The Passaic River Basin, which spans 935 mi2 over northern New Jersey and parts of New York, is defined by both its glacial and post-glacial history. The retreating ice sheet (~22-18 ka) created Glacial Lake Passaic, impounded behind the Watchung Mountains until a new outlet was opened at Little Falls. Glacial rerouted the Passaic River to a northeastward course, with wetlands developing on the glacial lake sediments. One such wetland, the Great Piece Meadows, covers 2,343 acres of undeveloped floodplain within the Central Basin. Three oxbows within these wetlands, named Oxbow2, RC, and TZS, were cored to determine the flooding and geomorphological history of the central Passaic's floodplain. Radiocarbon dates and grain size data suggests that oxbow TZS was cut off from the main channel around 9-9.5 ka B.P., and that the Oxbow2 and RC were cut off around 3.6 B.P. These dates fall within a transition from a dry to a wet period during the Holocene, which may have been a cause for the avulsions. Using mercury soil concentrations, deposition from the past ~180 years were determined to be within the upper 5-17 cm of the cores. The Passaic's central and lower basin have long been plagued by flooding problems, with the worst flood on record occurring in 1903. Analysis of peak discharge at gages along the Passaic and its tributaries for 27 major floods confirms observed flashy discharge of the tributaries and the backup of floodwaters from Little Falls to the central basin during flooding. While the Passaic Basin's morphology makes it prone to flooding, there are anthropogenic factors as well. While peak discharges for major floods in the Passaic have decreased since the turn of the century, major flood frequency is increasing. Reservoirs are shown to significantly decrease annual runoff and flood discharge along rivers directly downstream from them, but while they can reduce the intensity of flooding, they do not prevent major floods. Annual average runoff ratio values have increase for most areas of the Passaic Basin's streams as well, despite the construction of reservoirs and diversions for water supply. This implies that an increase in urban and suburban development is a factor in the river's increasing flooding problems.