Marshfield & Duxbury Coastal Resilience Project
Answers to Frequently Asked Questions
What is the purpose and scope of this current project?
The primary purpose of the project is to identify areas along the Marshfield and northern Duxbury shorelines where beach and dune nourishment can be utilized effectively to build shoreline resiliency. While the existing shore protection structures provide a last line of defense against landward retreat of the shoreline, they have caused long-term erosion and lowering of the beach. The critically eroded beaches have increased the potential for storm damage to the seawalls and leave public and private properties along the shoreline vulnerable to wave overtopping and flooding. The Towns are seeking ways to augment the regular repair and maintenance of existing shore protection structures with strategies that will protect the seawalls, public and private infrastructure and offer increased resiliency to the impacts of climate change.
The project includes field investigations to identify sensitive resources and map 5.4 miles of shoreline between Rexhame Public Beach in Marshfield and the developed coastline in Duxbury along Gurnet Road. Beach and dune nourishment alternatives for enhancing the resiliency of the shoreline are being evaluated and the permitting process is being initiated for the selected alternatives at appropriate beach locations. Public education and outreach on the importance of building increased resiliency is a key ongoing component of the project.
How is the project being funded and when will it be completed?
The project is being funded by a Coastal Resiliency (CR) Grant through the Massachusetts Office of Coastal Zone Management. The Towns were award the grant for $175,842 in September 2019. Marshfield and Duxbury are providing a match of $58,704 through cash and in-kind services. The project was originally scheduled to be complete on June 30, 2020; however, due to the extraordinary circumstances surrounding the COVID-19 pandemic, an extension to September 30, 2020 was granted. This project is a continuation of a 2018 CR grant that looked at the feasibility of using dredge material from Green Harbor for beneficial reuse for beach and dune nourishment. (see beneficial reuse section below)
What are the sediment characteristics of the existing beaches?
In general, the beaches are composed of a mixture of sand and gravel sized sediments. In some locations the beaches are sandier and in other locations the beaches have a higher percentage of gravel sized material. The distribution of sand and coarse-grained material at a given beach varies seasonally and even over shorter time scales of days to weeks.
What does it mean for a beach to be sediment starved?
In natural coastal beaches, sediment is supplied to the system through erosion of beaches, dunes and coastal banks. When the natural sediment supply to a beach is interrupted or eliminated through the construction of shore protection structures (i.e., seawalls, revetments, groins, jetties), the beaches become sediment starved. Since there is a constant movement of sediment alongshore by waves, tides, and currents, a reduced sediment supply results in less volume in the beach and dunes, resulting in the shoreline retreating landward. These factors combine to allow wave energy from storms to break further inland, resulting in more storm damage, wave overtopping, and flooding. The beaches of Marshfield and northern Duxbury are considered sediment starved.
What alternatives are being considered for building resiliency?
The Towns are considering traditional nature-based alternatives such as beach and dune nourishment and cobble berms as the primary means of building coastal resiliency. These nature-based alternatives have been shown to benefit beaches with similar characteristics to those in Marshfield and Duxbury. These strategies restore sediment to the system and act to buffer the shoreline and existing shore protection structures from storm waves. The current project is a continuation of a 2018 CZM funded project that identified Green Harbor as one potential source of beach compatible sediment for nourishment on nearby beaches.
For areas where beach or dune nourishment is not considered an effective method to build shoreline resiliency, a range of hybrid conceptual alternatives have been identified, such as offshore reefs and nearshore boulder fields. These alternatives serve to reduce damaging wave energy that impacts shore protection structures and reduce risks to public and private infrastructure caused by wave overtopping. These alternatives introduce much more complexity in terms of design and permitting than those posed by beach nourishment, and may be selected for further evaluation in separate study.
Which areas were identified for beach and dune nourishment and why?
Beach and/or dune nourishment was identified as the preferred alternative at six different beach sites in the two towns. In Marshfield the sites include: Rexhame Public Beach, Winslow Avenue Beach, Fieldston Beach, Sunrise Beach and Bay Avenue Beach. In Duxbury, the Gurnet Road Beach was selected. These beach and/or dune nourishment projects will enhance the resiliency of approximately 2.8 miles of shoreline in the Towns of Marshfield and Duxbury by reducing wave overtopping and coastal flooding during storms.
