Land-based damage to properties and infrastructure by the Storm was Readily Apparent, but damage to the State’s Navigation Channels was Unclear. Parsons Brinckerhoff (Now part of WSP | Parsons Brinckerhoff) was Contracted to Evaluate the Damage and Support Channel Recovery and Restoration.
On October 29, 2012 at about 8 PM EDT the eye of “Superstorm Sandy” made landfall near Atlantic City, New Jersey. A full moon made the high tides approximately 20 percent higher and amplified the record storm surge. The destructive “right hook” of Sandy’s hurricane wind pattern devastated the New Jersey and New York coastline situated north of where the eye made landfall. Along New Jersey’s Raritan Bayshore region, the tidal surge was recorded to be more than 9 feet above the mean high water elevations.
After Superstorm Sandy, the land-based damage to properties and infrastructure was readily apparent, but damage to the state’s navigation channels was unclear. Prior to the storm, New Jersey’s navigation channels were maintained by the New Jersey Department of Environmental Protection’s (NJDEP’s) Bureau of Coastal Engineering. To develop a more dynamic program to maintain the state’s navigation channels, the responsibility for maintenance was transferred from the NJDEP to the New Jersey Department of Transportation’s (NJDOT’s) Office of Maritime Resources (OMR).
WSP | Parsons Brinckerhoff’s role in Channel Assessment and Recovery
The NJDOT selected a team, led by WSP | Parsons Brinckerhoff, to perform bathymetric surveys1 and side-scan sonar2 along 209 state channels, comprising nearly 200 nautical miles, to evaluate the damage done by Superstorm Sandy. This evaluation served multiple purposes in enabling the team and client to: review the physical condition of the channels to identify shoals and debris targets; prioritize remediation efforts through an evaluation of the economic value and usage of specific channels; and prioritize the restoration of the channels in order to protect the public from hazardous conditions.
After the completion of the channel assessment phase, the WSP | Parsons Brinckerhoff team was awarded a follow-on contract for continued work with NJDOT to prioritize channel maintenance dredging projects and assist the NJDOT in developing, funding, and executing an annual $15 million capital program to design, permit, and construct the maintenance dredging of the state’s channel system.
The WSP | Parsons Brinckerhoff team is responsible for the following activities in supporting channel recovery and restoration:
- Project management;
- Evaluation of various design alternatives for the dredging of navigation channels and sediment disposal utilizing existing upland confined disposal facilities (CDFs);
- Evaluation and geotechnical investigation of existing CDFs along the New Jersey shore to determine their available capacity and ability to accept dredged material;
- Complete design plans, environmental permits, and contract documents for maintenance dredging projects;
- Design and permitting of confined disposal facility construction for the placement of dredge material;
- Assisting NJDOT with the advertisement and award phases of maintenance dredging projects;
- Monitoring the progress of and providing construction services for the active maintenance dredging projects to clear the channels across the state’s navigation system; and
- Providing contract documents for maintenance dredging projects on an accelerated schedule.
Confined Disposal Facilities
Confined disposal facilities (CDFs) are basically constructed, earthern bowls where the dredge slurry mix of water and sediment is pumped (see Figure 1). The perimeter of a CDF is constructed out of earthern berms that can vary in height from 5 feet to 30 feet. Depending upon the geotechnical properties of the available material, the confining berms have slopes somewhere between 2 feet horizontal to 1 foot vertical (2:1) and 3 to 1 (3:1). Confining berms are also designed to have an 8-foot to 10-foot wide flat top, to allow for construction vehicle maintenance equipment access. The sole function of a CDF is to hold the dredge slurry until the solid matter can settle out. After a settling period, clean water is drained from the CDF using a weir-type outlet structure and the solids are retained within the CDF.
Dredging in the Raritan Bayshore region and Providing Resiliency Simulataneously
The biggest challenge in dredging is the availability of placement sites. State regulations dictate that if the dredge material is less than 75 percent sand, then it must be contained in an upland CDF. Dredge material that is 75 percent to 90 percent sand can be used for dune restoration and material that is 90 percent or greater sand is considered beach quality sand.
