To help make informed decisions, coastal managers, shorefront landowners, and potential property buyers need information on shoreline trends, including erosion and accretion rates. The goal of CZM's Shoreline Change Project is to develop and distribute scientific data that will support local land-use decisions.
This project illustrates how the shoreline of Massachusetts has shifted between the mid-1800s and 2018. Using data from historical and modern sources, up to 10 shorelines depicting the local high water line (i.e., the landward limit of wave runup at the time of local high tide) have been generated with transects at roughly 50-meter (164-feet) intervals along the ocean-facing shore. For each of these more than 25,000 transects, data are provided on net distances of shoreline movement, shoreline change rates, and uncertainty values.
Please read the following before viewing the interactive Coastal Erosion Viewer: Coastal shorelines change constantly in response to wind, waves, tides, sea level fluctuation, seasonal and climatic variation, human alteration, and other factors that influence the movement of sand and other material within a shoreline system. The loss (erosion) and gain (accretion) of coastal land is a visible result of the way shorelines are reshaped in the face of these dynamic conditions. The information below explains the process of shoreline change, discusses its impacts, summarizes the Shoreline Change Project, and explains how to interpret and apply the shoreline change data.
A word of caution to shorefront landowners, potential buyers, and others interested in this information as it relates to a particular property: The Shoreline Change Project presents both long-term (approximately 175-year) and short-term (approximately 50-year) shoreline change rates at 50-meter intervals along ocean-facing sections of the Massachusetts coast. In a broad sense, this information provides useful insight into the historical migration of Massachusetts shorelines and erosional hot spots. Care must be used, however, when applying this information to a specific property or section of coastline. Due to the multitude of natural and human-induced factors that influence shoreline positions over time, correct interpretation of the data requires knowledge of coastal geology and mapping and the other forces that affect shorelines. CZM recommends consulting with a professional when applying the Shoreline Change Project data for land-use decisions and planning purposes. In no case should the long-term shoreline change rate be used exclusively before the short-term rate, uncertainty associated with each shoreline position, patterns of erosion and accretion, and other contributing factors are understood and assessed.
How and Why Shorelines Change
As waves gently lap the shore of a beautiful stretch of sandy beach, do you ever wonder where that sand came from? The answer is: erosion. The sources of sand that created and continue to feed the beaches, dunes, and barrier beaches in Massachusetts come primarily from eroding coastal landforms. For example, material eroded from Atlantic-facing coastal banks of the Cape Cod National Seashore supplies sand to downdrift (i.e., down current) beaches of Cape Cod.
Erosion, transport, and the accretion that results are continuous and interrelated processes. Every day, wind, waves, and currents move sand, pebbles, and other materials along the shore or out to sea. Shorelines also change seasonally, tending to accrete gradually during the summer months when sediments are deposited by relatively low energy waves and erode dramatically during the winter when sediments are moved offshore by high energy storm waves, such as those generated by northeasters.
Shoreline Change and Coastal Property
Given its aesthetic and recreational appeal, the Massachusetts coast has been and continues to be subject to intense development. Much of this development is susceptible to on-going risks from winds, waves, storm surge, flooding, relative sea level rise, and the associated erosion of coastal landforms. Consequently, shoreline change is an important issue in Massachusetts.
While erosion is necessary and natural, it does have the potential to damage coastal property and related infrastructure—particularly when development is sited close to the shoreline, in unstable or low-lying areas. Erosion can expose septic systems and sewer pipes, contaminating shellfish beds and other resources; release oil, gasoline, and other toxins into the marine environment; and sweep construction materials and other debris out to sea. Public safety is also jeopardized when buildings collapse or water supplies are contaminated.
Erosion can result in significant economic and emotional loss in a system of fixed property lines. Attempting to halt the natural process of erosion with seawalls and other hard structures, however, simply shifts the problem, subjecting downdrift property owners to similar or greater losses. Also, without the sediment transport associated with erosion, some of the Commonwealth's greatest assets and attractions—beaches, dunes, barrier beaches, salt marshes, and estuaries—will be threatened and slowly disappear as the sand sources that feed and sustain them are eliminated.
The challenge, therefore, is to site and manage coastal development in a manner that allows natural physical coastal processes, such as erosion, to continue. To meet this challenge, coastal managers, property owners, and developers must work with erosion—not against it—by understanding the magnitude and causes of erosion and applying appropriate management techniques that will allow its beneficial functions to continue.
