Conservation Spotlight: Dunes at Shoal Harbor Shoreline Protection

Hurricane Sandy was the largest storm to ever originate in the Atlantic ocean. It badly damaged several countries in the Caribbean, caused over $50 billion in damages along the Eastern Seaboard, and left dozens dead. While hurricanes are a natural part of our climate system, research shows that intense hurricane activity has been on the rise in the North Atlantic since the 1970s. This trend is likely to be exacerbated by sea level rise and growing populations along coastlines. Natural coastal habitats — like wetlands and dunes — have proven to shield people from storms and sea-level rise, and have protected coastal communities from hundreds of millions of dollars in damage.

The Dunes at Shoal Harbor, a residential community in Monmouth County, New Jersey, is situated adjacent to both the Raritan Bay and the New York City Ferry channel. The site, previously utilized for industrial purposes, consisted of a partially demolished docking/berthing facility. A significantly undersized 6” diameter, 8-foot long stone revetment was also constructed on the property.

During Hurricane Sandy, the revetment failed and the community was subjected to direct wave attack and flooding. Homes were damaged, beach access was impaired, and the existing site-wide stormwater management basin and outfall was completely destroyed.

Princeton Hydro performed a wave attack analysis commensurate with a category three hurricane event, and used that data to complete a site design for shoreline protection. Consistent with the analysis, the site design includes the installation of a 15-foot rock revetment (one foot above the 100-year floodplain elevation) constructed with four-foot diameter boulders. The project also consists of replacing a failed elevated timber walkway with a concrete slab-on-grade walkway, restoring portions of the existing bulkhead, clearing invasive plants, and the complete restoration of the failed stormwater basin and outlet.

A rendering of the “Dunes at Shoal Harbor” shoreline protection design by Princeton Hydro.

The plan incorporates natural barriers to reduce the impacts of storm surges and protect the coastal community, including planting stabilizing coastal vegetation to prevent erosion and installing fencing along the dune to facilitate natural dune growth.

These measures will discourage future erosion of the shoreline, protect the residential community from future wave attacks and flooding, and create a stable habitat for native and migratory species.  The project is currently in the permitting phase, and will move to construction when all permits are obtained from local, state, and federal agencies.

This project is an great example of Princeton Hydro’s ability to coordinate multi-disciplinary projects in-house. Our Water Resources Engineering, Geosciences Engineering, and Natural Resources teams have collaborated efficiently to analyze, design, and permit this shoreline protection project. For more information on our engineering services, go here.

Conservation Spotlight: FORTESCUE SALT MARSH AND AVALON TIDAL MARSH RESTORATION

HABITAT RESTORATION THROUGH APPLICATION OF DREDGED MATERIAL

New Jersey, like other coastal states, has been losing coastal wetland habitats to a combination of subsidence, erosion and sea level rise. The New Jersey Department of Environmental Protection received a grant from the National Fish and Wildlife Federation to address this issue and rejuvenate these critical habitats. Grantees were charged with providing increased resilience to natural infrastructure that will in turn increase the resiliency of coastal communities in the face of future storms like Hurricane Sandy.

As a consultant for GreenTrust Alliance, a land conservancy holding company, Princeton Hydro worked with several project partners, including NJDEP, the US Army Corps of Engineers, NJDOT, The Wetlands Institute, and The Nature Conservancy, to increase the marsh elevation to an optimal range where vegetation, and the wildlife that depends on it, can flourish. One of the techniques used for this project included the use of dredged material disposal placement, which involves using recycled sand and salt dredged from navigation channels to boost the elevation of the degraded marsh.

A media statement from NJDEP further explained the process, “sediments dredged from navigation channels and other areas are pumped onto eroding wetlands to raise their elevations enough to allow native marsh grasses to flourish or to create nesting habitats needed by some rare wildlife species. Healthy marshes with thick mats of native grasses can cushion the impact of storm surges, thereby reducing property damage.”

FORTESCUE SALT MARSH

The salt marsh at the Fortescue project site is part of the Fortescue Wildlife Management Area. The specific goal of the project was to restore and enhance the interior high and low marsh, coastal dune and beach habitats.

To achieve these habitat enhancements, the Princeton Hydro project team first established biological benchmarks of each targeted habitat type and evaluated them to determine the upper and lower elevational tolerances for target communities and plant species. Approximately 33,300 cubic yards of dredged materials were used to restore a degraded salt marsh, restore an eroded dune, and replenish Fortescue Beach. The eroded dune was replaced with a dune designed to meet target flood elevations and protect the marsh behind it against future damage. The dune was constructed using dredged sand, and, to prevent sediment from entering the waterways, a Filtrexx containment material was used.

AVALON TIDAL MARSH

This project site is a tidal marsh complex located within a back-bay estuary proximal to Stone Harbor and Avalon. Princeton Hydro and project partners aimed to enhance the marsh in order to achieve the primary goal of restoring the natural function of the tidal marsh complex.

Two main activities were conducted in order to apply the dredged material to the impaired marsh plain: 1.) the placement of a thin layer of material over targeted areas of existing salt marsh to increase marsh elevations, 2.) the concentrated placement of material to fill expanding pools by elevating the substrate to the same elevation as the adjacent marsh. In total, dredged material was distributed among eight distinct placement areas throughout the property’s 51.2 acres.

These coastal wetland restoration activities will help to prevent the subsidence-based marsh loss by filling isolated pockets of open water and increasing marsh platform elevation. In addition, the beneficial reuse of dredged material facilitates routine and post-storm dredging and improves the navigability of waterways throughout the U.S.