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Summary & Conclusions

This sediment characterization and management of New Jersey's coastal waterways project is a reconnaissance-level study of all dredged material placement sites and adjacent bay waters sediments.  The purpose of the study is to compile a comprehensive database for which coastal zone managers, coastal engineers, and scientists can better manage New Jersey's navigable waterways and dredging projects, as well as promote the reuse of dredged material contained in existing placement sites.  This report focused on Atlantic County and south-easternmost area of Burlington County as the initial sub-set of the work in the four coastal counties in New Jersey.

In Atlantic County, New Jersey, numerous datasets were collected and compiled to:

  • Analyze different types of bay floor sediments that exist in various channels, lagoons and bays in Atlantic County’s coastal zone.
  • Locate dredged material placement sites found within the tidal waters of the County.
  • Analyze sediments within dredged material disposal sites.
  • Select priority areas where the reuse of and excavation of dredged materials would promote perpetual use.
  • Identify areas that require dredging and present options to enhance future dredge materials handling/storage

The bottom of the Intracoastal Waterway (NJIWW), and adjoining channels and bays from Great Bay to Great Egg Harbor Bay were evaluated for sediment properties and the degree of shoaling.  A regional bay floor sediment distribution map was created from sediment sample analyses and shows the sediment distribution patterns within the study area.  Sandy bay bottoms are common adjacent to inlets and in areas with greater tidal flow through the NJIWW and adjacent channels.  Finer sediments are found at the mouths of creeks that empty into the coastal bays and in the enclosed bays with limited tidal flow.

A shoaling analysis was conducted to predict areas of sediment accumulation.  The model incorporated the sediment characteristics of the NJIWW and in state channels.  Sands were found in channels that have flow-through connections. Silts and mud were found in the sharp turns of NJIWW and state channels and in channels that enter enclosed bays (e.g. Absecon Bay).  The area with the greatest amount of sediment dredged in repeat episodes is at a meander in the NJIWW in the southern section of Great Bay (Region # 14-15).  Convergence zones such as Region # 10-11 at Reed’s Bay and the NJIWW are also areas of repeat dredging.  The 20-year demand for storage of dredged material is greatest for these areas as well as in channels, canals, and marina entrances and basins where there is heavy vessel use and where shoaling rates exceed 0.03 feet per year.

Out of the 66 sites delineated, there are 10 CDFs, 20 CDS, 21 UDS, 12 U Is, and 3 other.   Staff visited 41 sites in the county, surveyed the perimeter to obtain elevations, and took cores to determine the sediment character of past disposal activities.  These sites are found along the NJIWW and adjoining channels, and some can be accessed by vehicle.  All of the sites are included in a geospatial database that provides information on location and ownership.

This study has shown that legacy sites presently support an extensive ornithological, mammalian and reptile ecology as nesting sites for shore birds, homes for fox, raccoons, possum, and rodents, and nesting areas for thousands of diamondback terrapin turtles.  Since these sites lack a confinement berm, and are small in size, they should be left as they are.   

Sediment characteristics were determined from the cores that were taken at the 41 sites and are included in this report.  Of those 41 sites, six contain accessible material that could be used for industrial purposes and reopened for future disposal.  These priority areas were chosen for location, access, sediment composition, and current disposal use.

Recommendations:

Dredging is an episodic repetitive process that is relatively easy to conduct but requires two challenging conditions with the immediate post-dredging portion of the project.  Once the dredge collects the material the disposal process begins.  First, the material must be stored and a storage location must be within 2-3 miles of the hydraulic dredge (most commonly used for large volume projects).  Each dredging project could be located anywhere in the tidally-flowed portion of the County, but current environmental laws preclude creating disposal locations at points of project convenience.  Secondly, once the disposal site is available, recurrent projects fill the site with material that prevents placing later discharge within them.

From the study, a number observations and findings demonstrate the following:

General Conditions in Atlantic County;

1.       Channels shoal naturally with material sized according to the average tidal flow velocity.

2.      Channels lead to the interior of the coastal lagoon/bay system where the finest sized material is ultimately deposited.

3.      The New Jersey coastal zone has little impact from uplands freshwater runoff discharge through the coastal environment.

4.      The New Jersey coastal zone is deposited on a low-gradient coastal plain with a southeast regional slope of just 11 feet per mile toward the southeast, making the coastal zone wide and shallow without adding coastal sediment deposition.

5.      The base sediments are gravel, sand and silt, of which only the silt runs off into the coastal lagoons.

6.      Farming exacerbated this silt discharge 200 years ago rapidly filling in and shoaling all but the major tidal channels.

Consistent Observations About Atlantic County Sites;

1.      Manmade lagoons and marina basins act as effective sediment traps because they are dug deep for the vessels, have no through-going tidal flow and produce four-time per day slack tidal flow periods accelerating fine sediment deposition.

2.      Marinas also are most common near high development areas, the inhabitants of which tend to reject new sediment disposal sites anywhere in proximity to homes.

3.      The existing disposal sites tend to contain greater than 60% sand by volume, with many along the NJIWW containing 85% sand.

4.      Some sites contain over 15 vertical feet of sediment and cover 15 or more acres.

5.      Bore holes reaching the original marsh surface find between 3 and 5 feet of surface elevation compression below the current marsh elevation outside the site perimeter walls.  This is due to isostatic adjustments in the soft substrate due to the weight of the disposed sediment and the berm walls and the decay of the organic fraction of the original marsh sod.

Basic Recommendations;

1.      CDF’s with interior cells would allow sectional filling, dewatering and potential recycling of the contained material.

2.      Priority CDF’s will require either dock landing development on those sites adjacent to deep tidal channels or heavy duty road access across the marsh from the causeways leading to the barrier islands or from either the barrier island or the mainland.

3.      Re-use of the site will require simple removal with processing elsewhere, but could include on-site blending to create suitable products.  90% sand material is always directly useable for many purposes.

4.      Dredging in Atlantic County is concentrated along Beach Thorofare on the western side of Absecon Island in highly developed areas of the four island municipalities.

5.      Outlier sites such as Mystic Islands, Somers Point, Absecon Creek and Pleasantville will require site-associated dredge material storage/handling sites.

6.      Present site capacity near the Absecon Island marine development is entirely inadequate to handle future dredging needs both in location of sites and the existing site capacity to hold more material.

7.      Some municipal effort has started in Ventnor, Margate and Little Egg Harbor Township to establish new sites on degraded pieces of land that have vehicle access (ex. The former Ventnor City municipal dump site along Beach Thorofare)

The focus should be on those identified priority sites where size, berm integrity, and proximity to successful access for re-cycling of the material is maximized.  It is the opinion of the CRC that Bass Harbor, Shad Island, Black Point, Broad Thorofare #1 and Broad Thorofare #2 have the greatest potential for reuse. Pork Island north and perhaps one of the sites adjacent to the Atlantic City Expressway could become reuse sites if the problems associated with heavy truck traffic and the roadway configuration can resolved.