AN EXAMINATION OF THE IMPACT OF URBANIZATION ON FLOODING PATTERNS, CENTRAL AND LOWER PASSAIC RIVER, NJ

The Passaic River, with drainage area of 935 mi² , is the second largest watershed in New Jersey. The river flows from southwest to the northeast then southeast into Newark Bay. It was affected by post-glacial isotastic rebound (i.e. reduced gradient) and is subjected to chronic flooding exacerbated with the onset of the Anthropocene. Average annual discharge from 1945-1970 is ~1080 cfs and the highest documented flood event (Q = 35,700 cfs) occurred in 1903. Since 1903, 11 floods have warranted federal disaster declarations, although frequent minor floods have also occurred. Urban development along the floodplain of the river has continued from the 1700s to the present, causing a decrease in wetlands and forested areas, and an increase in impervious surfaces and channel restrictions. Populations in the heavily urbanized Lower Passaic reach values of over 5,000 people per sq. mile (2010 U.S. Census). Between 1985 and 2007, the floodplain lost an estimated 4.5% of wetlands, and 7.5% of forested areas. Landscape changes associated with urban development has undoubtedly affected the intensity and frequency of floods. Loss of vegetation and an increase in impervious surfaces leads to higher amounts of runoff, discharge and bank destabilization, while construction and development narrow river channels and floodplains. To examine the nature and extent of the river’s flooding history, the Passaic River floodplain was augered and oxbow lakes were cored using a Livingston corer.

The Central and Lower Passaic basins are the most affected by floods. However, the wetlands of the Great Piece Meadows within the Central Passaic Basin serve as a buffer to flood discharge to the Lower Passaic. These wetlands provide a wide floodplain to retain flood deposits, making it an ideal location to study the river’s flooding history through the sedimentary records. Up to three meters of core were taken at each the oxbow lake site within the Great Piece Meadows. Samples of organics will be analyzed for history of post-glacial re-vegetation and radiocarbon dates (analyses underway) in order to correlate deposits with flooding events and their discharge and height data recorded at the Two Bridges and Little Falls gaging stations. These data provide a better understanding as to how urbanization alters the extent, frequency, and intensity of flooding.