded/deposited area polygons, and measurements of the maximum migration normal to the flow. The rate of deposition on islands was also measured by coring floodplain trees and determining their age from the number of annual rings. The age of the oldest tree on a floodplain surface represented the time that the surface was deposited. At-a-station hydraulic geometry at Conklin, NY was analyzed for the years 1985 to the present using USGS records of channel geometry, and results were merged with a previously published analysis for the years 1938 – 1985.

Long-term changes in hydraulic geometry were minimal, and were generally related to downstream bar migration. Island migration has been much greater than channel bank migration, and islands have migrated downstream, been eroded away entirely, and expanded laterally. Channel width was increased where islands were carved from the floodplain, and was decreased where islands were assimilated into the floodplain. Meander bends have shown little migration, but the large delta of Choconut Creek has migrated downstream by over 21 meters. The proximity of regions with significant migration to modified sections of channel suggests that human channel alteration has caused changes in the modes and rates of channel migration.