The placement of sand on the beach and/or restoring or creating protective dunes is an excellent example of the dual benefits of dredging and coastline resiliency provided by this program. The channels are cleared to their permitted design depth and the dredge material can be used to protect the coastline from tidal surges and flooding.
Another concept that serves this dual purpose is the construction of CDFs in a linear fashion parallel to the coastline (see Figure 2). This would allow for the placement of more fine-grained material adjacent to the shoreline. After placement, the filled CDF would actually be more stable than a dune made solely of sand since fine-grained material has more natural cohesion. The CDF constructed in the borough of Keansburg in Monmouth County, NJ is precisely this application (see Section A-A on Figure 3).
The borough of Keansburg in the Raritan Bayshore region of New Jersey was severely impacted by Superstorm Sandy. Prior to the storm, contract documents were prepared and environmental permits were issued for the maintenance dredging of Waackaack (pronounced way’ cake) Creek and Thorns Creek. In Keansburg, the U.S. Army Corps of Engineers created a flood protection levee and installed a floodgate on Waackaack Creek back in the late 1960’s. The floodgate separated the inland portion of Waackaack Creek and Thorns Creek from the portion of Waackaack Creek that extends into Raritan Bay and out to the NJ Intracoastal Waterway (see Figure 3). The nature of the material to be dredged was beach-quality sand in the outer channel and a more fine-grained material in the channels inside the floodgate.
An upland CDF already existed less than 200 feet from the mean high water line, but it was already filled to present capacity with dredge material from the previous maintenance cycle. NJDOT approached the borough with the prospect of removing the dredge material for the construction of another coastal CDF in another Monmouth County town. The borough did not accept this proposal and viewed this coastal CDF and the material in it as an added protection to their town from the next superstorm.
The design team took this idea and ran with it. If the proposed CDF stayed within the original permitted footprint, we could use some of the material on the inside of the CDF to raise the confining berms, thereby creating more capacity. This would allow for the placement of the fine-grained material into the raised portion of the CDF and provide the town with an even larger natural barrier to Raritan Bay storm surges. The coarse-grained material from outside the floodgate was designed into a dune-like feature simply by extending the top of the confining berm’s elevation waterward for a set distance, and then transitioning down to the existing beach grade at a 3 foot horizontal to 1 foot vertical (3:1) slope. The slope met the existing beach grade well upland of the mean high water elevation line.
The dual benefits of the long-awaited dredging of Waackaack Creek and Thorns Creek, combined with a naturally hardened section of coastline, had the borough so pleased that they suggested that the state construct more CDFs along the coastline. The CDFs would be aligned linearly and parallel to the coastline adjacent to the CDF used during this dredge cycle. The state and the borough have been having preliminary negotiations to make that concept a reality.
The WSP | Parsons Brinckerhoff team completed the design, permitting, and construction of the following projects in 2014:
- Maintenance dredging and channel improvements for Waackaack Creek and Thorns Creek in the borough of Keansburg, Monmouth County;
- Maintenance dredging and channel improvements for St. Georges Thorofare in the city of Brigantine, Atlantic County; and
- Maintenance dredging and channel improvements for Spicers Creek, Cape Island Creek, Schellengers Creek, Devils Reach and Middle Thorofare, Lower Township and the City of Cape May, Cape May County.
The team is presently advancing eight to ten more maintenance dredging projects for construction in 2015 and beyond. The implementation of this annual maintenance dredging program will provide the navigation channels with resilience against future storms, and the strategic placement of the dredged material can provide resilience and protection for the adjacent coastal communities.
The author would like to acknowledge Kavita Dave, PE a water resources engineer in WSP | Parsons Brinckerhoff’s Lawrenceville, NJ office who contributed to this article. Gahagan and Bryant Associates (GBA) were absolutely essential for the success of this project. GBA are the dredged material management subject matter experts on the WSP | Parsons Brinckerhoff team.
1Bathymetric surveys are conducted to collect data to determine the depths of water bodies, the topography of the sea floor and coastline, and other physical features of water bodies.
2Side-scan sonar is a category of sonar system that is used to efficiently create an image of large areas of the sea floor to locate and define physical obstructions on the floor of a water body.