Clean Ocean Action: Shrewsbury River Maintenance and Beach Replenishment

Thursday, February 1, 2018

Shrewsbury River Maintenance and Beach Replenishment

Dredging is critical to manage sediment shoaling and maintaining the navigability of our waterways and to protecting the commercial and recreational benefits that they provide. The disposal and management of dredged material have been debated for years, especially within the communities that thrive along these water bodies. Some of the routine issues of concern are: scope and extent of dredging, dredged material management strategy, impacts to the local community including economic and aesthetic impacts, and potential risks to the local environment.

Clean Ocean Action (COA) believes that dredged material can be a valuable resource, reused for beneficial purposes if and when it meets criteria that helps protect the environment. COA also believes that community awareness and involvement are vital for implementing suitable beneficial reuse alternatives using dredged materials. For more than three decades, COA has actively reviewed dredged material management solutions in the NJ-NY area and continues to advocate for identifying and implementing options for beneficial reuse of dredged materials. COA monitors various dredging projects occurring in the region and engages and promotes awareness among the communities.

COA has been following maintenance dredging projects in the state of New Jersey and sharing updates regularly through various platforms (website, blog, newsletter, social media etc.) including the recent maintenance dredging in the Shrewsbury River in New Jersey. The New Jersey Department of Transportation (NJDOT) recently began sand shoal maintenance dredging in three state navigation channels on the Shrewsbury River in Monmouth County, NJ. This is the first part of a two-phase project on the Shrewsbury River under NJDOT’s State Channel Dredging Program that was started to address the impacts from Superstorm Sandy. According to the permit, approximately 17,500 cubic yards of dredged material with more than 90% sand will be removed using hydraulic dredging from selected cores in three channels of the river in Monmouth County, which are listed below. The dredged material will be used for beach placement, which is a beneficial reuse that COA supports under the right conditions. Dredged material which meets the greater than 90% sand criteria as per NJ’s dredge material management guidelines will be transported through pipelines and used as beach fill for beach replenishment nourishment along the eroded shoreline of Monmouth Beach. For this project, the sand will be placed in front of the existing dune between Central and Park Road.

The Shrewsbuy river maintenance dredging officially began on October 23, 2017, and as per permit conditions was scheduled to be completed on Dec 31, 2017. At the time of completing this report, COA is awaiting confirmation from DOT about the status update on this project.

The following three channels were dredged under this project:

· Monmouth Beach channel (#016) in the boroughs of Monmouth Beach and Sea Bright – max. depth 6 ft. below the plane of mean low water level (MLW)

· Rumson Country Club Y channel (#017) in the boroughs of Rumson and Sea Bright - 5 ft. MLW

· Oceanport Creek entry channel (#025) in the borough of Oceanport – 4 ft. MLW

COA was granted permission from NJDOT and NJDEP to visit the dredging site with a few staff and local stakeholders for a firsthand experience of the various stages under this project, which can be used to inform the local community. On Dec 18, 2017, COA staff Cindy Zipf (Executive Director), Alison McCarthy (Coastal Watershed Protection Coordinator), and Dr. Swarna Muthukrishnan (Staff Scientist) visited the NJDOT field office in Monmouth Beach to meet personnel and view the dredging/beach replenishment activity. They were joined by Dave Stickle (Monmouth Beach Councilman) and Brian Williams (Monmouth Beach Environmental Commission). Bill Henderson and Sherif Ismail, engineers from the Office of Maritime Resources in NJDOT organized the visit for COA. The dredging contractor Tristate Environmental was represented by their site supervisor Wayne. As part of the dredging team, Audrey from JBA consulting who is the field inspector onsite was also present during the visit. Together they offered COA’s team a tour around the dredging location and explained the various processes involved in the dredging and beach replenishment.

At the time of our visit, the dredging was already completed in channel #016, and dredging of #017 was in progress. The actual dredging operation runs for 12 hours every day on a 5-day schedule typically, and a 1-3 member crew from TriState Environmental is in attendance to monitor the dredging and to make sure that all activities proceed smoothly. The pipes that carry the dredged material to the booster pump located in-river in Monmouth Beach are sunk and weighted in the bottom of the river. The booster pump is sited to ensure that the heavy sand-slurry that is dredged from the river can be transported to the dewatering zone on the beach, which is located across the road. As the dredged material is pumped into the dewatering zone continuously, a trash trap removes any debris that is transported with the dredged material. Once in the dewatering zone, the slurry material starts to dry up, which typically is a few days (1-3). As the continuous flow of slurry dries, the clearer water flows to the ocean, and the sand, which is in different stages of drying appear in various shades of grey initially. This should not be of concern as these materials have been dredged from a few feet below the MLW that are not exposed to direct sunlight. As per NJ monitoring requirements for dredge material beach replenishment activity, the dried sand materials are routinely visually inspected by NJDOT and the project personnel to ensure they meet greater than 90% sand criteria. Periodically, the dewatered, dried sand material is hauled up and spread on the beach as beach fill in the designated location. These dredged materials, once dewatered, subsequently lighten due to bleaching from sunlight. Once the maintenance dredging activity is completed and the sand completely dries, the beach replenishment activity will be completed.

According to NJDOT and Tristate Environmental, daily maintenance activities include cleaning and flushing the pipelines after dredging every day. The trash trap in the dewatering zone is also removed and cleaned every day. The following photos show the various stages of sludge dewatering and beach replenishment that is part of this maintenance dredging project. (i) dewatering zone with the trash trap (ii) sand in varying stages of drying and color (iii) flow of clearer water towards the ocean (iv) beach replenishment using the dewatered sludge with greater than 90% sand.