The Shoreline Change Project
Through the Shoreline Change Project, the ocean-facing shorelines of Massachusetts have been delineated and statistically analyzed to demonstrate trends from the mid-1800s to 2018. CZM launched the Shoreline Change Project in 1989 and produced maps for the entire coast with shorelines from the mid-1800s to 1982. In 1997, CZM distributed shoreline change maps with erosion and accretion rates to coastal conservation commissions, helping local decision makers identify coastlines prone to storm damage and erosion. An update of the Shoreline Change Project was completed in 2001 using 1994 National Oceanic and Atmospheric Administration (NOAA) aerial photographs of the Massachusetts shoreline. CZM established an agreement with the U.S. Geological Survey (USGS), the Woods Hole Oceanographic Institution Sea Grant Program, and Cape Cod Cooperative Extension to produce the 1994 shoreline and calculate shoreline change rates. In addition to paper maps, an online shoreline change browser was provided.
CZM then incorporated the shorelines and shore-perpendicular transects with shoreline change rates into the Coastal Erosion Viewer to provide better access to the shoreline change data. In 2013, through continued collaboration with USGS, CZM released a new shoreline that spans 2007 to 2009. USGS delineated and analyzed this shoreline with other shorelines at 50-meter (approximately 164-feet) intervals to compute long-term (approximately 175-year) and short-term (approximately 50-year) rates of shoreline change. Other shorelines added as part of this update include a 2000 shoreline derived by USGS that covers most of the ocean-facing coastline, as well as a 2001 shoreline for the South Shore that was delineated by Applied Coastal Research and Engineering. The latest lidar-derived shorelines delineated for the years 2013-2014 and 2018 and more than 25,000 transects with updated change rates, uncertainty values, and net distances of shoreline movement have been added to the Coastal Erosion Viewer.
How to Interpret the Data
To interpret and apply the shoreline change data, both general shoreline trends and long- and short-term rates must be analyzed and evaluated in light of current shoreline conditions, recent changes in shoreline uses, and the effects of human-induced alterations to natural shoreline movement. In areas that show shoreline change reversals (i.e., where the shoreline fluctuates between erosion and accretion) and areas that have been extensively altered by human activities (e.g., seawalls and jetties), professional judgment and knowledge of natural and human impacts are typically required for proper data interpretation and incorporation of the data into project planning and design.
For example, a group of 10 transects along Sankaty Head on Nantucket indicate a generally stable (close to zero) long-term trend of shoreline change from 1846 to 2009. The beach is not stable, however, as illustrated by the short-term erosion rates of approximately -9.5 feet per year and the approximately 300-feet of erosion experienced in this area from 1978 to 2009. In this particular example, the beach was accreting up until the 1950s, when it began to erode rapidly. The accretion and erosion in essence mathematically "cancel each other out," leaving a long-term shoreline change rate of around zero.
Where the shoreline has been armored with sea walls, revetments, and other structures, the shoreline change data must be looked at very closely to determine the effects of the structures. The natural sources of beach sand for North Scituate Beach were severely diminished by seawall and revetment construction during the 1940s through the 1970s. Consequently, the trend of erosion is not only continuing in this area—it is increasing from approximately -0.5 to -2.5 feet per year. Transects on Scusset Beach in Bourne show long-term accretion rates of more than seven feet per year. However, the short-term accretion rates of approximately five feet per year are more reflective of the current shoreline trend. The north jetty of the Cape Cod Canal was constructed in the early 1900s and resulted in an initial rapid growth of Scusset Beach, contributing to the higher long-term rates that have since leveled off.
In addition, the shorelines were derived from different historical maps, aerial photographs, and LIDAR (light detection and ranging) topographic data sources. Each shoreline was assigned an uncertainty value based on an estimate of errors inherent in the source material and method used to delineate the local high water line. These estimates of total shoreline position uncertainty, which ranged from approximately 11.6 meters (38.1 feet) for 1800s shorelines to approximately1.3 meters (4.2 feet) for LIDAR-derived shorelines, should be considered when analyzing shoreline movement over time and were included in the calculation of uncertainty at each transect. Each transect has values for long- and short-term rates, as well as estimated uncertainty values for those rates. The shoreline change rates should be looked at as a range, particularly for transects with uncertainty values that are greater than the shoreline change rate. For example, for a transect with an erosion rate of -1.0 feet per year with an uncertainty range of ±2.5 feet per year, the range for the shoreline change rate would be +1.5 to -3.5 feet per year—meaning that the area may be either eroding or accreting. To best protect coastal properties in the long term, the most aggressive rate of erosion over the expected life of the building or structure should be used for project design.
See the USGS Open-File Report, Massachusetts Shoreline Change Mapping and Analysis Project, 2013 Update, for an in-depth explanation of the shoreline change project and data interpretation.
If you experience difficulties with the Coastal Erosion Viewer, please contact Daniel Sampson at email@example.com. Other questions regarding the Shoreline Change Project should be directed to Julia Knisel at firstname.lastname@example.org or Rebecca Haney at email@example.com.
I have read the above information on shoreline change and want to proceed to the Coastal Eosion Viewer.