Newark Bay Study - Passaic River Public Digital Library

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sediment transport, there is considerable information available on the rates in Newark Bay, and it is
clear from this information that sediment accumulation is a dynamic process. Rates range from
tenths of a cm/year in the side Bay areas to 10 – 15 cm/year or more in the primary depositional
zones. This range in rates has important implications for modeling purposes, especially when it is
time to perform projections. The reason is that it is the combination of the depth of the mixed layer
and the net sedimentation rate that will control the response time of the system to future changes in
sediment characteristics and inputs to the system. Surface sediment concentrations can be expected
to respond relatively rapidly in areas having high net sedimentation rates.
Suszkowski (1978) identified three areas in the Newark Bay where enhanced sediment
accumulation was occurring. These areas are the lower Passaic River, Port Newark, and the area
north of Shooters Island. A variety of processes were thought to be contributing to the high rates
of deposition in these areas. For example, the density-induced circulation pattern in the lower
Passaic leads to the downstream transport of particles from the upstream Passaic River in the
surface layer; settling of these particles such that they mix with lower layer sediment and are then
transported in a net upstream direction in the bottom layer, a process which increases the residence
time of the particles in this region, thereby promoting sedimentation. Alternatively, the enhanced
deposition in the Port Newark area was attributed to what was described as “scouring and settling
lag effects” in a closed-ended channel. Finally, a high influx of solids from the Kills, combined with
low current speeds and extended slack water periods (as long as 2 hours) were thought to be the
cause of enhanced deposition in the area north of Shooters Island (Suszkowski, 1978).
The preceding phenomena provide a useful working model for how to represent the
processes that control sediment transport in the Passaic River-Newark Bay system. Planned
evaluations with a high-resolution model will further elucidate the importance of these and other
processes that are controlling sediment deposition in these localized areas. Initial diagnostic testing
with the model will be needed to define the level of grid resolution that is required to represent these
fine-scale features. It may ultimately be necessary to unify these different model grids to obtain a
finalized overall model calibration for the system. However, separation of these analyses for initial
model development purposes will allow for more computationally efficient model runs to be
performed during the initial stages of model development.
1.6 CONCEPTUAL SITE MODEL (CSM)
The purpose for developing a CSM is to establish a clear relationship between site-specific
conditions and the types of models that are to be applied. The CSM should describe, in as much
detail as possible, each of the important physical, chemical and biological processes that are
operative at the site of interest. This will help to ensure that the models to be applied will be
suitable for their intended use, at least to the degree that the current understanding of the system
permits. The CSM will typically include consideration of hydrodynamic processes, sediment and
contaminant fate and transport processes, as well as biotic processes. While many of the important