These sites were chosen based on a combination of factors including ability to provide enhanced storm damage protection and flood control, reduce wave energy and wave overtopping, proximity of sensitive marine resources, constructability, and project lifetime or duration.
Is nourishment an appropriate resiliency alternative for all beaches?
Depending on the site, beach and/or dune nourishment can be a very effective method of buffering the shoreline from storm waves. It should be understood that nourishment is not a long-term solution to beach erosion since wave action, winds, and tides will continue to act on and erode the nourished beach. The benefits of a nourishment project in protecting coastal infrastructure are directly related to how long the sand lasts before renourishment is needed. Ideal sites are those where enough material remains in the vicinity of the project site so that frequent renourishment is not required. Beaches such as these have been identified/prioritized as part of this study.
Areas that have steeper nearshore slopes with extreme wave energy during storms are generally not appropriate for beach nourishment. In these locations, larger storm waves pull sediment from the beach to deeper water offshore where it is no longer available to be transported back onshore during periods of lower wave energy. Nourishment material placed on these beaches would be permanently lost from the nearshore system, and therefore not available to provide storm damage protection for public and private infrastructure. In these areas frequent renourishment would be required at great expense to the community in order to provide the desired level of storm damage protection.
Where will the sediment come from for the beach nourishment?
The current project is focused on identifying suitable sites and designs for beach and dune nourishment and starting the permitting process to place compatible sediment on the beaches. The permit applications will cover all six (6) beach sites, which will allow Towns the flexibility to utilize material from different sources, such as nearby dredging projects, offshore borrow sites, and upland processing facilities, as the material becomes available. The Towns will be able to pursue sediment sources from offshore borrow sites and upland processing facilities and the towns will be well positioned to take advantage of “situations of opportunity” should unanticipated compatible material become available.
Can sediment from nearshore bars, just seaward of the beach, be used for beach nourishment?
Sediment stored in nearshore sandbars plays an important role in dissipating incoming wave energy and is part of a larger “littoral” sand sharing system. As water depths grow shallower over the bars, larger waves are forced to break and the wave energy is dissipated before reaching the shoreline. Depending on their location, nearshore bars can also serve as a natural sediment source for the beach during low energy conditions, and through longshore sediment transport, this material is shared with adjacent beaches. Removing sediment from the bars would allow waves to break closer to the shoreline, reducing the storm damage protection provided to the shoreline. For these reasons, nearshore bar mining for beach nourishment material is generally not an accepted practice. To improve the ability of the entire beach and nearshore system to provide better storm damage protection, it is important to add volume to the system from off-site sediment sources, rather than borrow from sandbars within the littoral system.
Nearshore bars can also serve as important habitat for certain species of shellfish and marine benthic organisms. Many nearshore areas are protected by local, state and federal environmental regulations which prohibit alteration and sediment removal.
Do beach nourishment projects require maintenance?
Like all shore protection projects (including seawalls and revetments), beach and dune nourishment projects require regular maintenance in order to continue providing storm damage and flood protection. Some movement and drifting of sediment offshore and alongshore is unavoidable on any beach nourishment project. The grain size, slope, position on the beach relative to mean high tide and placement method will affect the amount and rate of shifting and spreading that occurs. In general, sediment is pulled offshore during storms and transported back onshore during periods of lower wave energy. Over time beach nourishment projects also lose sediment as it is transported alongshore to adjacent beaches. On beaches that are sediment starved like Marshfield and Duxbury, the migration of sand out of the original nourishment footprint continues to provide a benefit to the system as a whole, as sediment is transported to and shared with adjacent beaches. Accepted practice calls for renourishment of the beach once the project has lost 70% of material from the original footprint.
Why are the Towns not considering retreat as a more cost-effective solution to climate change?
Consideration of options for retreating from the shoreline are outside scope of this project. However, both Towns are actively engaged in planning efforts needed to respond to and manage the impacts of climate change. As information is developed on future coastal flooding and storm impacts, the Towns of Marshfield and Duxbury will be in a better position to identify both short- and long-term climate adaptation strategies. For some areas of the coast that show unavoidable vulnerability to flooding in the future, the long-term strategy will likely include retreat. In the short-term however, beach and dune nourishment provides a strategy that will improve storm damage protection, minimize wave overtopping, and protect private and public infrastructure.
