Nantucket Harbors Sediment Transport Study and Dredge Plan

Project Purpose

The Nantucket Harbors Sediment Transport Study and Dredge Plan will support the Town’s understanding of sediment transport within Nantucket, Madaket and Polpis Harbors through a data-driven modeling approach informed by the community’s coastal resilience goals. The outputs of this effort will be used to guide decision-making and maximize sediment resources on Nantucket and improve navigation in the harbors for the benefit of the public.

Project Overview

Sedimentation in the harbors is an obstacle to navigation and many life activities on Nantucket, from recreational sailing to essential travel to and from Cape Cod. Additionally, to effectively implement many of the erosion management recommendations made by the Coastal Resilience Plan (CRP) in 2021 and the Hazard Mitigation Plan (HMP) in 2019, additional data collection and analysis is necessary to understand sediment movement. A sediment transport study was a priority recommendation of the CRP to understand sand and sandbar movements. To fill the need identified in the CRP and address maritime navigational needs, the Nantucket Harbors Sediment Transport and Dredge Plan kicked-off in April 2023, with an emphasis on potential beneficial reuse of recovered materials. This initial effort prioritizes understanding sediment transport in Nantucket Harbor, Madaket Harbor and Polpis Harbor as these areas are critical to navigation.

This project will include several related tasks:

Development of a sediment transport model
Identification, prioritization and planning of dredge projects
Identification, prioritization and planning of nourishment projects, and
Permitting for priority projects.

Together, these tasks will help answer the following questions:

How does sand in Nantucket’s harbors move over time?
Where and how often will dredging be needed?
Can dredged sand be used for beach nourishment? If yes, where should beach nourishment be prioritized?

Data collected throughout this process and outputs of the sediment transport model will help guide resilient decision-making by identifying sediment resources and prioritizing erosion management locations; identify opportunities for the development of an island sand bank; collect data to better understand and protect sensitive habitats; and inform other completed and ongoing sediment management efforts.

Project Timeline

The Nantucket Harbors Sediment Transport and Dredge Plan will take place over the course of 24 months which began in April 2023. Field data collection in May 2023 included bathymetric survey, sediment coring and water level monitoring and informed the sediment transport model. From spring 2023 through spring 2024, the sediment transport model will be developed using the best available data and state-of-the-art modeling approaches. Using the outputs of this model and stakeholder feedback, the project team will identify and prioritize opportunities for dredging and beach nourishment and assist the Town in securing required permits for priority projects.

Project Team

Town of Nantucket Staff
The Town of Nantucket is leading the Nantucket Harbors Sediment Transport and Dredge Plan. Working closely with the consultant team, Town staff will direct contact with local resources as well as state and federal agencies.

Consultant Team
The Nantucket Harbors Sediment Transport and Dredge Plan will require survey and field work, state-of-the-art sediment modeling, dredge and erosion management planning, and sensitive habitats protection to make the project successful. To support this work, an interdisciplinary team of consultants led by Dutch engineering firm Arcadis and including Baird & Associates, Tighe & Bond and Alyssa Novak, PhD. will work directly with Town staff in developing the CRP.