STONE HARBOR – At a special meeting of the Stone Harbor Council on Dec. 13, coastal consultant Douglas Gaffney of Mott MacDonald made a presentation on options for greater stabilization of the borough’s oceanfront – including entering into an agreement with neighboring towns to obtain dredging equipment.
The preliminary results of Mott MacDonald’s feasibility study include long-term and more immediate options to improve beach management. Stone Harbor has experienced serious beach erosion issues exacerbated by the fact that the borough was left out of the most recent federal beach fill project, in 2019.
The study looked at ways to minimize the degree of disequilibrium experienced along its beachfront in the period between large scale nourishment efforts by the U.S. Army Corps of Engineers (USACE). Generally federally sponsored beach nourishment projects are conducted on a three year cycle. The goal of study recommendations is greater sand retention in the intervening years.
The presentation also looked at the borough’s need for beach maintenance permits from the state Department of Environmental Protection (DEP). Stone Harbor’s general permit for maintenance expired in September. Theborough is seeking a new general permit, as well as an individual permit which would allow a greater level of maintenance and repair.
A part of the effort to develop the feasibility study involved the creation of computer models that uselongitudinal data from past years to capture natural wave action and sand transport. These models are then used to test the potential benefits of various options for retaining sand on the beaches.
Gaffney described beach erosion as an “appetite.” Beaches are in equilibrium when there is sufficient sand to feed the appetite of the waves. Sediment transfer, Gaffney said, is the natural movement of sand in directions that are either along the shore front or across it. This transport depends on the characteristics of wave action.
If there is not enough sand the waves will erode the beach and dunes as they have in Stone Harbor, Gaffney said. Rising sea levels further complicate this natural process. In many ways the periodic beach nourishment is feeding the appetite and putting the beaches in equilibrium for a time. Actions that the borough might take could potentially extend the time of that equilibrium by keeping more sand on the beach longer. The periodic large scale nourishments would remain essential to the long-term health of the beach.
The draft feasibility study focused on a set of actions that can have a long-term benefit. It also proposes two ways of harvesting sand to repair eroded beaches in the years between large scale fills.
The most simple option presented involves using fencing to trap sand blown on to the beaches by wind action. This process of windblown sand is a contributing factor in dune development. In this case, Gaffney said, the borough would need an understanding with the DEP that the sand captured is not for dune system but rather for eventual return to the dry beach area when needed. Gaffney noted that capturedwindblown sand will never equal the volume of sand taken from the beach by wave action, but it can be a source of sand for certain beach repairs.
Another recommended option is scraping sand from just off shore and returning it to the dry beach area. This is a way to use sand that was taken from the beach and deposited in sand bars just off the water line. It is in some ways similar to the back passing efforts – moving sand from one area to another – that have worked well in Avalon but it involves no action to truck the scraped sand to another area of the beach. The sand remains in the same beach area and is movedfrom the low water area to the dry beach. Permitting for this type of effort would have to be done under the more involved individual permit application.
A more long term option recommended in the study is the repair and extension of the 127th Street terminal jetty. Gaffney said that all eight of the borough’s jetties are in a significant state of disrepair and none are working in the manner they were designed to work. Many of them are 50 to 60 years old and have never been maintained.
Whether maintenance of the jetties was a task for the state or the municipality is unclear according to Gaffney, but nobody took on the task. They have lost length and height and cannot retain sand as designed. At this point, the modeling suggests that the only jetty that would provide a cost benefit to the beaches if repaired is the terminal jetty at 127th Street. A longer and higher jetty would help retain sand north of 127th Street and over time would result in more sand on beaches in a progressively northern direction. This would all have to be calibrated so as not to negatively impact the sand needs of the Point.
Gaffney proposed a fourth consideration by the borough, in some form of arrangement with other coastal municipalities, ofpurchase of a used dredgein order to mine sand for the beaches. He pointed out that the sand in Hereford Inlet is available, with appropriate permits, as a sand borrow area as long as federal funds are not involved. The dredge could also be used for back bay operations in periods between major channel dredging projects.
Staffing and maintaining a dredge would be beyond the responsiblefinancial burdens of a single municipality. Gaffney said some form of joint arrangement would be necessary. At the meeting he was unable to point to another site where a municipality maintains its own dredging operation, but such sites do exist.
The recommendation from the Stone Harbor feasibility study is novel but not without precedent., Florida, maintains its own dredge, crew and support vessel to keep channels open for navigation. The municipal website describes the process and notes that “material dredged from the inlet is placed above the mean high water line of the beaches 500 feet south of the southern jetty of the inlet.” The recommendation from the Stone Harbor feasibility study is novel but not without precedent.aton, Florida, maintains its own dredge, crew and support vessel to keep channels open for navigation. The municipal website describes the process and notes that “material dredged from the inlet is placed above the mean high-water line of the beaches 500 feet south of the southern jetty of the inlet.”
There was no discussion of costs associated with the study recommendations and options.
The presentation slides are available on the borough’s website. The full study in draft form is expected to be completed and delivered to council early in 2023 with a final report to follow after council discussion and public comment.
To reach Vince Conti, email vconti@cmcherald.com.