What is a beneficial reuse nourishment project?
Beneficial reuse refers to the use of clean, compatible sediment from a nearby navigational dredging project to augment the volume of material on a beach or dune. This is generally accomplished by directly placing compatible sediment on the beach and/or dune. Beach nourishment projects can also be designed and engineered to place a specified volume of material on the beach to provide a desired level of storm damage protection and flood control. The expectation and results associated with each type of project are different as they are largely determined by the amount of material placed on the beach. Beneficial reuse projects typically place lower volumes of material on the beach and are intended to keep dredged sediment in the littoral system, but not necessarily to provide a specific level of protection or have a specific design life. Engineered beach nourishment projects typically place larger volumes of sediment on the beach to provide a specified level of storm damage and flood protection. Because of the lower volume of material, beneficial reuse projects typically have a shorter life span than engineered projects, but still provide a benefit by adding critically needed material to the beach. Also, frequently recurring dredge projects, such as with Green Harbor can provide periodic infusions of beneficial reuse material to engineered beach projects to help supplement any needed renourishment.
What permits will be needed for the beach nourishment projects?
Beach and/or dune nourishment projects typically require permits from a number of local, state and federal agencies. The permitting agencies enforce a variety of regulations, each designed to protect different interests and natural resources. Complicating the permitting process is that some resources overlap - coastal areas, wetlands, fish, birds and water are not "neatly" divided under the various agency oversight roles. While the agencies communicate with each other during review of a project, each agency serves a different purpose, set of regulations, and priorities, and often, the comments of one agency will affect the permitting conditions and decision-making of other agencies.
The Marshfield and Duxbury beach nourishment projects will require the following permits from local, state and federal agencies.
- Certificate from the Secretary of Energy and Environmental Affairs
- Orders of Conditions from the Marshfield and Duxbury Conservation Commissions
- Chapter 91 Permit from Massachusetts Department of Environmental Protection Division of Waterways
- Coastal Consistency from Massachusetts Coastal Zone Management
- Individual Permit from the US Army Corps of Engineers
How long does it take to get the permits and do the permits expire?
Environmental permitting for a large-scale beach and/or dune nourishment project takes a significant amount of time and resources. Time is required to prepare the permit applications, coordinate meetings with the agencies, respond to questions from the agencies, and respond to comments from the public. As a project proceeds through the permitting process it is common for input from one agency to inform the development of subsequent applications. All of this work takes time.
For the Marshfield and Duxbury project, the entire permitting process is expected to take 1.5 to 2 years. The permit application required to get the Certificate from the Secretary of Energy and Environmental Affairs will be filed in mid to late July 2020. It is expected that the remaining permit applications will be filed by late June 2021. The resulting permits should be issued between Fall 2021 and Spring 2022. The permits have varying expiration periods ranging from 3 to 10 years. Time extensions can be granted for permits with shorter expiration periods.
When can the Towns expect to construct the beach nourishment?
The timing for construction of beach and/or dune nourishment will depend on a number of factors including:
- Completion of permitting - The earliest the Towns would be ready to build the beach nourishment projects would be in the Fall 2022, after the final permit is issued.
- Time of year restrictions that will be included in the permits to protect threatened and endangered species - It is expected that construction activities will be restricted to the winter months between November 1 and January 15, to protect threatened and endangered species that frequent the site during the spring, summer and fall.
- Sources of sediment identified for the nourishment – Sediment from nearby dredging projects such as Green Harbor, could be used beneficially for beach nourishment as soon as the permits are issued. Renourishment using dredge materials could occur for as long as the permits are valid. Nourishment using an upland source would require additional time to identify beach compatible sediment, however, additional permitting would not be required for this source. Further field investigations, engineering design, impact studies and permitting would be required to evaluate sources of sediment from an offshore source. The process of designating an offshore sediment source for beach nourishment in Massachusetts can take 2-3 years.
- Availability of monies to fund construction – State and federal grant opportunities are available to help fund beach nourishment construction; however, many of these grants require a local match. As such, the Towns would need to appropriate funds to supplement any grants received for construction.
How much would the beach nourishment projects cost?
Costs for beach nourishment vary depending on the size of the project and the source of material. Information on expected costs is currently being developed assuming sources from an offshore borrow site and from an upland location. This information will be posted as soon as it is available.