Project 2:

Overview

In order to implement a sustainable regional approach to dredged material management, a comprehensive understanding of the nature of sediment that is in the system is necessary. Program 2 is aimed at determining the bay floor sediment characteristics and gain information on sediment distribution dynamics in thorofares and channels in New Jersey's back-bays. This portion of the project was designed to measure the physical sedimentary parameters of grainsize and distribution, to define the variables and provide them in a concise standardized database.

The projects specific goals were to:

• Provide information to assist in prioritizing relative importance of individual disposal sites as part of the process of achieving the goal of   maintaining navigability along New Jersey's waterways,

• Define the character of in-situ bay-floor sediments, and

• Determine sediment transport dynamics in and around the NJIWW, state channels and rivers.

Sediment Collection

Identifying and mapping the distribution of sediments is important to developing a regional framework for dredged material management. Knowing what comprises the bay-floor helps reduce the need to “reinvent the wheel” each time a dredge project occurs.
Bayfloor sediment samples were collected throughout Atlantic County to map and characterize (i.e. percent sand vs. percent silt/clay) the sediment and show movement/distribution of sediment in the coastal waterways. Sediment sample locations were randomly generated using ArcView GIS software. Engineering judgment was used to determine sufficient point coverage/ sample location density to assure that major thorofares and waterways were covered by the sampling plan. Samples collected were later analyzed for stratigraphic trends/changes, sand/silt ratio, and mean grain size.

Sediment Distribution

Distribution mapping of in-situ bay-floor resources is a valuable tool for observing and predicting sediment transport rates in much of New Jerseys backbays and waterways and identifying areas as depositional “hotspots” or priority areas for future dredging. Physical characterization of sediments (i.e. grain size) is a useful for providing location and quantity of sediment types that could potentially be utilized in a variety of projects that might incorporate dredge material in the project development and execution. The material found in these channels is what comprises New Jersey’s various coastal habitats. Therefore, the possibility exists for utilizing this material in wetland, coastal marsh or beach-front restoration. Bottom substrate is a key factor in defining sub-aqueous habitats, so this information will also benefit fishery, shell fishery, and other environmental assessments of New Jersey’s inland waters.
Sediment distribution maps were created in ArcView GIS using data collected during the bayfloor sediment sampling phase of the project. The resulting maps have information showing the distribution of sediment types (sand vs. silt/clay) throughout Atlantic County.

Shoaling Analysis
 

Modeling sediment transport and potential shoaling hotspots was done using remote sensing techniques incorporating elevation and imagery data in a GIS environment. Using this technique, in conjunction with ground truthing/field observations during bayfloor sediment sampling efforts, it was possible to identify areas where shoaling is occurring or likely to occur.  This information, combined with data from the bayfloor sediment sample collection is integral in determining priority areas of New Jersey’s back bays that are in need of, or are soon to be in need of dredging, as well as a reasonable determination of the material to be dredged.

Bayfloor sediment sample collection using a piston core over the side of a Stockton vessel.

Photograph displaying typical stratigraphy of a bayfloor sediment sample collected in Atlantic County.