Dredging and Beneficial Use - Part 2: Shark River Dredging Project

Introduction

For over 30 years, Clean Ocean Action has worked to review, develop, and advocate for community driven dredged material management solutions. By viewing dredged material as a resource, and emphasizing community input and engagement, COA has reviewed and identified potential beneficial use options for dredged material placement in many different contexts and uses. Above all, throughout this process, COA has advocated for environmental protection, and community involvement and support as key tenets of our position. As we say here at Clean Ocean Action, “we know mud”.

This is part two of our series on the beneficial use of dredged material.

SHARK RIVER - Critical Navigation, Innovative Dewatering, and Beneficial Use

 

The Shark River is a tidal estuary bordered by five towns - Neptune Township, Neptune City, Avon, Belmar and Wall Township. The river is popular for stand up and kayak paddling and bird watching, as well as safe harbor for hundreds of commercial and recreational fishing and pleasure boats. The marinas surrounding the river have also become a focus of redevelopment with bars and restaurants flanking these marina hubs. For over two decades, critical dredging of channels was needed to allow the passage of vessels into and out of the estuary. However, no satisfactory location was available to place the estimated 102,000 cubic yards of dredged material. In fact, the old CDF for Shark River is actually the site of the Seaview at Shark River Island condominium community; a clear example of the lack of open space in the area. Everyone agreed that the river needed to be dredged, but there was no consensus as to where the material could be placed, or even dewatered for transport. An innovative solution was necessary to get this project off the ground.

Enter a dedicated coalition of State, County and local leaders that effectively advocated for the project, including Senator Jen Beck, Committeeman Randy Bishop, County of Monmouth, Board of Chosen Freeholders, New Jersey Department of Transportation (NJ DOT) Office of Maritime Resources, New Jersey Department of Environmental Protection (NJ DEP), and the governing bodies of the participating municipalities including Neptune City, Neptune, Belmar, and Wall. Recognition must also go to the Shark River Cleanup Coalition, who has been advocating for the dredging of the Shark River for many years now. 

NJDOT put a concept and "workable plan" out to bid. Mobile Dredging and Pumping Co., out of Chester, PA. Mobile Dredging was awarded the $7.6 million contract in the summer of 2015, as the responsible low cost bidder for the project, and with coordination from NJDOT and NJDEP, a workable solution was created that used innovative technology to dewater the dredged material slurry on a very small footprint surrounded by homes, businesses, and marinas, before trucking it to the Monmouth County Reclamation Center for use as landfill cover. The project removed approximately 102,000 cubic yards of sediment from the River comprised of sand and silt using hydraulic dredging, and then piped the slurry via a secure welded pipeline to the selected dewatering location.

Caption: far off in the Shark River, the hydraulic dredge removes sediment to improve navigation (photo courtesy of Cindy Zipf).

The dredging had started late last fall and was halted on January 1, 2016, due to state regulations in place to protect spawning and the early life stages of winter flounder and anadromous fish. During this initial phase of the project, “geotubes” were used to dewater the slurry before trucking the material off to be used. Geotubes are large fabric bags that the slurry is pumped into, with pressure forcing the water out of the bag while the sediment remains.

Caption: this image shows the piping system that moves the dredge slurry to the dewatering site, as well as the pipe that takes the water that has been removed out of the sediment and returns it back to the river (photo courtesy of Cindy Zipf).

Caption:  dredge slurry is pumped into the geotube. The fabric is designed to let water escape, leaving behind the sediment for removal and use as cover at a landfill.

When the project was restarted in July, the dewatering process was changed to handle larger amounts of material and get the project done before the dredge window closed.

Caption: a first look at the dewatering site. (video courtesy of Cindy Zipf).

This dewatering process is called “mechanical dewatering” and utilizes transportable and modular centrifuges and belt presses to separate usable sand out of the finer sediment, then mechanically squeeze the water out of the slurry. The process is rather impressive to behold, and when up and running, is able to process a huge amount of material on a very small footprint – perfect for the heavily built up mid-Atlantic coastline.

Let’s walk through the process:

First, a hydraulic dredge removed sediment in a slurry that is piped to the dewatering location. This pipe runs to a large tank that slows down the flow of water and allows larger pieces of debris to settle out.

Caption: Rick, from Clean Ocean Action, talks to the contractor supervisor in front of one of the large tanks where the dredge slurry is first pumped to (photo courtesy of Cindy Zipf).

The slurry is then pumped into several centrifuge and screen type machines, that are able to sort out debris and coarse sand sediments from the muds and silts. These machines are also able to remove large amounts of debris and trash from the sediment as well. The idea is that the larger pieces of debris and sand can actually harm the belt presses which squeeze the water out, so removing them on the front end of this process saves those machines, and also allows for use of sand! This project produced about 500 cubic yards of sand that was trucked and placed on the Township of Neptune’s beaches.

Caption: Bill from NJDOT shows us the centrifuge systems which remove the larger sediments and debris on the front end of this process (photo courtesy of Cindy Zipf).

Caption: The centrifuges are able to remove debris and shell fragments which are removed from river and properly disposed of (photos courtesy of Cindy Zipf).

 Caption: Zach from COA inspects the sand removed off of the front end this process - over 90% sand = perfect for beach placement (photo courtesy of Cindy Zipf).

The slurry then travels to belt presses which wring the water out of the slurry and extrude a dredge material “brownie” (photo courtesy of Cindy Zipf)..

Caption:  the mechanical dewatering process in a series of videos (courtesy of Cindy Zipf).

1. After having larger sediment and debris removed, a polymer is added to the slurry and then spread out onto the fabric conveyor belts

2. The conveyor belts transport the slurry through a series of belt presses, which mechanically squeeze the water out of the material. This process occurs several times. Water from this process is treated and sent back into the Shark River.

3. The dredge material, now dewatered, is extruded out of the belt presses.

Caption: the result of this dewatering process is a sediment "brownie" that has been wrung dry, and easily transportable (photo courtesy of Cindy Zipf).

This material is then scooped up and put in a holding area, where dump trucks then take it to the Monmouth County Reclamation center, where it will be mixed with sand and used as landfill cover (photo courtesy of Cindy Zipf).

The Shark River project is a great example of coupling an innovative dewatering process with beneficial use of the material, in order to meet the constrains of the project. The mechanical dewatering process took up about an acre of area, was self contained and rather unobtrusive to the surrounding area, and allowed sand to be harvested off the front end for beach placement, and sediment off the back end for landfill cover (photo courtesy of Cindy Zipf).

A final note: the footprint of one acre for dewatering was barely enough room to get this job done. A larger footprint for dewatering would have made the project less expensive and faster to complete. Furthermore, Monmouth County Landfill accepting the material for free was a key in making this project feasible. This all goes to show that finding large scale, affordable, beneficial use opportunities is really challenging - and cooperation and coordination between all entities is absolutely essential to the success of these types of projects.