Abstract

This study investigates the potential hydraulic conditions of catastrophic floods in the West Branch of the Susquehanna River (West Branch) during the middle to late Pleistocene period and the influence of these paleofloods on the current river bed form. The current channel bed form is characterized using sonar bathymetry data collection techniques. The paleofloods are hypothesized based on published geological evidence of early Pleistocene glacial Lake Lesley in the West Branch Valley, which was formed by a glacial ice dam that potentially failed during mild climate cycles in the Pleistocene period. A one‐dimensional, steady hydraulic model is developed to simulate estimates of paleoflood peak discharges and the modern 100 year return period peak discharge. The computed water‐surface profiles, shear stresses, and flood inundation maps could explain the erosional and depositional features identified by other researchers as being formed during the Pleistocene and could explain features revealed by the bathymetry data. Therefore, the hydraulic modeling results support previously inferred hypotheses of the occurrence of glacial dam‐break floods on the West Branch of the Susquehanna River. The differences that are evident between the paleoflood simulations and the simulation of the modern 100 year peak discharge are attributable to valley constrictions that cause substantial backwater effects for the larger paleoflood discharges but not for the lower modern flood discharge volume. The ability to simulate potential paleofloods in the West Branch of the Susquehanna River complements the paleostage indicator work done by other researchers and enables innovative analysis of glaciofluvial processes and their effect on the current river bed form.

Key Points

Potential paleofloods are simulated on the West Branch Susquehanna River Hydraulic model results support Pleistocene glacial dam‐break hypotheses Important hydraulic differences are found between modern floods and paleofloods