Effects of historical morphologic change on sediment accumulation in Newark Bay, New Jersey
Date
2011
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Publisher
University of Delaware
Abstract
This thesis investigates known and presumed morphological and sedimentological changes that have occurred in the Newark Bay estuary, New Jersey, since 1934 as a consequence of dredging and shoreline development activities. Understanding how the Bay's sedimentary environment has changed during historical times is important given the economic significance of waterway and environmental concerns over its contaminated sediments. Data from single-beam bathymetric surveys and seven age-dated vibracores collected in 2008 were used to investigate how modifying the hydraulic geometry of an estuary can lead to changes in sedimentation patterns and rates. Comparison of 1934 and 2008 bathymetric surveys shows that there was an overall decrease of -371 m in the average width of Newark Bay, a 3.5 m increase in average depth, and a 3,231 m2 increase in average cross-sectional area. The overall volume of the Bay increased from 82,021,217 m3 in 1934 to 125,785,982 m3 in 2008, which is equivalent to a net loss of 39,425 million kg in sediment mass. The decrease in width was mostly due to construction of the marine terminals after 1934, whereas the increase in depth was mostly a consequence of further deepening of the shipping channel that existed in 1934. The altered hydraulic geometry apparently changed the hydrodynamics of the Bay in a way that was conducive for increasing the net import and trapping of suspended sediments. Bathymetric change analysis indicated that the mouth of the Passaic River, the channel south of Shooter’s Island, and localized areas on the subtidal flats were regions of significant fine-grained sediment accumulation between 1934 and 2008. At the same time, the analysis illustrated that other areas of the flats are on the long term non-depositional or erosional. Sediment on the flats was mostly silt-sized and the sedimentary structures were generally interlaminated beds with varying degrees of bioturbation. Spatial patterns of sediment accumulation, bypass, and erosion indicated by the coring data were in broad agreement with sedimentation patterns predicted by the repeat echosounding surveys and bathymetric change measurements. Channel deepening since 1934 has not had a wholesale impact on patterns and rates of sediment accumulation on subtidal flats in the Bay; however, the post-1934 sediment column at some depositional sites fines upward, suggesting that the supply of fine sediment (mud) to the flats has increased locally over time, perhaps as a consequence of changes in the flow regime of the Newark Bay.